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aluminum laminated composites fabricated by ultrasonic additive consolidation
Materials Science & Engineering A 749 (2019) 74–78
Contents lists available at ScienceDirect
Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Microstructure and mechanical properties of amorphous strip/aluminum laminated composites fabricated by ultrasonic additive consolidation ⁎
T
⁎
Yu Wanga,1, Qiang Yanga,1, Xiaona Liua, Yaxin Liua, Bin Liua, , R.D.K. Misrab, , Hong Xua, Peikang Baia a b
School of Materials Science and Engineering, North University of China, Taiyuan 030051, China Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at EI Paso, EI Paso, TX 79968, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Laminated composites Ultrasonic consolidation Amorphous alloy Deformation
Ultrasonic consolidation is a novel forming process for fabricating laminated composites with alternate stacking of tough layer and stiff layer to achieve the desired properties. Laminate composites stacking with Al foil and Febased amorphous strip were produced by ultrasonic consolidation. X-ray diffraction and microhardness measurements indicated that the respective structure of the individual layers was preserved together with excellent hardness and stiffness of the amorphous layer. Shear bands in the amorphous strip combined with thermodynamic stability measurements by differential scanning calorimeter (DSC) indicated that the plastic deformation of amorphous layer led to coordinated deformation and mechanical bonding during the ultrasonic consolidation process.
1. Introduction Laminated composites are high-performance composite materials based on the principle of bionics that alternate stacking of high-hardness brittle layer with the lower hardness tough layer [1]. Ultrasonic consolidation provides solid state welding of metal foils, where high frequency vibration is combined with the static pressure to fabricate laminated composites with dissimilar metal layers [2–5]. The ultrasonic consolidation process creates favorable conditions at the interface by removing the initial oxide film with ultrasonic vibration, provides local heat source and plastic flow across the interfaces by high-frequency friction that consolidating the laminated layer at low temperatures (the reported welding temperature of aluminum foils is ~90 °C) [6,7]. Ultrasonic consolidation can also be used as a novel additive manufacturing process where 3-D metallic objects are fabricated layer by layer in an automated method from thin metal foils [8]. Amorphous alloys exhibit excellent mechanical properties and corrosion resistance，However, the low plasticity and limited size of bulk amorphous alloys limits its application, for instance, to electromagnetic core rather than structural materials. There is a strong focus in preparing amorphous laminated composites by combining the amorphous strips with tough metal foils. Kreye et al. [9] and Maeda et al. [10] prepared Zr-based amorphous laminate composites with copper metal
by ultrasonic welding technology and hot rolling. However, industrialized iron-based amorphous strips are rarely used as a matrix for preparing laminated composites. In the study described here, a novel approach of combining ductile Al metal with iron-based amorphous strips into a laminated composite by using ultrasonic additive consolidation at relatively low temperatures is described. The macroscopic and interfacial microstructure of iron-based amorphous strip laminates was studied together with mechanical properties and interface bonding mechanism of the laminate. 2. Experimental Commercial purity aluminum 1060 and iron-based amorphous strips were used as raw materials. They were cut to dimensions of 800 × 20 × 0.2 mm. The surface oxide film on the foil was removed by washing with 4–10 wt% concentrated NaOH and then dried with acetone. Rolls coupled with ultrasonic vibration penetrated through the surface of amorphous and aluminum strips at a certain speed consolidating them layer by layer [11], as shown in Fig. 1. The energy introduced by lateral vibration, substrate preheating and axial pressure on the foil breaks the initial oxide layer and fuses the interface. The obtained Al/amorphous laminated composite material was selected from an orientation perpendicular to the direction of the ultrasonic
⁎
Corresponding authors. E-mail addresses: [email protected] (B. Liu), [email protected] (R.D.K. Misra). 1 These authors contribute equally to this paper. https://doi.org/10.1016/j.msea.2019.01.039 Received 9 November 2018; Received in revised form 7 January 2019; Accepted 9 January 2019 Available online 10 January 2019 0921-5093/ © 2019 Published by Elsevier B.V.
