Effect of Mn Modification on Microstructure and Mechanical Properties of Magnesium Alloy with Low Gd Content

Abstract

The evolution of microstructure and mechanical properties of the dilute Mg–Gd alloy with Mn modification were investigated systematically in this paper. The results show that the combination of Mn and different processing states could adjust the solid solubility of Gd in the Mg matrix, thereby changing the morphology of the second phases and improving the properties of the alloy. With the addition of 0.8 wt% Mn into the Mg–4Gd alloy, the atomic utilization ratio of Gd atoms decreases from 61.5 to 51.8% during the water-cooling casting process, but it increases from 73.8 to 81.0% during homogenization treatment and increases from 72.3 to 84.1% during hot extrusion. Thus, the mean diameter of granular phases of the Mg–4Gd alloy is larger than that of Mg–4Gd–0.8Mn alloy after the isothermal heat treatment. The Mn addition has little effect on the Hall–Petch constant KY and KH of Mg–4Gd alloy, but improves the σ0 value significantly due to the increase of the atomic utilization ratio of Gd atoms. Mn element can improve the mechanical properties of Mg–4Gd alloy, and the increase of yield strength and ductility of as-extruded Mg–4Gd–0.8Mn alloy is mainly attributed to grain refinement and the decrease of the texture intensity. The solid solubility of Gd in Mg matrix can be regulated by the combination of Mn and different processing states, thereby changing the morphology of the second phases and improving the properties of the alloy.