Microstructural Characterization and Investigation on Corrosion Properties of Mg-Zn-RE-Ca Alloy as a Possible Biomedical Implant

Influences of heat-treatment and anodizing procedures on microstructure evolution and corrosion performance of two as-cast magnesium alloys containing different amounts of Ca and rare earth elements and same amounts of Zn were investigated, with the ultimate goal of developing a new biodegradable metallic implant. The first alloy (hereafter, denoted as F1) had higher RE element content but less calcium than the second one (denoted as F2). The same procedures of solution heat-treatment and aging were applied to alloys. Microstructures, together with the distribution and composition of secondary phases of all samples, were investigated by optical microscopy, field emission scanning electron microscopy, and energy-dispersive spectroscopy. Moreover, corrosion properties were evaluated in the phosphate-buffered saline solution using potentiodynamic polarization and also immersion tests at 37 °C. The results showed that corrosion performance is affected by both chemical composition and heat-treatment procedures. As-cast F2 has the least corrosion rate achieved by the polarization test. However, immersion test results show that solution heat-treated F1 has the lowest corrosion rate among all other specimens, including pure commercial Mg. In the next step, the anodizing process was performed in 3 current densities on solution heat-treated F1 alloy, and a 60% reduction in the corrosion rate was observed.