Investigation of Microstructure and Mechanical Properties of Extruded Mg–6Bi and Mg–6Bi–1Ag Alloys

The extruded Mg–6Bi alloy and Mg–6Bi–1Ag alloy subjected to extrusion at 300 °C with the extrusion ratio of 25:1 and die-exit speed of 2 m/min were used to investigate microstructure characteristics and mechanical behavior. The experimental results demonstrate that the bimodal microstructure, composed of coarse dynamic unrecrystallized (unDRXed) grains and fine dynamic recrystallized (DRXed) grains, was obtained after extrusion. The Ag addition can obviously promote dynamic recrystallization and average grain size. It also indicates that the dynamic precipitation is significantly promoted by Ag addition during extrusion, obtaining more fraction of the Mg3Bi2 precipitates. Moreover, the extruded Mg–6Bi–1Ag alloy has a high tensile yield strength of 304 ± 2.0 MPa, which is increased by 19% compared to the extruded Mg–6Bi alloy, and elongation of 11.0 ± 1.7%, almost the same as 11.9 ± 0.9% of the extruded Mg–6Bi alloy. This result also shows that the extruded Mg–6Bi–1Ag alloy exhibits better strain hardening capacity. Therefore, Ag exhibits an effective role in promoting dynamic recrystallization and dynamic precipitation, resulting in the enhancement of strength and strain hardening capacity of the extruded Mg–6Bi–1Ag alloy, as well as keeping high ductility.