Effects of Nd on microstructures and properties at the elevated temperature of a Mg-0.3Zn-0.32Zr alloy

The effects of Nd addition on the microstructures and mechanical properties at elevated temperatures of a Mg-0.3Zn-0.32Zr alloy were investigated in this study. The grain sizes of Mg-0.3Zn-0.32Zr alloys were decreased from 120 mu m to 76 mu m and grain morphologies were changed from hexahedron to rosette-like by increasing Nd addition from 0.21% to 2.65%. Both Nd and Zn are fully dissolved into the Mg matrix when Nd addition is less than 0.84% and the as-cast structure consists of only alpha-Mg. Increasing Nd concentration over 1.62%, intermetalitics Mg-12(Nd,Zn) phase confirmed by X-ray diffractometer (XRD) occurs at the grain boundaries and triple grain boundaries. The heat treatment results in the Nd fully dissolved and then re-precipitated as Mg-12(Nd,Zn), distributing as cluster within the grains and along the grain boundaries. The heat treatment also results in some grain coarsening, and Nd acts as effective barriers for the grain agglomeration. The existing of Mg-12(Nd,Zn) phase within the grains and along the grain boundaries for the alloys containing high Nd acts to lock the grain boundaries and reduce grain boundary and dislocation sliding, leading to obvious improvements both in tensile strength and yield strength as well as a slight decrease in elongation at elevated temperatures. (C) 2010 Elsevier Ltd. All rights reserved.