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Cu dissimilar lap joints
Journal of Manufacturing Processes 45 (2019) 312–321
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Influence of laser power on microstructure and mechanical property of laserwelded Al/Cu dissimilar lap joints
T
Shenghong Yana,b,c, Yan. Shia,b,c,
⁎
a
School of Mechanical and Electric Engineering, Changchun University of Science and Technology, Changchun, 130022, PR China National Base of International Science and Technology Cooperation for Optics, Changchun, 130022, PR China c Ministry of Education Key Laboratory for Cross-Scale Micro and Nano Manufacturing, Changchun University of Science and Technology, Changchun, 130022, PR China b
ARTICLE INFO
ABSTRACT
Keywords: Laser welding Aluminum Copper Al2Cu Al-Cu eutectic
Laser welding is used in joining 6061 aluminum and 110 copper. The effect of laser power on the microstructure and mechanical properties of Al/Cu lap joints are investigated by using of the optical microscopy (OM), scanning electron microscope (SEM), tensile test device and Vickers hardness device, respectively. The investigation results indicate that the weld metal (WM) mainly consists of the (Al) solid solution and the Al-Cu eutectic alloy, and the interface zone between the copper base metal (BM) and the WM mainly consists of the (Cu) solid solution, the Al2Cu IMC with the shape of serrated and the Al-Cu eutectic alloy with the shape of vermicular. The shear strength of Al/Cu joints first increases and then decreases with the increase of the laser power, maximum is about 99.8 MPa with the 2.45 kW laser power. The fracture surface mainly occurs in Al-Cu eutectic region with the characteristic of brittle fracture. The highest Vickers hardness of Al/Cu lap joints located at the interface zone.
1. Introduction Joining of Al/Cu is a kind of indispensable processing because of low density and excellent corrosion resistance of aluminum as well as the excellent electrical and thermal conductivity of copper, which contributes to the traditional structure to undergo reduction of mass and cost, so Al/Cu dissimilar joints are widely applied industrial fields such as electronic products, heat exchange devices, and the field of battery technology [1–3]. However, joining of Al/Cu dissimilar metals is a signification challenge due to the great difference in physical and chemical properties such as melting point, thermal conductivity, and expansion coefficient [4], meanwhile, the joining components of Al/Cu also have other difficulties which involve the formation of pores, cracks and brittle intermetallic compounds(IMCs) [5,6]. At present, the main researches pay attention to the application of suitable welding methods, optimization of process parameters, reduction of IMCs and etc to improve performances of Al/Cu components. Researchers have tried various welding methods include the ultrasonic spot welding [7,8], the cold welding [9,10], the explosive welding [11,12], the friction stir welding(FSW) [13] and the laser welding [14,15], and have been successfully applied in various industrial fields. However, the formation of representative brittle phases such as Al2Cu,
AlCu, Al4Cu9, AlCu3 IMCs is inevitable, and seriously deteriorate the mechanical properties of the Al/Cu joints when these methods are used to the joining of Al/Cu dissimilar metals. So researchers try to inhibit the formation of IMCs, and find that the strength of Al/Cu dissimilar joints will be rapidly reduced when the thickness of IMCs more than the critical width is about 2.5 μm [16]. Solid-state welding is an effective method to mitigate and even eliminate IMCs especially. Friction stir welding which possesses significant advantages in terms of controlling the formation of IMCs can finish joining of multiple dissimilar metals at the temperature lower than the melting point of materials. It has been proved that the suitable pin and shoulder geometry and the optimized process parameters can inhibit the formation of IMCs during FSW [17–19]. The ultrasonic welding can also prevent the formation of IMCs, Zenglei Ni [20] et al perform ultrasonic spot welded-Al/Cu with Al 2219 alloy particle interlayer, and no IMCs are produced. Fusion welding as a kind of welding method with welding temperature above the melting point of materials, it is impossible to completely avoid the formation of IMCs. Zhou [21] et al have proved that the amount of generated IMCs varies with the heat input. Otten [22] et al and Solchenbach [23] et al and Zhou [24]et al have demonstrated that minimizing the melting amount of Cu can reduce the thickness of IMCs during fusion welding, so that
⁎ Corresponding author at: School of Mechanical and Electric Engineering, Changchun University of Science and Technology, No. 7089 Weixing Road, Changchun, 130022, P R China. E-mail address: [email protected] (Y. Shi).
https://doi.org/10.1016/j.jmapro.2019.07.009 Received 6 May 2019; Received in revised form 27 June 2019; Accepted 2 July 2019 1526-6125/ © 2019 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
Journal of Manufacturing Processes 45 (2019) 312–321
S. Yan and Y. Shi
the tensile strength of joints can be increased. In addition, the addition of additional elements can also inhibit the formation of IMCs to improve the mechanical property of dissimilar joints. The Zn element is added to Al/Cu dissimilar joints, which can significantly reduce continuousness and thickness of the Al2Cu and Al4Cu9 layers [25], and the addition of Ag element can also refine the grain and hamper the growth of Al2Cu [26]. Shi Yu [27] et al also study the effect of filler wires on the pulsed double electrode gas arc welding 1060 aluminum/T2 copper, and conclude that Si element can inhibit the diffusion of Al and Cu atoms and the formation of IMCs, which can enhance the tensile strength of joints. During the laser welding, many researchers have studied the effect of reasonable welding technology such as the filler material, the laser welding track and the laser-hybrid welding on the evolution mechanism of IMCs [23,28,29]. In this paper, in order to research the influence of heat input on the evolution mechanism of IMCs as well as improve the welding efficiency, so it is necessary that control energy precisely and obtain high processing speed. The laser welding with high energy density, high processing rate and highly flexible which is the first choice. To our best knowledge, only limited researches focus on dissimilar metal joining of 6061 aluminum to 110 pure copper by laser welding technology. It can be seen that the core issues related to the reliability of joint are that the formation and growth of intermetallic compounds during welding dissimilar metals, so controlling the interfacial reaction is an important process to improve product quality, it is of great significance for industrial application. The main purpose of this paper is to provide an understanding of the effects of laser power on the evolution mechanism of IMCs, and focused on under the different heat input, how the IMCs to influence the shear strength of weldments.
Table 2 Physical properties of aluminum and copper. Material
Tensile strength (MPa)
Elongation (%)
6061aluminum copper
239.4-307.8 289.4
8-12 14
Fig. 1. Schematic of Al/Cu laser lap welding. Table 3 Processing parameters of laser-welded Al/Cu dissimilar lap welding. Number
O1
O2
O3
O4
Power (W) Welding speed (m/min)
2000 2
2450
2900
3350
2. Experimental procedure H2O) for 15 s, and observed by the OM(LeiCaDM2700 M) and the SEM (FEI Nova Nanolab 200 FIB/SEM System) equipped with an energy dispersive X-ray spectroscopy (EDAX) for microstructure and chemical compositions analysis, respectively. The X-ray diffractometer (Brucker D8 advance) is used to identify the constitution of phases. The mechanical properties of Al/Cu lap joints are characterized by tensile tests (MTS Exceed E43) and microhardness tests (MH-60) for 200gf load with 10 s.
In this test, All welded samples of 6061 aluminum alloy and 110 pure copper of dimension of 50 mm × 25 mm × 1.6 mm are prepared from the BM with help of wire-cut electrical discharge machine, and the chemical compositions of the 6061aluminum alloy are listed in Table 1 as well as the physical properties of both materials are listed in Table 2. The schematic of Al/Cu lap welding as shown in Fig.1 (aluminum on top of copper). The heat source of the lap welding experiment adopts the 4 kW HLD4002 disk laser, and the laser beam directly irradiates on the aluminum surface with the defocusing amount of 0 mm. All samples should be degreased by ultrasonic in acetone and drying treatment. Especially, the aluminum oxide layer (Al2O3) can induce inclusion, and adsorb moisture to cause formation of hydrogen porosity, so the surface of all samples must be brushed by a steel brush before the lap welding to remove the surface oxide layer, and the absorptivity of the material can also be increased due to the increase of roughness of aluminum alloy surface. The mixture gas of argon (10 L/min) and helium gas (10 L/min) is used as shielding gas when performing laser lap welding. The processing parameters of laser lap welding of Al/Cu dissimilar metals are listed in Table 3. After lap welding, the wire-cut electrical discharge machine is used to cut the metallographic samples and tensile samples from weldments as shown in Fig.1, then the metallographic samples are ground by using 400#, 800#, 1000#, 1500#, 2000# grit sic paper gradually, following polished with the polishing suspensions, cleaned with the ultrasonic in alcohol and drying treatment. The metallographic samples are immersed in the Keller's reagent (5 ml HNO3+3 ml HCl+2 ml HF+19 ml
3. Results and discussion 3.1. Microstructure Fig.2 depicts the top view of the Al/Cu lap joints. The relatively flat appearance of Al/Cu lap joints can be obtained and no visible defects can be observed. The top surface of weldments appears the undercut phenomenon, and the red dashed lines represent the undercut in Fig.11. The cross-sectional images of Al/Cu lap joints as shown in Fig.3. The WM can be divided into the upper WM located in aluminum alloy and the lower WM located in copper alloy. It can be observed that the WM mainly consists of the aluminum alloy when the power is 2.0 kW, and only a small amount of copper is melted, the joining of Al/Cu depends on the wetting and spreading characteristic of aluminum on the copper surface. The fusion area of the aluminum and copper also obviously increase with the increase of laser power. However, the amount of molten copper during the welding processing is very less compare with that of aluminum alloy, which caused by the different physical properties of both materials are that the melting point of aluminum alloy is about 600 °C and the copper is about 1083 °C, and the thermal conductivity of copper is extremely high so that extremely difficult to accumulate the heat energy. From Fig. 3, some pores can be observed in WM, as we know that the formation of pore during laser welding aluminum are divided into two types [30]:(1) The keyhole-induced pore
Table 1 Chemical composition of 6061 aluminum alloy (wt.%). Si 0.4-0.8
Fe 0.7
Cu 0.15-0.4
Mn 0.15
Mg
Cr
0.8-1.2
0.04-0.8
Ni 0.05
Zn 0.25
Al Bal
313
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Fig. 2. Top view of Al/Cu lap joints; (a) P = 2.0 kW, (b) P = 2.45 kW, (c) P = 2.9 kW, (d) P = 3.35 kW.
