针对含有根部“弱连接”缺陷的铝合金搅拌摩擦焊接头，采用4点弯曲疲劳试验方法，对比了超声冲击、超声喷丸及超声冲击 + 超声喷丸处理对疲劳性能的影响. 对比分析了试样处理前后根部“弱连接”形貌、显微硬度数值和残余应力分布，探究了其提升焊接接头疲劳性能的机制. 结果表明，相较于超声冲击仅对2 × 106周次以下疲劳强度的提高，超声喷丸、超声冲击 + 超声喷丸均显著提升了高周疲劳性能，对应于2 × 106周次，疲劳强度分别提高13%和40%. 超声冲击 + 超声喷丸复合处理不仅在接头根部缺陷处形成了致密的加工硬化层，而且利用超声喷丸处理引入了更宽的压缩残余应力区域，消除了超声冲击后可能残留的叠形缺陷，进而显著改善了疲劳性能.
Four-point bending fatigue tests were carried out to investigate the effects of ultrasonic impact treatment (UIT), ultrasonic peening (UP) and UIT + UP on the fatigue properties of aluminum alloy FSW joints with root “kissing bonding” defects, and the mechanism of the fatigue performance improvement was explored by analyzing the defect morphologies, microhardness values and residual stress distributions of the samples before and after treatments. Compared with the result that the fatigue strength of FSW joints treated by ultrasonic impact treatment at the root is improved only under 2 × 106 cycles, the results show that UP and UIT + UP can significantly improve the high-cycle fatigue performance, and the fatigue strength is increased by 13% and 40% respectively, corresponding to 2 × 106 cycles. UIT combined with UP cannot only form the compact work hardening layer at the root defects of the FSW joint, increase the microhardness, but also introduce the wider compressive residual stress region near the weld root by UP, eliminate the fold defects probably caused by UIT, significantly improving the fatigue performance.
[1] Magalhase V M, Leitao C, Rodrigues D M. Friction stir welding industrialization and research status[J]. Science and Technology of Welding and Joining, 2018(23): 400 ? 409.
[2] Mishra R S, Ma Z Y. Friction stir welding and processing[J]. Materials Science and Engineering: R: Reports, 2005, 50(1?2): 1 ? 78.
[3] 高崇, 李书磊, 刘贞山, 等. 焊接速度对5754铝合金FSW接头微观组织和力学性能的影响[J]. 焊接学报, 2020, 41(2): 80 ? 86
Gao Chong, Li Shulei, Liu Zhenshan, et al. Effect of travel speeds on microstructures and mechanical properties of friction-stir welded 5754 aluminum alloy sheets[J]. Transactions of the China Welding Institution, 2020, 41(2): 80 ? 86
[4] Lü Zongliang, Han Zhenyu, Zhu Dong, et al. Enlarged-end tool for friction stir lap welding towards hook defect controlling[J]. China Welding, 2020, 29(1): 1 ? 7.
[5] Zhou Caizhi, Yang Xing, Luan Guohong. Effect of root flaws on the fatigue property of friction stir welds in 2024-T3 aluminum alloys[J]. Materials Science and Engineering A, 2006, 418(1?2): 155 ? 160.
[6] 郭超. 基于垫板/凹槽设计铝合金FSW接头完整性及力学性能研究[D]. 南京: 南京航空航天大学, 2019.
Guo Chao. Research on integrity and mechanical properties of friction stir welding of aluminum alloy adopting upper sheet/grooved backing plate[D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2019.
[7] 戴启雷, 王秀义, 侯振国, 等. 焊接速度对AA6082搅拌摩擦焊接头根部缺陷及性能的影响[J]. 焊接学报, 2006, 36(8): 27 ? 30
Dai Qilei, Wang Xiuyi, Hou Zhenguo, et al. Effect of travel speed on the root-defects and mechanical properties of friction stir welded AA6082 alloy joint[J]. Transactions of the China Welding Institution, 2006, 36(8): 27 ? 30
[8] Dickerson T L, Przydatek J. Fatigue of friction stir welds in aluminum alloys that contain root flaws[J]. International Journal of Fatigue, 2003(25): 1399 ? 1409.
[9] Guo Shiqing, Luqman Shah, Rakesh Ranjan, et al. Effect of quality control parameter variations on the fatigue performance of aluminum friction stir welded joints[J]. International Journal of Fatigue, 2019(118): 150 ? 161.
[10] 郝宗斌, 李晓泉, 李阳, 等. 多重旋转碾压对铝合金搅拌摩擦焊缝表面的影响[J]. 焊接学报, 2017, 38(2): 125 ? 128
Hao Zongbin, Li Xiaoquan, Li Yang, et al. Impact of multiple rotating rolling on aluminum alloy friction stir weld surface[J]. Transactions of the China Welding Institution, 2017, 38(2): 125 ? 128
[11] Hatamleh O. A comprehensive investigation on the effects of laser and shot peening on fatigue crack growth in friction stir welded AA2915 joints[J]. International Journal of Fatigue, 2009, 31(5): 974 ? 988.
[12] Li W Y, Li N, Yang X W, et al. Impact of cold spraying on microstructure and mechanical properties of optimized friction stir welded AA2024-T3 joint[J]. Materials Science and Engineering: A, 2018(702): 73 ? 80.
[13] 金玉花, 吴永武, 王希靖, 等. 滚动轧制对铝合金搅拌摩擦焊接头性能的影响[J]. 焊接学报, 2019, 40(4): 50 ? 54
Jin Yuhua, Wu Yongwu, Wang Xijing, et al. Effect of rolling on friction stir welded joints of aluminum alloy[J]. Transactions of the China Welding Institution, 2019, 40(4): 50 ? 54
[14] 梁行, 姜云禄, 陈怀宁, 等. 残余应力对薄板激光搭接接头力学性能的影响[J]. 焊接学报, 2017, 38(10): 112 ? 116
Liang Hang, Jiang Yunlu, Chen Huaining, et al. Effect of residual stress on mechanic properties of sheet laser overlap welding joints[J]. Transactions of the China Welding Institution, 2017, 38(10): 112 ? 116
