Influence of short heat-treatment on microstructural and mechanical inhomogeneity of constrained groove pressed Cu-Zn alloy

Constrained groove pressing (CGP) is a severe plastic deformation (SPD) technique which results in enhanced strength of materials, however, it is also known that this technique leads to inhomogeneity and anisotropy in materials' properties owing to the geometry of CGP die used. Microstructural, as well as strain inhomogeneity, can be alleviated by inducing discontinuous recrystallization, but this may also lead to decrease in strength. In this work, a Cu-Zn alloy was processed through CGP for a single pass and then heat treated at 700 degrees C for short durations of 1, 2, 4, and 10 min. The aim of the work is to examine the influence of short heat-treatment (SHT) on microstructural evolution and mechanical behavior of single pass CGP processed Cu-Zn alloy. It was found that SHT at 700 degrees C induces recrystallization and leads to homogenization of microstructure and materials' properties. Tensile test showed that constrained groove pressed sample and the sample heat-treated for 1 min fractured before attaining the necking zone, which can be directly related to the presence of voids or micro-cracks while samples heat treated beyond 1 min showed the necking. It was found that recrystallization leads to healing of internal voids or micro-cracks, which results in high ductility for samples given SHT beyond 1 min. Strain hardening behavior of various sample conditions was also examined, and it was found that heat-treatment of 2 min and longer duration completely transforms the hardening behavior of severely deformed samples. This implies that a minimum fraction of recrystallization is required for healing of voids/micro-cracks to alleviate the problem of premature fracture. We further analyzed the thermal stability of partially recrystallized samples and found these to be stable up to 300 degrees C. This study shows that post-process heat-treatment can be used as a design tool for severely deformed materials to obtain tailored microstructures with desired properties.