Materials Science & Engineering A 749 (2019) 74–78
Y. Wang et al.
Fig. 1. Schematic diagram of ultrasonic consolidation process.
interface via ultrasonic consolidation. In Fig. 3(a) and (b), the tensile plots of aluminum 1060 and aluminum/amorphous laminate fabricated by ultrasonic consolidation are prepared. The maximum tensile strength of the composite was ~165 MPa. In the elastic region, the slope of the Al/amorphous laminate is smaller than Al. There are no significant yield region in the two curves of Aluminum laminate and aluminum/amorphous laminate. In the reinforcement stage, because greater resistance to plastic deformation is required during work hardening, significantly higher strain was seen in Al laminate. In the final stage, the Al/amorphous laminate did not fracture abruptly and there was a fracture step, as shown in the red region of Fig. 3(b). The nature of fracture of Al/amorphous was complex (brittle fracture of amorphous layer + ductile fracture of aluminum layer). The fracture morphology at the amorphous fracture interface in Fig. 3(e) indicated that the amorphous layer first experienced brittle failure forming the first step in Fig. 3(b). After the brittle fracture of the amorphous layer, cracking of the interface occurred which continually increased the axial stress of the aluminum layer. Next, the aluminum layer experiences a certain contraction and produces a strong deformation strengthening phenomenon causing tear of Al layer and formation of the second step. The above-mentioned statement is confirmed in Fig. 3(d), where the broken aluminum layer had a deep step in the black frame and burrs and tearing of Al layer are shown in the red frame. In addition, the fracture structure at the bonded interface in Fig. 3(f) showed that tearing occurred near the edge of the aluminum layer without breaking the amorphous/Al interface. The results are consistent with the hardness analysis that suggested that laminate interface formed by ultrasonic consolidation had superior mechanical properties than the aluminum layer. Bonding aluminum and amorphous strip via ultrasonic consolidation is not an atomic diffusion or a chemical reaction process. The interface is consolidated by coordinated severe plastic deformation driven by ultrasonic factors such as amplitude and substrate preheating. In order to better understand the coordinated plastic deformation of aluminum and amorphous layer, the deformation mechanism of each layer under ultrasonic consolidation is separately analyzed below. First, the aluminum layer at the interface experiences partial softening and partial recrystallization through coordinated deformation of ultrasonic waves. Kelly et al. [12] found that acoustic softening and a small amount of thermal softening caused plastic deformation of aluminum. Sriraman et al. [13] proposed that the interface temperature of ultrasonic consolidation can be calculated by adiabatic effect and thermal softening effect, and the calculated results can be used to determine whether the ultrasonic consolidation process triggered recrystallization of aluminum foil. The consolidation interface temperaτγβ ture is given by: ΔT = ρc ,where Tδ is the matrix preheating temperature, τ is the shear stress, γ is the shear strain, β is the thermal
consolidation and the cross-section was subjected to standard grinding and polishing. The cross-sectional interface hardness was measured at least three times via micro-hardness tester. The tensile properties of laminated composite were determined using Instron 3382. The ZEISS optical microscope, SU5000 scanning electron microscope (SEM) combined with EDS was used to study the interface microstructure, chemical distribution of elements and fracture morphology of tensile samples. The original and consolidated amorphous strip were measured by DSC,respectively. A single consolidated amorphous/Al layer was prepared with bare amorphous strip on the top side, as shown in Fig. 2(c) to conduct XRD measurements for confirming if crystallization occurred in the amorphous strip after ultrasonic consolidation. 