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AA5182 jointed by FSW
Journal of Materials Processing Tech. 268 (2019) 107–116
Contents lists available at ScienceDirect
Journal of Materials Processing Tech. journal homepage: www.elsevier.com/locate/jmatprotec
Microstructure and mechanical properties of AA7075/AA5182 jointed by FSW
T
Edip Cetkina, , Y.H Çelika, Semsettin Temizb ⁎
a b
Department of Mechanical Engineering, Faculty of Engineering-Architecture, Batman University, Batman, Turkey Department of Mechanical Engineering, Faculty of Engineering, Inonu University, Malatya, Turkey
ARTICLE INFO
ABSTRACT
Keywords: FSW Fatigue strength Microstructure Tensile strength
In this study, AA7075 and AA5182 aluminium alloys were joined using different rotation speeds (980, 1325 and 1800 rpm), feed rates (108 and 233 mm/min) and stirred pins having two different geometries (conical helical and triangular). Microstructures of welding joints were examined by an optical microscope and a scanning electron microscope (SEM). Vickers hardness measurements were performed in the welding zone of samples removed from each welded plate. Tensile and fatigue tests were also applied to the test specimens taken from the welded plates. After the tensile tests, the surface fractures and possible welding defects were scanned via SEM. The best mechanical properties were obtained when conical helical shape stirrer pins were used. The values were 265 MPa for tensile test and 159 MPa for fatigue test. The hardness value was very close to each other and varied depending on the rotation speed. The highest hardness value was determined as 87 HV in the weld center at 1325-rpm rotation speed.
1. Introduction Aluminium and its alloys have been joined with joining processes such as bonding, soldering, rivet, and bolt (Mathers, 2002). Along with the development of welding technology, they have been joined with welding joints, too. In fact, welding joints is the basic method for repairing aluminium and its alloys (Thomas et al., 1999). However, the welding of aluminium is difficult and complex compared to materials such as steel with its intensive use (Threadgill, 1997; Dawes and Thomas, 1995). Therefore, physical and metallurgical properties of the material to be welded must be well known; and precautions should be taken according to these properties. In this direction, a solid phase welding method called friction stir welding (FSW) was developed by The Welding Institute-TWI (Thomas and Nicholas, 1997; Cabello et al., 2008). In FSW joints; Cavaliere and Panella (2008) tried to determine the mechanical properties and microstructure characteristics of the welded joints of AA2024/AA7075 aluminium alloy pairs. As they moved away from the welding center, they saw that microhardness values decreased. Scialpi et al. (2007) investigated the influence of shoulder geometry on microstructure and mechanical properties in the welded joints of the AA6082 alloy. They emphasized that shoulder geometries played important roles in the welding’s surface quality and mechanical properties. Aval et al. (2013) examined the effects of welding parameters on the microstructure and mechanical properties in ⁎
joints of the AA5086 aluminium plate. It was found that the grain size and hardness in the welding zone changed depending on the feed rate and rotational speed. Zhang et al. (2013) compared them as experimental and numerical (ANSYS) fatigue properties of welding joints joined with forehead and overlapping methods of the 2524-T3 aluminium alloy pairs. They determined that the fatigue strength of forehead method was better than overlapping method. Güngör et al. (2014) determined the effect of welding parameters on mechanical and microstructural properties in the welding joints of 5083-H111 and 6082-T651 aluminium alloys. Ghogheri et al. (2016) investigated the effects of welding parameters on hardness in the welding joints of commercially pure titanium and aluminium 5083 alloys. They saw that the highest hardness was in the stirred zone of the joints and that the areas outside the stirrer zone were affected from the welding process. Infante et al. (2016) examined the fatigue properties of AA5754 and AA6082 aluminium alloy pairs. They determined that the welding joints of different aluminium alloys showed better fatigue performance than the welds of similar aluminium alloys at low–stress range. Sharma et al. (2017) joined armour steels with different welding parameters. They investigated the effects of welding parameters on the microstructure and mechanical properties. They found that the mechanical properties of the welded material (microhardness, ultimate strength and elongation at break) increased with the increase of the tool rotation speed and the decrease of welding speed. Hynes and Velu (2018) investigated the
Corresponding author. E-mail addresses: [email protected] (E. Cetkin), [email protected] (Y.H. Çelik), [email protected] (S. Temiz).
https://doi.org/10.1016/j.jmatprotec.2019.01.005 Received 1 September 2018; Received in revised form 2 January 2019; Accepted 7 January 2019 Available online 07 January 2019 0924-0136/ © 2019 Elsevier B.V. All rights reserved.
Journal of Materials Processing Tech. 268 (2019) 107–116
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Table 1 Chemical compositions of aluminium alloys (%wt). Material
Cu
Cr
Fe
Si
Zn
Mn
Mg
Ti
Al
AA5182-H111 AA7075-T6
0.15 1.2–2.0
0.10 0.18–0.28
0.35 0.40
0.20 0.40
0.25 5.10–6.10
0.20–0.50 0.30
4–5 2.1–2.9
0.10 0.20
Bal. Bal.
and welding parameters on the microstructure, tensile strength, fatigue strength and hardness of welding joints were experimentally investigated. The fatigue strengths of the welding joints are investigated as bending fatigue generally. So, it was observed that there was a need for a comprehensive study on pull–pull type fatigue behaviour. For this purpose; AA7075 alloy used in common areas such as aerospace and defense industries and AA5182 alloy used in marine industries were joined by FSW welding method. The effects of the rotation speed, feed rate and stirrer tip on microstructure and mechanical properties (hardness, tensile and fatigue strength) were analyzed in detail.
Table 2 Mechanical properties of aluminium alloys. Material
Tensile str. (MPa)
Elongation (%)
R0.2 Yield Str. (MPa)
Elastic mod. (GPa)
Hardness (HV)
AA5182-H111 AA7075-T6
320 505
25 9
140 440
69.6 72
71 150
Table 3 Physical properties of aluminium alloys (http://asm.matweb.com; https:// www.makeitfrom.com). Material
Density (kg/m−3)
Thermal exp. (μm m−1 K−1)
Electric conductivity (% IACS)
Thermal conductivity (Wm−1 K−1)
AA5182-H111 AA7075-T6
2710 2810
24 23.5
28 33
123 134
2. Material and method 2.1. Materials AA7075 and AA5182 aluminium alloys with dimensions of 2100 mm × 1500 mm × 5 mm were attained. The chemical compositions, the mechanical properties, and physical properties of these alloys are given in Tables 1–3, respectively. The stirrer pins having two different geometries (triangular and conical) were manufactured from K100 steel material. In order to increase their hardness, heat treatment was applied to them for 35 min at 850 °C and they were quenched by oil. Images and technical drawings of the produced pins are given in Fig. 1.
