Effect of Hybrid Surface Nanocrystallization Before Welding on Microstructure and Mechanical Properties of Friction Stir Welded 2A14 Aluminum Alloy Joints
1 Rocket Force University of Engineering, Xi'an 710025, China 2 School of Materials Science and Engineering, Xi'an University of Technology, Xi'an 710048, China 3 Chang Zheng Machinery Factory, China Aerospace Science and Technology Corporation, Chengdu 610100, China
Cite this article:
Jianhai YANG,Yuxiang ZHANG,Liling GE,Xiao CHENG,Jiazhao CHEN,Yang GAO. Effect of Hybrid Surface Nanocrystallization Before Welding on Microstructure and Mechanical Properties of Friction Stir Welded 2A14 Aluminum Alloy Joints. Acta Metall Sin, 2017, 53(7): 842-850.
2A14 aluminum alloy is the important raw materials of aerospace, which belongs to the heat treatment aluminum alloy. Friction stir welding (FSW) can weld aluminum alloy with high quality, and can avoid the pores and cracks of fusion welding effectively. In order to obtain better mechanical properties of FSW joints, the surface nanocrystallization method is introduced into FSW technology. By means of the hybrid surface nanocrystallization (HSNC) method of both supersonic fine particles bombarding (SFPB) and surface mechanical rolling treatment (SMRT), a smooth gradient nanostructured (GNS) layer was formed on the surface of 2A14 aluminum alloy before FSW. The FSW joints microstructure and fracture morphology of the original and HSNC specimens were researched by OM, SEM and TEM. The results showed that nanostructure layer zone (NLZ) was formed when GNS with shape similar to the "S" line was distributed in the thermal-mechanical affected zone (TMAZ) and the nugget zone (NZ) of the HSNC specimen. The lowest micro-hardness and fracture position of the original specimen occurred on the TMAZ of advancing side (AS). The lowest micro-hardness and fracture position of the HSNC specimen occurred on the NZ. The tensile strength of HSNC specimen was 6.4% higher than the original sample. The elongation of HSNC specimen was 14.1% more than the original specimen. The fracture mode of both specimens was toughness fracture. The fracture morphology of the HSNC was isometric dimple when the fracture morphology of original specimen were non-isometric dimple and avulsion dimple. Analysis showed that the NLZ of the FSW joints was beneficial to improving the strength and the plastic deformation capability simultaneously.
Fund: Supported by National Natural Science Foundation of China (No.51275517), Science and Technology Project of Shaanxi Province (No.2009K06-22) and Special Project of Xi'an University of Technology (No.2014TS002)
Fig.1 Schematic of surface mechanical rolling treatment equipment[19]
Fig.2 Photo of friction stir welding (FSW) head
Fig.3 Cross-sectional OM images of the FSW joints of the original (a) and the hybrid surface nanocrystallization (HSNC) (b) specimens (TMAZ—thermal-mechanical affected zone, NZ—nugget zone, HAZ—heat affected zone, BM—base metal, AS—advancing side, RS—retreating side)
Fig.4 OM image of the 2A14 aluminum alloy BM
Fig.5 OM images of the original and HSNC specimens (NLZ—nanostructure layer zone)(a) TMAZ of the original specimen(b) TMAZ of AS of the HSNC specimen(c) TMAZ of RS of the HSNC specimen(d) NZ of the original specimen(e) NZ of the HSNC specimen
Fig.6 TEM images of the original and HSNC specimens (1—nanocrystalline, 2—submicron grain)(a) TMAZ of the original specimen(b) NZ of the original specimen(c) TMAZ of AS of the HSNC specimen(d) TMAZ of RS of the HSNC specimen(e) NZ of the HSNC specimen
Fig.7 Micro-hardness distributions of the FSW joints of 2A14 aluminum alloy
Fig.8 Fracture positions of FSW joints of the original (a) and HSNC (b) specimens
Sample
Yield strength / MPa
Ultimate strength / MPa
Elongation / %
Fracture position
Base metal
315
429
15.0
Original
210
362
7.8
TMAZ (AS)
HSNC
220
385
8.9
NZ
Table 1 Mechanical properties and fracture positions of FSW joints of the original and HSNC specimens
Fig.9 Low (a, c) and locally high (b, d) magnified fracture SEM images of FSW joints in the original (a, b) and HSNC (c, d) specimens
