Galvanic corrosion behavior of magnesium alloy substrate/Fe-based amorphous coating

The galvanic corrosion behavior between AZ31B magnesium alloy and Fe-based amorphous coatings was systematically investigated using salt spray corrosion and electrochemical techniques. The results revealed that penetrating defects within the coating, including direct pores (0.49 %/AMCs150, 0.07 %/AMCs350) and interconnected lamellar pathways, serve as the primary initiation sites for galvanic corrosion between the coating and the substrate. Once triggered, the coupled magnesium alloy suffered severe corrosion, forming a thick (~268.6 μm) but non-protective surface layer with cracks and vacancies that undermined its barrier function. While the Fe-based AMCs themselves form a protective passive film, the galvanic coupling induces severe solution alkalization (pH ~10.9) and Mg(OH)₂ deposition within the coating's lamellar structure. This promotes delamination and degrades the coating's overall corrosion resistance. • Penetration defects primarily drive coating-substrate galvanic corrosion. • Galvanic corrosion causes localized coating cracking and delamination. • Mg alloy corrosion alkalizes the solution, degrading the coating passivation film. • Mg(OH)₂ in coating pores and lamellar gaps promotes interlayer delamination.