Developing Sol–Gel Hydroxyapatite-Bone Powder Composite Coatings on Mg-Zn-Ca Alloy and Studying Their Corrosion Behavior

Hydroxyapatite/bone powder composite coatings on ZX504 alloy have been developed using the sol–gel process and their corrosion behavior has been explored. The alloy was anodized in 1 M NaOH + 0.5 M Na₂SiO₃ solution. An 0.5 P₂O₅ + z 1.67 Ca(NO₃)₂.4H₂O solution with 10 g/L, 20 g/L, and 30 g/L bone powder concentrations and 50 s, 100 s, and 150 s dip-coating durations, followed by calcination at 400°C, was used to develop the coatings. Microscopic analysis results disclosed the formation of a uniform and highly porous MgO film on the alloy to guarantee the subsequent coating adhesion. The results also confirmed the fruitful formation of smoother hydroxyapatite + bone powder composite coatings on the film. Electrochemical corrosion tests revealed that the alloy exhibited the lowest corrosion resistance, while the hydroxyapatite + 30 g/L bone powder composite-coated alloy possessed the best performance with a significantly low corrosion rate of 0.07 mm/year, suggesting the composite-coated alloy is a desired candidate for implant application.