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.