In-vitro corrosion assessment of silicate-coated AZ31 Mg alloy in Earle’s solution

Abstract

Magnesium alloys are promising materials for biodegradable implants. In the present investigation, AZ31 Mg alloy was anodized in alkaline silicate electrolyte and anodization time period was optimized. From the current transient (i–t) curve and corrosion analysis, it was confirmed that 60-min anodization was sufficient to obtain a silicate coating with a better corrosion resistance of 37.05 kΩ. The hydrophilic nature of the coating was confirmed by the contact angle measurement. XRD results revealed the formation of MgO (periclase) and biocompatible Mg2SiO4 (forsterite) phases. Hydrogen evolution studies showed that the degradation rate of the anodized sample correlated with the real-time corrosion behavior. At the end of 7 days of immersion in Earle’s solution, bone-like apatite was precipitated with Ca/P ratio at 1.39 indicating the incorporation of silica in the apatite. From scanning electrochemical microscopic studies, the current density of anodized sample was found to be minimum and uniform over the entire surface. Increase in immersion time resulted in fluctuation in current density signifying the coating’s interaction with Earle’s solution and initiation of apatite formation.