Aging response on the stress corrosion cracking behavior of wrought precipitation-hardened magnesium alloy

Constant immersion testing and slow strain rate testing (SSRT) are conducted on wrought magnesium alloy in a 3.5 wt% NaCl solution. After solution annealing (SA) at 525 °C for 8 h, the alloy was isothermally aged at 210 °C for 15 h, 48 h, and 144 h to obtain underaged (UA), peak-aged (PA), and overaged (OA) microstructures, respectively. After 32 days of constant exposure in chloride solution, the SA and UA samples showed the lowest (~ 0.10 mg cm−2 day−1) and the highest (~ 0.20 mg cm−2 day−1) weight loss, respectively. SSRT was carried out at an initial strain rate of 10−6 s−1 in air and 3.5 wt% NaCl solution to investigate stress corrosion cracking (SCC) susceptibility. SCC susceptibility index was in the order PA > UA > SA > OA. Intergranular failure morphology on the fractured surface after SSRT in chloride solution can be attributed to micro-galvanic activity between grain boundary second phase and adjacent regions. Comparison of electrochemical measurements in unstressed and stressed conditions indicated two orders of magnitude difference in electrochemical resistance of the alloy.

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