Precipitation and its effect on the mechanical properties of a cast Mg-Gd-Nd-Zr alloy

Microstructural characterization of a Mg-11Gd-2Nd-0.5Zr (wt.%) alloy processed by isothermal aging at 250 degrees C has been performed using transmission electron microscopy, and the mechanical properties of the alloy after aging for different time have been evaluated using Vickers hardness, room- and high-temperature tensile tests. A four-stage precipitation sequence of the alloy can be described as follows: supersaturated alpha-Mg solid solution -> beta(D0(19)) -> beta '(bco) -> beta(1)(fcc) -> beta(fcc), where the later precipitate can coexist with the former. The precipitation inside the grains is accompanied by the formation and growth of grain boundary precipitates (GBPs) and precipitation free zones (PFZs). Discussion on the structure-properties relationships reveals that microstructure with dense beta ' precipitates in triangular arrangement is the optimum strengthening structure for the alloy. The existence of GBPs and PFZs in the alloy deteriorates the mechanical properties. (C) 2007 Elsevier B.V. All rights reserved.