Improvement of Microstructure and Mechanical Properties of Rapid Cooling Friction Stir-welded A1050 Pure Aluminum

Abstract

Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding (FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO₂ coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.

Keywords

aluminum alloy / friction stir welding / recrystallization / microstructure / mechanical properties

References

[1] Muangjunburee P, Naktewan J, Prachasaree W. Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Friction Stir Welded SSM7075 Aluminum Alloy[J]. Journal of Wuhan University of Technology-Mater. Sci. Ed., 2017, 32: 1 420-1 425.

[2] Massardier V, Epicier T, Merle P. Correlation Between the Microstructural Evolution of A6061 Aluminum Alloy and The Evolution of Its Thermoelectric Power[J]. Acta Mater., 2000, 48: 2 911-2 924.

[3] Zhu Z, Wang M, Zhang H J, et al. Simulation on Temperature Field of Friction Stir Welding of 2A14 Aluminum Alloy Based on Equivalent Film Method[J]. Key Eng. Mater., 2016, 723: 62-67.

[4] Huang Y X, Wang Y B, Wan L, et al. Material-flow Behavior During Friction-stir Welding of 6082-T6 Aluminum Alloy[J]. Int. J. Adv. Manuf. Technol., 2016, 87: 1 115-1 123.

[5] Huang Y X, Meng X C, Lv Z L, et al. Microstructures and Mechanical Properties of Micro Friction Stir Welding (uFSW) of 6061-T4 Aluminum Alloy[J]. J. Mater. Res. Technol., 2019, 8: 1 084-1 091.

[6] Sinhmar S, Dwivedi D K. Investigation of Mechanical and Corrosion Behavior of Friction Stir Weld Joint of Aluminum Alloy[J]. Mater Today: Proc., 2019, 18: 4 542-4 548.

[7] Sato Y S, Urata M, Kokawa H, et al. Retention of Fine Grained Microstructure of Equal Channel Angular Pressed Aluminum Alloy 1050 by Friction Stir Welding[J]. Scripta Mater., 2001, 45: 109-114.

[8] Singh V P, Patel S K, Kuriachen B. Mechanical and Microstructural Properties Evolutions of Various Alloys Welded Through Cooling Assisted Friction-stir Welding: A Review[J]. Intermetallics, 2021, 133: 107 122.

[9] Zhang H, Wang D, Xue P, et al. Achieving Ultra-high Strength Friction Stir Welded Joints of High Nitrogen Stainless Steel by Forced Water Cooling[J]. J. Mater. Sci. Technol., 2018, 34(11): 2 183-2 188.

[10] Xu N, Ueji R, Morisada Y, et al. Modification of Mechanical Properties of Friction Stir Welded Cu Joint by Additional Liquid CO₂ Cooling[J]. Mater Des., 2014, 56: 20-25.

[11] Xu N, Song Q N, Bao Y F, et al. Twinning-induced Mechanical Properties’ Modification of CP-Ti by Friction Stir Welding Associated with Simultaneous Backward Cooling[J]. Sci. Technol. Weld. Joining, 2017, 22: 610-616.

[12] Caballero V, Varma S K. Effect of Stacking Fault Energy and Strain Rate on the Microstructural Evolution during Room Temperature Tensile Testing in Cu and Cu-Al Dilute Alloys[J]. J. Mater. Sci., 1999, 34: 461-468.

[13] Guo Z, Miodownik A P, Saunders N, et al. Influence of Stacking-fault Energy on High Temperature Creep of Alpha Titanium Alloys[J]. Scripta Mater., 2006, 54: 2 175-2 178.

[14] Liu X C, Sun Y F, Nagira T, et al. Effect of Stacking Fault Energy on the Grain Structure Evolution of FCC Metals during Friction Stir Welding[J]. Acta Metall. Sin. (Engl. Lett.), 2020, 33: 1 001-1 012.

[15] Tochigi E, Nakamura A, Shibata N, et al. Dislocation Structures in Low-Angle Grain Boundaries of a-Al2O3[J]. Crystals, 2018, 8: 133-147.

[16] Xu N, Song Q N, Jiang Y F, et al. Large Load Friction Stir Welding of Mg–6Al–0.4Mn–2Ca Magnesium Alloy[J]. Mater Sci. Technol., 2018, 34: 1 118-1 130.

[17] Raturi M, Bhattacharya A. Microstructure and Texture Correlation of Secondary Heating Assisted Dissimilar Friction Stir Welds of Aluminum Alloys[J]. Mater. Sci. Eng. A, 2021, 825: 141 891.

[18] Mironov S, Sato YS, Kokawa H. Microstructural Evolution During Friction Stir-Processing of Pure Iron[J]. Acta Mater., 2008, 56: 2 602-2 614.

[19] Liu X C, Sun Y F, Fujii H. Clarification of Microstructure Evolution of Aluminum During Friction Stir Welding Using Liquid CO₂ Rapid Cooling[J]. Mater. Des., 2017, 129: 151-163.

[20] Fonda R W, Knipling K E. Texture Development in Friction Stir Welds[J]. Sci. Technol. Weld. Joining, 2013, 16: 288-294.

[21] Sakai T, Belyakov A, Kaibyshev R, et al. Dynamic and Post-dynamic Recrystallization under Hot, Cold and Severe Plastic Deformation Conditions[J]. Prog. Mater. Sci., 2014, 60: 130-207.

[22] Butler G C, Mcdowell D L. Polycrystal Constraint and Grain Subdivision[J]. Int. J. Plasticity, 1998, 14: 703-717.

[23] Bay B, Hansen N, Hughes D A, et al. Evolution of FCC Deformation Structures in Polyslip[J]. Acta Metal. Mater., 1992, 40: 205-219.

[24] Zhang J J, Yi Y P, Huang S Q, et al. Dynamic Recrystallization Mechanisms of 2195 Aluminum Alloy During Medium/High Temperature Compression Deformation[J]. Mater. Sci. Eng. A, 2021, 804: 140 650.

[25] Huang T L, Shuai L F, Aneela W, et al. Strengthening Mechanisms and Hall-Petch Stress of Ultrafine Grained Al-0.3%Cu[J]. Acta Mater., 2018, 156: 369-378.

[26] Wei Z, Shen Y, Zhang N, et al. Rapid Hardening Induced by Electric Pulse Annealing in Nanostructured Pure Aluminum[J]. Scripta Mater., 2012, 66: 147-150.

[27] Kamikawa N, Huang X X, Tsuji N, et al. Strengthening Mechanisms in Nanostructured High-purity Aluminum Deformed to High Strain and Annealed[J]. Acta Mater., 2009, 57: 4 198-4 208.

[28] Patel S K, Singh V P, Kumar D, et al. Microstructural, Mechanical and Wear Behavior of A7075 Surface Composite Reinforced with WC Nanoparticle Through Friction Stir Processing[J]. Mater. Sci. Eng. B, 2022, 276: 115 476.

[29] Liu Q, Huang XX, Lloyd D J, et al. Microstructure and Strength of Commercial Purity Aluminum (AA 1200) Cold-rolled to Large Strains[J]. Acta Mater., 2002, 50: 3 789-3 802.