Tailoring the microstructural characteristic and improving the corrosion resistance of extruded dilute Mg–0.5Bi–0.5Sn alloy by microalloying with Mn

Mg–0.5Bi–0.5Sn alloys with and without microalloying with 0.5 wt% Mn were subjected to extrusion, and the effect of Mn microalloying on the microstructural characteristic and corrosion behavior of the extruded alloys was investigated. The results indicated that the average grain size and the density of dislocations decreased, and a new Mg26.67Mn65.47Fe7.86 second phase as well as grain boundary segregation of Sn atoms could be observed in certain micro-regions of the extruded dilute Mg–0.5Bi–0.5Sn–0.5Mn alloy. The tailoring of microstructure resulted in the significant enhancement in corrosion resistance (Rp increased from 1095.91 Ω cm2 to 5008.79 Ω cm2). In addition, grain boundary segregation resulted in intergranular corrosion and led to the dissolution of Sn atoms. Hence, the dissolution rate of the matrix in Mg–0.5Bi–0.5Sn–0.5Mn alloy could be inhibited by the corrosion product film containing an intermediate product (SnO2)