[1]
Wang Y R, Teng W H, Yu Y, et al.Microstructure and characteristics of joint of electron beam welds of 2A14 aluminum alloy[J]. Chin. J. Nonferrous Met., 2012, 22: 3307
Thomas W M, Nicholas E D, Needham J C, et al. Friction stir welding [P]. Great Britain Pat, 9125978.8, 1991
[3]
Thomas W M, Nicholas E D, Needham J C, et al. Improvements relating to friction stir welding [P]. US Pat, 5460317, 1991
[4]
Luan G H, North T H, Guo D L, et al.Characterizations of friction stir welding on aluminum alloy[J]. Trans. China Weld. Inst., 2002, 23(6): 62
[4]
(栾国红, North T H, 郭德伦 等. 铝合金搅拌摩擦焊接头行为分析[J]. 焊接学报, 2002, 23(6): 62)
[5]
Lu K, Lu J.Surface nanocrystallization (SNC) of metallic materials——Presentation of the concept behind a new approach[J]. J. Mater. Sci. Technol., 1999, 15: 193
[6]
Lu L, Sui M L, Lu K.Superplastic extensibility of nanocrystalline copper at room temperature[J]. Science, 2000, 287: 1463
[7]
Lu K, Lu J. Nanostructured surface layer on metallic materials induced by surface mechanical attrition treatment [J]. Mater. Sci. Eng., 2004, A375-377: 38
[8]
Yang J H, Zhang Y X, Ge L L, et al.Effect of hybrid surface nanocrystallization on the electrochemical corrosion behavior in 2A14 aluminum alloy[J]. Acta Metall. Sin., 2016, 52: 1413
Ge L L, Lu Z X, Jing X T, et al.Effect of surface nanocrystallization and thermal stability of 0Cr18Ni9 stainless steel on low temperature nitriding behavior[J]. Acta Metall. Sin., 2009, 45: 566
Xu W F, Liu J H, Luan G H, et al.Microstructures and mechanical properties of friction stir welded aluminium alloy thick plate[J]. Acta Metall. Sin., 2008, 44: 1404
Zhang H J, Wang M, Zhang X, et al.Characteristics and joint microstructure-property analysis of bobbin tool friction stir welding of 2A14-T6 aluminum alloy[J]. Trans. China Weld. Inst., 2015, 36(12): 65
Malarvizhi S, Balasubramanian V.Fatigue crack growth resistance of gas tungsten arc, electron beam and friction stir welded joints of AA2219 aluminium alloy[J]. Mater. Des., 2011, 32: 1205
[13]
Liu H J, Zhang H J, Huang Y X, et al.Mechanical properties of underwater friction stir welded 2219 aluminum alloy[J]. Trans. Nonferrous Met. Soc. China, 2010, 20: 1387
[14]
Zhang H J, Liu H J, Yu L.Microstructure and mechanical properties as a function of rotation speed in underwater friction stir welded aluminum alloy joints[J]. Mater. Des., 2011, 32: 4402
[15]
Zhang H J, Liu H J, Yu L.Microstructural evolution and its effect on mechanical performance of joint in underwater friction stir welded 2219-T6 aluminium alloy[J]. Sci. Technol. Weld. Joining, 2011, 16: 459
[16]
Zhang H J, Liu H J.Mathematical model and optimization for underwater friction stir welding of a heat-treatable aluminum alloy[J]. Mater. Des., 2013, 45: 206
[17]
Kang J, Li J C, Feng Z C, et al.Investigation on mechanical and stress corrosion cracking properties of weakness zone in friction stir welded 2219-T8 Al alloy[J]. Acta Metall. Sin., 2016, 52: 60
Wang D, Wang Q Z, Xiao B L, et al.Effect of heat treatment before welding on microstructure and mechanical properties of friction stir welded SiCp/Al-Cu-Mg composite joints[J]. Acta Metall. Sin., 2014, 50: 489
Bai T.Research on the stress corrosion cracking susceptibility of the stainless steel with surface nanocrystallization by small punch test [D]. Shanghai: East China University of Science and Technology, 2013
Ji S D, Wen Q, Ma L, et al.Microstructure along thickness direction of friction stir welded TC4 titanium alloy joint[J]. Acta Metall. Sin., 2015, 51: 1391
Huang H W, Wang Z B, Liu L, et al.Formation of a gradient nanostructured surface layer on a martensitic stainless steel and its effects on the electrochemical corrosion behavior[J]. Acta Metall. Sin., 2015, 51: 513
Roland T, Retraint D, Lu K, et al. Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability [J]. Mater. Sci. Eng., 2007, A445-446: 281
[23]
Liu J, Yang J H, Han F W, et al.Microstructures and properties of thickness aluminium alloy eleocellarium repairing welding joint by friction stir welding[J]. J. Mater. Eng., 2012, (7): 29