effects of different rotational speeds on the weld quality in the welding joints of Ti-6Al-4V/AA6061 alloys. They pointed out that the increase in rotational speed increased the heat on the surface of friction at the interface, and that this situation led to dynamic recrystallization. Jafarlou et al. (2018) determined the effects of stirring pin geometries (flat cylindrical, conical cylindrical, threaded cylindrical, triangular and square) on the corrosion behaviour of Al5086 alloy using Tafel polarization and electrochemical impedance spectroscopy tests. They pointed out that the highest corrosion resistance was obtained from the joints where square pin geometry was used. They emphasized that this situation was due to the fact that the dynamic-to-static ratio was higher and the pin geometry caused vibrational stirring. Mishra and Nidigonda (2018) studied the effects of welding parameters on mechanical properties by joining AA6061-T6 aluminium alloy plates. In FSW welding joints in this study, the effects of stirrer geometry
2.2. Manufacturing FSW and welding parameters Commercially available standard aluminium plates were machined in the milling at the dimension of 80 cm × 12 cm × 5 mm. The surfaces of the plates were cleaned from dirt, rust and oxide layers. All alloys to be joined were made ready for welding. After AA7075 and AA5182 plates were marked, plates and stirrer pin were fixed in a milling machine. The test setup is given in Fig. 2. Before the milling machine was started in clockwise direction, the tool angle was set up as 3°. The stirrer
Fig. 1. Stirrer pins used in the FSW. 108
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Fig. 2. The FSW test setup.
microhardness tester. Measurements were carried out over the unilateral surfaces of the welding joints at 1 mm intervals. A load of 1 N was applied to the material for 10 s to determine hardness values. The tensile tests were applied to determine the maximum tensile strength of the welding joints. Tensile specimens were obtained in accordance with ASTM E8 standard by plasma cutting in the welding direction perpendicular at welded plates. Tensile tests were made in the tensile speed of 1 mm/min at SHIMADZU brand 250 kN universal tester. In order to determine the fatigue strength of welding joints, samples were prepared according to ASTM E466 standards. Fatigue tests were carried out as pull/pull amplitude ratio R = σmin / σmax = 0.1 at SHIMADZU brand 100 kN universal tester. For all tests, the processing frequency was set up as 10 Hz and all joints were subjected to axial sinusoidal loading. Microstructure images and fracture surfaces were analyzed in magnification rate of 200×, 500× and 1000× with SEM device of JSM-6510 brand.
Table 4 Process parameters used in FSW experiments. Stirrer Geometry
Rotational Speed (rpm)
Feed rate (mm/ min)
Conical and Triangle
980
108 233 108 233 108
1325 1800
233
pin was immersed in the workpiece at shoulder depth of 0.2 mm. In this position, the stirrer pin was made to wait to heat the shoulder area for about 1 min. After it was determined that the friction temperature was obtained with the help of testo-881 thermal camera measurement, experiments were performed on different welding parameters. The welding parameters are given in Table 4. 2.3. Devices used in the welding joints
3. Experimental results
The surfaces of welding joints were polished using sandpaper and broadcloth. The polished surfaces were dipped into the Kroll alumina solution consisting of 6 ml of nitric acid, 2 ml of HF and 92 ml of distilled water for 55–75 s to etch the surface of the sample. All surfaces were examined in magnification of 4×, 10× and 40× with the optical microscope of Leica DM2500 P brand. Hardness measurements were made with a Shimadzu HMV
3.1. Macro and microstructure observations The metallographic structure of the samples taken from AA7075 and AA5182 alloy pairs, which were joined with the FSW welding method, were examined in detail. In FSW joints, structures consisting of base metal (BM), heat affected zone (HAZ), thermomechanically affected
Fig. 3. Formed zones in the weld cutaway in the FSW method. 109
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Fig. 4. Macro and microstructures in welding joints joined with the conical stirrer pin.
Fig. 5. Macro and microstructures in welding joints joined with the triangular stirrer pin.
zone (TMAZ) and dynamic recrystallization zone (DCZ) zones (Fig. 3) were investigated in macro and micro size. Macro and microstructure images taken from the cross-sectional surfaces of welding joints of AA7075 and AA5182 alloys joined by FSW method using conical stirrer
pin are given in Fig. 4. In Fig. 4, when the macro and microstructure images in the welded joint zones were examined, it was observed that the structure such as TMAZ, HAZ, DCZ and porosity in the joint zones formed. These 110
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Fig. 6. SEM images of the sample at rotation speed of 980 rpm and feed rate of 108 mm/min (a) AA5182 alloy (200×), (b) Welding interface transition zone (200×), (c) AA7075 alloy (200×).
structures changed depending on feed rate and rotation speed. When the microstructure of the welded sample with the feed rate of 233 mm/ min and the rotation speed of 1800 rpm was examined, it was observed that there were wide gaps in the joining zones. Besides, when the microstructure of the welded sample with a feed rate of 108 mm/min and rotation speed of 980 rpm was examined, it was seen that less porosity occurred at the joining zones, and the material was better extruded to join. Macro and microstructure images taken from the cross-sectional surfaces of welding joints of AA7075 and AA5182 alloys joined by FSW method using triangular stirrer pin are given in Fig. 5. In Fig. 5, when the AA7075 and AA5182 alloys were joined using a triangular stirrer pin in the rotation speed of 980 rpm and feed rate of 108 mm/min, it was observed that there were gaps in the welding center and the zones at the bottom of DCZ. This situation was clearly visible that the size and amount of gaps in the welded joints increased with the increasing rotational speed and feed rate. The increase in the size of these defects was predicted to be caused by the decrease in temperature in the unit area and time, the lack of sufficient plasticity temperature by means of the triangular stirrer, and the decrease in the ability to extrude. Cavaliere and Squillace (2005) emphasized that the porosity and tunnel formation along the joint in semi-plastic material to be transported before reaching the viscosity-temperature increased. Considering the operation ability of the triangular stirrer pin in the stirring zone, it is very important to provide sufficient temperature in
terms of the extrusion ability in the welding process. When the AA7075 and AA5182 alloys were joined with the conical and triangular stirrer pins, the AA5182 alloy was stirred more since it is more ductile than AA7075 alloy. The SEM images of AA7075/AA5182 alloy pairs joined using the conical and triangular stirrer pins are given in Figs. 6–8. SEM images of the joints where the best strength values used the conical stirrer pin were obtained are given in Figs. 6 and 7 are given. Also, in Fig. 8, SEM images of the triangular stirrer pin are given. In all experimental conditions, the stirrer pin geometry, the rotational speed and the feed rate had a significant effect on the microstructure of the welded joints. The welding quality of samples shown in Fig. 6 was obtained very well, whereas a very small joint failure occurred in the sample in Fig. 7, which was related to increasing feed rate. In joints made through using conical stirrer pins; while the weld quality decreased with increasing feed rate, it did not change with increasing rotation speed. However, the welding quality also decreased with replacing the triangular pin with the conical pin. These welding qualities can be seen in Fig. 8, where some joining failures were obtained. In joints made by using triangular stirrer pins; increasing the feed rate reduced the weld quality, while increasing rotation speed increased the weld quality.
