Influence of pre-strain on de-twinning activity in an extruded AM30 magnesium alloy

Abstract

This study was aimed at examining the compressive deformation behavior of an extruded AM30 alloy along the normal direction (ND) after different amounts of pre-strain along the extrusion direction (ED), with a focus on the strain hardening behavior, texture evolution, and deformation mechanisms. Compressive loading directly in the ND gave a slip-dominated flow behavior due to the presence of two sets of basal textures with c-axes aligned almost parallel to the ND, which was unfavorable for extension twinning. In the two-step ED–ND compression, the compressive yield strength decreased, while the ultimate compressive strength increased with increasing pre-strain. At the lower pre-strain levels two hardening stages of B and C occurred, while three hardening stages of A, B and C were present at the higher pre-strain levels. The peak value between stages B and C and the slope of strain hardening rate in stage B linearly decreased with increasing pre-strain. The phenomenon of de-twinning (or back-twinning) was observed, and the de-twinning activity decreased with increasing pre-strain in the ED while keeping the re-compression amount in the ND constant. Texture measurements revealed that the c-axes of hcp unit cells were always rotated towards the anti-compression direction, regardless of compression in the ED or ND. Texture weakening was achieved via the pre-compression in the ED and subsequent re-compression in the ND.