Influence of Ce addition and homogenization temperature on microstructural evolution and mechanical properties of extruded Mg-Sn-Al-Zn alloy

The effects of Ce addition and homogenization temperature (HT) on the microstructure and tensile properties of extruded Mg-7Sn-1Al-1Zn (TAZ711) alloy were investigated. It was found that Ce addition resulted in the formation of a thermally stable lath-type Ce3Sn5 phase and that a decrease in HT caused an undissolved spherical Mg2Sn phase to remain in the homogenized billets. With an increase in the amount of the Ce3Sn5 and Mg2Sn particles, the number of fine Mg2Sn precipitates formed dynamically during extrusion decreased gradually owing to a reduction in the amount of Sn dissolved in the matrix, which, in turn, led to an increase in the size of dynamically recrystallized grains because of a weakened grain boundary pinning effect. The tensile strength of the extruded alloys decreased with increasing amount of added Ce and decreasing HT, mainly because of the reduced number of precipitates and enlarged grain size. The yield strength and ultimate tensile strength of the alloy were inversely proportional to the area fraction of the Ce3Sn5 and Mg2Sn particles present in the homogenized billets, whereas the strain-hardening ability of the alloy was directly proportional to the area fraction.