Microstructure and Properties of Biomedical Mg-Zn-Ca-Ag Alloy and the Micro-Arc Oxidation Coatings

This study investigates the influence of Ag addition on the microstructure, mechanical behavior, corrosion resistance, and antibacterial performance of Mg-Zn-Ca-Ag alloys and their micro-arc oxidation (MAO) coatings. Four casting alloys containing 0.2, 0.4, 0,6 and 0.8 wt.% Ag were fabricated and characterized by SEM, XRD, and TEM. The microstructure consisted mainly of α-Mg, Mg2Ca, Mg7Zn3, and Mg6Ca2Zn3 phases, and the elastic modulus (~25.8 GPa) was comparable to that of human bone. MAO coatings produced in a bio-functional electrolyte exhibited pit-like morphologies due to Ag-induced melt fluidity and self-sealing effects. The coatings were composed primarily of MgO, Mg2SiO4, Ca3(PO4)2, CaCO3, and Ag2O, with the ZQ 0.8-MAO sample showing the highest Ca/P ratio (1.75), indicative of superior bioactivity. Electrochemical impedance spectroscopy revealed optimal corrosion resistance (2.56 × 104 Ω·cm2), while antibacterial efficiency exceeded 96%. Overall, Ag alloying enhanced both the bulk and surface properties of Mg-Zn-Ca alloys, yielding robust, corrosion-resistant, and antibacterial coatings with excellent biocompatibility-highlighting their potential for biodegradable orthopedic implant applications.