Influences of metallurgical factors on the corrosion behaviour of extruded binary Mg–Sn alloys

Abstract

The corrosion behaviour of extruded Mg–(2–8wt%)Sn alloys was investigated in aqueous chloride solutions, and the influences of the volume fraction of Mg2Sn intermetallics, solutionised Sn, and area fraction of grain boundaries on the corrosion behaviour were discussed. The Sn addition to α-Mg increased the solutionised Sn content in the matrix, increased the volume fraction of Mg2Sn intermetallics to 7.3%, and changed the grain size distribution. Regarding the corrosion behaviour, the Sn addition up to 8wt% increased the overall dissolution rate of the alloys, although it promoted the passivity, which resulted from the increased H2 evolution rate and increased numbers of initiation sites for pitting corrosion. The overall corrosion behaviour primarily depended on the amount of Mg2Sn intermetallics, which promoted passivity and notably increased the H2 evolution rate, and functioned as pitting corrosion initiation sites. As the area fraction of grain boundaries increased, the H2 evolution rate was also accelerated. In contrast, the solutionised Sn decreased the H2 evolution rate.