Improving mechanical performance of biodegradable ZX10 alloy in Hanks’ solution through thermo-mechanical treatment

We investigate the effect of different types of thermo-mechanical treatment on the microstructure, corrosion, mechanical performance in air, and stress corrosion cracking (SCC) susceptibility of low-alloyed biodegradable Mg-Zn-Ca alloy. The as-cast ZX10 alloy in the heat-treated state (HT) was processed by extrusion or multiaxial isothermal forging (MIF). The microstructure of the obtained materials was investigated with the aid of scanning electron microscopy (SEM) powered by electron-backscattering diffraction (EBSD) and energy dispersive spectroscopy (EDX) techniques. The specimens after heat treatment, extrusion and forging were subjected to immersion testing in Hanks’ solution to assess the corrosion rate as well as to slow-strain rate tensile (SSRT) testing in air and Hanks’ solution to evaluate the SCC susceptibility. It is found that ultrafine-grained microstructure featured by a high fraction of low-angle dislocation boundaries created in the course of MIF demonstrates remarkably higher SCC resistance if compared to that of the extruded alloy characterized by fully recrystallized equiaxed grains having no appreciable low-angle substructure. It is suggested that the SCC performance of the MIF-processed alloy can be further enhanced through the microstructure control of its corrosion rate, which is found greater than that of the extruded alloy due to the presence of nanosized precipitates of the noble ternary secondary phase.