result from the solidification rate of the weld pool more than the backfilling speed of the molten metal during the unstable keyhole collapse. (2) The reason for the formation of pores caused by metallurgical factors is that the temperature of the weld pool exceeds low evaporation temperature of the low-boiling elements such as H, O and N in aluminum alloys or the gasification of pollutant on the aluminum surface, in addition the excellent thermal conduction performance of copper results in the cooling rate of weld pool is further accelerated, the bubbles that cannot overflow from the weld pool before the weld pool solidifies form pores eventually. It can find that a lot of holes locate at both side of joining interface of Al/Cu BM from Fig. 3 and the fracture surface of Fig. 14, which remarkably decreases the effective joining area of Al and Cu BM, so the width of the molten Cu is measured to represent the effective joining area of Al/Cu joints, as shown in Fig.4. It can be seen that the width of WM increases obviously with the increase of power. The stirring effect of the weld pool contributes to the diffusion of Cu atoms from the interface zone to the weld pool when laser welding the Al/Cu dissimilar metals, so with the cooling of the weld pool, the brittle IMCs will be precipitated in the WM and the interface zone, which not only influences on the mechanical properties of Al/Cu joints, but also affects its electrical conductivity [31–33]. The SEM and EDAX are used to further analyze the microstructure of WM. Fig. 5 shows the microstructure images of the lower WM with 2.45 kW and 2.9 kW laser power. The EDAX analysis of red points in
Fig. 4. The width of molten Cu BM.
Fig. 5 is listed in Table 4, and it can be concluded that the Al-Cu eutectic alloy is eventually generated in all points. It can be obviously observed that the copper alloy occur agglomeration phenomenon during weld pool solidification process, and the phenomenon is severer with the increase of laser power because of the higher laser power (heat input) contributes to increasing the melting amount of Cu and more Cu atoms diffuse to the lower WM. Compare the EDAX analysis results of Table 4,
Fig. 3. Cross section images of Al/Cu lap joints with different power; (a) P = 2.0 kW, (b) P = 2.45 kW, (c) P = 2.9 kW, (d) P = 3.35 kW. 314
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Fig. 5. Microstructure images of the lower WM; (a) Overview with P = 2.45 kW, (b) Enlarged view of zone Ⅲ,(c) Enlarged view of zone Ⅳ, (d) Overview with P = 2.9 kW, (e) Enlarged view of zone Ⅴ, (f) Enlarged view of zone Ⅵ.
According to 2.95%.at (4.75%.wt) Cu content of the marked point 1 and 6.32%.at (13.71 wt.%)Cu content of the marked point 2, it can be concluded that the WM above the eutectic region where occurs the hypoeutectic reaction, and mainly consists of the (Al) solid solution and the Al-Cu eutectic, as indicated by the zone Ш which includes the marked point 1 and 2, because of the maximum solid solubility of copper in aluminum is 5.65 wt.% Cu [35]. The XRD analysis of theⅠzone (WM) also reveals the presence of the (Al) solid solution and the Al2Cu IMC. Fig. 7 depicts the interface zone of the Al/Cu lap joints with different power. From Fig. 7, we can conclude that some shape characteristics of the IMCs with the different power are similar, but the thickness of IMCs is different. When the laser power is 2.0 kW, only a small amount of the Al2Cu IMC is formed. With the increase of laser power, namely the heat input increases, and the more copper BM is melted as well as the weld pool with relatively slower cooling rate, so the chemical reaction of Al/Cu has sufficient time and Al/Cu atoms to form more and coarser IMCs. According to Fig. 7, it is also found that the weld pool presents the serious Cu elements segregation phenomenon so that there are different microstructures in different zones. When the temperature of the weld pool reaches 821k, the eutectic reaction generates the Al-Cu eutectic alloy above the Al2Cu region, and the thickness of the Al-Cu eutectic alloy also increases with the increase of laser power. It can be seen that the presence of the free-state Al2Cu IMC in the eutectic region when laser power reaches to 3.35 kW because of more copper atoms diffuse from the interface zone to the WM.
Table 4 Chemical compositions of denoted zones in Fig.5. points
Al (at.%)
Cu (at.%)
1 2 3 4 5 6 7 8
76.65 76.07 92.15 84.28 78.21 72.13 70.16 73.84
23.35 23.93 7.85 15.72 21.79 27.87 29.84 26.16
these all reveal that the content of Cu element of the lower WM with 2.9 kW more than that of 2.45 kW. With the more copper alloy diffuses into WM, which also causes the WM to transition from hypoeutectic reaction to hypereutectic reaction, and to form more Al2Cu in the eutectic region of the WM. The Al alloy is corroded and the Al2Cu IMC is retained when the WM is etched by the Keller's reagent. Compare with 2.9 kW, more Al alloy in the eutectic region of the 2.45 kW WM is corrode, so one can be noted that the dendritic microstructure of the higher laser power is coarser, as shown in Fig. 5(c) and (f). Fig. 6 depicts the microstructure of the interface zone of the Al/Cu lap joints with 2.45 kW laser power. The chemical compositions of the marked point in Fig. 6 are listed in Table 5. The maximum solubility of Al in Cu is about 19.7 at.% [34], according to the EDAX analysis results of Table 5 and the Al-Cu Phase diagram, the Al atoms diffuse into the copper BM from the weld pool, which leads to the content of aluminum element of the marked point 6 in Fig. 6 is 18.41 at. %. It is known that the (Cu) solid solution is formed on the copper side. There is the content of the Al increases to about 66.36 at.% adjacent the (Cu) solid solution region and the atom ratio of Al to Cu was approximately 2:1, which induces the formation of the Al2Cu IMC of the presented zigzag shape on the WM side, its the surface on copper alloy side is relatively uniform, as indicated by the marked points 4 and 5. The Al2Cu IMC grows into the weld pool, its growth direction is perpendicular to the fusion line and parallel to the temperature gradient. Then on the top of the Al2Cu IMC where occurs the hypereutectic reaction to precipitate the Al-Cu eutectic (α-Al + Al2Cu), as indicated by the marked points 3.
3.2. Phase analysis and reaction mechanism The X-ray diffractometer is performed to analyze the phase composition ofⅠzone(WM) andⅡzone(interface zone) in Fig. 3, and the results as shown in Fig. 8. The diffraction peaks of (Al) solid solution ofⅠzone is stronger than that ofⅡzone due to the WM mainly consists of (Al) solid solution, but only a little of Al atoms diffuse into interface zone and copper BM. On the contrary, the diffraction peaks of (Cu) solid solution ofⅡzone is stronger than that ofⅠzone because of (Cu) solid solution mainly concentrate on the interface zone and presence of Cu BM, but only a little of Cu atoms diffuse into the upper zone of the weld pool. It can be also observed that Al2Cu IMC can be detected in the 315
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Fig. 6. Interface microstructure images of Al/Cu lap weld joint (P = 2.45 kW);(a) Enlarged view of Fig.2 zone Ⅱ,(b) Enlarged view of zone Ш,(c) Enlarged view of zone Ⅳ.
weld pool, meanwhile the aluminum atoms diffuse into the interface zone and the copper BM. However, the solidification process is very fast so that the insufficient diffusion time of atoms, the aluminum/copper element segregation phenomenon is severe. With the decrease of weld pool temperature, the weld pool solidifies and crystallizes. (c) With the rapid cooling of the weld pool, the (Al) solid solution forms in the weld pool when the temperature decreases to about 933.5 K. When the temperature further decreases to about 864k, the formed (Al) solid solution further develops, and the Al2Cu IMC precipitates from the weld pool adjacent to the (Cu) solid solution, then the formed zigzag Al2Cu IMC gradually grows up into the weld pool and consumes Al and Cu atoms. (d) With the further cooling, and the reduction of the copper element, the Al-Cu eutectic alloy began to nucleate and grow adjacent to the Al2Cu IMC region on the interface zone, but only a bit of the Al-Cu eutectic alloy is generated on the WM because of relatively a fewer copper atoms diffuse to the weld pool. When the entire weld pool solidifies, a large amount of (Al) solid solution and a small amount of the Al-Cu eutectic alloy is generated in the WM, and the Al2Cu, Al-Cu eutectic alloy and (Cu) solid solution exist in the interface zone, which are identical with the analysis results of Figs. 5–8 in the previous section of the article.
