Optimization of microstructure and mechanical property of a Mg-Zn-Y-Nd alloy by extrusion process

Abstract

A new type of biomedical Mg-Zn-Y-Nd alloy was fabricated and hot extruded in different passes to investigate the influence of extrusion process on its microstructure and mechanical property. The results show that the as-cast alloy (alloy C) is composed of coarse equiaxed grains and large intergranular secondary phases. After one-pass hot extrusion, the incomplete dynamic recrystallization has led to a mixed grain structure with fine equiaxed grains and coarse elongated grains in the alloy (E1). Besides, the secondary phases break into small particles and distribute linearly along the extrusion direction (ED). After two-pass hot extrusion, dynamic recrystallization continues and both equiaxed grains and elongated grains are further refined (alloy E2). The volume fraction of equiaxed grains increases to 82.4%. Moreover, the secondary phases change into smaller ones. The tensile property of Mg-Zn-Y-Nd alloy is improved dramatically by extrusion. The one-pass extrusion enhances the strength of the alloy obviously but contributes little to the elongation. While the two-pass extrusion not only enhances the strength but also improves the ductility of the alloy remarkably. The mechanical properties improvement of the Mg-Zn-Y-Nd alloy should be attributed to the combining effects of grain refinement, texture strengthening and precipitation strengthening generated by hot extrusion process.