Research on the Effect of Sr and Zr on Microstructure and Properties of Mg–4Zn Alloy

In this study, the effects of Zr and Sr on the microstructure, tensile properties and in vitro biocorrosion behavior of Mg–4Zn alloy were investigated. The results show that the grain size of Mg–4Zn alloy is refined by adding Zr or Sr elements, but the tensile properties of Mg–4Zn alloy with Zr element are improved, while those with Sr element are decreased. Grains of Mg–4Zn–0.3Zr become uniform and the average grain size is 91 μm. The yield strength, tensile strength and elongation of Mg–4Zn–0.3Zr alloy are 95 ± 2.1 MPa, 188 ± 1.5 MPa and 15.00 ± 0.3%, respectively. The average grain size of Mg–4Zn–0.5Sr alloy is only 80 μm, but Mg 17 Sr 2 phases precipitate at the grain boundary, which causes a decrease in mechanical properties. The yield strength, tensile strength and elongation of Mg–4Zn–0.5Sr alloy are 82 MPa, 161 MPa and 10.30%, respectively. After hot extrusion, the grain is obviously refined, and the broken second phases are dispersed in the matrix. The yield strength, tensile strength and elongation of as-extruded Mg–4Zn–0.5Sr alloy increase to 207 ± 3.2 MPa, 252 ± 3.0 MPa and 18.81 ± 0.3%, while the tensile properties of the as-extruded Mg–4Zn–0.3Zr alloy are slightly lower. The immersion tests and electrochemical measurements show that the corrosion resistance of the as-extruded alloys is better than that of the as-cast alloys. As-extruded Mg–4Zn–0.3Zr alloy has the best corrosion resistance, the average corrosion rate is 0.3453 ± 0.009 mm/year by the immersion test, and the current density is 9.71 μA/cm 2 .