Microstructural control of corrosion in Mg–9Al–Zn alloys: Transition from pitting to uniform attack via β-phase engineering

This study explores the synergistic effects of titanium (Ti) powder addition and severe plastic deformation via equal channel angular pressing (ECAP) on the corrosion resistance and mechanical performance of AZ91 magnesium alloy. The alloy was fabricated through conventional casting with varying Ti content, followed by multiple ECAP passes to enhance microstructural characteristics. Corrosion behavior was evaluated using potentiodynamic polarization in a 3.5 wt% NaCl solution, while microstructural evolution was analyzed through scanning electron microscopy (SEM) and X-ray diffraction (XRD). ECAP treatment, particularly in Ti-enriched samples, resulted in significant grain refinement and a more homogeneous phase distribution. These changes reduced galvanic coupling between the α-Mg matrix and the β-Mg 17 Al 12 phase, promoting the formation of a stable protective surface film. The Ti/ECAPed composite exhibited superior corrosion resistance, with V corr and I corr values of −1.457 V and 4.30 × 10 − 6 A·cm −2 , respectively. Mechanical testing revealed a substantial strength enhancement, with ECAP-treated samples reaching 267 MPa compared to 180 MPa in the untreated alloy. These findings present a promising strategy for improving the durability of AZ91-Mg alloys in structural and automotive applications.