Dependence of compressive deformation on pre-strain and loading direction in an extruded magnesium alloy: Texture, twinning and de-twinning

This study was aimed at identifying compressive deformation behavior of an extruded AM30 magnesium alloy after different amounts of pre-strain along the extrusion direction (ED), with focus on the effect of re-loading direction, texture evolution, and deformation mechanisms. Compressive loading in both ED and transverse direction (TD) resulted in a similar sigmoidal true stress-true strain behavior due to the presence of two sets of basal textures with c-axes aligned nearly parallel to the plate normal direction which facilitated the occurrence of {101¯2} extension twinning. In the two-step ED-ED compression, the compressive yield strength (YS) linearly increased, while the ultimate compressive strength (UCS) and hardening capacity linearly decreased with increasing pre-strain. The disappearance of twin boundaries or the coalescence of twins via twin growth was observed, but the twin boundaries were more visible and the intensity of cumulative textures with c-axes rotating towards the anti-compression direction was lower, in comparison with the one-step continuous compression at an equivalent strain level. In the two-step ED-TD compression, both YS and UCS increased, and hardening capacity decreased with increasing pre-strain. After a 4.0% pre-strain along the ED plus 4.0% re-compression along the TD, two seemingly opposite phenomena, i.e., the formation of new twins and de-twinning were observed to be co-existent due to the presence of multiple sets of textures after the first-step pre-straining. Both the reversal of textures and microstructural examinations corroborated the occurrence of de-twinning or twin narrowing/shortening as a result of the change of deformation path in the second-step compression.