Effects of thermomechanical processing on microstructures, mechanical properties, and biodegradation behaviour of dilute Zn–Mg alloys

Currently, zinc has been considered as one new attractive biodegradable metal for medical implant applications due to its favoured properties such as biocompatibility and recyclability. However, the cast pure zinc usually possesses coarsening microstructures, which hinders it to obtain a suitable combination of mechanical strength and degradation rate. Here, the microstructural controlling of zinc was firstly realized via alloying dilute Mg contents and thermomechanical processing. Then, the in vitro biodegradation behaviour of dilute Zn–Mg alloys was investigated accordingly using the Hank's solution. Finally, the mechanisms of mechanical strengthening and in vitro biodegradation were explored. Specifically, the Mg-50wt%Zn master alloy was added into cast Zn melt to form the binary Zn–Mg alloys with different Mg addition contents (i.e. 0, 0.05wt%, 0.1wt%, and 0.4wt%). The initial reduction of grain sizes was achieved by over 90% owing to the grain refinement generated by master alloy. In the as-cast alloys, the average grain size was decreased from over 2 mm for pure Zn to 23.7 μm for Zn-0.4wt%Mg. Subsequently, the thermomechanical processing (i.e. hot rolling at room temperature, 100°C, 150°C, and 250°C) was applied onto the cast Zn–Mg alloys to achieve further microstructural manipulation. Further grain refinement occurred in the different as-rolled Zn–Mg alloys. The in vitro corrosion resistance of all samples was assessed through the potentiodynamic polarization (PDP) test in the Hanks' solution for 14 days at 37°C. The corrosion rates depended on alloying contents, grain sizes, twins and texture. The synergetic regulation of mechanical strength and degradation rate could be adjusted by appropriately using master alloys and thermomechanical processing. For practical medical applications, the present work provides some insights on solving the dilemma between mechanical properties and biodegradation process.