The performance degradation of MAO/GPTMS coating on magnesium alloy under combined corrosive environment and cyclic loading

Magnesium alloys hold promise as biodegradable orthopedic implants but suffer from rapid corrosion and poor corrosion fatigue performance. This study evaluates the efficacy of a micro-arc oxidation (MAO) layer combined with 3-glycidyloxypropyltrimethoxysilane (GPTMS) sealing in enhancing the corrosion fatigue behavior of ZE21B magnesium alloy in Hanks’ Balanced Salt Solution (HBSS). Electrochemical testing revealed a two-order-of-magnitude reduction in corrosion current density compared to bare alloy, while immersion tests demonstrated sustained protection against degradation. Corrosion fatigue experiments under cyclic loading showed stress-dependent performance: the composite coating improved fatigue life at low stress amplitudes (60 MPa) by mitigating corrosion pit formation, but interfacial weakness between GPTMS and MAO layers reduced performance at high stresses (90–80 MPa). Fractographic analysis identified asynchronous deformation and stress gradient-dependent coating spallation as key failure modes. These results provide mechanistic insights into coating degradation pathways and offer design strategies for developing robust surface modification systems to advance magnesium-based orthopedic applications.