3. Results and discussion Fig. 2(a, b) shows the macroscopic and microscopic microstructure of amorphous/aluminum laminated composites prepared by ultrasonic consolidation. The alternate stacking of amorphous and Al layers had a straight and well bonded interface. XRD analysis of the exposed amorphous layer of the two-layer-consolidated Al/amorphous laminates showed a diffracted "Taro peak" at a diffraction angle of 35–60° with no sharp crystallization peaks in Fig. 2(c). This means that the amorphous layer did not crystallize after low temperature ultrasonic consolidation and the respective properties of the amorphous state were expected to be preserved in the laminated composite. The microstructure and corresponding EDS line scan of the amorphous/Al interface (Fig. 2(d)) shown ~6 µm mechanically bonded layer and there was no diffusional zone or intermetallic compound formed at the interface. The calculated bonding time of the amorphous/Al laminate was ~6 s based on the rolling speed and the bond length of the foils, which is too short for elements to diffuse across the interface. Thus, it is reasonable to believe that the bonding mechanism of ultrasonic consolidation is mainly dependent on the synergistic plastic deformation of aluminum and amorphous strip at the local interface area. The coordinated flow of soft aluminum, driven by the sufficient energy of ultrasonic vibration, substrate preheating and axial pressure, fills the gaps and unevenness between the interface and produces a smooth interface, as shown in Fig. 2(d). Fig. 2(e) shown the hardness distribution across the Al/amorphous. The corresponding hardness value of aluminum layer, interface area and amorphous layer increased from ~109 HV to ~913.9 HV and ~1729.4 HV respectively, which suggested that the ultrasonic consolidation process successfully consolidated the high strength layer (amorphous) with the ductile layer (pure aluminum) forming hardness gradient distribution. In addition, in Fig. 2(f), the hardness indentation did not cause significant delamination or crack at the Al/ amorphous interface, which means good bonding properties of Al/amorphous 75
Materials Science & Engineering A 749 (2019) 74–78
Y. Wang et al.
Fig. 2. (a) (b) Macroscopic and microscopic images of laminated composites, (c) XRD analysis of amorphous layers, (d) interface EDS line scan, (e) hardness distribution across the interface, and(f) hardness indentations.
transition rate, ρ is the material density, c is the specific heat of the workpiece. The surface roughness of the ultrasonic generator is 14 µm. According to the investigation, at room temperature γ = 40 × 10−6 / 14 × 10−6, τ ≈ 55, ρ = 2700 kg/m3, C = 880 J/kg −1 °C−1, β ≈ 0.95. The calculated results of Al/ amorphous interface is T = 253 °C which is equivalent to 0.38 Tm of aluminum and approaches recrystallization temperature range (0.24–0.29Tm) of pure aluminum. Therefore, we speculate that recrystallization occurs in the vicinity of the interface that locally softens aluminum and synergistic deformation with amorphous layer.
Second, plastic deformation of amorphous foil is characterized by localized shear zone, which acts as a carrier of plastic deformation. The shear band in the amorphous plastic deformation is mainly formed by the local strain superimposed by the movement of atomic groups forming a macroscopic plastic deformation zone [14]. In Fig. 4(a), it was obviously observed that the white shear band was existence in the consolidated amorphous layer, confirming the plastic deformation in the amorphous layer. Furthermore, Van et al. [15] studied that the energy released by structural relaxation in the linear scan DSC curve is proportional to the free volume content of the amorphous alloy. In Fig. 4(b), the relationship between the energy released by the
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Materials Science & Engineering A 749 (2019) 74–78
Y. Wang et al.
Fig. 3. (a) Tensile plot of aluminum 1060, (b) nature of aluminum/amorphous laminate, (c) fracture morphology, (d) interface burr, (e) fracture of each layer, and (f) interface fracture morphology.
formation of shear bands in the local area. At the same time, it also recrystallizes aluminum layer, where the viscosity drops rapidly and the plastic flow is enhanced. Both these effects finally trigger the synergistic plastic deformation of the two layers leading to the formation of a mechanically bonded interface.
relaxation of the structure and the consolidation deformation can be clearly seen by comparing the exothermic peak area between the original amorphous sample and the consolidated sample on the DSC curve. The overall upward trend of free volume content in the consolidating amorphous sample further proved the plastic deformation in the amorphous layer. Under the action of pressure and ultrasonic vibration, the free volume content of the amorphous part increases, resulting in the 77
Materials Science & Engineering A 749 (2019) 74–78
Y. Wang et al.
Fig. 4. (a) shear zone as observed by SEM (b) DSC data for original amorphous and the solidified laminate.
