Overview of stress corrosion cracking of magnesium alloys

An overview is provided of current understanding of stress corrosion cracking (SCC) of Mg alloys. Nearly continuous second phases along grain boundaries (GBs) cause intergranular stress corrosion cracking (IGSCC). The second phase causes significant micro-galvanic acceleration of the corrosion of the adjacent matrix phase. The applied stress opens the stress corrosion crack and allows propagation through the alloy. IGSCC is expected in all creep resistant Mg alloys, whenever creep resistance is produced by a continuous second phase along GBs. Transganular SCC (TGSCC) is most probably caused by Hydrogen (H) so a detailed study of H-trap interactions is needed to understand this damage mechanism and to design alloys resistant to TGSCC. This is urgently needed if wrought alloys are to be used safely in service because prior research indicates that many Mg alloys have a SCC threshold stress of half the yield stress in common environments including high-purity water.