Failure analysis of pit assisted stress corrosion cracking 2026 Engineering

Stress corrosion cracking (SCC) initiation in WE43 magnesium alloy exposed to simulated body fluid (SBF) at 37 °C was investigated using mechanism-based failure analysis. Microstructural characterisation, immersion corrosion testing, XPS, SEM/EDS, and surface crack analysis were combined to identify features associated with crack initiation. The alloy contained rare-earth-rich intermetallic particles along grain boundaries and within the α-Mg matrix. These regions were frequently spatially associated with localised corrosion, pit formation, and crack-damaged areas. Immersion testing showed an early transient corrosion response, with the corrosion rate decreasing from 2.1 mm y−1 at Day 1 to 0.31 mm y−1 at Day 28. However, mass loss and hydrogen evolution continued throughout exposure, indicating partial film protection rather than uniform passivation. Post-exposure cleaning revealed pits and trenches preferentially located near intermetallic-rich regions. XPS analysis identified a heterogeneous corrosion film containing Mg-O/Mg-OH species, P-rich Ca-P-containing products, and trace chloride. This chemistry is consistent with non-uniform film protectiveness and local chloride-associated film destabilisation in SBF. Using the previously reported quasi-static SCC initiation threshold of 178 MPa as a mechanical reference boundary, SEM/EDS observations showed that SCC-type cracks were frequently associated with pits and RE/Zr-rich regions. The combined results support a pit-assisted SCC initiation sequence involving intermetallic particles-associated localised corrosion, heterogeneous film stability, pit growth, and pit-root stress concentration. Subsequent crack advance may involve dissolution-assisted processes, with possible hydrogen-assisted contribution requiring further direct verification.