4. Conclusions
[2] D.R. Foster, M.J. Dapino, S.S. Babu, Elastic constants of ultrasonic additive manufactured Al 3003-H18, Ultrasonics 53 (1) (2013) 211–218. [3] R. Gonzalez, B. Stucker, Experimental determination of optimum parameters for stainless steel 316L annealed ultrasonic consolidation, Rapid Prototyp. J. 18 (2) (2012) 172–183. [4] C.Y. Kong, R.C. Soar, P.M. Dickens, Ultrasonic consolidation for embedding SMA fibres within aluminium matrices, Compos. Struct. 66 (1–4) (2004) 421–427. [5] R.J. Friel, R.A. Harris, A nanometre-scale fibre-to-matrix interface characterization of an ultrasonically consolidated metal matrix composite, Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 224 (2010) 31–40. [6] G.S. Kelly, S.G. Advani, J.W.G. Jr, A model to describe stick–slip transition time during ultrasonic consolidation, Int. J. Adv. Manuf. Technol. 79 (9–12) (2015) 1931–1937. [7] P.J. Wolcott, A. Hehr, C. Pawlowski, M.J. Dapino, Process improvements and characterization of ultrasonic additive manufactured structures, J. Mater. Process. Technol. 233 (2016) 44–52. [8] G.D.J. Ram, Y. Yang, B.E. Stucker, Effect of process parameters on bond formation during ultrasonic consolidation of aluminum alloy 3003, J. Manuf. Syst. 25 (3) (2006) 221–238. [9] H. Kreye, M. Hammerschmidt, G. Reiners, Ultrasonic welding of metallic alloy glass to copper, Scr. Metall. 12 (11) (1978) 1059–1061. [10] M.H. Lee, J.S. Park, J.H. Kim, W.T. Kim, D.H. Kim, Synthesis of bulk amorphous alloy and composites by warm rolling process, Mater. Lett. 59 (8–9) (2005) 1042–1045. [11] R.R. Dehoff, S.S. Babu, Characterization of interfacial microstructures in 3003 aluminum alloy blocks fabricated by ultrasonic additive manufacturing, Acta Mater. 58 (13) (2010) 4305–4315. [12] G.S. Kelly, S.G. Advani, J.W.G. Jr, T.A. Bogetti, A model to characterize acoustic softening during ultrasonic consolidation, J. Mater. Process. Technol. 213 (11) (2013) 1835–1845. [13] M.R. Sriraman, S.S. Babu, M. Short, Bonding characteristics during very high power ultrasonic additive manufacturing of copper, Scr. Mater. 62 (8) (2010) 560–563. [14] A.S. Argon, Plastic deformation in metallic glasses, Acta Metall. 27 (1) (1979) 47–58. [15] M.L. Trudeau, R. Schulz, D. Dussault, N.A. Van, Structural changes during highenergy ball milling of iron-based amorphous alloys: is high-energy ball milling equivalent to a thermal process? Phys. Rev. Lett. 64 (1) (1990) 99.
1. In the present study, an aluminum/iron-based amorphous composite was prepared by ultrasonic consolidation. The respective properties of the amorphous state are preserved in the laminated composite as suggested by XRD studies. 2. The interface of the laminate had no obvious crack initiation at the tip of the hardness indentation, and the tensile test indicated that the interface bonding force was higher than the tensile strength of Aluminum layer and fracture occurred in steps. The fracture mode was a combination of brittle fracture + ductile fracture. 3. The mechanism of interface bonding involved local softening and partial recrystallization of aluminum layer combined with shear band formation within the amorphous alloy. DSC thermal analysis of the consolidated amorphous sample further confirms the significant plastic deformation occurred in the amorphous layer. Acknowledgements The author would like to thank Professor Fengchun Jiang in Harbin Engineering University for allowing us to use the ultrasonic consolidation equipment for our experiments. This research work was financially funded by the National Natural Science Foundation of China (Project no. 51701185). References [1] T. Sano, J. Catalano, D. Casem, D. Dandekar, Microstructural and Mechanical Behavior Characterization of Ultrasonically Consolidated Titanium-Aluminum Laminates, 1, 2009.
