In Vitro Immersion Testing of Mg–0.5Zr–0.5Ca–xZn Alloys in the as-Cast, Homogenized, and Extruded Conditions

Abstract

This study investigated the effects of zinc addition, homogenization treatment, and thermomechanical processing via hot extrusion on the microstructure, corrosion behavior, and mechanical properties of biodegradable Mg–0.5Zr–0.5Ca alloy. Zinc alloying not only resulted in the formation of Ca₂Mg₆Zn₃ and Mg₇Zn₃ compounds, but also reduced the grain size up to 4.5 times in the as-cast condition, which improved the mechanical properties. Immersion tests in the simulated body fluid (SBF) solution at 37°C showed that a Zn content higher than 1 wt.% significantly improved corrosion resistance and reduced the corrosion rate to about five times smaller than the base alloy. While the extrusion process induced a remarkable grain refinement via dynamic recrystallization (DRX) and improved the strength-ductility balance, it had a detrimental effect on the corrosion resistance due to the higher volume fraction of the grain boundaries. On the other hand, the homogenization treatment improved the mechanical properties and reduced the weight loss during immersion tests by dissolving secondary phases, increasing the solute Zn content, and formation of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ film.