Novel Mg-based alloys by selective laser melting for biomedical applications: microstructure evolution, microhardness and in vitro degradation behaviour

Laser-melted Mg-3Zn-xDy (x = 0, 1, 3, 5 wt. %) alloys were investigated as candidate materials for biodegradable metallic implant applications. The results showed that the alpha-Mg, MgZn2 and Mg-Zn-Dy phases were distributed in the Dy-containing alloys. Due to the addition of Dy, the grain size was significantly refined. As the grain size decreased and the second phase content increased, the hardness monotonously increased. The degradation characteristics analysis via immersion testing indicated that the degradation rate of the laser-melted Mg-3Zn-1Dy alloys was remarkably reduced, evidenced by the corresponding lower average hydrogen evolution rate. Consequently, the Mg-3Zn-1Dy was considered to be a promising candidate for implant applications, due to the appropriate rate of mechanical integrity loss during degradation. Overall, the mitigated degradation rate was attributed to the refined grains, the homogeneous microstructure as well as a certain amount of second phase produced during the process of selective laser melting.