A study on the SCC susceptibility of friction stir welded AZ31 Mg sheet

In this study, the stress corrosion cracking (SCC) behaviour of a friction stir welded (FSW) AZ31 Mg alloy was examined using the slow strain rate tensile (SSRT) test method. Electrochemical impedance spectroscopy (EIS) and salt spray tests were conducted to understand the general and localized corrosion behaviour of the base material and the FSW joint. It was found that the FSW AZ31 Mg samples exhibited higher SCC susceptibility than the base material under SSRT testing in the corrosive environment. The failure of these FSW AZ31 Mg samples occurred in the stir zone (SZ), whereas failure occurred in the thermo mechanically affected zone (TMAZ) for samples tested in air. The EIS and salt spray test results demonstrate that the SZ exhibits higher uniform and pitting corrosion resistance than the base material. The present study suggests that the hydrogen assisted cracking mechanism predominates in the failure of FSW AZ31 Mg samples during SSRT test in the corrosive environment.