Corrosion Control of Mg-Zn Implant Alloys in Simulated Body Fluid

Abstract

Magnesium alloys have recently attracted the attention as a new biodegradable material.  In this study, Mg-Zn alloys (1-4wt.% Zn) were fabricated with high purity raw materials using a clean melting process (fluxless method) and a protective atmosphere of CO₂ + 0.4 SF₆. The as-cast microstructures of the investigated alloys were characterized by optical and scanning electron microscopes, EDS and XRD. Corrosion properties of the prepared alloys were examined in simulated body fluid (SBF) by electrochemical techniques and immersion test (hydrogen evolution method).  Surface modification of the prepared alloys was performed using micro arc oxidation (MAO) treatment and hydroxiapatite (HA) coating.

The results of the as-cast microstructure showed that Zn up to 2 wt% was completely dissolved in a-Mg matrix. On increasing Zn content (> 2wt%) the grain size decreased and a second MgZn₂ phase was observed. Corrosion testing results revealed that Mg-1,2,3 wt% Zn have almost the same corrosion rates (0.025 mm/y) whereas Mg-4Zn has the highest degradation rate. Hydroxiapatite (HA) coating on micro-arc oxidation (MAO) treated magnesium alloys formed a dense and compact layer on the surface of magnesium alloys which had greatly improved surface properties and enhanced corrosion resistance of the prepared alloys.

Keywords: Mg alloys, implants, biodegradable, corrosion, surface modification