Effect of Sr addition on texture evolution of Mg–3Al–1Zn (AZ31) alloy during extrusion

An experimental investigation of texture evolution during the elevated temperature extrusion of AZ31 alloys containing strontium (Sr) additions is reported. The crystallographic texture of hot extruded alloys containing different levels of Sr has been examined. Hot compression tests have been carried out in order to investigate the hot deformation behavior of the as-cast alloys. It was seen that, at different extrusion temperatures and levels of Sr, different dynamic recrystallization (DRX) mechanisms become dominant which affect the final texture. At lower temperatures and at low levels of Sr, the bulging of grain boundaries was activated, resulting in a necklaced grain structure. Furthermore, a strong deformation texture of 〈10.0〉 parallel to extrusion direction was developed as a result of bulging at the grain boundaries. Twining which was activated in the early stages of deformation, acted as nucleation sites for DRX. In contrast, at high temperatures and high levels of Sr, particle stimulated nucleation (PSN) becomes significant resulting in the weakening of the overall texture with the recrystallization of new grains of random orientation. In order to prevent the surface cracking in the extruded sample, a limit for Sr concentration and deformation temperature was determined. A shoulder region was found in between the bulging and PSN-dominant areas where both mechanisms are active.

Research highlights▶ Hot compression tests were conducted on AZ31(0–1)Sr alloys at different temperatures. ▶ Micro-mechanisms were divided into 4 sections (high and low T, high and low Sr). ▶ A general micro mechanism map has been plotted based on the texture result. ▶ The map is divided into two bulging and PSN regions and a mixed region in between. ▶ The extremes of the two regions are limited by surface cracking and twining.