Influence of magnesium addition in Al–Zn–Si coatings on sacrificial corrosion behavior and corrosion product formation on steel substrates

The role of Mg in promoting LDH formation via solution chemistry or matrix effects remains unresolved, hindering the design of optimized protective coatings. Here, we demonstrate that Mg incorporated in the coating matrix triggers controlled dissolution of the Al-phase, creating nucleation sites for a compact LDH on exposed steel, whereas Mg 2+ in solution has negligible effect. Under galvanostatic corrosion in 3.5 wt% NaCl, the Mg-containing coating (AZSM) dissolves uniformly and suppresses Fe release. It exhibits more than 10-fold higher Al dissolution yet ∼ 50% the Zn consumption compared with Mg-free AZS, resulting in the formation of a thin, crack-free, fine-grained LDH layer. After 21 days, EIS shows a ∼4–fold higher total resistance for AZSM. These data support a mechanism in which solute Mg disrupts Al passivity, providing Al(OH) 3 nuclei that accelerate compact LDH formation and deliver dual sacrificial–barrier protection.