Table 5 Chemical compositions of denoted zones in Fig.6. points Ш
1 2 3 4 5 6
Al (at.%)
Cu (at.%)
Possible phase
97.92 93.68 73.98 66.36 67.14 18.41
2.95 6.32 26.02 33.64 32.86 81.59
(Al) solid solution + Al-Cu eutectic Al-Cu eutectic Al2Cu Al2Cu (Cu) solid solution
upper WM, but the diffraction peaks of Al2Cu at the interface zone is stronger, which indicates the Al2Cu IMC mainly located in the interface zone. The diffraction peaks of Al2Cu does not exist when the laser power is 2.0 kW because of the insufficient laser power only melts a small amount Cu alloy, so that the formed Al2Cu is not enough to be detected. With the increase of laser power in the range of 2.45 kW–3.35 kW, the diffraction peaks of Al2Cu and Cu gradually increases, as mentioned in the previous section of the article is that the increase of laser power results in the increase of molten Cu and thickness of IMCs. So it can be concluded that the WM is mainly constituted by (Al) solid solution and a little of Al-Cu eutectic alloy, the interface zone forms a mass of (Cu) solid solution and the Al2Cu IMC, and the AlCu eutectic alloy. According to the above analysis results and Al-Cu binary phase diagram, the reaction mechanism of WM and interface zone is discussed as follows and the schematic as described in Fig. 9. (a–b) The aluminum alloy and the copper alloy are melted when laser irradiates on the welded samples, the molten aluminum is located at the weld pool, but the molten copper mainly concentrates on the interface zone between the weld pool and the copper BM. Under the action of stirring and convection, the copper atoms diffuse from the interface zone to the
3.3. Mechanical properties and fracture behavior Fig.10 shows Vickers hardness distribution of Al/Cu joints along vertical direction as shown the red arrow in Fig.11. The Vickers hardness tests adopt the load of 200gf for 10 s. The Vickers hardness of the interface zone is highest because of the presence of Al2Cu IMC with hard and brittle characteristics. Since the thickness of the IMCs varies with laser power, the size of the hardness indentation is not equal to the thickness of the IMCs, so that the Vickers hardness of the interface zone 316
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Fig. 7. SEM images of interface zone of Al/Cu lap joints with different laser power; (a) P = 2.0 kW, (b) P = 2.45 kW, (c) P = 2.9 kW, (d) P = 3.35 kW.
is different under different power conditions. From Fig.10, it is also found that the Vickers hardness of WM gradually increases with the increase of laser power, by reason of the percent of molten copper in the WM the high laser power is obviously
more than that of the low laser power, which results in the more molten copper diffuse into WM, and induces the formation of more IMCs. The Vickers hardness of WM is equal to that of the aluminum BM when the laser power is 2.0 kW because of the WM completely consists of the
Fig. 8. XRD analysis patterns of Al/Cu lap joints. (a)P = 2.0 kW,(b)P = 2.45 kW,(c)P = 2.9 kW,(d)P = 3.35 kW. 317
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Fig. 9. Schematic of interface reaction of Al/Cu lap joints.
Fig. 10. Vickers hardness distribution of the cross-section of Al/Cu lap joints. (The green rectangle represents the interface between the Al BM and the copper BM).
Fig. 12. Variation of the tensile strength of the Al/Cu lap joints with the different laser power.
aluminum alloy. We can also see that the fluctuation of the hardness value of WM is more obvious and intense when the laser power is 2.9 kW and 3.35 kW, which indicates that microstructure is nonuniform. As shown in Figs. 3 and 11, we can see that the color of the WM is nonuniform, the copper also appears agglomeration phenomenon in the WM. Fig. 12 shows the shear strength of Al/Cu lap joints as a function of
laser power. The shear strength value of 99.8 MPa of lap joint is highest when the laser power of 2.45 kW. The shear strength of Al/Cu lap joints is obviously weakened by reason of the presence of pores and IMC. The shear strength of Al/Cu lap joints increases first and then reduces with the increase of laser power. The shear strength of Al/Cu lap joints is weakest when the laser power is 2.0 kW because of the joining area of 2.0 kW lap joint is the smallest, and the presence of pores further decrease the joining area of Al/Cu joints. When the laser power in the
Fig. 11. Optical images of Al/Cu lap joints. (a) P = 2.45 kW, (b) P = 2.9kw, (C) P = 3.35 kW (the red arrow represents test direction of Vickers hardness). 318
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Fig. 13. Fracture surfaces of Al/Cu lap joint in the Al side; (a) Overview, (b) Overview, (c) Overview, (d) Enlarged view of zoneⅤ, (e) Enlarged view of zone Ⅵ.
Fig. 14. Fracture surfaces of Al/Cu lap joint in the Cu side; (a) Overview, (b) Overview, (c) Enlarged view of zone Ⅷ.
range of 2.0 kW–2.45 kW, the joining area of joints gradually increase with the increase of laser power, which promotes the increase of joint strength. The weight percent of copper alloy also increase in weld pool when laser power increases in the range of 2.45 kW–3.35 kW, which results in the increase of the content of the formed IMCs. The more
content of brittle IMCs in the joint, the lower shear strength of Al/Cu joint [24,36]. As mentioned in the previous section of the article is that the thickness of Al2Cu region and Al-Cu eutectic region also increases with the increase of laser power, which causes the decrease of the strength of Al/Cu joints [22,31]. 319
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solid solution region when the joints are subjected to tensile load, so the fail surfaces mainly locate at the Al-Cu eutectic region of Al-rich phase, as shown in Fig.15. C. Otten [22] et al adopt the electron beam to perform the joining of Al/Cu, and find that the fracture surface is formed in the eutectic region eventually. D. Zuo [31] et al have also proved that when the Al/Cu joints are subjected to tensile load, the crack sources are easily generated in the Al2Cu region because of the presence of the brittle Al2Cu at room temperature. Therefore, the presence of Al2Cu is the main cause of fracture failure of Al/Cu joints. In Fig.13(c) and larger magnification Fig.13 (d), it indicates that a relatively coarse fracture surface and the existence of dimple with the characteristic of ductile fracture. The content of Cu element of the measurement point 3 is 7.85at. % (16.71 wt.%), while the maximum solubility of copper in Al is 5.65 wt.% [35]. According to the phase diagram, this eutectic region mainly consists of the (Al) solid solution, the ductile fracture with dimples characteristic is the main fracture form of 6061 aluminum alloy [35,40,41]. Di Zuo [31] et al also demonstrate the presence of ductile fracture of Al/Cu lap weld in the Al side. The fracture surfaces of Al/Cu joint in the Cu side as shown in Fig.14. It is also found that the presence of pores. According to Fig.14 (b), (c) and the EDAX analysis results listed in Table 7, the results show that the fracture surfaces mainly occur in the Al-Cu eutectic zone, meanwhile it is noted that the cracks expand into the Al2Cu IMC region, as shown in Fig.15, and we can conclude that the entire fracture surface is a brittle fracture with cleavage characteristic.
Table 6 EDAX measurement of marked points of the Fig.13. Marked points
Al (at.%)
Cu (at.%)
Possible phase
1 2 3 4
79.36 85.23 92.15 78.09
20.64 14.77 7.85 21.91
Al + Al2Cu Al+(Al-Cu eutectic) Al+(Al-Cu eutectic) Al + Al2Cu
Table 7 EDAX measurement of marked points of the Fig.14. Marked points
Al (at.%)
Cu (at.%)
Possible phase
5 6 7 8
69.3 71.22 62.06 62.26
31.7 28.77 37.94 37.74
Al + Al2Cu Al + Al2Cu Al2Cu Al2Cu
Figs.13 and 14 show that fracture surfaces of Al/Cu laser lap joint with the laser power of 2.45 kW. We execute the constitute analysis of fracture surface and the EDAX analysis are marked in Figs.13 and 14. The results of EDAX analysis are listed in Tables 6, 7 and shown in Fig.13 (e), respectively. Fig.13 depicts the fracture surface of Al/Cu joint on the Al side. From Fig.13, it can be seen that the presence of pores which is generated during the processing of welding aluminum, which has a significantly negative influence on the mechanical properties of joints [37–39]. From Fig.13(a) and (b), the relatively smooth and flat fracture surfaces with the characteristic of cleavage can be observed, the cleavage phenomena indicates that the fracture mode of Al/Cu is the typical characteristic of brittle fracture. According to Table 6, Fig.13 (e) and Table 7, it can be concluded that the cracks extend along the Al-Cu eutectic region, and also propagate into the Al2Cu region and the (Cu)
4. Conclusions In this paper, the effect of laser power on mechanical and microstructure of the laser-welded Al/Cu dissimilar lap joints are studied, we can draw conclusions as follows:
Fig. 15. Cross-section fracture image of Al/Cu lap joint; (a) (b) Cross-section fracture image, (c) Schematic of the location of the fracture surface. 320
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(1) The laser beam is applied to welding Al/Cu dissimilar metal, we can come true precisely to control the heat input so that the melting amount of Cu can be controlled. Although the formation of pores is inevitable, the acceptable Al/Cu lap joints are acquired. (2) With the increase of laser power, the molten Cu is obviously increased, the more copper diffuses into WM, which results in the formation of coarser Al2Cu IMC and severer agglomeration phenomenon of Cu element in WM. The (Cu) solid solution and the serrate Al2Cu IMC and the Al-Cu eutectic alloy with the shape of vermicular can be observed at the interface zone. The thickness of all IMCs region increases with the increase of laser power. (3) The shear strength first increases and then decreases with the increase of laser power, the maximum shear strength is about 99.8 MPa with the laser power of 2.45 kW. The fracture surface mainly located at the Al-Cu eutectic region, but the crack also propagates into the (Cu) solid solution region and the Al2Cu IMC region of the interface zone, as well as the WM. The hardness of the interface zone is highest because of presence of a large amount of IMCs, and compare with low laser power, the Vickers hardness of the WM with high laser power fluctuates more acute.
