<p>The study aims to develop a composite coating for magnesium aluminum alloy (MA) to improve its corrosion/infection resistance. MA was coated with carboxymethyl chitosan (CMCS) and nano-hydroxyapatite (HA) through electrophoretic deposition, followed by the deposition of vancomycin-loaded polymer nanoparticles to obtain the ternary composite coating alloy (VAN@PLGA/HA/CMCS-MA). In simulated body fluid (SBF), the average corrosion rate of the coating alloy was 0.27 ± 0.03 mg/cm⁻¹/day⁻¹, while maintaining a pH level of approximately 7.2, indicating that the composite coatings effectively mitigated erosion in SBF and ensured a stable physiological pH. In vitro antibacterial experiments showed that VAN@PLGA/HA/CMCS-MA exhibited enhanced antibacterial activity against staphylococcus aureus and enterococcus faecalis compared to single MA owing to sustained antibiotic release. Furthermore, the composite coating promoted alkaline phosphatase activity and induced extracellular Ca²⁺ mineralization, suggesting good bone-promoting ability of the alloy. Finally, the biocompatibility studies confirmed that the composite coating could reduce mild toxicity of the alloy following corrosion, resulting in enhanced cell viability and reduced hemolysis rate. Overall, the ternary composite alloy coating delayed MA degradation and provided long-term effective corrosion/infection resistance.</p> Graphical Abstract <p></p>