Effects of post-weld heat treatment on microstructures and mechanical properties of AA7204-T4 aluminum alloy FSW joint
DENG Yun-lai1,2, DENG Shu-hao1, YE Ling-ying1, LIN Sen1, SUN Lin3, JI Hua2
1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Light Alloy Research Institute, Central South University, Changsha 410083, China;
3. China Railway Rolling Stock Corporation Qingdao Sifang Co., Ltd., Qingdao 266000, Shandong, China
Abstract：AA7204-T4 aluminum alloy plates were welded by friction stir welding(FSW), and the effect of post-weld heat treatment on the microstructure and mechanical properties of the FSW joints were studied. The results show that the average grain size(AGS) and recrystallization fraction of nugget zone(NZ) are 4.7 μm and 81.9% in as-welded(AW) treatment, 4.8 μm and 82.4% under the post-weld artificial aging(AA) treatment, 5.9 μm and 86.5% under the heat treatment of solid solution followed by artificial aging(SAA), respectively. The grain structure of NZ is not obviously affected by AA treatment, and the AGS and recrystallization fraction of NZ increase by 25.5% and 5.6% under SAA treatment. The ultimate tensile strength(UTS) of the FSW joints are 296.6, 318.2, 357.4 MPa under the heat treatments of AW, AA and SAA, respectively. The improvement of the mechanical properties of FSW joints is limited by AA treatment, while that can be effectively improved by SAA treatment which leads to the welding coefficient reaching 92.0%. Additionally, the microcracks tend to generate on the "S" line under the effect of water quenching after solid solution, which would lead to the fracture location at this zone and the serious decrease of the elongation.
邓运来, 邓舒浩, 叶凌英, 林森, 孙琳, 吉华. 焊后热处理对AA7204-T4铝合金搅拌摩擦焊接头组织与力学性能的影响[J]. 材料工程, 2020, 48(4): 131-138.
DENG Yun-lai, DENG Shu-hao, YE Ling-ying, LIN Sen, SUN Lin, JI Hua. Effects of post-weld heat treatment on microstructures and mechanical properties of AA7204-T4 aluminum alloy FSW joint. Journal of Materials Engineering, 2020, 48(4): 131-138.
 QIN C,GOU G Q,CHE X L,et al. Effect of composition on tensile properties and fracture toughness of Al-Zn-Mg alloy (A7N01S-T5) used in high speed trains[J]. Materials & Design,2016,91:278-285.
 陈东方,张铁浩,张风东,等. 高速列车用7N01铝合金搅拌摩擦焊研究[J]. 焊接技术,2015,44(3):74-76. CHEN D F,ZHANG T H,ZHANG D F,et al. Investigation on friction stir weld of 7N01 aluminum alloy for high-speed strain[J]. Welding Technology,2015,44(3):74-76.
 王振苏,黄凌骄,柴鹏,等. 7N01铝合金搅拌摩擦焊接头组织与性能分析[J]. 焊接学报,2017,38(9):115-118. WANG Z S,HUANG L J,CHAI P,et al. Microstructure and mechanical properties of friction stir welded 7N01 aluminum alloy lap joints[J]. Transactions of the China Welding Institution,2017,38(9):115-118.
 戴启雷,孟立春,梁志芳,等. A6N01-T5合金FSW和MIG焊接头疲劳裂纹扩展行为的对比[J]. 焊接学报,2015,36(9):9-12. DAI Q L,MENG L C,LIANG Z F,et al. Comparison of fatigue crack propagation behavior of friction stir welded and metal inert-gas welded A6N01 joints[J]. Transactions of the China Welding Institution,2015,36(9):9-12.
 邵盈恺,王玉玺,杨志斌,等. 基于焊缝熔深优化的7075铝合金等离子-MIG复合焊接热裂纹敏感性[J]. 金属学报,2018,54(4):547-556. SHAO Y K,WANG Y X,YANG Z B,et al. Plasma-MIG hybrid welding hot cracking susceptibility of 7075 aluminum alloy based on optimum of weld penetration[J]. Acta Metallurgica Sinica,2018,54(4):547-556.
