Ductility drop of the solutionized Mg-Gd-Y-Zr alloy during tensile deformation at 350 °C

The effect of temperature and strain rate on tensile ductility of a solutionized Mg-Gd-Y-Zr alloy was investigated using uniaxial tensile testing. The result revealed an interesting phenomenon that with the increment of temperature, this alloy exhibited drop of ductility at 350 °C along with intergranular fracture. Detailed microstructure observation manifested that local precipitation at grain boundary due to holding process before tension was responsible for the grain boundary embrittlement at 350 °C. It was thought that plastic deformation preferentially occurred at the softer solute-depleted zones concurrent with grain boundary precipitates (GBPs), whereas dislocation movement would be effectively inhibited at the hard GBPs, inducing stress concentration and cracking along grain boundary as the solute-depleted zone deformed to its plastic limit. Moreover, it should be noted that the ductility at 350 °C was closely related to the holding time which significantly determined the size and distribution of precipitates. The occurrence of local grain boundary precipitation dependent on temperature and time was predominantly attributed to RE elements segregation to grain boundary.