Hot Deformation Behaviors Of As-cast Mg-8Gd-3Y-1Nd-0.5Zr Magnesium Alloy

The hot deformation behavior of as-cast Mg-8Gd-3Y-1Nd-0.5Zr magnesiumalloy was studied by isothermal compression testing method with Gleeble-1500thermal simulator. The interdependences of flow stress σ, strain rate anddeformation T for the alloy have been studied with the aids of regression analysis. Theflow stress constitutive equation of the alloy was established. The character ofmicrostructure of the alloy was also studied with the aid of the optimal microscopy(OM). The processing maps of the as-cast Mg-8Gd-3Y-1Nd-0.5Zr magnesium alloywas built and analyzed according to the dynamic model. Accordingly, the optimumparameters for hot working of the alloy were obtained.The as-cast microstructure of the Mg-8Gd-3Y-1Nd-0.5Zr magnesium alloyconsists of primary α-Mg solid solution, skeleton-like eutectic structures, smallcuboid-shaped phases.The true stress-strain curves of as-cast Mg-8Gd-3Y-1Nd-0.5Zr magnesium alloyhave a characteristic of dynamic recrystallization during hot deformation in the rangeof460~520℃and0.001~1s-1. The steady flow stress increases with the decrease ofdeformation temperature and the increase of strain rate. During the hot deformation,the original organization is an important factor affecting the flow stress, in addition tothermal deformation parameters. With the increase of deformation temperature,eutectic alloy softening, deformation resistance alloy will decline.This indicates that there is the process of hot activation under hot deformationfor as-cast Mg-8Gd-3Y-1Nd-0.5Zr magnesium alloy. The values of characteristicconstants of material A, α and n, are1.92×1014s-1,0.023MPa-1and2.878,respectively. Its activation energy for hot deformation Q is234.28kJ/mol．Flow instability region are mainly distributed in the high strain rate zone basedon the processing maps and flow localization and the original eutectic are responsiblefor the deformation instability. The optimal deformation region for as-cast Mg-8Gd-3Y-1Nd-0.5Zr magnesium alloy is in the range of460~510℃and0.01~0.1s-1, corresponding to a peak power dissipation efficiency of47%. Under thisregion, the soften mechanism mainly contributed by DRX takes a dominate role,which is beneficial to ductility shaping of the alloy.