Stress corrosion cracking in magnesium alloys: Characterization and prevention

Abstract

The positive environmental infuence of magnesium alloy usage in transportatioapplications could be compromised by catastrophic fast fracture caused by stress corrosion cracking (SCC). Transgranular stress corrosion cracking (TGSCC) of AZ91 has been evaluated using the linearly increasing stress test and the constant extension rate test. The TGSCC threshold stress was 55–75 MPa in distilled water and in 5 g/L NaCl. The TGSCC velocity was 7x10–10 m/s to 5x10–9 m/s. A delayed hydride-cracking model for TGSCC was implemented using a fi nite element script in MATLAB and the model predictions were compared with the experiment. A key outcome is that, during steady-state TGSCC propagation, a high dynamic hydrogen concentration is expected to build up behind the crack tip. In this paper, recommendations are given for preventing SCC of magnesium alloys in service. One of the most important recommendations might be that the total stress in service should be below a threshold level, which, in the absence of other data, could be estimated to be ~50% of the tensile yield strength.