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Fig. 7. SEM images of the sample at rotation speed of 980 rpm and feed rate of 233 mm/min (a) AA5182 alloy (200×–1000×), (b) Welding interface transition zone (200×–1000×), (c) AA7075 alloy (200×–1000×).
Fig. 8. SEM images of weld interface zones in joining made by using triangular stirrer pins.
3.2. Hardness measurements
profile, were measured. The measurements were carried out through the along line from the BM to the joining line and from the joining line to the BM. The measurement results are given in Fig. 9. When the hardness values of all the specimens joined with conical
The microhardness values of AA7075 and AA5182 alloys, which were joined using different rotational speed, feed rate and stirrer 112
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Fig. 9. Microhardness values depending on welding parameters.
Fig. 10. Stress strain curves where conical stirrer pin was used.
Fig. 11. Stress strain curves where triangular stirrer pin was used.
and triangular profiled pins were examined, it was observed that different measurement results were obtained in the weld zones (HAZ, TMAZ, and DCZ). However, when it was reached to BM, the results were close to the main hardness values of the aluminium alloys in the different types. In Fig. 9a and b, the increase in rotation speed led to a slight increase in hardness. However, as the feed rate increased, the hardness partly decreased as well. Also, the hardness of the DCZ zone was found to be higher than those of TMAZ zones. In Fig. 9c and d, the increase in rotation speed and feed rate led to a slight increase in hardness. The minimum hardness value was obtained in the TMAZ zone
near AA5182 (BM) alloy. This increase in DCZ was higher than the hardness value of AA5182 (BM) alloy and lower than the hardness value of AA7075 (BM) alloy. For all experimental conditions, when the effects of the feed rate and the rotation speed variables were evaluated together, it was seen that the hardness values of the joints were close to each other. Since stirrer pins performed stirring in the direction of rotation, the hardness values of all the weld centers of the samples were high. As the size of the grains inside the alloys was reduced, hardening occurred because of plastic deformation and severe extrusion. However, it was 113
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Fig. 11. When the Stress–Strain curves depending on feed rate and rotation speed were examined, the triangular stirrer pin behaved differently than conical stirrer pin. The tensile strength values were obtained at low levels in the triangular stirrer pin because the triangular stirrer pin did not achieve adequate stirring. The tensile strength values of the welding joints in different welding parameters are given in Table 5. After the tensile test, the samples were damaged. Damaged samples brought side by side (Fig. 12). It was seen that the welding joints were broken in the ductile form from the welding zone. However, fracture surfaces must be examined by SEM to be able to make detailed comments; and fracture mechanism must be determined. Some fracture surfaces are given in Fig. 13. In Fig. 13, it was seen that heterogeneously–homogeneously distributed particles with large voids were formed on the fracture surfaces of the welding joints the joined with the conical stirrer tip with high rotation speed, low feed rate, high cutting speed and high feed rate. However, it was observed that the fracture surfaces were homogeneously distributed at low rotational speeds and feed rates (980 rpm, 108 mm/rev). Micro-voids of different sizes and shapes were formed on these surfaces. Also, local ductile fracture mechanisms were observed on fracture surface. When the fracture surfaces of the samples joined with the help of the triangular stirrer pins were examined, it was seen that heterogeneously distributed particles with wider voids were formed. It is thought that the triangular stirrer pin is not able to stir aluminium alloys well enough. Brittle fracture mechanisms occurred on fracture surfaces.
Table 5 Tensile strengths values depending on welding parameters. Stirrer geometry
Rotation speed (rpm)
Feed rate (mm/ min)
Tensile strength (MPa)
Conical
980
108 233 108 233 108 233 108 233 108 233 108 233
265 166 227 144 188 130 203 162.6 211 199 218.2 158.1
1325 1800 Triangular
980 1325 1800
seen that the hardness values at the weld center of the samples joined using the conical stirrer pin were slightly higher than those joined with the triangular stirrer. This was due to the difference in the stirrer shapes of the pin. And the conical stirrer pin stirred by pushing the material in front backward with the aid of helical conical grooves. The triangular stirrer also pushed the material on the front backward from the welding direction depending on the feed rate. The mechanisms at the stirrer pins affected the hardness values of the welded joints. 3.3. Tensile strengths and fracture surfaces of weldings In order to analyse the effects of welding parameters on tensile strength, the tensile strengths of welded joints were applied; and the fracture surfaces obtained from the tensile tests were compared with one another. The Stress–Strain curves of the welding parameters in the welding joints joined using the conical stirrer pin is given in Fig. 10. As seen in Fig. 10, the tensile strength of welding joints decreased with increasing of the rotation speed and the feed rate. The best tensile strength was obtained as 264.75 MPa from the rotation speed of 980 rpm and the feed rate of 108 mm/rev, because conical channels involved in the stirring task was better stirred the material. A good stirring increased the amount of material both in transporting per revolution and extruding backward. This situation contributed to the increase of the plastic deformation. Therefore, in the welded aluminium alloy joints, the mechanical properties were improved and the grain size was reduced. The results obtained from the tensile tests proved that the helical channel played an important role in the stirring of the material. Fujii et al. (2006) also stated that helical channels play an important role in the stirring of materials. The tensile strength-unit elongation graphs of the weld parameters in the welding joints joined using the triangular stirrer pin is given in
3.4. Fatigue test results of welding joints The fatigue emerged from plastic deformation as a result of the interaction tensile stress, and fatigue cyclic tension. The load applied under a stress amplitude causes to form cracks with time. The fatigue (S/N) diagrams of the specimens joined together by using the different rotation speeds and feed rates for conical stirrer pins and triangular stirrer pins are given in Figs. 14 and 15, respectively. In Fig. 14, it was observed that the fatigue strength values of welding joints at the rotation speed of 1800 rpm were lower than those at joints at the rotation speed of 980 rpm. This situation was a result of high working temperature, which was a significant effect on the mechanical properties of the welding joints. At high working temperatures, the microstructure of the material was deteriorated. Therefore, the material flow limit and modulus of elasticity were low. This also reduced the fatigue life of the material. It was also observed that the fatigue strength values in low feed rates were higher than high feed rates. This situation was due to well stirring process in low feed rate. When the fatigue strength, yield limit, tensile strength and hardness
Fig. 12. Damaged zones for the triangular stirrer pin. 114
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Fig. 13. SEM images of fracture surfaces depending on welding parameters (200×).
