Transgranular Stress Corrosion Cracking of Mg alloys

AZ91, AZ21 and ZE41

Andrej Atrens

Professor of Materials Engineering, The University of Queensland, Aus

a.atrens@minmet.uq.edu.au

Abstract: As the usage of Mg alloys increases in stressed applications, it is worthwhile remembering that many Mg alloys are susceptible to stress corrosion cracking in environments such as distilled water or atmospheric exposure. In the absence of data to the contrary, it is prudent to assume that stress corrosion cracking occurs for stresses above the threshold stress of ~50% of the tensile yield stress.

For AZ91, AZ21 and ZE41 our research aims to compare the critical parameters of TGSCC with a Mg TGSCC model. The TGSCC parameters are the threshold stress for TGSCC, the threshold stress intensity for TGSCC and the crack velocity for TGSCC. The model of Mg TGSCC is based on the most probable mechanism. Hydrogen, released by the cathodic partial reaction at a bare crack tip, diffuses to the stressed region ahead of the crack tip; a brittle hydride precipitates and grows once the hydrogen concentration exceeds the terminal solid solubility; a brittle crack advances through the hydride once the hydride has reached a critical size; the process repeats and the sub-critical crack advances until final fracture occurs when the crack reaches a critical size.