Effect of surface mechanical attrition treatment on biodegradable Mg-1Ca alloy.

Surface mechanical attrition treatment (SMAT) is considered to be an effective approach to obtain a nanostructured layer in the treated surface of metals. In this study, we evaluated the effect of SMAT on the microstructure, mechanical properties and corrosion properties of biodegradable Mg-1Ca alloy, with pure Mg as control. Grain refinement layers with grain size at the nanometer scale in the topmost surface were successfully prepared on Mg-1Ca alloy using SMAT technique, similar to pure Mg. The SMAT not only refined the surface layer of Mg-1Ca alloy, but also promoted the re-dissolution of the Mg2Ca phase into the matrix. As a result, the microhardness of the SMATed samples in the near-surface region was considerably enhanced, and the surface roughness and wettability of the SMATed samples were increased. However, the SMAT led to high density of crystalline defects such as grain boundaries (subgrain boundaries) and dislocations, which severely weakened the corrosion resistance of Mg-1Ca alloy, same as pure Mg.