Microstructural Inhomogeneity in Constrained Groove Pressed Cu-Zn Alloy Sheet

Severe plastic deformation (SPD) is routinely employed to modify microstructure to obtain improved mechanical properties, particularly strength. Constrained groove pressing (CGP) is one of the SPD techniques that has gained prominence recently. However, the efficacy of the method in terms of homogeneity of microstructure and properties has not been well explored. In this work, we examine the microstructure and mechanical properties of CGP processed Cu-Zn alloy sheet and also explore homogeneity in their characteristics. We found that CGP is very effective in improving the mechanical properties of the alloy. Although the reduction in grain size with the number of passes in CGP is not as huge (~38 µm in annealed sample to ~10.2 µm in 1 pass sample) as is expected from a SPD technique, but there is a drastic improvement in ultimate tensile strength (~230 to ~380 MPa) which shows the effectiveness of this process. However, when mechanical properties were examined at smaller length scale using micro-indentation technique, it was found that hardness values of CGP processed samples were non-uniform along transverse direction with a distinct sinusoidal variation. Uniaxial tensile test data also showed strong anisotropy along principal directions. The cause of this anisotropy and non-uniformity in mechanical properties was found to lie in microstructural inhomogeneity which was found to exist at the length scale of the grooves of the die.