Unveiling advanced corrosion resistance of novel Al-5Si/Al2O3 cold spray coatings for enhanced durability of AZ31 magnesium alloy

Abstract

An innovative corrosion-resistant Al-5Si/Al₂O₃ composite coating was effectively deposited on AZ31 magnesium alloy using the supersonic cold spray technique. The corrosion performance of both coated and uncoated AZ31 samples was systematically evaluated through a 1000-h salt spray test in 5 wt% NaCl and electrochemical methods. Comprehensive morphological and chemical characterizations were conducted using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), white light interferometry (WLI), X-ray diffraction (XRD), and high-resolution X-ray photoelectron spectroscopy (HR-XPS). The uncoated AZ31 alloy exhibited severe corrosion degradation, characterized by deep pits, microcracks, and a ∼ 4 × times thicker corrosion layer compared to coated samples, primarily attributed to the formation of non-protective MgO/Mg(OH)₂ layers and the presence of Mg₇Zn₃ intermetallic phases. In contrast, the Al-5Si/Al₂O₃ composite coating demonstrated outstanding corrosion resistance, with minimal surface degradation, a ∼ 3× reduced corrosion depth. Electrochemical measurements revealed a substantial decrease in corrosion rate from 82.51 μm/year (bare AZ31) to 4.17 μm/year (composite-coated AZ31). Unlike conventional Al-based cold spray coatings, this study introduces a dual-phase Al-5Si/Al₂O₃ composite that promotes the formation of stable Al₂O_3, and in-situ generated SiO₂ passive films, thereby offering superior and long-term corrosion protection in aggressive chloride environments. These findings underscore the efficacy of the composite coating in significantly enhancing the corrosion resistance of AZ31 magnesium alloy.