滚动轧制对7050铝合金FSW接头组织的影响

Effect of rolling on microstructure of 7050 aluminum alloy FSW joint

采用自制的滚动轧制头对5 mm厚的7050铝合金搅拌摩擦焊接头进行表面滚动轧制处理,并对滚动轧制前后接头的表面粗糙度、变形程度及横截面纵深方向微观组织演化进行了分析.结果表明:滚动轧制后接头的表面粗糙度得到改善,R_(a)由焊接态的7.45μm减小至6.82μm.接头横截面纵深方向从表面向下分为过渡良好的3层,依此为变形层、过渡层及微塑性变形层.变形层是应变最显著的微区,应变呈梯度分布,表层变形最大,随着距接头表面深度的增大而降低.变形层因经历了最大的变形,焊核区原始的等轴状晶粒变形细化,在距接头表面一定深度范围内形成厚度不等的纳米结构.

The 5 mm-thick joint of 7050 aluminum alloy friction stir welding was rolled by self-made rolling tool on the surface,and the surface roughness,deformation degree and microstructure evolution of the joints before and after rolling were analyzed.The results showed that the surface roughness of the joint is improved after rolling,and R_(a) decreases from 7.45μm as-welded to 6.82μm.The depth direction of the joint is divided into three layers from the surface down,which are the deformation layer,transition layer and microplastic deformation layer.The deformation layer is the microregion with the most significant strain,the strain of which shows the gradient distribution.The surface deformation is the largest and decreases with increasing depth from the joint surface.The deformed layer undergoes maximum deformation as a result of which the original isoaxial grain in the nugget zone is deformed and refined,forming nanostructures of varying thickness within a certain depth from the joint surface.