solar thermal absorbers. Mater Des 2018;155:148–60. [15] Reisgen U, Olschok S, Jakobs S, Holtum N. Influence of the degree of dilution with laser beam vacuum-welded Cu-Al mixed joints on the electrical properties. Procedia Cirp 2018;74:23–6. [16] Salehia MT. Growth rate of intermetallic compounds in AL/CU bimetal produced by Cold Roll Welding Process. J Alloys Compd 2001;319:233–41. [17] Zhou L, Zhang RX, Li GH, Zhou WL, Huang YX, Song XG. Effect of pin profile on microstructure and mechanical properties of friction stir spot welded Al-Cu dissimilar metals. J Manuf Process 2018;36:1–9. [18] Galvão I, Oliveira JC, Loureiro A, Rodrigues DM. Formation and distribution of brittle structures in friction stir welding of aluminium and copper: influence of shoulder geometry. Intermetallics 2012;22:122–8. [19] Bhattacharya TK, Das H, Pal TK. Influence of welding parameters on material flow, mechanical property and intermetallic characterization of friction stir welded AA6063 to HCP copper dissimilar butt joint without offset. Trans Nonferrous Met Soc China 2015;25:2833–46. [20] Ni Z, Zhao H, Mi P, Ye F. Microstructure and mechanical performances of ultrasonic spot welded Al/Cu joints with Al 2219 alloy particle interlayer. Mater Des 2016;92:779–86. [21] Li Z, Zhi-yong L, Hong-yun Z, Yu X, Yong-xian H, Ji-cai F. Microstructure and mechanical properties of Al/brass dissimilar metals TIG welding-brazing joint. Chin J Nonferrous Metals 2015;29. [22] Otten C, Reisgen U, Schmachtenberg M. Electron beam welding of aluminum to copper: mechanical properties and their relation to microstructure. Weld World 2015;60:21–31. [23] Solchenbach T, Plapper P. Mechanical characteristics of laser braze-welded aluminium–copper connections. Opt Laser Technol 2013;54:249–56. [24] Zhou L, Li ZY, Song XG, Tan CW, He ZZ, Huang YX, et al. Influence of laser offset on laser welding-brazing of Al/brass dissimilar alloys. J Alloys Compd 2017;717:78–92. [25] Boucherit A, Avettand-Fènoël MN, Taillard R. Effect of a Zn interlayer on dissimilar FSSW of Al and Cu. Mater Des 2017;124:87–99. [26] Man Z, Pengfei W, Lincai Z, Yuebin L. Microstructure and mechanical properties of Cu/Al joint brazed with Zn-Al-Ag filler metal. Trans China Welding Inst 2013;34:55–8. [27] Yu S, Xianglong Z, Ming Z, Yufen G, Ding F. Effect of filler wires on brazing interface microstructure and mechanical properties of Al/Cu dissimilar metals welding-brazing joint. Mater Sci Eng R Rep 2017;31:61–4. [28] Fei X, Ying Y, Jin L, Wang H, Lv S. Special welding parameters study on Cu/Al joint in laser-heated friction stir welding. J Mater Process Technol 2018;256:S0924013618300499. [29] Kraetzsch M, Standfuss J, Klotzbach A, Kaspar J, Brenner B, Beyer E. Laser beam welding with high-frequency beam oscillation: welding of dissimilar materials with brilliant Fiber lasers. Phys Proc 2011;12:142–9. [30] Wang Z, Oliveira JP, Zeng Z, Bu X, Peng B, Shao X. Laser beam oscillating welding of 5A06 aluminum alloys: microstructure, porosity and mechanical properties. Opt Laser Technol 2019;111:58–65. [31] Zuo D, Hu S, Shen J, Xue Z. Intermediate layer characterization and fracture behavior of laser-welded copper/aluminum metal joints. Mater Des 2014;58:357–62. [32] Lee W-B, Bang K-S, Jung S-B. Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing. J Alloys Compd 2005;390:212–9. [33] Braunovic M, Alexandrov N. Intermetallic compounds at aluminum-to-copper electrical interfaces: effect of temperature and electric current. Comp Packag Manuf Technol Part A IEEE Trans on 1994;17:78–85. [34] Elliot J, Massalaski T, Murray J, Bennett L, Baker H. Binary alloy phase diagrams. Metals Park, OH: American Society for Metals; 1986. [35] Mai TA, Spowage AC. Characterisation of dissimilar joints in laser welding of steel–kovar, copper–steel and copper–aluminium. Mater Sci Eng A 2004;374:224–33. [36] Zhou L, Luo LY, Tan CW, Li ZY, Song XG, Zhao HY, et al. Effect of welding speed on microstructural evolution and mechanical properties of laser welded-brazed Al/ brass dissimilar joints. Opt Laser Technol 2018;98:234–46. [37] Wen L, Wang HP, Lu F, Cui H, Tang X. Investigation on effects of process parameters on porosity in dissimilar Al alloy lap fillet welds. Int J Adv Manuf Technol 2015;81:843–9. [38] Lin R, Wang HP, Lu F, Solomon J, Carlson BE. Numerical study of keyhole dynamics and keyhole-induced porosity formation in remote laser welding of Al alloys. Int J Heat Mass Transf 2017;108:244–56. [39] Huang L, Hua X, Wu D, Jiang Z, Ye Y. A study on the metallurgical and mechanical properties of a GMAW-welded Al-Mg alloy with different plate thicknesses. J Manuf Process 2019;37:438–45. [40] Chu Q, Bai R, Jian H, Lei Z, Hu N, Yan C. Microstructure, texture and mechanical properties of 6061 aluminum laser beam welded joints. Mater Charact 2018;137:269–76. [41] Huang Y, Meng X, Lv Z, Huang T, Zhang Y, Cao J, et al. Microstructures and mechanical properties of micro friction stir welding (μFSW) of 6061-T4 aluminum alloy. J Mater Res Technol 2018.
Acknowledgements The authors wish to acknowledge Professor of Jyotirmoy Mazumder, University of Michigan, for her help in the financial and technical support of this research. The authors are also grateful for the financial aids from the Scientific and Technological Planning Project of Jilin Province (Grant No. 20170204065GX and No. 20180201063GX), and the National Key Research and Development Program of China (Grant No. 2017YFB1104601), and the Project supported by the Equipment preresearch field Foundation of China (Grant No. 61409230509). References [1] Solchenbach T, Plapper P. Combined laser beam braze-welding process for fluxless al-cu connections. PROCEDINGS International Conference on Competitive Manufacturing 2013;13:131–6. [2] B.J. P, P. F, S. R. Solid-state welding of aluminum to copper—case studies. Weld World 2013;57:541–50. [3] Zoeram AS, Anijdan SHM, Jafarian HR, Bhattacharjee T. Welding parameters analysis and microstructural evolution of dissimilar joints in Al/Bronze processed by friction stir welding and their effect on engineering tensile behavior. Mater Sci Eng A 2017;687:288–97. [4] Martinsen K, Hu SJ, Carlson BE. Joining of dissimilar materials. CIRP Ann Manuf Technol 2015;64:679–99. [5] Wang X-G, Li X-G, Wang C-G. Influence of diffusion brazing parameters on microstructure and properties of Cu/Al joints. J Manuf Process 2018;35:343–50. [6] Zhang M, Xue S, Feng JI, Lou Y, Wang S. Effect of CuAl_2 phase on properties and microstructure of Cu/Al brazed joint. Trans China Weld Inst 2011;32:93–6. [7] Feng M-N, Xie Y, Zhao C-F, Luo Z. Microstructure and mechanical performance of ultrasonic spot welded open-cell Cu foam/Al joint. J Manuf Process 2018;33:86–95. [8] Fujii HT, Endo H, Sato YS, Kokawa H. Interfacial microstructure evolution and weld formation during ultrasonic welding of Al alloy to Cu. Mater Charact 2018;139:233–40. [9] Koberna M, Fiala J. Intermetallic phases in cold-welded Al-Cu joints. Mater Sci Eng A 1992;159:231–6. [10] WOŹNIAK H. The results of the so far performed investigations of Al-Cu butt cold pressure welding by the method of upsetting. Arch Civ Mech Eng 2009;9:135–45. [11] Akbari Mousavi SAA, Al-Hassani STS, Atkins AG. Bond strength of explosively welded specimens. Mater Des 2008;29:1334–52. [12] Honarpisheh M, Asemabadi M, Sedighi M. Investigation of annealing treatment on the interfacial properties of explosive-welded Al/Cu/Al multilayer. Mater Des 2012;37:122–7. [13] Sharma N, Khan ZA, Siddiquee AN. Friction stir welding of aluminum to copper—an overview. Trans Nonferrous Met Soc China 2017;27:2113–36. [14] Kermanidis AT, Christodoulou PI, Hontzopoulos E, Haidemenopoulos GN, Kamoutsi H, Zervaki AD. Mechanical performance of laser spot-welded joints in Al-Al/Cu
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Influence of laser power on microstructure and mechanical property of laserwelded Al/Cu dissimilar lap joints
T
Shenghong Yana,b,c, Yan. Shia,b,c,
⁎
a
School of Mechanical and Electric Engineering, Changchun University of Science and Technology, Changchun, 130022, PR China National Base of International Science and Technology Cooperation for Optics, Changchun, 130022, PR China c Ministry of Education Key Laboratory for Cross-Scale Micro and Nano Manufacturing, Changchun University of Science and Technology, Changchun, 130022, PR China b
ARTICLE INFO
ABSTRACT
Keywords: Laser welding Aluminum Copper Al2Cu Al-Cu eutectic
Laser welding is used in joining 6061 aluminum and 110 copper. The effect of laser power on the microstructure and mechanical properties of Al/Cu lap joints are investigated by using of the optical microscopy (OM), scanning electron microscope (SEM), tensile test device and Vickers hardness device, respectively. The investigation results indicate that the weld metal (WM) mainly consists of the (Al) solid solution and the Al-Cu eutectic alloy, and the interface zone between the copper base metal (BM) and the WM mainly consists of the (Cu) solid solution, the Al2Cu IMC with the shape of serrated and the Al-Cu eutectic alloy with the shape of vermicular. The shear strength of Al/Cu joints first increases and then decreases with the increase of the laser power, maximum is about 99.8 MPa with the 2.45 kW laser power. The fracture surface mainly occurs in Al-Cu eutectic region with the characteristic of brittle fracture. The highest Vickers hardness of Al/Cu lap joints located at the interface zone.
