Microstructural effects on mechanical properties and degradation behavior of Mg-Cu alloy

In this work, mechanical properties, degradation behavior and biocompatibility of as-extruded and solid solution treated Mg-Cu binary alloy with 0.22 and 0.45 wt.% Cu additions have been investigated, and the effects of main microstructural parameters (grain size, dislocation, second phase distribution and content) on these properties are analyzed. Mechanical tests revealed that as-solutionized Mg-Cu alloys (with larger grain size and less content of Mg2Cu phase) exhibited better mechanical properties than the as-extruded alloys. Strengthening effects of the microstructural parameters have been analyzed and quantified. The results suggested that the inverse elevation of the yield strength was mainly related to the over-solubility of Cu atom in the matrix. Immersion tests showed that the solid solution treatment improved the corrosion resistance of Mg-0.2Cu alloy (with 0.22 wt.% Cu) but deteriorated it seriously for Mg-0.5Cu alloy (with 0.45 wt.% Cu). The enhanced corrosion resistance of Mg-0.2Cu alloy was owing to the apparent decrease of Mg2Cu phase content. In contrast, the deterioration of corrosion resistance for Mg-0.5Cu alloy was attributed to the distribution change of the Mg2Cu phase from diffuse to local, because large localized Mg2Cu particles can lead to severer corrosion of the matrix. Cytotoxicity experiments revealed that the as-solutionized Mg-0.2Cu alloy with the least Mg2Cu phase content exhibited the best biocompatibility due to its slower degradation rate.