Corrosion studies and microstructure of Mg - Zn - Ca alloys for biomedical applications

Magnesium and magnesium-zinc-calcium based alloys are so attractive as a biodegradable implant materials. The corrosion behavior of pure Mg (>= 99.99% wt.) and three Mg based alloys Mg-xZn-yCa (x = 1,2 and 2.5 wt% & y = 0.6, 0.6 and 1.5 wt%) have been performed in simulated body fluid (SBF) at 37 degrees C using hydrogen evolution, weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Surface morphology and microstructure was studied using scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX). The addition of Ca and Zn to magnesium alloys has a grain refinement and improving its hardness. The microstructure of the alloys containing primary Mg and eutectic phases (a Mg + Mg2Ca + Ca2Mg6Zn3) mainly dispersed straight to the grain boundaries. The electrochemical tests proved that the Mg-2Zn-0.6Ca alloy has the highest corrosion resistance. Adding Zn improved well the corrosion behavior of the alloy due to the construction of Ca2Mg6Zn3 phase. Whereas adding Ca more than 0.6 wt. % resulted in a decrease of the corrosion behavior owing to the formation of Mg2Ca.