Influence of creep aging on structural and mechanical properties of Mg-9Gd-2Nd-0.5Zr alloys

Abstract

Secondary phase changes after traditional aging and creep aging and corresponding effects on mechanical properties of Mg-9Gd-2Nd-0.5Zr alloys were studied. The results reveal that the presence of stress during the creep aging increases the concentration of dislocations in the alloy and provides abundant nucleus positions for β′ phase, promoting the precipitation rate of β′ phase in the alloy, which plays a critical role in shortening the peak aging time. In addition, the creep aging under unidirectional stress leads to the anisotropy of the solute atomic diffusion coefficient in the alloy, and the diffusion coefficient (Da/D) along the direction of tensile stress gradually decreases. At the same time, the tensile stress reduces the system energy and releases more energy to the β′ variants (C1) perpendicularly to the stress direction, resulting in preferentially-oriented precipitation and a decrease in alloy strength. There is a decrease in yield strength (YS) from 180.1 MPa to 166.8 MPa and ultimate tensile strength (UTS) from 321.3 MPa to 292.3 MPa after doing creep aging. Moreover, the presence of unidirectional stress during creep aging reduces the angle between the texture pole and basal plane texture, promoting the rotation of the grain orientation towards the basal plane in the alloy and increasing the alloy elongation to 9.5%.