1. Introduction Joining of Al/Cu is a kind of indispensable processing because of low density and excellent corrosion resistance of aluminum as well as the excellent electrical and thermal conductivity of copper, which contributes to the traditional structure to undergo reduction of mass and cost, so Al/Cu dissimilar joints are widely applied industrial fields such as electronic products, heat exchange devices, and the field of battery technology [1–3]. However, joining of Al/Cu dissimilar metals is a signification challenge due to the great difference in physical and chemical properties such as melting point, thermal conductivity, and expansion coefficient [4], meanwhile, the joining components of Al/Cu also have other difficulties which involve the formation of pores, cracks and brittle intermetallic compounds(IMCs) [5,6]. At present, the main researches pay attention to the application of suitable welding methods, optimization of process parameters, reduction of IMCs and etc to improve performances of Al/Cu components. Researchers have tried various welding methods include the ultrasonic spot welding [7,8], the cold welding [9,10], the explosive welding [11,12], the friction stir welding(FSW) [13] and the laser welding [14,15], and have been successfully applied in various industrial fields. However, the formation of representative brittle phases such as Al2Cu,
AlCu, Al4Cu9, AlCu3 IMCs is inevitable, and seriously deteriorate the mechanical properties of the Al/Cu joints when these methods are used to the joining of Al/Cu dissimilar metals. So researchers try to inhibit the formation of IMCs, and find that the strength of Al/Cu dissimilar joints will be rapidly reduced when the thickness of IMCs more than the critical width is about 2.5 μm [16]. Solid-state welding is an effective method to mitigate and even eliminate IMCs especially. Friction stir welding which possesses significant advantages in terms of controlling the formation of IMCs can finish joining of multiple dissimilar metals at the temperature lower than the melting point of materials. It has been proved that the suitable pin and shoulder geometry and the optimized process parameters can inhibit the formation of IMCs during FSW [17–19]. The ultrasonic welding can also prevent the formation of IMCs, Zenglei Ni [20] et al perform ultrasonic spot welded-Al/Cu with Al 2219 alloy particle interlayer, and no IMCs are produced. Fusion welding as a kind of welding method with welding temperature above the melting point of materials, it is impossible to completely avoid the formation of IMCs. Zhou [21] et al have proved that the amount of generated IMCs varies with the heat input. Otten [22] et al and Solchenbach [23] et al and Zhou [24]et al have demonstrated that minimizing the melting amount of Cu can reduce the thickness of IMCs during fusion welding, so that
⁎ Corresponding author at: School of Mechanical and Electric Engineering, Changchun University of Science and Technology, No. 7089 Weixing Road, Changchun, 130022, P R China. E-mail address: [email protected] (Y. Shi).
https://doi.org/10.1016/j.jmapro.2019.07.009 Received 6 May 2019; Received in revised form 27 June 2019; Accepted 2 July 2019 1526-6125/ © 2019 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
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the tensile strength of joints can be increased. In addition, the addition of additional elements can also inhibit the formation of IMCs to improve the mechanical property of dissimilar joints. The Zn element is added to Al/Cu dissimilar joints, which can significantly reduce continuousness and thickness of the Al2Cu and Al4Cu9 layers [25], and the addition of Ag element can also refine the grain and hamper the growth of Al2Cu [26]. Shi Yu [27] et al also study the effect of filler wires on the pulsed double electrode gas arc welding 1060 aluminum/T2 copper, and conclude that Si element can inhibit the diffusion of Al and Cu atoms and the formation of IMCs, which can enhance the tensile strength of joints. During the laser welding, many researchers have studied the effect of reasonable welding technology such as the filler material, the laser welding track and the laser-hybrid welding on the evolution mechanism of IMCs [23,28,29]. In this paper, in order to research the influence of heat input on the evolution mechanism of IMCs as well as improve the welding efficiency, so it is necessary that control energy precisely and obtain high processing speed. The laser welding with high energy density, high processing rate and highly flexible which is the first choice. To our best knowledge, only limited researches focus on dissimilar metal joining of 6061 aluminum to 110 pure copper by laser welding technology. It can be seen that the core issues related to the reliability of joint are that the formation and growth of intermetallic compounds during welding dissimilar metals, so controlling the interfacial reaction is an important process to improve product quality, it is of great significance for industrial application. The main purpose of this paper is to provide an understanding of the effects of laser power on the evolution mechanism of IMCs, and focused on under the different heat input, how the IMCs to influence the shear strength of weldments.
Table 2 Physical properties of aluminum and copper. Material
Tensile strength (MPa)
Elongation (%)
6061aluminum copper
239.4-307.8 289.4
8-12 14
Fig. 1. Schematic of Al/Cu laser lap welding. Table 3 Processing parameters of laser-welded Al/Cu dissimilar lap welding. Number
O1
O2
O3
O4
Power (W) Welding speed (m/min)
2000 2
2450
2900
3350
2. Experimental procedure H2O) for 15 s, and observed by the OM(LeiCaDM2700 M) and the SEM (FEI Nova Nanolab 200 FIB/SEM System) equipped with an energy dispersive X-ray spectroscopy (EDAX) for microstructure and chemical compositions analysis, respectively. The X-ray diffractometer (Brucker D8 advance) is used to identify the constitution of phases. The mechanical properties of Al/Cu lap joints are characterized by tensile tests (MTS Exceed E43) and microhardness tests (MH-60) for 200gf load with 10 s.
In this test, All welded samples of 6061 aluminum alloy and 110 pure copper of dimension of 50 mm × 25 mm × 1.6 mm are prepared from the BM with help of wire-cut electrical discharge machine, and the chemical compositions of the 6061aluminum alloy are listed in Table 1 as well as the physical properties of both materials are listed in Table 2. The schematic of Al/Cu lap welding as shown in Fig.1 (aluminum on top of copper). The heat source of the lap welding experiment adopts the 4 kW HLD4002 disk laser, and the laser beam directly irradiates on the aluminum surface with the defocusing amount of 0 mm. All samples should be degreased by ultrasonic in acetone and drying treatment. Especially, the aluminum oxide layer (Al2O3) can induce inclusion, and adsorb moisture to cause formation of hydrogen porosity, so the surface of all samples must be brushed by a steel brush before the lap welding to remove the surface oxide layer, and the absorptivity of the material can also be increased due to the increase of roughness of aluminum alloy surface. The mixture gas of argon (10 L/min) and helium gas (10 L/min) is used as shielding gas when performing laser lap welding. The processing parameters of laser lap welding of Al/Cu dissimilar metals are listed in Table 3. After lap welding, the wire-cut electrical discharge machine is used to cut the metallographic samples and tensile samples from weldments as shown in Fig.1, then the metallographic samples are ground by using 400#, 800#, 1000#, 1500#, 2000# grit sic paper gradually, following polished with the polishing suspensions, cleaned with the ultrasonic in alcohol and drying treatment. The metallographic samples are immersed in the Keller's reagent (5 ml HNO3+3 ml HCl+2 ml HF+19 ml
3. Results and discussion 3.1. Microstructure Fig.2 depicts the top view of the Al/Cu lap joints. The relatively flat appearance of Al/Cu lap joints can be obtained and no visible defects can be observed. The top surface of weldments appears the undercut phenomenon, and the red dashed lines represent the undercut in Fig.11. The cross-sectional images of Al/Cu lap joints as shown in Fig.3. The WM can be divided into the upper WM located in aluminum alloy and the lower WM located in copper alloy. It can be observed that the WM mainly consists of the aluminum alloy when the power is 2.0 kW, and only a small amount of copper is melted, the joining of Al/Cu depends on the wetting and spreading characteristic of aluminum on the copper surface. The fusion area of the aluminum and copper also obviously increase with the increase of laser power. However, the amount of molten copper during the welding processing is very less compare with that of aluminum alloy, which caused by the different physical properties of both materials are that the melting point of aluminum alloy is about 600 °C and the copper is about 1083 °C, and the thermal conductivity of copper is extremely high so that extremely difficult to accumulate the heat energy. From Fig. 3, some pores can be observed in WM, as we know that the formation of pore during laser welding aluminum are divided into two types [30]:(1) The keyhole-induced pore
Table 1 Chemical composition of 6061 aluminum alloy (wt.%). Si 0.4-0.8
Fe 0.7
Cu 0.15-0.4
Mn 0.15
Mg
Cr
0.8-1.2
0.04-0.8
Ni 0.05
Zn 0.25
Al Bal
313
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Fig. 2. Top view of Al/Cu lap joints; (a) P = 2.0 kW, (b) P = 2.45 kW, (c) P = 2.9 kW, (d) P = 3.35 kW.
