Effect of natural ageing on microstructure and mechanical properties of Mg–10Gd–2Y–0.8Zr Alloy

Abstract

The effect of natural aging on the microstructure and mechanical properties of Mg–10wt%Gd–2wt%Y–0.5wt%Zn–0.5wt%Zr alloy (GW102) was investigated via optical microscopy (OM), field emission gun scanning electron microscopy (FEGSEM), high-resolution transmission electron microscopy (HRTEM), and differential scanning calorimetry (DSC). The results indicated that the natural placement had a significant effect on the microstructure, mechanical properties, and subsequent artificial aging behaviors of the extruded GW102 alloy. The α(Mg) isometric crystal of the as-extruded alloy was composed entirely of deformation structures, formed by several types of cross-slip. However, the deformation structure within α(Mg) was significantly reduced by performing a 3-year natural aging treatment after extrusion. Many strain-free zones were observed near the grain boundary. Moreover, the β″ phase precipitated within the α(Mg) crystalline grains. The alloy was subjected to a 3-year natural aging treatment, followed by artificial aging at 200°C; the resulting hardness and tensile strength were relatively high during the early stage, but decreased significantly at peak aging and the time required to reach peak aging was shortened. In addition, an aging peak platform (44–132h) was observed. Moreover, the formation of β″ and the reduction of the deformation zone at natural aging process promoted the subsequent artificial aging process.