Effects of Homogenization on Hot Deformation Behavior of As-Cast Mg-8Gd-3Y-1Nd-0.5Zr Magnesium Alloy

The flow stress behaviors of both the as-cast and homogenized Mg-8Gd-3Y-1Nd-0.5Zr alloy were investigated using a Gleeble-1500 thermal simulation test machine in the temperature range of 460-520 degrees C and strain rate range of 0.001-1 s(-1). The processing maps for the two alloys were developed on the basis of flow stress data obtained at a strain of 0.5. It was found that the processing maps of both the as-cast alloy and homogenized alloy consisted of one stability and one instability domains. According to the processing maps and the microstructural observations, the optimum hot-working parameters for the two alloys were determined to be at a temperature of 500 degrees C and at a strain rate of 0.01 s(-1). The hot workability of the homogenized alloy was better than the as-cast alloy in the safe domain, while the homogenization treatment increased the instability domain. The microvoids, which initiated along the dynamic recrystallized (DRX) grain boundaries and led to intercrystalline cracking, were an important factor contributing to the expanded instability domains for the homogenized alloy. Dynamic precipitation in the DRX grain in the as-cast alloy contributed to a lower DRX, hence prevented the formation of microvoids, which resulted in a reduced tendency for DRX intercrystalline cracking during hot deformation.