 SQUILLACE A,De FENZO A,GIORLEO G,et al. A comparison between FSW and TIG welding techniques:modifications of microstructure and pitting corrosion resistance in AA 2024-T3 butt joints[J]. Journal of Materials Processing Technology,2004, 152(1):97-105.
 ERICSSON M,SANDSTRÖM R. Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG[J]. International Journal of Fatigue,2003,25(12):1379-1387.
 张海军. 7N01铝合金搅拌摩擦焊焊接工艺和接头力学性能研究[D]. 成都:西南交通大学,2015. ZHANG H J. Study on welding technology and joint mechanical properties of friction stir welding of 7N01 aluminum alloy[D]. Chengdu:Southwest Jiaotong University,2015.
 王文,李天麒,乔柯,等. 转速对水下搅拌摩擦焊接7A04-T6铝合金组织与性能的影响[J]. 材料工程,2017,45(10):32-38. WANG W,LI T Q,QIAO K,et al. Effect of rotation rate on microstructure and properties of underwater friction stir welded 7A04-T6 aluminum alloy[J]. Journal of Materials Engineering,2017,45(10):32-38.
 LIN H,WU Y,LIU S,et al. Effect of cooling conditions on microstructure and mechanical properties of friction stir welded 7055 aluminium alloy joints[J]. Materials Characterization,2018,141:74-85.
 HAKAN A,BAYRAM A,I·SMAIL D. The effect of post-weld heat treatment on the mechanical properties of 2024-T4 friction stir-welded joints[J]. Materials & Design,2010,31:2568-2577.
 SHARMA C,DWIVEDI D K,KUMAR P. Effect of post weld heat treatments on microstructure and mechanical properties of friction stir welded joints of Al-Zn-Mg alloy AA7039[J]. Materials & Design,2013,43:134-143.
 任淑荣,马宗义,陈礼清,等. 焊后热处理工艺和背部二次焊接对搅拌摩擦焊接7075-T651铝合金性能的影响[J]. 金属学报, 2007,43(3):225-230. REN S R,MA Z Y,CHEN L Q,et al. Effects of post weld heat treatment and second welding on tensile properties of friction stir welded 7075-T651 aluminum alloy[J]. Acta Metallurgica Sinica,2007,43(3):225-230.
 HASSAN K A A,NORMAN A F,PRICE D A,et al. Stability of nugget zone grain structures in high strength Al-alloy friction stir welds during solution treatment[J]. Acta Materialia,2003,51(7):1923-1936.
 李帅贞,韩晓辉,毛镇东,等. 焊前清理对铝合金厚板搅拌摩擦焊接头S线及性能的影响[J]. 电焊机,2018,48(3):80-85. LI S Z,HAN X H,MAO Z D,et al. Effect of pre-welding cleaning on S-line and properties of friction stir welded joints of aluminum alloy thick plates[J]. Electric Welding Machine,2018,48(3):80-85.
 戴明亮,胡志力,万心勇,等. S线对搅拌摩擦焊热处理接头力学性能的影响[J]. 金属热处理,2017,42(7):46-50. DAI M L,HU Z L,WAN X Y,et al. Effect of zigzag line on mechanical properties of joint after friction stir welding and heat treatment[J]. Heat Treatment of Metals,2017,42(7):46-50.
 HUMPHREYS F J,HATHERLY M. Recrystallization and related annealing phenomena[M]. Amsterdam,Holand:Academic Press,2004:188-200.
 饶栋. 7N01铝合金自然时效对后续人工时效性能的影响[D]. 长沙:湖南大学,2016. RAO D. Effect of natural aging on subsequent artificial aging performance of 7N01 aluminum alloy[D].Changsha:Hunan University,2016.
 崔俊华,柯黎明,刘文龙,等. 搅拌摩擦焊接全过程热力耦合有限元模型[J]. 材料工程,2014(12):11-17. CUI J H,KE L M,LIU W L,et al. Thermo-mechanical coupled finite element model for whole process of friction stir welding[J]. Journal of Materials Engineering,2014(12):11-17.