Depth Profile of Residual Stresses to Analyze Textures in Extruded A6XXX

The extruded profiles of A6XXX alloys have a textured surface structure, different from those having the inner cube and Goss orientations. This structure possibly contributes to the decrease in bending strength. Although the mechanism of degradation has been discussed for precipitates, it is necessary to reconsider it from the viewpoint of residual stress distribution. In this study, we first determine the optimal method to evaluate the residual stress in a textured structure. The cosa method with 3-axis oscillation successfully yielded highly precise residual stress values even in extruded aluminum alloys. Although the inner layers of A6063 and A6005C had the cube and Goss orientation, the surface layer at a depth of ∼400 μm had a (112) orientation in A6063 and that at ∼200 μm had a (110) orientation in A6005C. The residual stress increased further from the surface, and changes in the preferred orientation corresponded well with those of residual stress, especially in A6005C. It is suggested that the residual stress increases as the tensile strength increases.