Comparison of the Linearly Increasing Stress Test and the Constant Extension Rate Test in the Evaluation of Transgranular Stress Corrosion Cracking of Magnesium

Abstract

Transgranular stress corrosion cracking (TGSCC) of the Mg alloy AZ91 in distilled water and 5 g/L NaCl solution has been evaluated using the Linearly Increasing Stress Test (LIST) and the Constant Extension Rate Test (CERT). The differences between these techniques, with respect to fractography and the measurement of SCC parameters, are discussed. The LIST and CERT techniques are both useful in identifying the occurrence of SCC and, when coupled with a technique for characterizing crack extension, measuring the threshold stress and crack velocity. During a LIST fast fracture ensues a relatively short time after the threshold stress is attained, whereas during CERT crack growth over a much longer time period is facilitated by a reduction in stress. Consequently, the LIST is typically 30 - 50 % shorter in duration, whereas the CERT produces a larger SCC fracture surface.