Fig. 14. S/N diagram depending on welding parameters for conical stirrer pin.
value of the material in the S/N diagrams were considered as a whole, the fatigue strength increased with increasing yield strength, hardness and tensile strength. The highest fatigue strength in the welding joints joined by using the conical stirrer pin was obtained from the rotation speed of 980 rpm and the feed rate of 108 mm/rev. This value was 159 MPa. The lowest fatigue strength was obtained as 52 MPa from the rotation speed of 1800 rpm and the feed rate of 233 mm/rev. In Fig. 15, it was seen that the fatigue strength values decreased
with increase in feed rate. In low feed rate, the increase of rotation speed contributed to the increase of the fatigue strength. Nevertheless, in the high feed rate, the increase of rotation speed caused decrease in the fatigue strength. The high fatigue strength in the welding joints joined by using the triangular stirrer pin was obtained as 120 MPa from low feed rate (108 mm/rev) and high rotation speed (1800 rpm).
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Fig. 15. S/N diagram depending on welding parameters for triangular stirrer pin.
4. Conclusions
References
The metallurgical properties, microhardness values, tensile strengths, fracture surfaces and fatigue strengths of the welding joints of AA7075 and AA5182 aluminium alloy pairs joined by FSW method were investigated. The results are given below.
Aval, H.J., Serajzadeh, S., Kokabi, A.H., Loureiro, A., 2013. Effect of tool geometry on mechanical and microstructural behaviours in dissimilar friction stir welding of AA 5086–AA 6061. Sci. Technol. Weld. Joining 16 (7), 597–604. Cabello, M.A., Rückert, G., Huneau, B., Sauvage, X., 2008. Comparison of TIG welded and friction stir welded Al–4.5Mg–0.26Sc alloy. J. Mater. Process. Technol. 197, 337–343. Cavaliere, P., Panella, F., 2008. Effect of tool position on the fatigue properties of dissimilar 2024-7075 sheets joined by Friction stir Welding. J. Mater. Process. Technol. 206, 249–255. Cavaliere, P., Squillace, A., 2005. High temperature deformation of friction stir processed AA7075 aluminum alloy. Mater. Charact. 55, 136–142. Dawes, C.J., Thomas, W., 1995. Friction Stir Joining of Aluminum Alloys. TWI Bulletin 6, Reprint 493/6/95. Cambridge, UK, pp. 124–127. Fujii, H., Cui, L., Maeda, M., Nogi, K., 2006. Effect of tool shape on mechanical properties and microstructure of friction stir welded aluminum alloys. Mater. Sci. Eng. 419, 25–31. Ghogheri, S.M., Kasırı-Asgarani, M., Amini, K., 2016. Friction stir welding of dissimilar joint of aluminum alloy 5083 and commercially pure titanium. Kovove Mater. 54, 71–75. Güngör, B., Kaluç, E., Taban, E., 2014. Mechanical, fatigue and microstructural properties of friction stir welded 5083-H111 and 6082-T651 aluminum alloys. Mater. Des. 56, 84–90. Hynes, N.R.J., Velu, P.S., 2018. Effect of rotational speed on Ti-6Al-4V-AA 6061 friction welded joints. J. Manuf. Process. 32, 288–297. Infante, V., Braga, D.F.O., Duarte, F., Moreira, P.M.G., Freitas, Mde., Castro, P.M.S.T., 2016. Study of the fatigue behaviour of dissimilar aluminum joints produced by friction stir welding. Int. J. Fatigue 82, 310–316. Jafarlou, H., Jamalian, H.M., Eskandar, M.T., 2018. Investigation into the role of pin geometry on the corrosion behavior of multi-pass FSW joints of Al5086 besides applying Al2O3nanoparticles. J. Manuf. Process. 32, 425–431. Mathers, G., 2002. The Welding of Aluminum and its Alloys. Woodhead Publishing Limited, Cambridge, UK. Mishra, A., Nidigonda, G., 2018. Comparative mechanical and microstructure properties analysis of friction stir welded and TIG welded AA6061-T6 similar joints. J. Adv. Res. Manuf. Mater. Sci. Metall. Eng. 5 (1–2), 1–8. Scialpi, A., Filippis, L.A.C., Cavaliere, P., 2007. Influence of shoulder geometry on microstructure and mechanical properties of friction stir welded 6082 aluminum alloy. Mater. Des. 28, 1124–1129. Thomas, W.M., Nicholas, E.D., 1997. Friction stir welding for the transportation industries. Mater. Des. 18 (4/6), 269–273. Thomas, W.M., Treadgill, P.L., Nicholas, E.D., 1999. The Feasibility of friction stir welding steel. Sci. Technol. Weld. Joining 4 (6), 365–372. Threadgill, P., 1997. Friction Stir Welds in Aluminium Alloys — Preliminary Microstructural Assessment. TWI Bulletin March/April TWI. Abington, UK. Zhang, T., He, Y., Shao, Q., Zhang, H., Wu, L., 2013. Comparative study on fatigue properties of friction stir welding joint and lap joint. 13th International Conference on Fracture.
• Macro and microstructures of welding joints joined by FSW method •
• • •
showed that welding seams varied depending on pin geometry, and welding parameters. The microhardness value was affected by pin geometry and welding parameters. Even though the hardness values of the joints made with both pin geometries were close to each other, the only difference between them was that the hardness values differed with the influence of heat. The highest and lowest hardness values were measured in the experiments where the conical stirrer pin was used. The minimum and maximum hardness values were obtained for the rotation speed of 980 rpm, the feed rate of 108 mm/rev, and the rotation speed of 1325 rpm, the feed rate of 108 mm/rev, respectively. The minimum and maximum hardness values were 67.1 and 87 HV, respectively. The maximum tensile strength was obtained as 265 MPa for the rotation speed of 980 rpm and the feed rate of 108 mm/min. The minimum tensile strength was obtained as 130.4 MPa for the rotation speed of 1800 rpm and the feed rate of 233 mm/min. The minimum and maximum fatigue strengths were measured as 52.2 MPa and 159 MPa, for the rotation speed of 1800 rpm and the feed rate of 233 mm/min and the rotation speed of 980 rpm and the feed rate of 108 mm/min, respectively. In the joints where the triangle stirrer pin was used, the minimum fatigue strength was measured as 71.1 MPa for the rotation speed of 1800 rpm and the feed rate of 233 mm/rev. The maximum fatigue strength was measured as 120 MPa for the rotation speed of 1800 rpm and the feed rate of 108 mm/rev.
Acknowledgment The authors would like to thank the Batman University due to the financial support of Batman University Scientific Research Projects Unit (BTUBAP) under the project of 2017-PhD-2.