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Contents lists available at ScienceDirect
Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Microstructure and mechanical properties of amorphous strip/aluminum laminated composites fabricated by ultrasonic additive consolidation ⁎
T
⁎
Yu Wanga,1, Qiang Yanga,1, Xiaona Liua, Yaxin Liua, Bin Liua, , R.D.K. Misrab, , Hong Xua, Peikang Baia a b
School of Materials Science and Engineering, North University of China, Taiyuan 030051, China Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at EI Paso, EI Paso, TX 79968, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Laminated composites Ultrasonic consolidation Amorphous alloy Deformation
Ultrasonic consolidation is a novel forming process for fabricating laminated composites with alternate stacking of tough layer and stiff layer to achieve the desired properties. Laminate composites stacking with Al foil and Febased amorphous strip were produced by ultrasonic consolidation. X-ray diffraction and microhardness measurements indicated that the respective structure of the individual layers was preserved together with excellent hardness and stiffness of the amorphous layer. Shear bands in the amorphous strip combined with thermodynamic stability measurements by differential scanning calorimeter (DSC) indicated that the plastic deformation of amorphous layer led to coordinated deformation and mechanical bonding during the ultrasonic consolidation process.
1. Introduction Laminated composites are high-performance composite materials based on the principle of bionics that alternate stacking of high-hardness brittle layer with the lower hardness tough layer [1]. Ultrasonic consolidation provides solid state welding of metal foils, where high frequency vibration is combined with the static pressure to fabricate laminated composites with dissimilar metal layers [2–5]. The ultrasonic consolidation process creates favorable conditions at the interface by removing the initial oxide film with ultrasonic vibration, provides local heat source and plastic flow across the interfaces by high-frequency friction that consolidating the laminated layer at low temperatures (the reported welding temperature of aluminum foils is ~90 °C) [6,7]. Ultrasonic consolidation can also be used as a novel additive manufacturing process where 3-D metallic objects are fabricated layer by layer in an automated method from thin metal foils [8]. Amorphous alloys exhibit excellent mechanical properties and corrosion resistance，However, the low plasticity and limited size of bulk amorphous alloys limits its application, for instance, to electromagnetic core rather than structural materials. There is a strong focus in preparing amorphous laminated composites by combining the amorphous strips with tough metal foils. Kreye et al. [9] and Maeda et al. [10] prepared Zr-based amorphous laminate composites with copper metal
by ultrasonic welding technology and hot rolling. However, industrialized iron-based amorphous strips are rarely used as a matrix for preparing laminated composites. In the study described here, a novel approach of combining ductile Al metal with iron-based amorphous strips into a laminated composite by using ultrasonic additive consolidation at relatively low temperatures is described. The macroscopic and interfacial microstructure of iron-based amorphous strip laminates was studied together with mechanical properties and interface bonding mechanism of the laminate. 2. Experimental Commercial purity aluminum 1060 and iron-based amorphous strips were used as raw materials. They were cut to dimensions of 800 × 20 × 0.2 mm. The surface oxide film on the foil was removed by washing with 4–10 wt% concentrated NaOH and then dried with acetone. Rolls coupled with ultrasonic vibration penetrated through the surface of amorphous and aluminum strips at a certain speed consolidating them layer by layer [11], as shown in Fig. 1. The energy introduced by lateral vibration, substrate preheating and axial pressure on the foil breaks the initial oxide layer and fuses the interface. The obtained Al/amorphous laminated composite material was selected from an orientation perpendicular to the direction of the ultrasonic
⁎
Corresponding authors. E-mail addresses: [email protected] (B. Liu), [email protected] (R.D.K. Misra). 1 These authors contribute equally to this paper. https://doi.org/10.1016/j.msea.2019.01.039 Received 9 November 2018; Received in revised form 7 January 2019; Accepted 9 January 2019 Available online 10 January 2019 0921-5093/ © 2019 Published by Elsevier B.V.
