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

Abstract

Compressive creep tests were performed on sand-cast and peak-aged Mg–14Gd–1Zn–0.4Zr (wt.%) alloys at 250 °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 β′-series precipitates or a combination of β-type and γ′ precipitates, could effectively enhance the creep resistance of Mg alloys. Large amounts of β'+β′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 γ′ and β-type precipitates. In contrast, transformation of β′-series precipitates to β1 or β 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 β1 precipitates and dense rectangular networks composed of γ′ and β-type precipitates within the whole grain, which was superior to the uneven distribution of β-type and γ′ 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.