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Contents lists available at ScienceDirect
Journal of Materials Processing Tech. journal homepage: www.elsevier.com/locate/jmatprotec
Microstructure and mechanical properties of AA7075/AA5182 jointed by FSW
T
Edip Cetkina, , Y.H Çelika, Semsettin Temizb ⁎
a b
Department of Mechanical Engineering, Faculty of Engineering-Architecture, Batman University, Batman, Turkey Department of Mechanical Engineering, Faculty of Engineering, Inonu University, Malatya, Turkey
ARTICLE INFO
ABSTRACT
Keywords: FSW Fatigue strength Microstructure Tensile strength
In this study, AA7075 and AA5182 aluminium alloys were joined using different rotation speeds (980, 1325 and 1800 rpm), feed rates (108 and 233 mm/min) and stirred pins having two different geometries (conical helical and triangular). Microstructures of welding joints were examined by an optical microscope and a scanning electron microscope (SEM). Vickers hardness measurements were performed in the welding zone of samples removed from each welded plate. Tensile and fatigue tests were also applied to the test specimens taken from the welded plates. After the tensile tests, the surface fractures and possible welding defects were scanned via SEM. The best mechanical properties were obtained when conical helical shape stirrer pins were used. The values were 265 MPa for tensile test and 159 MPa for fatigue test. The hardness value was very close to each other and varied depending on the rotation speed. The highest hardness value was determined as 87 HV in the weld center at 1325-rpm rotation speed.
1. Introduction Aluminium and its alloys have been joined with joining processes such as bonding, soldering, rivet, and bolt (Mathers, 2002). Along with the development of welding technology, they have been joined with welding joints, too. In fact, welding joints is the basic method for repairing aluminium and its alloys (Thomas et al., 1999). However, the welding of aluminium is difficult and complex compared to materials such as steel with its intensive use (Threadgill, 1997; Dawes and Thomas, 1995). Therefore, physical and metallurgical properties of the material to be welded must be well known; and precautions should be taken according to these properties. In this direction, a solid phase welding method called friction stir welding (FSW) was developed by The Welding Institute-TWI (Thomas and Nicholas, 1997; Cabello et al., 2008). In FSW joints; Cavaliere and Panella (2008) tried to determine the mechanical properties and microstructure characteristics of the welded joints of AA2024/AA7075 aluminium alloy pairs. As they moved away from the welding center, they saw that microhardness values decreased. Scialpi et al. (2007) investigated the influence of shoulder geometry on microstructure and mechanical properties in the welded joints of the AA6082 alloy. They emphasized that shoulder geometries played important roles in the welding’s surface quality and mechanical properties. Aval et al. (2013) examined the effects of welding parameters on the microstructure and mechanical properties in ⁎
joints of the AA5086 aluminium plate. It was found that the grain size and hardness in the welding zone changed depending on the feed rate and rotational speed. Zhang et al. (2013) compared them as experimental and numerical (ANSYS) fatigue properties of welding joints joined with forehead and overlapping methods of the 2524-T3 aluminium alloy pairs. They determined that the fatigue strength of forehead method was better than overlapping method. Güngör et al. (2014) determined the effect of welding parameters on mechanical and microstructural properties in the welding joints of 5083-H111 and 6082-T651 aluminium alloys. Ghogheri et al. (2016) investigated the effects of welding parameters on hardness in the welding joints of commercially pure titanium and aluminium 5083 alloys. They saw that the highest hardness was in the stirred zone of the joints and that the areas outside the stirrer zone were affected from the welding process. Infante et al. (2016) examined the fatigue properties of AA5754 and AA6082 aluminium alloy pairs. They determined that the welding joints of different aluminium alloys showed better fatigue performance than the welds of similar aluminium alloys at low–stress range. Sharma et al. (2017) joined armour steels with different welding parameters. They investigated the effects of welding parameters on the microstructure and mechanical properties. They found that the mechanical properties of the welded material (microhardness, ultimate strength and elongation at break) increased with the increase of the tool rotation speed and the decrease of welding speed. Hynes and Velu (2018) investigated the
Corresponding author. E-mail addresses: [email protected] (E. Cetkin), [email protected] (Y.H. Çelik), [email protected] (S. Temiz).
https://doi.org/10.1016/j.jmatprotec.2019.01.005 Received 1 September 2018; Received in revised form 2 January 2019; Accepted 7 January 2019 Available online 07 January 2019 0924-0136/ © 2019 Elsevier B.V. All rights reserved.
Journal of Materials Processing Tech. 268 (2019) 107–116
E. Cetkin et al.
Table 1 Chemical compositions of aluminium alloys (%wt). Material
Cu
Cr
Fe
Si
Zn
Mn
Mg
Ti
Al
AA5182-H111 AA7075-T6
0.15 1.2–2.0
0.10 0.18–0.28
0.35 0.40
0.20 0.40
0.25 5.10–6.10
0.20–0.50 0.30
4–5 2.1–2.9
0.10 0.20
Bal. Bal.
and welding parameters on the microstructure, tensile strength, fatigue strength and hardness of welding joints were experimentally investigated. The fatigue strengths of the welding joints are investigated as bending fatigue generally. So, it was observed that there was a need for a comprehensive study on pull–pull type fatigue behaviour. For this purpose; AA7075 alloy used in common areas such as aerospace and defense industries and AA5182 alloy used in marine industries were joined by FSW welding method. The effects of the rotation speed, feed rate and stirrer tip on microstructure and mechanical properties (hardness, tensile and fatigue strength) were analyzed in detail.
Table 2 Mechanical properties of aluminium alloys. Material
Tensile str. (MPa)
Elongation (%)
R0.2 Yield Str. (MPa)
Elastic mod. (GPa)
Hardness (HV)
AA5182-H111 AA7075-T6
320 505
25 9
140 440
69.6 72
71 150
Table 3 Physical properties of aluminium alloys (http://asm.matweb.com; https:// www.makeitfrom.com). Material
Density (kg/m−3)
Thermal exp. (μm m−1 K−1)
Electric conductivity (% IACS)
Thermal conductivity (Wm−1 K−1)
AA5182-H111 AA7075-T6
2710 2810
24 23.5
28 33
123 134
2. Material and method 2.1. Materials AA7075 and AA5182 aluminium alloys with dimensions of 2100 mm × 1500 mm × 5 mm were attained. The chemical compositions, the mechanical properties, and physical properties of these alloys are given in Tables 1–3, respectively. The stirrer pins having two different geometries (triangular and conical) were manufactured from K100 steel material. In order to increase their hardness, heat treatment was applied to them for 35 min at 850 °C and they were quenched by oil. Images and technical drawings of the produced pins are given in Fig. 1.
