The microstructure evolution of electromagnetic stirred Mg-4 Zn-0.3 Zr alloy and the effect of the initial microstructure of the alloy on the microstructure and mechanical properties of extruded Mg-4 Zn-0.3 Zr alloy tubes were investigated. The results reveal that the grains of the Mg-4 Zn-0.3 Zr alloy after electromagnetic stirring can be refined and more uniform

and the average grain size is reduced from 91.3 μm to 85.7 μm. The quantities of MgZn phases are decreased

with twins formed inside the grains

and there exists more low-angle grain boundaries. The tensile strength and yield strength of the alloy reach up to 189 MPa and 105 MPa

respectively

and the elongation is increased to 17.3%. Due to the existence of twins and low-angle grain boundaries in the electromagnetic stirred alloy

the dynamic recrystallization degree of the electromagnetic stirred Mg-4 Zn-0.3 Zr alloy after hot extrusion presents higher and the grain size is the finer. The tensile strength

yield strength and elongation of the alloy reach 241 MPa

178 MPa and 25.2%

respectively.