Materials Science & Engineering A 749 (2019) 74–78
Y. Wang et al.
Fig. 1. Schematic diagram of ultrasonic consolidation process.
interface via ultrasonic consolidation. In Fig. 3(a) and (b), the tensile plots of aluminum 1060 and aluminum/amorphous laminate fabricated by ultrasonic consolidation are prepared. The maximum tensile strength of the composite was ~165 MPa. In the elastic region, the slope of the Al/amorphous laminate is smaller than Al. There are no significant yield region in the two curves of Aluminum laminate and aluminum/amorphous laminate. In the reinforcement stage, because greater resistance to plastic deformation is required during work hardening, significantly higher strain was seen in Al laminate. In the final stage, the Al/amorphous laminate did not fracture abruptly and there was a fracture step, as shown in the red region of Fig. 3(b). The nature of fracture of Al/amorphous was complex (brittle fracture of amorphous layer + ductile fracture of aluminum layer). The fracture morphology at the amorphous fracture interface in Fig. 3(e) indicated that the amorphous layer first experienced brittle failure forming the first step in Fig. 3(b). After the brittle fracture of the amorphous layer, cracking of the interface occurred which continually increased the axial stress of the aluminum layer. Next, the aluminum layer experiences a certain contraction and produces a strong deformation strengthening phenomenon causing tear of Al layer and formation of the second step. The above-mentioned statement is confirmed in Fig. 3(d), where the broken aluminum layer had a deep step in the black frame and burrs and tearing of Al layer are shown in the red frame. In addition, the fracture structure at the bonded interface in Fig. 3(f) showed that tearing occurred near the edge of the aluminum layer without breaking the amorphous/Al interface. The results are consistent with the hardness analysis that suggested that laminate interface formed by ultrasonic consolidation had superior mechanical properties than the aluminum layer. Bonding aluminum and amorphous strip via ultrasonic consolidation is not an atomic diffusion or a chemical reaction process. The interface is consolidated by coordinated severe plastic deformation driven by ultrasonic factors such as amplitude and substrate preheating. In order to better understand the coordinated plastic deformation of aluminum and amorphous layer, the deformation mechanism of each layer under ultrasonic consolidation is separately analyzed below. First, the aluminum layer at the interface experiences partial softening and partial recrystallization through coordinated deformation of ultrasonic waves. Kelly et al. [12] found that acoustic softening and a small amount of thermal softening caused plastic deformation of aluminum. Sriraman et al. [13] proposed that the interface temperature of ultrasonic consolidation can be calculated by adiabatic effect and thermal softening effect, and the calculated results can be used to determine whether the ultrasonic consolidation process triggered recrystallization of aluminum foil. The consolidation interface temperaτγβ ture is given by: ΔT = ρc ,where Tδ is the matrix preheating temperature, τ is the shear stress, γ is the shear strain, β is the thermal
consolidation and the cross-section was subjected to standard grinding and polishing. The cross-sectional interface hardness was measured at least three times via micro-hardness tester. The tensile properties of laminated composite were determined using Instron 3382. The ZEISS optical microscope, SU5000 scanning electron microscope (SEM) combined with EDS was used to study the interface microstructure, chemical distribution of elements and fracture morphology of tensile samples. The original and consolidated amorphous strip were measured by DSC,respectively. A single consolidated amorphous/Al layer was prepared with bare amorphous strip on the top side, as shown in Fig. 2(c) to conduct XRD measurements for confirming if crystallization occurred in the amorphous strip after ultrasonic consolidation. 