The effect of severe surface deformation on microstructure refinement, corrosion, and biocompatibility of Mg5Zn0.2Ca alloy

The Mg5Zn0.2Ca alloy’s microstructure refinement by surface mechanical attrition treatment (SMAT) and its influence on corrosion and biocompatibility behaviour are examined in this study. Non-treated specimens (NSA) are SMATed with ~5 and 10 m/s ball velocities (SA1 and SA2, respectively). A significant grain refinement has occurred in surface-treated specimens, with higher ball velocity causing a fine grain size of ~21 nm and lower velocity instigating nanotwins near the surface. Moreover, SMAT has improved the surface hardness by 1.7-2.0 times the non-treated specimen’s hardness. Electrochemical and immersion tests performed in a cell culture medium have indicated the highest corrosion resistance for SA2, followed by SA1, with NSA exhibiting the least resistance. This response is ascribed to the thicker, more stable protective layer formation on the surface-treated specimens. Cytotoxicity tests performed by the extract method using murine fibroblast L929 have shown lower cytotoxicity for the surface-treated specimens. This behaviour is linked to the lower corrosion rate with reduced Mg²⁺ ion release and smaller pH increase. Enhanced bovine fibronectin adsorption on SMATed specimens further supports their improved biological performance. The grain refinement, increased surface energy, and grain boundary area have positively influenced the biocompatibility behaviour of the SMATed alloy.