Investigating the Mg-Zn-RE(Y,Gd) alloys as potential biodegradable implant materials

Abstract

Mg alloys have recently attracted interest as biodegradable implant materials due to their biocompatibility and suitable mechanical properties. However, their rapid degradation rate re- quires further tailoring through alloying additions and thermomechanical processing. This work investigates the effects of Gd (0,1,2 wt.%) alloying and post-casting rolling and extrusion on the microstructure, mechanical performance, and corrosion of Mg-2Zn-0.5Y (wt.%) alloys. XRD and microscopy analysis revealed that the cast alloys consist of α-Mg and Mg3Zn6Y (I-phase), while Gd additions promote the formation of W Phase (Mg3Zn3Gd2) secondary phases. The presence of the W phase induces significant grain refinement down to an average grain size of 204.67 µm from 265.56 µm in Gd-free alloys. Furthermore, severe plastic deformation and dynamic recrystallization during rolling and extrusion lead to a more refined grain structure compared to the cast condition. Hardness increases with Gd content and with the rolling and extrusion process, resulting from precipitation strengthening and additional Hall-Petch strengthening enabled by extensive grain refinement. However, the corrosion rate increases in Gd-containing alloys due to an increase in surface roughness, as determined by AFM studies and galvanic coupling between W-phase particles and the Mg matrix. Weight loss testing shows that the corrosion rate increases in Gd added alloys relative to the Gd-free alloy. In contrast, rolling and extrusion disrupt galvanic effects and improve surface protection, reducing corrosion rate compared to as-cast alloys on average across compositions. These insights on synergies among composition, microstructure, and thermomechanical processing advance knowledge for designing biodegradable Mg implants with tailored degradation.