result from the solidification rate of the weld pool more than the backfilling speed of the molten metal during the unstable keyhole collapse. (2) The reason for the formation of pores caused by metallurgical factors is that the temperature of the weld pool exceeds low evaporation temperature of the low-boiling elements such as H, O and N in aluminum alloys or the gasification of pollutant on the aluminum surface, in addition the excellent thermal conduction performance of copper results in the cooling rate of weld pool is further accelerated, the bubbles that cannot overflow from the weld pool before the weld pool solidifies form pores eventually. It can find that a lot of holes locate at both side of joining interface of Al/Cu BM from Fig. 3 and the fracture surface of Fig. 14, which remarkably decreases the effective joining area of Al and Cu BM, so the width of the molten Cu is measured to represent the effective joining area of Al/Cu joints, as shown in Fig.4. It can be seen that the width of WM increases obviously with the increase of power. The stirring effect of the weld pool contributes to the diffusion of Cu atoms from the interface zone to the weld pool when laser welding the Al/Cu dissimilar metals, so with the cooling of the weld pool, the brittle IMCs will be precipitated in the WM and the interface zone, which not only influences on the mechanical properties of Al/Cu joints, but also affects its electrical conductivity [31–33]. The SEM and EDAX are used to further analyze the microstructure of WM. Fig. 5 shows the microstructure images of the lower WM with 2.45 kW and 2.9 kW laser power. The EDAX analysis of red points in
Fig. 4. The width of molten Cu BM.
Fig. 5 is listed in Table 4, and it can be concluded that the Al-Cu eutectic alloy is eventually generated in all points. It can be obviously observed that the copper alloy occur agglomeration phenomenon during weld pool solidification process, and the phenomenon is severer with the increase of laser power because of the higher laser power (heat input) contributes to increasing the melting amount of Cu and more Cu atoms diffuse to the lower WM. Compare the EDAX analysis results of Table 4,
Fig. 3. Cross section images of Al/Cu lap joints with different power; (a) P = 2.0 kW, (b) P = 2.45 kW, (c) P = 2.9 kW, (d) P = 3.35 kW. 314
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Fig. 5. Microstructure images of the lower WM; (a) Overview with P = 2.45 kW, (b) Enlarged view of zone Ⅲ,(c) Enlarged view of zone Ⅳ, (d) Overview with P = 2.9 kW, (e) Enlarged view of zone Ⅴ, (f) Enlarged view of zone Ⅵ.
According to 2.95%.at (4.75%.wt) Cu content of the marked point 1 and 6.32%.at (13.71 wt.%)Cu content of the marked point 2, it can be concluded that the WM above the eutectic region where occurs the hypoeutectic reaction, and mainly consists of the (Al) solid solution and the Al-Cu eutectic, as indicated by the zone Ш which includes the marked point 1 and 2, because of the maximum solid solubility of copper in aluminum is 5.65 wt.% Cu [35]. The XRD analysis of theⅠzone (WM) also reveals the presence of the (Al) solid solution and the Al2Cu IMC. Fig. 7 depicts the interface zone of the Al/Cu lap joints with different power. From Fig. 7, we can conclude that some shape characteristics of the IMCs with the different power are similar, but the thickness of IMCs is different. When the laser power is 2.0 kW, only a small amount of the Al2Cu IMC is formed. With the increase of laser power, namely the heat input increases, and the more copper BM is melted as well as the weld pool with relatively slower cooling rate, so the chemical reaction of Al/Cu has sufficient time and Al/Cu atoms to form more and coarser IMCs. According to Fig. 7, it is also found that the weld pool presents the serious Cu elements segregation phenomenon so that there are different microstructures in different zones. When the temperature of the weld pool reaches 821k, the eutectic reaction generates the Al-Cu eutectic alloy above the Al2Cu region, and the thickness of the Al-Cu eutectic alloy also increases with the increase of laser power. It can be seen that the presence of the free-state Al2Cu IMC in the eutectic region when laser power reaches to 3.35 kW because of more copper atoms diffuse from the interface zone to the WM.
Table 4 Chemical compositions of denoted zones in Fig.5. points
Al (at.%)
Cu (at.%)
1 2 3 4 5 6 7 8
76.65 76.07 92.15 84.28 78.21 72.13 70.16 73.84
23.35 23.93 7.85 15.72 21.79 27.87 29.84 26.16
these all reveal that the content of Cu element of the lower WM with 2.9 kW more than that of 2.45 kW. With the more copper alloy diffuses into WM, which also causes the WM to transition from hypoeutectic reaction to hypereutectic reaction, and to form more Al2Cu in the eutectic region of the WM. The Al alloy is corroded and the Al2Cu IMC is retained when the WM is etched by the Keller's reagent. Compare with 2.9 kW, more Al alloy in the eutectic region of the 2.45 kW WM is corrode, so one can be noted that the dendritic microstructure of the higher laser power is coarser, as shown in Fig. 5(c) and (f). Fig. 6 depicts the microstructure of the interface zone of the Al/Cu lap joints with 2.45 kW laser power. The chemical compositions of the marked point in Fig. 6 are listed in Table 5. The maximum solubility of Al in Cu is about 19.7 at.% [34], according to the EDAX analysis results of Table 5 and the Al-Cu Phase diagram, the Al atoms diffuse into the copper BM from the weld pool, which leads to the content of aluminum element of the marked point 6 in Fig. 6 is 18.41 at. %. It is known that the (Cu) solid solution is formed on the copper side. There is the content of the Al increases to about 66.36 at.% adjacent the (Cu) solid solution region and the atom ratio of Al to Cu was approximately 2:1, which induces the formation of the Al2Cu IMC of the presented zigzag shape on the WM side, its the surface on copper alloy side is relatively uniform, as indicated by the marked points 4 and 5. The Al2Cu IMC grows into the weld pool, its growth direction is perpendicular to the fusion line and parallel to the temperature gradient. Then on the top of the Al2Cu IMC where occurs the hypereutectic reaction to precipitate the Al-Cu eutectic (α-Al + Al2Cu), as indicated by the marked points 3.
3.2. Phase analysis and reaction mechanism The X-ray diffractometer is performed to analyze the phase composition ofⅠzone(WM) andⅡzone(interface zone) in Fig. 3, and the results as shown in Fig. 8. The diffraction peaks of (Al) solid solution ofⅠzone is stronger than that ofⅡzone due to the WM mainly consists of (Al) solid solution, but only a little of Al atoms diffuse into interface zone and copper BM. On the contrary, the diffraction peaks of (Cu) solid solution ofⅡzone is stronger than that ofⅠzone because of (Cu) solid solution mainly concentrate on the interface zone and presence of Cu BM, but only a little of Cu atoms diffuse into the upper zone of the weld pool. It can be also observed that Al2Cu IMC can be detected in the 315
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Fig. 6. Interface microstructure images of Al/Cu lap weld joint (P = 2.45 kW);(a) Enlarged view of Fig.2 zone Ⅱ,(b) Enlarged view of zone Ш,(c) Enlarged view of zone Ⅳ.
weld pool, meanwhile the aluminum atoms diffuse into the interface zone and the copper BM. However, the solidification process is very fast so that the insufficient diffusion time of atoms, the aluminum/copper element segregation phenomenon is severe. With the decrease of weld pool temperature, the weld pool solidifies and crystallizes. (c) With the rapid cooling of the weld pool, the (Al) solid solution forms in the weld pool when the temperature decreases to about 933.5 K. When the temperature further decreases to about 864k, the formed (Al) solid solution further develops, and the Al2Cu IMC precipitates from the weld pool adjacent to the (Cu) solid solution, then the formed zigzag Al2Cu IMC gradually grows up into the weld pool and consumes Al and Cu atoms. (d) With the further cooling, and the reduction of the copper element, the Al-Cu eutectic alloy began to nucleate and grow adjacent to the Al2Cu IMC region on the interface zone, but only a bit of the Al-Cu eutectic alloy is generated on the WM because of relatively a fewer copper atoms diffuse to the weld pool. When the entire weld pool solidifies, a large amount of (Al) solid solution and a small amount of the Al-Cu eutectic alloy is generated in the WM, and the Al2Cu, Al-Cu eutectic alloy and (Cu) solid solution exist in the interface zone, which are identical with the analysis results of Figs. 5–8 in the previous section of the article.
