Interfacial microstructure and degradation of Zn/Mg bioalloys composite structures prepared by friction stir diffusion bonding

The fabrication of biometal composite structures (CS) based on material properties represents a promising approach to degradable metal implants with excellent degradability, biocompatibility, and mechanical properties. In this paper, Zn/Mg alloy CS was successfully prepared by friction stir diffusion bonding (FSDB) and ultrasound-assisted friction stir diffusion bonding (Ua-FSDB). The effects of welding speed and ultrasonic vibration on the microstructure, mechanical properties, and degradation properties of the CS were investigated, offering new insights for enhancing the properties of biodegradable alloys. The results indicate that the thickness of the interfacial bonding layer increased with the increase of welding heat input. As the heat input increased, the initial Mg2Zn3 layer gradually transformed into a more complex structure comprising the Mg2Zn3 layer, MgZn2, and α-Mg/MgZn mixed layer. The ultrasonic effect led to the MgZn2 and Mg2Zn3 layers being pure and uniform in thickness. Higher welding speeds and the addition of ultrasonic vibration significantly improved the tensile and shear loads on the joints. The in vitro degradation process of the Zn/Mg CS occurred layer-by-layer from the Mg matrix side to the Zn matrix side, with the inclusion of ultrasound proving beneficial for enhancing the corrosion resistance of the Zn-Mg CS.