摘要
通过表面机械滚压(SMRT)的方法在搅拌摩擦焊(FSW)接头表面制备了梯度晶粒结构.电子背散射衍射(EBSD)结果表明,SMRT后试样表层形成了厚度约为550μm的梯度晶粒层,表面光洁度显著提高,由于大塑性变形作用形成了厚度约为170µm的压缩残余应力层;应力比为0.1的单轴疲劳试验表明,焊态接头S-N曲线随应力的降低呈现线性下降的趋势,且疲劳裂纹萌生于试样表层,而经SMRT处理的搅拌摩擦焊接头S-N曲线呈现双折线特征;扫描电子显微镜(SEM)结果表明,S-N曲线第一阶段裂纹萌生于试样表层,第二阶段萌生于试样内部且呈现出“鱼眼”形貌特征.相较于焊态接头试样,SMRT后疲劳强度显著提高,特别是当疲劳裂纹萌生于内部时与母材疲劳强度相当.疲劳强度的提高归因于SMRT形成的梯度结构、形成厚的压缩残余应力层、表面光洁度的提升以及超高周疲劳(VHCF)特征.
The gradient grain structure was prepared on the surface of friction stir welding(FSW)joints by means of surface mechanical rolling treatment(SMRT).Electron backscatter diffraction(EBSD)results show that a gradient grain layer with a thickness of about 550μm is formed on the surface of the sample after SMRT,and the surface finish is significantly improved.A compressive residual stress layer with a thickness of about 170μm is formed due to the action of large plastic deformation.Uniaxial fatigue test at a stress ratio of 0.1 reveals that the S-N curves of welded joints exhibit linear descendance with the reduction of stress,and fatigue cracks exclusively initiate at specimen surfaces,whereas the S-N curves of FSW joints after SMRT demonstrate bilinear characteristics.Scanning electron microscope(SEM)results demonstrate that the cracks in the first stage of the S-N curve initiate at the specimen surface,while those in the second stage initiate inside the specimen,accompanied by fish-eye morphology characteristics.Compared with welded joint specimens,the fatigue strength after SMRT is significantly improved,especially when a fatigue crack is initiated internally,the fatigue strength is comparable to that of the base metal.The increase in fatigue strength can be attributed to the gradient structure formed by SMRT,the formation of a thick compressive residual stress layer,the improvement of surface finish,and the very high cycle fatigue(VHCF)characteristics.
作者
刘泽鹏
魏雅楠
罗丹
董鹏
LIU Zepeng;WEI Ya'nan;LUO Dan;DONG Peng(School of Mechanical and Electrical Engineering,Shanxi Datong University,Datong 037006,China;Daqin Railway Co.,Ltd.,Datong 037006,China;College of Materials Science and Engineering,Wuhan University of Technology,Wuhan 430070,China;College of Materials Science and Engineering,Taiyuan University of Technology,Taiyuan 030024,China)
出处
《焊接学报》
北大核心
2026年第2期126-133,共8页
Transactions of The China Welding Institution
基金
山西省自然科学基金(20210302123116)。
关键词
7075铝合金
搅拌摩擦焊
表面机械滚压
疲劳
7075 aluminum alloy
friction stir welding
surface mechanical rolling treatment
fatigue
