In-vitro corrosion properties of quaternary Mg-Zn-Re-xCa alloys for biomedical applications

Abstract

Magnesium (Mg) and its alloys have been intensively studied as biodegradable implant materials as they do not require secondary surgical procedure for removal compared to the traditional metallic implant materials such as stainless steels, titanium alloys and cobalt chromium alloys. Apart from that, their relatively similar mechanical properties to bone structure make them as the attractive candidates for orthopaedic applications. Nevertheless, Mg has relatively poor corrosion resistances, rapid degradation rate and hydrogen gas evolution. This phenomenon limited the usage of Mg in biomedical applications. Hence, the corrosion properties of Mg-Zn-RE-xCa alloy were investigated by adding different amount of calcium (Ca). The alloys were produced using casting process and followed by immersion in Kokubo solution for 168 hours at room temperature to investigate the corrosion properties. Apart from immersion test, polarization and pH variation tests were also conducted to study the corrosion behavior of the alloys. The microstructure and morphology of the as-cast alloys were observed using optical microscope (OM). Other characterizations such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to investigate the phase formation, microstructures and elemental compositions of the as-cast and corroded specimens. Mechanical property such as hardness was investigated using Vickers hardness tester. It was found that formation of secondary IM1 (Ca3MgxZn15-x) (4.6 = x = 12) and Mg2Ca phases were observed when the Ca added in the alloys. The results also showed that the addition of Ca refine the grain size thus provide higher hardness. The addition of 0.5 wt.% Ca content was found to produce the lowest dissolution rate and highest corrosion resistance. However, further addition of Ca up to 6 wt.% led to an increased in corrosion rate.