Given their high strength to density ratio, magnesium alloys, such as magnesium alloy AZ31B, offer unique weight reduction opportunities in structural applications. However, Mg alloys are inheritably susceptible to stress corrosion cracking (SCC) in a variety of environments, including distilled water and NaCl-containing electrolytes. Current recommendations to avoid SCC suggest limiting design stresses to less than 50% of the yield strength (YS), making these alloys less attractive for load-bearing applications.

Much debate still exists regarding the actual mechanism leading to SCC of Mg alloys. The objective of this work was to determine the relative importance of anodic dissolution vs. hydrogen embrittlement based processes for AZ31 magnesium alloy in chloride-containing solutions.
SCC of AZ31 alloy was studied in NaCl solutions at different potentials and chloride concentrations using the slow strain-rate technique (SSRT). A combination of pre-exposure tests followed by immediate straining or straining after a dry air exposure delay helped to weight the relative importance of anodic damage accumulation versus increased hydrogen charging during open circuit potential pre-exposure. The dependence of ductility with pre-exposure time and the fracture surface of embrittled samples suggest that hydrogen embrittlement of AZ31B was controlled by hydrogen diffusion.

CORROSION 2014 Presentation

In this presentation, a combination of pre-exposure tests followed by immediate straining or straining after a dry air exposure delay helped to weight the relative importance of anodic damage accumulation versus increased hydrogen charging during open circuit potential pre-exposure. The dependence of ductility with pre-exposure time and the fracture surface of embrittled samples suggest that hydrogen embrittlement of AZ31B was controlled by hydrogen diffusion.

You can view and download the final version of the talk, presented at CORROSION 2014 below.

Citation

M.A. Kappes, R. Carranza, M. Iannuzzi, Paper No 5138, “Pre-exposure embrittlement and stress corrosion cracking of magnesium alloy AZ31B in chloride solutions”, CORROSION 2014 (Research in Progress Symposium, NACE International, San Antonio, TX, March 9-14, 2014).