The formation mechanism and bio-corrosion properties of Ag/HA composite conversion coating on the extruded Mg-2Zn-1Mn-0.5Ca alloy for bone implant application

In this study, a silver and hydroxyapatite (Ag/HA) composite coating was generated on an extruded Mg-2Zn-1Mn-0.5Ca magnesium alloy through a chemical conversion process. Scanning electron microscopy (SEM) observation showed that a gray conversion coating was formed with white snow-like and gray globular particles or crystals located randomly above the coating. X-ray diffraction (XRD) combined with X-ray photoelectron spectroscopy (XPS) analysis indicated that the conversion coating was mainly composed of Ca10(PO4)6(OH)2 with limited quantities of Ag/Ag2CO3, CaHPO4·2H2O and CaSiO3. The formation mechanism of the Ag/HA composite conversion coating is discussed in this work. The electrochemical polarization and EIS tests showed that the conversion coating markedly improved the bio-corrosion resistance of the Mg-2Zn-1Mn-0.5Ca alloy in Hank's solution. Adhesion test showed that the coating has a strong bonding strength. The bactericidal activity was assessed with the zone of inhibition method, and the composite coating on the Mg alloy substrates exhibits good antibacterial performance.