Effect of hydroxyapatite (HA) coating on mechanical properties and biocorrosion behavior of Mg-3Zn-2Sr-1Cu alloy

In this study, Mg-3Zn-2Sr-1Cu alloy was coated with hydroxyapatite (HA) using a sol-gel technique to evaluate the coating’s effects on microhardness and biodegradability. Heat treatment was performed at 300°C, 350°C, 400°C, 450°C, 500°C to crystallize and enhance the adhesion of the HA coating. The microstructural analysis confirms that a continuous, crystalline, and phase-pure HA coating with interconnected needle-like morphologies and minimal visible substrate areas on the surface is formed at the heat treatment of 400 °C. The sol-gel-derived HA coating significantly enhanced the surface hardness, increasing from 88.7±4.4 HV (base-alloy) to 181.8±9.1 HV (HA-coated), and reduced the corrosion rate as observed during immersion tests in simulated body fluid (SBF). The corrosion rate decreased from 0.114±0.006 for the base- alloy to 0.036±0.002 for the HA-coated alloy, demonstrating a significant improvement in biodegradability. These enhancements are attributed to the formation of a uniform and adherent HA layer that mitigates rapid degradation while improving surface mechanical stability. This study highlights the potential of HA coatings in addressing the limitations of magnesium-based alloys, advancing their application in biodegradable implants.