Microstructural Evolution and Mechanical Properties of the As-Cast and Extruded Mg-Gd Alloys

The microstructure, hardness, and shear strength of two Mg-Gd alloys with 1 and 2 wt% Gd were studied in both as-cast and extruded conditions. In the as-cast condition, the addition of Gd has no significant effect on the grain size, but it results in a high volume fraction of Mg5Gd precipitates. Gd addition decreased the grain size of the extruded materials, by retarding recrystallization during hot deformation through solute drag effect of Gd atoms in Mg. The enhancements in strength and hardness of the cast materials are due to the formation of Mg5Gd particles, while in the extruded materials the severe grain refinement achieved after extrusion is responsible for such improvements.