3. Results and discussion Fig. 2(a, b) shows the macroscopic and microscopic microstructure of amorphous/aluminum laminated composites prepared by ultrasonic consolidation. The alternate stacking of amorphous and Al layers had a straight and well bonded interface. XRD analysis of the exposed amorphous layer of the two-layer-consolidated Al/amorphous laminates showed a diffracted "Taro peak" at a diffraction angle of 35–60° with no sharp crystallization peaks in Fig. 2(c). This means that the amorphous layer did not crystallize after low temperature ultrasonic consolidation and the respective properties of the amorphous state were expected to be preserved in the laminated composite. The microstructure and corresponding EDS line scan of the amorphous/Al interface (Fig. 2(d)) shown ~6 µm mechanically bonded layer and there was no diffusional zone or intermetallic compound formed at the interface. The calculated bonding time of the amorphous/Al laminate was ~6 s based on the rolling speed and the bond length of the foils, which is too short for elements to diffuse across the interface. Thus, it is reasonable to believe that the bonding mechanism of ultrasonic consolidation is mainly dependent on the synergistic plastic deformation of aluminum and amorphous strip at the local interface area. The coordinated flow of soft aluminum, driven by the sufficient energy of ultrasonic vibration, substrate preheating and axial pressure, fills the gaps and unevenness between the interface and produces a smooth interface, as shown in Fig. 2(d). Fig. 2(e) shown the hardness distribution across the Al/amorphous. The corresponding hardness value of aluminum layer, interface area and amorphous layer increased from ~109 HV to ~913.9 HV and ~1729.4 HV respectively, which suggested that the ultrasonic consolidation process successfully consolidated the high strength layer (amorphous) with the ductile layer (pure aluminum) forming hardness gradient distribution. In addition, in Fig. 2(f), the hardness indentation did not cause significant delamination or crack at the Al/ amorphous interface, which means good bonding properties of Al/amorphous 75
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Fig. 2. (a) (b) Macroscopic and microscopic images of laminated composites, (c) XRD analysis of amorphous layers, (d) interface EDS line scan, (e) hardness distribution across the interface, and(f) hardness indentations.
transition rate, ρ is the material density, c is the specific heat of the workpiece. The surface roughness of the ultrasonic generator is 14 µm. According to the investigation, at room temperature γ = 40 × 10−6 / 14 × 10−6, τ ≈ 55, ρ = 2700 kg/m3, C = 880 J/kg −1 °C−1, β ≈ 0.95. The calculated results of Al/ amorphous interface is T = 253 °C which is equivalent to 0.38 Tm of aluminum and approaches recrystallization temperature range (0.24–0.29Tm) of pure aluminum. Therefore, we speculate that recrystallization occurs in the vicinity of the interface that locally softens aluminum and synergistic deformation with amorphous layer.
Second, plastic deformation of amorphous foil is characterized by localized shear zone, which acts as a carrier of plastic deformation. The shear band in the amorphous plastic deformation is mainly formed by the local strain superimposed by the movement of atomic groups forming a macroscopic plastic deformation zone [14]. In Fig. 4(a), it was obviously observed that the white shear band was existence in the consolidated amorphous layer, confirming the plastic deformation in the amorphous layer. Furthermore, Van et al. [15] studied that the energy released by structural relaxation in the linear scan DSC curve is proportional to the free volume content of the amorphous alloy. In Fig. 4(b), the relationship between the energy released by the
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Y. Wang et al.
Fig. 3. (a) Tensile plot of aluminum 1060, (b) nature of aluminum/amorphous laminate, (c) fracture morphology, (d) interface burr, (e) fracture of each layer, and (f) interface fracture morphology.
formation of shear bands in the local area. At the same time, it also recrystallizes aluminum layer, where the viscosity drops rapidly and the plastic flow is enhanced. Both these effects finally trigger the synergistic plastic deformation of the two layers leading to the formation of a mechanically bonded interface.
relaxation of the structure and the consolidation deformation can be clearly seen by comparing the exothermic peak area between the original amorphous sample and the consolidated sample on the DSC curve. The overall upward trend of free volume content in the consolidating amorphous sample further proved the plastic deformation in the amorphous layer. Under the action of pressure and ultrasonic vibration, the free volume content of the amorphous part increases, resulting in the 77
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Fig. 4. (a) shear zone as observed by SEM (b) DSC data for original amorphous and the solidified laminate.
