Experimental insights toward understanding how the morphology of Mg2Si particles affects degradation behavior of the biodegradable as-cast Mg–Si alloys

Abstract

Considering the remarkable function of silicon in the development and growth of connective tissue and bone, building the immune system, and tissue healing, together with its positive effects on improving mechanical and degradation behavior of magnesium alloys, Mg–Si alloys can be a promising alloying system for making biodegradable implants. However, the morphology, size, and distribution of Mg2Si particles, as the only intermetallic phase in Mg–Si alloys, can affect the corrosion behavior of these alloys significantly. Therefore, in this investigation, the effects of Y addition (0.5 wt%) and heat treatment (HT, at 420 °C for 24 h) on degradation behavior of two hypo-eutectic Mg–1Si and hyper-eutectic Mg–2Si alloys are studied by hydrogen evolution, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) tests, all done in phosphate-buffered saline (PBS) solution. Also, the appearance of the corroded surfaces of the studied alloys after electrochemical and immersion tests was evaluated by scanning electron microscopy equipped with electron disperse spectroscopy. It was found that Y addition to the as-cast Mg–1Si alloy increased the corrosion resistance, corresponding to a decrease in the corrosion current density (Icorr) from 5.60 to 3.24 μA/cm2. On the contrary, the addition of Y to the as-cast Mg–2Si alloy did not significantly change the corrosion resistance. In addition, it was found that after applying HT on the as-cast Mg–1Si and Mg–2Si alloys, corrosion resistance was improved, which was mainly attributed to the modified eutectic Mg2Si particles.