effects of different rotational speeds on the weld quality in the welding joints of Ti-6Al-4V/AA6061 alloys. They pointed out that the increase in rotational speed increased the heat on the surface of friction at the interface, and that this situation led to dynamic recrystallization. Jafarlou et al. (2018) determined the effects of stirring pin geometries (flat cylindrical, conical cylindrical, threaded cylindrical, triangular and square) on the corrosion behaviour of Al5086 alloy using Tafel polarization and electrochemical impedance spectroscopy tests. They pointed out that the highest corrosion resistance was obtained from the joints where square pin geometry was used. They emphasized that this situation was due to the fact that the dynamic-to-static ratio was higher and the pin geometry caused vibrational stirring. Mishra and Nidigonda (2018) studied the effects of welding parameters on mechanical properties by joining AA6061-T6 aluminium alloy plates. In FSW welding joints in this study, the effects of stirrer geometry
2.2. Manufacturing FSW and welding parameters Commercially available standard aluminium plates were machined in the milling at the dimension of 80 cm × 12 cm × 5 mm. The surfaces of the plates were cleaned from dirt, rust and oxide layers. All alloys to be joined were made ready for welding. After AA7075 and AA5182 plates were marked, plates and stirrer pin were fixed in a milling machine. The test setup is given in Fig. 2. Before the milling machine was started in clockwise direction, the tool angle was set up as 3°. The stirrer
Fig. 1. Stirrer pins used in the FSW. 108
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Fig. 2. The FSW test setup.
microhardness tester. Measurements were carried out over the unilateral surfaces of the welding joints at 1 mm intervals. A load of 1 N was applied to the material for 10 s to determine hardness values. The tensile tests were applied to determine the maximum tensile strength of the welding joints. Tensile specimens were obtained in accordance with ASTM E8 standard by plasma cutting in the welding direction perpendicular at welded plates. Tensile tests were made in the tensile speed of 1 mm/min at SHIMADZU brand 250 kN universal tester. In order to determine the fatigue strength of welding joints, samples were prepared according to ASTM E466 standards. Fatigue tests were carried out as pull/pull amplitude ratio R = σmin / σmax = 0.1 at SHIMADZU brand 100 kN universal tester. For all tests, the processing frequency was set up as 10 Hz and all joints were subjected to axial sinusoidal loading. Microstructure images and fracture surfaces were analyzed in magnification rate of 200×, 500× and 1000× with SEM device of JSM-6510 brand.
Table 4 Process parameters used in FSW experiments. Stirrer Geometry
Rotational Speed (rpm)
Feed rate (mm/ min)
Conical and Triangle
980
108 233 108 233 108
1325 1800
233
pin was immersed in the workpiece at shoulder depth of 0.2 mm. In this position, the stirrer pin was made to wait to heat the shoulder area for about 1 min. After it was determined that the friction temperature was obtained with the help of testo-881 thermal camera measurement, experiments were performed on different welding parameters. The welding parameters are given in Table 4. 2.3. Devices used in the welding joints
3. Experimental results
The surfaces of welding joints were polished using sandpaper and broadcloth. The polished surfaces were dipped into the Kroll alumina solution consisting of 6 ml of nitric acid, 2 ml of HF and 92 ml of distilled water for 55–75 s to etch the surface of the sample. All surfaces were examined in magnification of 4×, 10× and 40× with the optical microscope of Leica DM2500 P brand. Hardness measurements were made with a Shimadzu HMV
3.1. Macro and microstructure observations The metallographic structure of the samples taken from AA7075 and AA5182 alloy pairs, which were joined with the FSW welding method, were examined in detail. In FSW joints, structures consisting of base metal (BM), heat affected zone (HAZ), thermomechanically affected
Fig. 3. Formed zones in the weld cutaway in the FSW method. 109
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Fig. 4. Macro and microstructures in welding joints joined with the conical stirrer pin.
Fig. 5. Macro and microstructures in welding joints joined with the triangular stirrer pin.
zone (TMAZ) and dynamic recrystallization zone (DCZ) zones (Fig. 3) were investigated in macro and micro size. Macro and microstructure images taken from the cross-sectional surfaces of welding joints of AA7075 and AA5182 alloys joined by FSW method using conical stirrer
pin are given in Fig. 4. In Fig. 4, when the macro and microstructure images in the welded joint zones were examined, it was observed that the structure such as TMAZ, HAZ, DCZ and porosity in the joint zones formed. These 110
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Fig. 6. SEM images of the sample at rotation speed of 980 rpm and feed rate of 108 mm/min (a) AA5182 alloy (200×), (b) Welding interface transition zone (200×), (c) AA7075 alloy (200×).
structures changed depending on feed rate and rotation speed. When the microstructure of the welded sample with the feed rate of 233 mm/ min and the rotation speed of 1800 rpm was examined, it was observed that there were wide gaps in the joining zones. Besides, when the microstructure of the welded sample with a feed rate of 108 mm/min and rotation speed of 980 rpm was examined, it was seen that less porosity occurred at the joining zones, and the material was better extruded to join. Macro and microstructure images taken from the cross-sectional surfaces of welding joints of AA7075 and AA5182 alloys joined by FSW method using triangular stirrer pin are given in Fig. 5. In Fig. 5, when the AA7075 and AA5182 alloys were joined using a triangular stirrer pin in the rotation speed of 980 rpm and feed rate of 108 mm/min, it was observed that there were gaps in the welding center and the zones at the bottom of DCZ. This situation was clearly visible that the size and amount of gaps in the welded joints increased with the increasing rotational speed and feed rate. The increase in the size of these defects was predicted to be caused by the decrease in temperature in the unit area and time, the lack of sufficient plasticity temperature by means of the triangular stirrer, and the decrease in the ability to extrude. Cavaliere and Squillace (2005) emphasized that the porosity and tunnel formation along the joint in semi-plastic material to be transported before reaching the viscosity-temperature increased. Considering the operation ability of the triangular stirrer pin in the stirring zone, it is very important to provide sufficient temperature in
terms of the extrusion ability in the welding process. When the AA7075 and AA5182 alloys were joined with the conical and triangular stirrer pins, the AA5182 alloy was stirred more since it is more ductile than AA7075 alloy. The SEM images of AA7075/AA5182 alloy pairs joined using the conical and triangular stirrer pins are given in Figs. 6–8. SEM images of the joints where the best strength values used the conical stirrer pin were obtained are given in Figs. 6 and 7 are given. Also, in Fig. 8, SEM images of the triangular stirrer pin are given. In all experimental conditions, the stirrer pin geometry, the rotational speed and the feed rate had a significant effect on the microstructure of the welded joints. The welding quality of samples shown in Fig. 6 was obtained very well, whereas a very small joint failure occurred in the sample in Fig. 7, which was related to increasing feed rate. In joints made through using conical stirrer pins; while the weld quality decreased with increasing feed rate, it did not change with increasing rotation speed. However, the welding quality also decreased with replacing the triangular pin with the conical pin. These welding qualities can be seen in Fig. 8, where some joining failures were obtained. In joints made by using triangular stirrer pins; increasing the feed rate reduced the weld quality, while increasing rotation speed increased the weld quality.
