Insights into creep behavior of Mg-14Gd-1Zn-0.4Zr (wt.%) alloy containing - and -type precipitates

Compressive creep tests were performed on sand-cast and peak-aged Mg-14Gd-1Zn-0.4Zr (wt.%) alloys at 250 degrees C in this study. The microstructures before creep and at the secondary creep stage were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that plenty of fine precipitates, especially beta '-series precipitates or a combination of beta-type and gamma ' precipitates, could effectively enhance the creep resistance of Mg alloys. Large amounts of beta'+beta '(F) precipitate chains in the regions near grain boundaries of the sand-cast alloy blocked the motion of -type dislocations, while the interaction of basal and prismatic dislocations could be inhibited by synergy of gamma ' and beta-type precipitates. In contrast, transformation of beta '-series precipitates to beta(1) or beta precipitates in the peak-aged alloy reduced their capacity to impede the dislocation movement, seemingly presenting worse microstructures for creep resistance. However, the peak-aged alloy exhibited a uniform distribution of numerous semi-coherent beta(1) precipitates and dense rectangular networks composed of gamma ' and beta-type precipitates within the whole grain, which was superior to the uneven distribution of beta-type and gamma ' precipitates as well as a lack of ample precipitates at the center of grain in the sand-cast alloy. Thus, the peak-aged Mg-14Gd-1Zn-0.4Zr alloy obtained better creep resistance than the sand-cast alloy to some extent.