Effect of Microstructure Factors on Stress Corrosion Behavior of Mg-xSn Alloys (x = 2, 5, 8 mass%)

Abstract

The effect of microstructure on the stress corrosion behavior of Mg–Sn alloys was investigated using a bent-beam method. The effects of an Mg₂Sn phase and Sn in the matrix on stress corrosion were investigated. Mg₂Sn phase mainly formed at the grain boundary. The volume fraction of the Mg₂Sn phase increased with increasing Sn content, and the morphology of Mg₂Sn changed from spherical to a semi-continuous network. The average volume fractions of Mg₂Sn phase increased from 0.07 ± 0.02% to 5.06 ± 0.92% as the Sn content was increased from 2 to 8 mass%. An increase in the amount of Mg₂Sn phase increased the pit density, whereas dissolution of the Mg₂Sn phase into the matrix resulted in decreased pit density. An intergranular cracking mode was observed. The solution heat treatment dissolved the Mg₂Sn phase and eliminated the micro-galvanic corrosion due to Mg₂Sn, thereby delaying crack initiation also enhancing stress corrosion resistance. Mg-8%Sn sample through solution heat treatment showed the best stress corrosion resistance.