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Fig. 7. SEM images of the sample at rotation speed of 980 rpm and feed rate of 233 mm/min (a) AA5182 alloy (200×–1000×), (b) Welding interface transition zone (200×–1000×), (c) AA7075 alloy (200×–1000×).
Fig. 8. SEM images of weld interface zones in joining made by using triangular stirrer pins.
3.2. Hardness measurements
profile, were measured. The measurements were carried out through the along line from the BM to the joining line and from the joining line to the BM. The measurement results are given in Fig. 9. When the hardness values of all the specimens joined with conical
The microhardness values of AA7075 and AA5182 alloys, which were joined using different rotational speed, feed rate and stirrer 112
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Fig. 9. Microhardness values depending on welding parameters.
Fig. 10. Stress strain curves where conical stirrer pin was used.
Fig. 11. Stress strain curves where triangular stirrer pin was used.
and triangular profiled pins were examined, it was observed that different measurement results were obtained in the weld zones (HAZ, TMAZ, and DCZ). However, when it was reached to BM, the results were close to the main hardness values of the aluminium alloys in the different types. In Fig. 9a and b, the increase in rotation speed led to a slight increase in hardness. However, as the feed rate increased, the hardness partly decreased as well. Also, the hardness of the DCZ zone was found to be higher than those of TMAZ zones. In Fig. 9c and d, the increase in rotation speed and feed rate led to a slight increase in hardness. The minimum hardness value was obtained in the TMAZ zone
near AA5182 (BM) alloy. This increase in DCZ was higher than the hardness value of AA5182 (BM) alloy and lower than the hardness value of AA7075 (BM) alloy. For all experimental conditions, when the effects of the feed rate and the rotation speed variables were evaluated together, it was seen that the hardness values of the joints were close to each other. Since stirrer pins performed stirring in the direction of rotation, the hardness values of all the weld centers of the samples were high. As the size of the grains inside the alloys was reduced, hardening occurred because of plastic deformation and severe extrusion. However, it was 113
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Fig. 11. When the Stress–Strain curves depending on feed rate and rotation speed were examined, the triangular stirrer pin behaved differently than conical stirrer pin. The tensile strength values were obtained at low levels in the triangular stirrer pin because the triangular stirrer pin did not achieve adequate stirring. The tensile strength values of the welding joints in different welding parameters are given in Table 5. After the tensile test, the samples were damaged. Damaged samples brought side by side (Fig. 12). It was seen that the welding joints were broken in the ductile form from the welding zone. However, fracture surfaces must be examined by SEM to be able to make detailed comments; and fracture mechanism must be determined. Some fracture surfaces are given in Fig. 13. In Fig. 13, it was seen that heterogeneously–homogeneously distributed particles with large voids were formed on the fracture surfaces of the welding joints the joined with the conical stirrer tip with high rotation speed, low feed rate, high cutting speed and high feed rate. However, it was observed that the fracture surfaces were homogeneously distributed at low rotational speeds and feed rates (980 rpm, 108 mm/rev). Micro-voids of different sizes and shapes were formed on these surfaces. Also, local ductile fracture mechanisms were observed on fracture surface. When the fracture surfaces of the samples joined with the help of the triangular stirrer pins were examined, it was seen that heterogeneously distributed particles with wider voids were formed. It is thought that the triangular stirrer pin is not able to stir aluminium alloys well enough. Brittle fracture mechanisms occurred on fracture surfaces.
Table 5 Tensile strengths values depending on welding parameters. Stirrer geometry
Rotation speed (rpm)
Feed rate (mm/ min)
Tensile strength (MPa)
Conical
980
108 233 108 233 108 233 108 233 108 233 108 233
265 166 227 144 188 130 203 162.6 211 199 218.2 158.1
1325 1800 Triangular
980 1325 1800
seen that the hardness values at the weld center of the samples joined using the conical stirrer pin were slightly higher than those joined with the triangular stirrer. This was due to the difference in the stirrer shapes of the pin. And the conical stirrer pin stirred by pushing the material in front backward with the aid of helical conical grooves. The triangular stirrer also pushed the material on the front backward from the welding direction depending on the feed rate. The mechanisms at the stirrer pins affected the hardness values of the welded joints. 3.3. Tensile strengths and fracture surfaces of weldings In order to analyse the effects of welding parameters on tensile strength, the tensile strengths of welded joints were applied; and the fracture surfaces obtained from the tensile tests were compared with one another. The Stress–Strain curves of the welding parameters in the welding joints joined using the conical stirrer pin is given in Fig. 10. As seen in Fig. 10, the tensile strength of welding joints decreased with increasing of the rotation speed and the feed rate. The best tensile strength was obtained as 264.75 MPa from the rotation speed of 980 rpm and the feed rate of 108 mm/rev, because conical channels involved in the stirring task was better stirred the material. A good stirring increased the amount of material both in transporting per revolution and extruding backward. This situation contributed to the increase of the plastic deformation. Therefore, in the welded aluminium alloy joints, the mechanical properties were improved and the grain size was reduced. The results obtained from the tensile tests proved that the helical channel played an important role in the stirring of the material. Fujii et al. (2006) also stated that helical channels play an important role in the stirring of materials. The tensile strength-unit elongation graphs of the weld parameters in the welding joints joined using the triangular stirrer pin is given in
3.4. Fatigue test results of welding joints The fatigue emerged from plastic deformation as a result of the interaction tensile stress, and fatigue cyclic tension. The load applied under a stress amplitude causes to form cracks with time. The fatigue (S/N) diagrams of the specimens joined together by using the different rotation speeds and feed rates for conical stirrer pins and triangular stirrer pins are given in Figs. 14 and 15, respectively. In Fig. 14, it was observed that the fatigue strength values of welding joints at the rotation speed of 1800 rpm were lower than those at joints at the rotation speed of 980 rpm. This situation was a result of high working temperature, which was a significant effect on the mechanical properties of the welding joints. At high working temperatures, the microstructure of the material was deteriorated. Therefore, the material flow limit and modulus of elasticity were low. This also reduced the fatigue life of the material. It was also observed that the fatigue strength values in low feed rates were higher than high feed rates. This situation was due to well stirring process in low feed rate. When the fatigue strength, yield limit, tensile strength and hardness
Fig. 12. Damaged zones for the triangular stirrer pin. 114
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Fig. 13. SEM images of fracture surfaces depending on welding parameters (200×).
