The influence of the LPSO on the deformation mechanisms and tensile properties at elevated temperatures of the Mg-Gd-Zn-Mn alloys

Abstract

The introduction of long period stacking ordered (LPSO) phase is an effective way to improve the performance of the magnesium alloys at elevated temperatures. In this paper, the hot tensile behaviors of two Mg-4Gd-1Zn-0.5Mn (wt.%) alloys with different lamellar LPSO volume fractions under the strain rate of 2.2 × 10–4 s –1 and at varied temperatures (150 °C–250 °C) were investigated. With the increasing of the deformation temperatures, the peak stresses of the alloy with lower volume fraction of the LPSO decreased (denoted as LL alloy). The hot tensile mechanical properties of the alloy with higher volume fraction of the LPSO (denoted as HL alloy) are significantly higher than those of LL alloy. When the deformation temperature was 250 °C, the LL alloys significantly underwent dynamic recrystallization (DRX) and the DRX dominated by discontinuous dynamic recrystallization (DDRX). However, the HL alloys did not have obvious DRX due to the lamellar LPSO hindering the grain boundary migration. The basal fiber texture of the alloy was produced after hot tensile. The deformation of the LL alloys was dominated by prismatic <a> slip during the hot deformation while the deformation of the HL alloys was dominated by the prismatic <a> slip and pyramidal <c+a> slip. The pyramidal <c+a> slip was activated by the Young's moduli mismatch between the α-Mg matrix and LPSO. Lamellar LPSO has an positive effect on strengthening the mechanical properties of the alloy which is attributed to the hinder of LPSO to non-basal slip, the prick function of kink to basal slip and the inhibition of LPSO to DDRX.