Stress corrosion cracking (SCC) of magnesium (Mg) alloys

Stress corrosion cracking (SCC) of Mg alloys is intergranular (IGSCC) or transgranular (TGSCC). A continuous or nearly continuous second phase, typically along grain boundaries, causes IGSCC by micro-galvanic corrosion of the adjacent Mg matrix. IGSCC is expected in all such alloys, typical of most creep resistant alloys, because each known second phase has a more positive corrosion potential than the matrix α-Mg; the degree of severity depends on the electrochemical properties of the second phase; these electrochemical properties need to be studied. Nearly continuous second phases can be avoided by Mg alloy design. TGSCC is most likely caused by an interaction of hydrogen (H) with the microstructure. A study of H-trap interactions is needed to understand this damage mechanism, and to design alloys resistant to TGSCC. Understanding is urgently needed if wrought alloys are to be used safely in service, because prior research indicates that many Mg alloys have a threshold stress for SCC of about half the yield stress in common environments including high-purity water.