Effect of stress relief annealing on microstructure, mechanical properties, and residual stress of a copper sheet in the constrained groove pressing process

Abstract

In this research, the effect of stress relief annealing heat treatment on mechanical properties, microstructure, and residual stresses of a severe plastic deformation technique, known as constrained groove pressing (CGP), was investigated. For this purpose, the CGP process was performed on the commercial pure copper sheet with 3-mm thickness. The hardness, strength, homogeneity, microstructure, and residual stresses before and after stress relief annealing heat treatment were evaluated. Hardness and homogeneity on the surface and thickness were investigated and strength in both of groove direction and transverse groove direction were determined. Also, microstructure was studied along the thickness of CGPed samples, and the contour method was used for 2D residual stress measurement. The results indicate, with increasing number of CGP passes, hardness, strength, and homogeneity increase, while the mean grain size and residual stress decrease. Stress relief annealing reduces the mean grain size in the first pass but increases the mean grain size in the subsequent passes, causing a decrease of mechanical properties. Also, stress relief annealing increases residual stresses due to increasing microstructure heterogeneity.