In vitro corrosion survey of Mg– x Ca and Mg–3Zn– y Ca alloys with and without calcium phosphate conversion coatings

Magnesium alloys are promising orthopaedic bioresorbable implant candidates, however, their inherent rapid corrosion rate in physiological media currently limits their clinical applications. In this work, the in vitro corrosion of a series of Mg–xCa and Mg–3Zn–yCa alloys (wt-%) was systematically studied. These compositions were selected so the alloys could be comprised of biocompatible elements and to explore the role of Ca in the alloy itself upon subsequent calcium phosphate (CaP) coating efficiency. A simulated body environment was reproduced via minimum essential medium (MEM) and exposure in a CO₂ incubator at 37°C. The effect of Ca and Zn additions on the corrosion rate of Mg was examined, indicating the corrosion rate increases with Ca additions, while adding Zn to Mg–Ca alloys decreases the rate of corrosion. The impact of a biomimetic CaP conversion coating applied onto these alloys indicated that although the coating alters the corrosion rates, the effect is dependent on the substrate alloy composition.