Different precipitation hardening behaviors of extruded Mg-6Gd-1Ca alloy during artificial aging and creep processes

How to effectively improve the precipitation hardness response of Mg alloys with relatively low RE content is an interesting and important topic. In the present study, an extra stress is added instead of just exposing the sample (extruded Mg-6Gd-1Ca alloy) in high temperature (175 °C) to modify the precipitation behavior and improve the hardness of alloy. Microstructural examinations of the aged alloy by transmission electron microscopy (TEM) show that the weak age-hardening response is mainly attributed to the low number intensity and relatively large size of precipitates in grains. The results suggest that the creep process can effectively promote precipitation response compared with the aging process. TEM analyses indicate a large amount of nano-scale precipitates (espically β' phase) can be formed in grains of the crept alloy, which is mainly responsible for the obvious hardness increase of the alloy after creep. Electron backscattered diffraction (EBSD) data suggest that the dislocation increase caused by strain during creep is responsible for the precipitate increase through providing more nucleation sites.