滚动轧制对铝合金搅拌摩擦焊接头性能的影响
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摘要
采用自制滚动轧制头对5 mm厚铝合金7050搅拌摩擦焊接头的上表面及背面进行滚动轧制,并与其焊接态的接头作对比,研究了滚动轧制对焊接接头性能的影响.结果表明,滚动轧制后接头表面的粗糙度由最大9.58μm降低到平均约0.85μm.表层发生了剧烈的塑性变形,晶粒明显细化形成约200μm厚的细晶层,亚表层晶粒细化程度降低,在焊核区伴有剪切带产生.接头表层硬度明显提高,其平均硬度高达HV210,相比轧制前硬度HV110提高了91%.接头表层残余应力由原来的拉应力转变为压应力,最大残余压应力场深度约为200μm.疲劳源由表层移至亚表层,疲劳寿命显著提高.
The upper and back surface of a friction stir welded joint of 5 mm thick 7050 aluminum alloy were rolled by a self-made rolling head. It was compared with the welded joints without rolling. The effect of rolling on the performance of welded joints was studied. The results showed that the roughness of joint surface was reduced from 9.58 μm(maximum value) to 0.85 μm(mean value). The surface layer happened severe plastic deformation, and the grains were remarkably refined to form a fine grain layer of about 200 μm thick. The grain refinement of the subsurface layer was reduced, and a shear band was generated in the weld nugget zone. The hardness of the joint surface was obviously improved, and the average hardness was as high as HV210,which was 91% higher than the hardness HV110 before rolling. The residual stress of the joint surface changed from the original tensile stress to the compressive stress, and the maximum residual compressive stress field depth was about200 μm. The source was moved from the surface layer to the subsurface layer, and the fatigue life was significantly improved.
The upper and back surface of a friction stir welded joint of 5 mm thick 7050 aluminum alloy were rolled by a self-made rolling head. It was compared with the welded joints without rolling. The effect of rolling on the performance of welded joints was studied. The results showed that the roughness of joint surface was reduced from 9.58 μm(maximum value) to 0.85 μm(mean value). The surface layer happened severe plastic deformation, and the grains were remarkably refined to form a fine grain layer of about 200 μm thick. The grain refinement of the subsurface layer was reduced, and a shear band was generated in the weld nugget zone. The hardness of the joint surface was obviously improved, and the average hardness was as high as HV210,which was 91% higher than the hardness HV110 before rolling. The residual stress of the joint surface changed from the original tensile stress to the compressive stress, and the maximum residual compressive stress field depth was about200 μm. The source was moved from the surface layer to the subsurface layer, and the fatigue life was significantly improved.
引文
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[2]Wang T,Wang D P,Liu G,et al.Investigations on the nanocrystallization of 40Cr using ultrasonic surface rolling processing[J].Applied Surface Science,2008,225(5):1824-1829.
[3]解瑞军,邱小明,陈芙蓉,等.超声冲击实现7A52铝合金焊接接头表面纳米化[J].焊接学报,2014,35(12):35-38.Xie Ruijun,Qiu Xiaoming,Chen Furong,et al.Surface nanocrystallization of 7A52 aluminum alloy welded joint using ultrasonic impact treatment[J].Transactions of the China Welding Institu-tion,2014,35(12):35-38.
[4]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.Effect of multiple rotary rolling on the surface of friction stir weld of aluminum alloy[J].Transactions of the China Welding Institution,2017,38(2):125-128.
[5]Hatamleh O.A comprehensive investigation on the effects of laser and shot peening on fatigue crack growth in friction stir welded AA2195 joints[J].International Journal of Fatigue,2009,31(5):974-988.
[6]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&Engineering A,2017,702:73-80.
[7]Wagner L,Mhaede M,Wollmann M,et al.Surface layer properties and fatigue behavior in Al 7075-T73 and Ti-6Al-4V:comparing results after laser peening:shot peening and burnishing[J].International Journal of Structural Integrity,2011,2(2):185-199.
[8]Chui P F,Suna K N,Suna C.Effect of surface induced by fast multiple rotation rolling on hardness and corrosion behavior of316L stainless steel[J].Applied Surface Science,2011,257(15):6787-6791.
[9]金玉花,霍仁杰,王希靖,等.旋转速度对7055铝合金搅拌摩擦焊接头断裂特征的影响[J].焊接学报,2017,38(2):10-13.Jin Yuhua,Huo Renjie,Wang Xijing,et al.Effect of rotation speed on fracture characteristics of 7055 aluminum alloy friction stir welding joint[J].Transactions of the China Welding Institution,2017,38(2):10-13.
[10]Fu R,Sun Z,Sun R,et al.Improvement of weld temperature distribution and mechanical properties of 7050 aluminum alloy butt joints by submerged friction stir welding[J].Material and Design,2011,32(10):4825-4831.
[11]Sato Y S,Kokawa H.Distribution of tensile property and microstructure in friction stir weld of 6063 aluminum[J].Metallurgical and Materials Transactions A,2001,32(12):3023-3031.
[12]石德珂.材料科学基础[M].北京:机械工业出版社,2005.
[13]Donald R.Askeland P P.The science and engineering of materials,fouth edition[M].Beijing:Tsinghua University Press,2005.