Review on Microstructure and Corrosion Resistance of Zn-Al-Mg Alloy Coatings

Zinc-aluminum-magnesium alloy coatings are widely used in the fields of electrical appliances, construction,automotive and photovoltaic industries due to their excellent corrosion resistance, self-healing properties at cut edges and ease of processing. They are expected to become a new generation of environmentally friendly, low-carbon strategic corrosion-resistant materials. The effects of Al, Mg alloying elements and phase structures on the properties of zinc-aluminum-magnesium alloy coatings, including studies on the crack propagation process influenced by dendritic aluminum phases, eutectic structures and dendritic zinc phases,were reviewed. The formation mechanisms of corrosion products and their protective mechanisms on the alloy coatings were also summarized. It had been found that the anodically dissolved magnesium ions can buffer the pH of the corrosive medium, inducing the formation of dense zinc salt precipitates(Zn₅（OH）₈ Cl₂·H₂O and Zn₆ Al₂（OH）₁₆（CO₃）₃·4H₂O),further enhancing the corrosion resistance of the zinc-aluminum-magnesium coatings. Current research on the corrosion resistance of zinc-aluminum-magnesium alloy coatings mainly focused on low-aluminum and medium-aluminum zinc-aluminummagnesium coatings, with corrosion environments mostly being atmospheric conditions of C1 to C4 levels. However, there was insufficient research on high-aluminum zinc-aluminum-magnesium alloy coatings in more complex application environments, such as stress corrosion environments or corrosion environments above C5 level. Finally, the challenges faced by zinc-aluminum-magnesium alloy coatings and prospects for future development were presented.