A comparative study on the microstructural features and mechanical properties of an Mg-Zn alloy processed by ECAP and SSE

Abstract

The influence of the equal channel angular pressing (ECAP) and simple shear extrusion (SSE) processes on the microstructural and textural developments, as well as mechanical properties of Mg-4Zn alloy was studied. Application of 1, 2, and 4 passes of ECAP and SSE resulted in remarkable grain refinement of the initial microstructure of extruded material. Due to the greater shear strain and finer second phase particles, acting as obstacles to grain growth, smaller grain sizes were developed in the SSEed samples compared to the ECAPed counterparts. The fiber texture component of the extruded alloy was gradually transformed to a shear texture component after 4 ECAP passes, while 1, 2, and 4 passes of SSE produced a semi-fiber texture, in which basal planes were parallel to the longitudinal axis of the processed sample. Due to the applied reversal shear strain to the sample inside the SSE die, the volume fraction of the dynamically recrystallized (DRXed) regions was lower than that in the ECAP process which exerted a one-step shear strain to the sample. Shear punch test (SPT) results indicated that both ECAP and SSE improved the strength of the extruded alloy due to the grain boundary strengthening, texture hardening, and dislocation-dislocation interaction mechanisms. The strength of the SSEed samples was greater than ECAPed specimens, due to the finer grain size, higher volume fraction of un-DRXed grains, and lower Schmid factor of the semi-fiber texture component of the former.