4. Conclusions
[2] D.R. Foster, M.J. Dapino, S.S. Babu, Elastic constants of ultrasonic additive manufactured Al 3003-H18, Ultrasonics 53 (1) (2013) 211–218. [3] R. Gonzalez, B. Stucker, Experimental determination of optimum parameters for stainless steel 316L annealed ultrasonic consolidation, Rapid Prototyp. J. 18 (2) (2012) 172–183. [4] C.Y. Kong, R.C. Soar, P.M. Dickens, Ultrasonic consolidation for embedding SMA fibres within aluminium matrices, Compos. Struct. 66 (1–4) (2004) 421–427. [5] R.J. Friel, R.A. Harris, A nanometre-scale fibre-to-matrix interface characterization of an ultrasonically consolidated metal matrix composite, Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 224 (2010) 31–40. [6] G.S. Kelly, S.G. Advani, J.W.G. Jr, A model to describe stick–slip transition time during ultrasonic consolidation, Int. J. Adv. Manuf. Technol. 79 (9–12) (2015) 1931–1937. [7] P.J. Wolcott, A. Hehr, C. Pawlowski, M.J. Dapino, Process improvements and characterization of ultrasonic additive manufactured structures, J. Mater. Process. Technol. 233 (2016) 44–52. [8] G.D.J. Ram, Y. Yang, B.E. Stucker, Effect of process parameters on bond formation during ultrasonic consolidation of aluminum alloy 3003, J. Manuf. Syst. 25 (3) (2006) 221–238. [9] H. Kreye, M. Hammerschmidt, G. Reiners, Ultrasonic welding of metallic alloy glass to copper, Scr. Metall. 12 (11) (1978) 1059–1061. [10] M.H. Lee, J.S. Park, J.H. Kim, W.T. Kim, D.H. Kim, Synthesis of bulk amorphous alloy and composites by warm rolling process, Mater. Lett. 59 (8–9) (2005) 1042–1045. [11] R.R. Dehoff, S.S. Babu, Characterization of interfacial microstructures in 3003 aluminum alloy blocks fabricated by ultrasonic additive manufacturing, Acta Mater. 58 (13) (2010) 4305–4315. [12] G.S. Kelly, S.G. Advani, J.W.G. Jr, T.A. Bogetti, A model to characterize acoustic softening during ultrasonic consolidation, J. Mater. Process. Technol. 213 (11) (2013) 1835–1845. [13] M.R. Sriraman, S.S. Babu, M. Short, Bonding characteristics during very high power ultrasonic additive manufacturing of copper, Scr. Mater. 62 (8) (2010) 560–563. [14] A.S. Argon, Plastic deformation in metallic glasses, Acta Metall. 27 (1) (1979) 47–58. [15] M.L. Trudeau, R. Schulz, D. Dussault, N.A. Van, Structural changes during highenergy ball milling of iron-based amorphous alloys: is high-energy ball milling equivalent to a thermal process? Phys. Rev. Lett. 64 (1) (1990) 99.
1. In the present study, an aluminum/iron-based amorphous composite was prepared by ultrasonic consolidation. The respective properties of the amorphous state are preserved in the laminated composite as suggested by XRD studies. 2. The interface of the laminate had no obvious crack initiation at the tip of the hardness indentation, and the tensile test indicated that the interface bonding force was higher than the tensile strength of Aluminum layer and fracture occurred in steps. The fracture mode was a combination of brittle fracture + ductile fracture. 3. The mechanism of interface bonding involved local softening and partial recrystallization of aluminum layer combined with shear band formation within the amorphous alloy. DSC thermal analysis of the consolidated amorphous sample further confirms the significant plastic deformation occurred in the amorphous layer. Acknowledgements The author would like to thank Professor Fengchun Jiang in Harbin Engineering University for allowing us to use the ultrasonic consolidation equipment for our experiments. This research work was financially funded by the National Natural Science Foundation of China (Project no. 51701185). References [1] T. Sano, J. Catalano, D. Casem, D. Dandekar, Microstructural and Mechanical Behavior Characterization of Ultrasonically Consolidated Titanium-Aluminum Laminates, 1, 2009.
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