Achieving strength-ductility synergy of AZ91 extruded sheet by balancing dual-heterostructure of grain size and precipitates

Abstract

In this study, the AZ91 alloy with different volume fraction of dual-heterostructure of grain size and precipitates was obtained by controlling the aging prior to extrusion (APE) time. After APE time at 16 h (APE-16 h), the sample with the proportion of 26.8% in fine grained (FG) layer and heterogeneous precipitates exhibited the excellent combination of strength and ductility, which is mainly due to the grain refinement, precipitates strengthening, weakened texture in FG layer and reducing the number of banded precipitates. Moreover, its optimal hetero-deformation induced (HDI) strengthening and hardening effect caused by dual-heterostructure also plays a significant role in the enhancement of mechanical properties. The coarse grained (CG) layer of APE-16 h sample has more space to accommodate the newly generated dislocations and provides strong work hardening ability. In FG layer, the nanoscale precipitates have an effect on pinning dislocation and relieving local stress concentration. Meanwhile, the activation of the basal and non-basal slips contributes to coordinate plastic deformation.