Table 5 Chemical compositions of denoted zones in Fig.6. points Ш
1 2 3 4 5 6
Al (at.%)
Cu (at.%)
Possible phase
97.92 93.68 73.98 66.36 67.14 18.41
2.95 6.32 26.02 33.64 32.86 81.59
(Al) solid solution + Al-Cu eutectic Al-Cu eutectic Al2Cu Al2Cu (Cu) solid solution
upper WM, but the diffraction peaks of Al2Cu at the interface zone is stronger, which indicates the Al2Cu IMC mainly located in the interface zone. The diffraction peaks of Al2Cu does not exist when the laser power is 2.0 kW because of the insufficient laser power only melts a small amount Cu alloy, so that the formed Al2Cu is not enough to be detected. With the increase of laser power in the range of 2.45 kW–3.35 kW, the diffraction peaks of Al2Cu and Cu gradually increases, as mentioned in the previous section of the article is that the increase of laser power results in the increase of molten Cu and thickness of IMCs. So it can be concluded that the WM is mainly constituted by (Al) solid solution and a little of Al-Cu eutectic alloy, the interface zone forms a mass of (Cu) solid solution and the Al2Cu IMC, and the AlCu eutectic alloy. According to the above analysis results and Al-Cu binary phase diagram, the reaction mechanism of WM and interface zone is discussed as follows and the schematic as described in Fig. 9. (a–b) The aluminum alloy and the copper alloy are melted when laser irradiates on the welded samples, the molten aluminum is located at the weld pool, but the molten copper mainly concentrates on the interface zone between the weld pool and the copper BM. Under the action of stirring and convection, the copper atoms diffuse from the interface zone to the
3.3. Mechanical properties and fracture behavior Fig.10 shows Vickers hardness distribution of Al/Cu joints along vertical direction as shown the red arrow in Fig.11. The Vickers hardness tests adopt the load of 200gf for 10 s. The Vickers hardness of the interface zone is highest because of the presence of Al2Cu IMC with hard and brittle characteristics. Since the thickness of the IMCs varies with laser power, the size of the hardness indentation is not equal to the thickness of the IMCs, so that the Vickers hardness of the interface zone 316
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Fig. 7. SEM images of interface zone of Al/Cu lap joints with different laser power; (a) P = 2.0 kW, (b) P = 2.45 kW, (c) P = 2.9 kW, (d) P = 3.35 kW.
is different under different power conditions. From Fig.10, it is also found that the Vickers hardness of WM gradually increases with the increase of laser power, by reason of the percent of molten copper in the WM the high laser power is obviously
more than that of the low laser power, which results in the more molten copper diffuse into WM, and induces the formation of more IMCs. The Vickers hardness of WM is equal to that of the aluminum BM when the laser power is 2.0 kW because of the WM completely consists of the
Fig. 8. XRD analysis patterns of Al/Cu lap joints. (a)P = 2.0 kW,(b)P = 2.45 kW,(c)P = 2.9 kW,(d)P = 3.35 kW. 317
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Fig. 9. Schematic of interface reaction of Al/Cu lap joints.
Fig. 10. Vickers hardness distribution of the cross-section of Al/Cu lap joints. (The green rectangle represents the interface between the Al BM and the copper BM).
Fig. 12. Variation of the tensile strength of the Al/Cu lap joints with the different laser power.
aluminum alloy. We can also see that the fluctuation of the hardness value of WM is more obvious and intense when the laser power is 2.9 kW and 3.35 kW, which indicates that microstructure is nonuniform. As shown in Figs. 3 and 11, we can see that the color of the WM is nonuniform, the copper also appears agglomeration phenomenon in the WM. Fig. 12 shows the shear strength of Al/Cu lap joints as a function of
laser power. The shear strength value of 99.8 MPa of lap joint is highest when the laser power of 2.45 kW. The shear strength of Al/Cu lap joints is obviously weakened by reason of the presence of pores and IMC. The shear strength of Al/Cu lap joints increases first and then reduces with the increase of laser power. The shear strength of Al/Cu lap joints is weakest when the laser power is 2.0 kW because of the joining area of 2.0 kW lap joint is the smallest, and the presence of pores further decrease the joining area of Al/Cu joints. When the laser power in the
Fig. 11. Optical images of Al/Cu lap joints. (a) P = 2.45 kW, (b) P = 2.9kw, (C) P = 3.35 kW (the red arrow represents test direction of Vickers hardness). 318
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Fig. 13. Fracture surfaces of Al/Cu lap joint in the Al side; (a) Overview, (b) Overview, (c) Overview, (d) Enlarged view of zoneⅤ, (e) Enlarged view of zone Ⅵ.
Fig. 14. Fracture surfaces of Al/Cu lap joint in the Cu side; (a) Overview, (b) Overview, (c) Enlarged view of zone Ⅷ.
range of 2.0 kW–2.45 kW, the joining area of joints gradually increase with the increase of laser power, which promotes the increase of joint strength. The weight percent of copper alloy also increase in weld pool when laser power increases in the range of 2.45 kW–3.35 kW, which results in the increase of the content of the formed IMCs. The more
content of brittle IMCs in the joint, the lower shear strength of Al/Cu joint [24,36]. As mentioned in the previous section of the article is that the thickness of Al2Cu region and Al-Cu eutectic region also increases with the increase of laser power, which causes the decrease of the strength of Al/Cu joints [22,31]. 319
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solid solution region when the joints are subjected to tensile load, so the fail surfaces mainly locate at the Al-Cu eutectic region of Al-rich phase, as shown in Fig.15. C. Otten [22] et al adopt the electron beam to perform the joining of Al/Cu, and find that the fracture surface is formed in the eutectic region eventually. D. Zuo [31] et al have also proved that when the Al/Cu joints are subjected to tensile load, the crack sources are easily generated in the Al2Cu region because of the presence of the brittle Al2Cu at room temperature. Therefore, the presence of Al2Cu is the main cause of fracture failure of Al/Cu joints. In Fig.13(c) and larger magnification Fig.13 (d), it indicates that a relatively coarse fracture surface and the existence of dimple with the characteristic of ductile fracture. The content of Cu element of the measurement point 3 is 7.85at. % (16.71 wt.%), while the maximum solubility of copper in Al is 5.65 wt.% [35]. According to the phase diagram, this eutectic region mainly consists of the (Al) solid solution, the ductile fracture with dimples characteristic is the main fracture form of 6061 aluminum alloy [35,40,41]. Di Zuo [31] et al also demonstrate the presence of ductile fracture of Al/Cu lap weld in the Al side. The fracture surfaces of Al/Cu joint in the Cu side as shown in Fig.14. It is also found that the presence of pores. According to Fig.14 (b), (c) and the EDAX analysis results listed in Table 7, the results show that the fracture surfaces mainly occur in the Al-Cu eutectic zone, meanwhile it is noted that the cracks expand into the Al2Cu IMC region, as shown in Fig.15, and we can conclude that the entire fracture surface is a brittle fracture with cleavage characteristic.
Table 6 EDAX measurement of marked points of the Fig.13. Marked points
Al (at.%)
Cu (at.%)
Possible phase
1 2 3 4
79.36 85.23 92.15 78.09
20.64 14.77 7.85 21.91
Al + Al2Cu Al+(Al-Cu eutectic) Al+(Al-Cu eutectic) Al + Al2Cu
Table 7 EDAX measurement of marked points of the Fig.14. Marked points
Al (at.%)
Cu (at.%)
Possible phase
5 6 7 8
69.3 71.22 62.06 62.26
31.7 28.77 37.94 37.74
Al + Al2Cu Al + Al2Cu Al2Cu Al2Cu
Figs.13 and 14 show that fracture surfaces of Al/Cu laser lap joint with the laser power of 2.45 kW. We execute the constitute analysis of fracture surface and the EDAX analysis are marked in Figs.13 and 14. The results of EDAX analysis are listed in Tables 6, 7 and shown in Fig.13 (e), respectively. Fig.13 depicts the fracture surface of Al/Cu joint on the Al side. From Fig.13, it can be seen that the presence of pores which is generated during the processing of welding aluminum, which has a significantly negative influence on the mechanical properties of joints [37–39]. From Fig.13(a) and (b), the relatively smooth and flat fracture surfaces with the characteristic of cleavage can be observed, the cleavage phenomena indicates that the fracture mode of Al/Cu is the typical characteristic of brittle fracture. According to Table 6, Fig.13 (e) and Table 7, it can be concluded that the cracks extend along the Al-Cu eutectic region, and also propagate into the Al2Cu region and the (Cu)
4. Conclusions In this paper, the effect of laser power on mechanical and microstructure of the laser-welded Al/Cu dissimilar lap joints are studied, we can draw conclusions as follows:
Fig. 15. Cross-section fracture image of Al/Cu lap joint; (a) (b) Cross-section fracture image, (c) Schematic of the location of the fracture surface. 320
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(1) The laser beam is applied to welding Al/Cu dissimilar metal, we can come true precisely to control the heat input so that the melting amount of Cu can be controlled. Although the formation of pores is inevitable, the acceptable Al/Cu lap joints are acquired. (2) With the increase of laser power, the molten Cu is obviously increased, the more copper diffuses into WM, which results in the formation of coarser Al2Cu IMC and severer agglomeration phenomenon of Cu element in WM. The (Cu) solid solution and the serrate Al2Cu IMC and the Al-Cu eutectic alloy with the shape of vermicular can be observed at the interface zone. The thickness of all IMCs region increases with the increase of laser power. (3) The shear strength first increases and then decreases with the increase of laser power, the maximum shear strength is about 99.8 MPa with the laser power of 2.45 kW. The fracture surface mainly located at the Al-Cu eutectic region, but the crack also propagates into the (Cu) solid solution region and the Al2Cu IMC region of the interface zone, as well as the WM. The hardness of the interface zone is highest because of presence of a large amount of IMCs, and compare with low laser power, the Vickers hardness of the WM with high laser power fluctuates more acute.