Fig. 14. S/N diagram depending on welding parameters for conical stirrer pin.
value of the material in the S/N diagrams were considered as a whole, the fatigue strength increased with increasing yield strength, hardness and tensile strength. The highest fatigue strength in the welding joints joined by using the conical stirrer pin was obtained from the rotation speed of 980 rpm and the feed rate of 108 mm/rev. This value was 159 MPa. The lowest fatigue strength was obtained as 52 MPa from the rotation speed of 1800 rpm and the feed rate of 233 mm/rev. In Fig. 15, it was seen that the fatigue strength values decreased
with increase in feed rate. In low feed rate, the increase of rotation speed contributed to the increase of the fatigue strength. Nevertheless, in the high feed rate, the increase of rotation speed caused decrease in the fatigue strength. The high fatigue strength in the welding joints joined by using the triangular stirrer pin was obtained as 120 MPa from low feed rate (108 mm/rev) and high rotation speed (1800 rpm).
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Fig. 15. S/N diagram depending on welding parameters for triangular stirrer pin.
4. Conclusions
References
The metallurgical properties, microhardness values, tensile strengths, fracture surfaces and fatigue strengths of the welding joints of AA7075 and AA5182 aluminium alloy pairs joined by FSW method were investigated. The results are given below.
Aval, H.J., Serajzadeh, S., Kokabi, A.H., Loureiro, A., 2013. Effect of tool geometry on mechanical and microstructural behaviours in dissimilar friction stir welding of AA 5086–AA 6061. Sci. Technol. Weld. Joining 16 (7), 597–604. Cabello, M.A., Rückert, G., Huneau, B., Sauvage, X., 2008. Comparison of TIG welded and friction stir welded Al–4.5Mg–0.26Sc alloy. J. Mater. Process. Technol. 197, 337–343. Cavaliere, P., Panella, F., 2008. Effect of tool position on the fatigue properties of dissimilar 2024-7075 sheets joined by Friction stir Welding. J. Mater. Process. Technol. 206, 249–255. Cavaliere, P., Squillace, A., 2005. High temperature deformation of friction stir processed AA7075 aluminum alloy. Mater. Charact. 55, 136–142. Dawes, C.J., Thomas, W., 1995. Friction Stir Joining of Aluminum Alloys. TWI Bulletin 6, Reprint 493/6/95. Cambridge, UK, pp. 124–127. Fujii, H., Cui, L., Maeda, M., Nogi, K., 2006. Effect of tool shape on mechanical properties and microstructure of friction stir welded aluminum alloys. Mater. Sci. Eng. 419, 25–31. Ghogheri, S.M., Kasırı-Asgarani, M., Amini, K., 2016. Friction stir welding of dissimilar joint of aluminum alloy 5083 and commercially pure titanium. Kovove Mater. 54, 71–75. Güngör, B., Kaluç, E., Taban, E., 2014. Mechanical, fatigue and microstructural properties of friction stir welded 5083-H111 and 6082-T651 aluminum alloys. Mater. Des. 56, 84–90. Hynes, N.R.J., Velu, P.S., 2018. Effect of rotational speed on Ti-6Al-4V-AA 6061 friction welded joints. J. Manuf. Process. 32, 288–297. Infante, V., Braga, D.F.O., Duarte, F., Moreira, P.M.G., Freitas, Mde., Castro, P.M.S.T., 2016. Study of the fatigue behaviour of dissimilar aluminum joints produced by friction stir welding. Int. J. Fatigue 82, 310–316. Jafarlou, H., Jamalian, H.M., Eskandar, M.T., 2018. Investigation into the role of pin geometry on the corrosion behavior of multi-pass FSW joints of Al5086 besides applying Al2O3nanoparticles. J. Manuf. Process. 32, 425–431. Mathers, G., 2002. The Welding of Aluminum and its Alloys. Woodhead Publishing Limited, Cambridge, UK. Mishra, A., Nidigonda, G., 2018. Comparative mechanical and microstructure properties analysis of friction stir welded and TIG welded AA6061-T6 similar joints. J. Adv. Res. Manuf. Mater. Sci. Metall. Eng. 5 (1–2), 1–8. Scialpi, A., Filippis, L.A.C., Cavaliere, P., 2007. Influence of shoulder geometry on microstructure and mechanical properties of friction stir welded 6082 aluminum alloy. Mater. Des. 28, 1124–1129. Thomas, W.M., Nicholas, E.D., 1997. Friction stir welding for the transportation industries. Mater. Des. 18 (4/6), 269–273. Thomas, W.M., Treadgill, P.L., Nicholas, E.D., 1999. The Feasibility of friction stir welding steel. Sci. Technol. Weld. Joining 4 (6), 365–372. Threadgill, P., 1997. Friction Stir Welds in Aluminium Alloys — Preliminary Microstructural Assessment. TWI Bulletin March/April TWI. Abington, UK. Zhang, T., He, Y., Shao, Q., Zhang, H., Wu, L., 2013. Comparative study on fatigue properties of friction stir welding joint and lap joint. 13th International Conference on Fracture.
• Macro and microstructures of welding joints joined by FSW method •
• • •
showed that welding seams varied depending on pin geometry, and welding parameters. The microhardness value was affected by pin geometry and welding parameters. Even though the hardness values of the joints made with both pin geometries were close to each other, the only difference between them was that the hardness values differed with the influence of heat. The highest and lowest hardness values were measured in the experiments where the conical stirrer pin was used. The minimum and maximum hardness values were obtained for the rotation speed of 980 rpm, the feed rate of 108 mm/rev, and the rotation speed of 1325 rpm, the feed rate of 108 mm/rev, respectively. The minimum and maximum hardness values were 67.1 and 87 HV, respectively. The maximum tensile strength was obtained as 265 MPa for the rotation speed of 980 rpm and the feed rate of 108 mm/min. The minimum tensile strength was obtained as 130.4 MPa for the rotation speed of 1800 rpm and the feed rate of 233 mm/min. The minimum and maximum fatigue strengths were measured as 52.2 MPa and 159 MPa, for the rotation speed of 1800 rpm and the feed rate of 233 mm/min and the rotation speed of 980 rpm and the feed rate of 108 mm/min, respectively. In the joints where the triangle stirrer pin was used, the minimum fatigue strength was measured as 71.1 MPa for the rotation speed of 1800 rpm and the feed rate of 233 mm/rev. The maximum fatigue strength was measured as 120 MPa for the rotation speed of 1800 rpm and the feed rate of 108 mm/rev.
Acknowledgment The authors would like to thank the Batman University due to the financial support of Batman University Scientific Research Projects Unit (BTUBAP) under the project of 2017-PhD-2.
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