solar thermal absorbers. Mater Des 2018;155:148–60. [15] Reisgen U, Olschok S, Jakobs S, Holtum N. Influence of the degree of dilution with laser beam vacuum-welded Cu-Al mixed joints on the electrical properties. Procedia Cirp 2018;74:23–6. [16] Salehia MT. Growth rate of intermetallic compounds in AL/CU bimetal produced by Cold Roll Welding Process. J Alloys Compd 2001;319:233–41. [17] Zhou L, Zhang RX, Li GH, Zhou WL, Huang YX, Song XG. Effect of pin profile on microstructure and mechanical properties of friction stir spot welded Al-Cu dissimilar metals. J Manuf Process 2018;36:1–9. [18] Galvão I, Oliveira JC, Loureiro A, Rodrigues DM. Formation and distribution of brittle structures in friction stir welding of aluminium and copper: influence of shoulder geometry. Intermetallics 2012;22:122–8. [19] Bhattacharya TK, Das H, Pal TK. Influence of welding parameters on material flow, mechanical property and intermetallic characterization of friction stir welded AA6063 to HCP copper dissimilar butt joint without offset. Trans Nonferrous Met Soc China 2015;25:2833–46. [20] Ni Z, Zhao H, Mi P, Ye F. Microstructure and mechanical performances of ultrasonic spot welded Al/Cu joints with Al 2219 alloy particle interlayer. Mater Des 2016;92:779–86. [21] Li Z, Zhi-yong L, Hong-yun Z, Yu X, Yong-xian H, Ji-cai F. Microstructure and mechanical properties of Al/brass dissimilar metals TIG welding-brazing joint. Chin J Nonferrous Metals 2015;29. [22] Otten C, Reisgen U, Schmachtenberg M. Electron beam welding of aluminum to copper: mechanical properties and their relation to microstructure. Weld World 2015;60:21–31. [23] Solchenbach T, Plapper P. Mechanical characteristics of laser braze-welded aluminium–copper connections. Opt Laser Technol 2013;54:249–56. [24] Zhou L, Li ZY, Song XG, Tan CW, He ZZ, Huang YX, et al. Influence of laser offset on laser welding-brazing of Al/brass dissimilar alloys. J Alloys Compd 2017;717:78–92. [25] Boucherit A, Avettand-Fènoël MN, Taillard R. Effect of a Zn interlayer on dissimilar FSSW of Al and Cu. Mater Des 2017;124:87–99. [26] Man Z, Pengfei W, Lincai Z, Yuebin L. Microstructure and mechanical properties of Cu/Al joint brazed with Zn-Al-Ag filler metal. Trans China Welding Inst 2013;34:55–8. [27] Yu S, Xianglong Z, Ming Z, Yufen G, Ding F. Effect of filler wires on brazing interface microstructure and mechanical properties of Al/Cu dissimilar metals welding-brazing joint. Mater Sci Eng R Rep 2017;31:61–4. [28] Fei X, Ying Y, Jin L, Wang H, Lv S. Special welding parameters study on Cu/Al joint in laser-heated friction stir welding. J Mater Process Technol 2018;256:S0924013618300499. [29] Kraetzsch M, Standfuss J, Klotzbach A, Kaspar J, Brenner B, Beyer E. Laser beam welding with high-frequency beam oscillation: welding of dissimilar materials with brilliant Fiber lasers. Phys Proc 2011;12:142–9. [30] Wang Z, Oliveira JP, Zeng Z, Bu X, Peng B, Shao X. Laser beam oscillating welding of 5A06 aluminum alloys: microstructure, porosity and mechanical properties. Opt Laser Technol 2019;111:58–65. [31] Zuo D, Hu S, Shen J, Xue Z. Intermediate layer characterization and fracture behavior of laser-welded copper/aluminum metal joints. Mater Des 2014;58:357–62. [32] Lee W-B, Bang K-S, Jung S-B. Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing. J Alloys Compd 2005;390:212–9. [33] Braunovic M, Alexandrov N. Intermetallic compounds at aluminum-to-copper electrical interfaces: effect of temperature and electric current. Comp Packag Manuf Technol Part A IEEE Trans on 1994;17:78–85. [34] Elliot J, Massalaski T, Murray J, Bennett L, Baker H. Binary alloy phase diagrams. Metals Park, OH: American Society for Metals; 1986. [35] Mai TA, Spowage AC. Characterisation of dissimilar joints in laser welding of steel–kovar, copper–steel and copper–aluminium. Mater Sci Eng A 2004;374:224–33. [36] Zhou L, Luo LY, Tan CW, Li ZY, Song XG, Zhao HY, et al. Effect of welding speed on microstructural evolution and mechanical properties of laser welded-brazed Al/ brass dissimilar joints. Opt Laser Technol 2018;98:234–46. [37] Wen L, Wang HP, Lu F, Cui H, Tang X. Investigation on effects of process parameters on porosity in dissimilar Al alloy lap fillet welds. Int J Adv Manuf Technol 2015;81:843–9. [38] Lin R, Wang HP, Lu F, Solomon J, Carlson BE. Numerical study of keyhole dynamics and keyhole-induced porosity formation in remote laser welding of Al alloys. Int J Heat Mass Transf 2017;108:244–56. [39] Huang L, Hua X, Wu D, Jiang Z, Ye Y. A study on the metallurgical and mechanical properties of a GMAW-welded Al-Mg alloy with different plate thicknesses. J Manuf Process 2019;37:438–45. [40] Chu Q, Bai R, Jian H, Lei Z, Hu N, Yan C. Microstructure, texture and mechanical properties of 6061 aluminum laser beam welded joints. Mater Charact 2018;137:269–76. [41] Huang Y, Meng X, Lv Z, Huang T, Zhang Y, Cao J, et al. Microstructures and mechanical properties of micro friction stir welding (μFSW) of 6061-T4 aluminum alloy. J Mater Res Technol 2018.
Acknowledgements The authors wish to acknowledge Professor of Jyotirmoy Mazumder, University of Michigan, for her help in the financial and technical support of this research. The authors are also grateful for the financial aids from the Scientific and Technological Planning Project of Jilin Province (Grant No. 20170204065GX and No. 20180201063GX), and the National Key Research and Development Program of China (Grant No. 2017YFB1104601), and the Project supported by the Equipment preresearch field Foundation of China (Grant No. 61409230509). References [1] Solchenbach T, Plapper P. Combined laser beam braze-welding process for fluxless al-cu connections. PROCEDINGS International Conference on Competitive Manufacturing 2013;13:131–6. [2] B.J. P, P. F, S. R. Solid-state welding of aluminum to copper—case studies. Weld World 2013;57:541–50. [3] Zoeram AS, Anijdan SHM, Jafarian HR, Bhattacharjee T. Welding parameters analysis and microstructural evolution of dissimilar joints in Al/Bronze processed by friction stir welding and their effect on engineering tensile behavior. Mater Sci Eng A 2017;687:288–97. [4] Martinsen K, Hu SJ, Carlson BE. Joining of dissimilar materials. CIRP Ann Manuf Technol 2015;64:679–99. [5] Wang X-G, Li X-G, Wang C-G. Influence of diffusion brazing parameters on microstructure and properties of Cu/Al joints. J Manuf Process 2018;35:343–50. [6] Zhang M, Xue S, Feng JI, Lou Y, Wang S. Effect of CuAl_2 phase on properties and microstructure of Cu/Al brazed joint. Trans China Weld Inst 2011;32:93–6. [7] Feng M-N, Xie Y, Zhao C-F, Luo Z. Microstructure and mechanical performance of ultrasonic spot welded open-cell Cu foam/Al joint. J Manuf Process 2018;33:86–95. [8] Fujii HT, Endo H, Sato YS, Kokawa H. Interfacial microstructure evolution and weld formation during ultrasonic welding of Al alloy to Cu. Mater Charact 2018;139:233–40. [9] Koberna M, Fiala J. Intermetallic phases in cold-welded Al-Cu joints. Mater Sci Eng A 1992;159:231–6. [10] WOŹNIAK H. The results of the so far performed investigations of Al-Cu butt cold pressure welding by the method of upsetting. Arch Civ Mech Eng 2009;9:135–45. [11] Akbari Mousavi SAA, Al-Hassani STS, Atkins AG. Bond strength of explosively welded specimens. Mater Des 2008;29:1334–52. [12] Honarpisheh M, Asemabadi M, Sedighi M. Investigation of annealing treatment on the interfacial properties of explosive-welded Al/Cu/Al multilayer. Mater Des 2012;37:122–7. [13] Sharma N, Khan ZA, Siddiquee AN. Friction stir welding of aluminum to copper—an overview. Trans Nonferrous Met Soc China 2017;27:2113–36. [14] Kermanidis AT, Christodoulou PI, Hontzopoulos E, Haidemenopoulos GN, Kamoutsi H, Zervaki AD. Mechanical performance of laser spot-welded joints in Al-Al/Cu
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