Effect of Free-End Torsion on the Corrosion and Mechanical Properties for Mg-3Zn-0.2Ca Alloy

Abstract

Magnesium alloys with excellent degradability and biocompatibility are promising materials for biomedical implants, saving patients the burden of second surgeries. However, their mechanical properties and corrosion resistance are significantly below the requirements for implant applications. This study aims to improve the mechanical and corrosion resistance properties of Mg-3Zn-0.2Ca alloy by pre-torsion treatment, and find out the optimal shear strain. The rod-shaped Mg-3Zn-0.2Ca alloy specimens were pre-torsion treated at different torsion angles. The effect of free-end torsion on Mg-3Zn-0.2Ca alloy was characterized through microstructure analysis, mechanical testing, and corrosion testing. Pre-torsion treatment can refine grain and induce twins and dislocations in Mg-3Zn-0.2Ca alloy. The surface hardness increases with the increase in torsion angle. Tensile yield strength and ultimate strength initially increase and then decrease with increasing torsion angle, while ductility decreases with increasing torsion angle. Specimens with a shear strain of 30% exhibit the highest tensile strength, reaching 284.78 ± 10.62 MPa, with an elongation of 19.37 ± 1.66%. Furthermore, they show a significant improvement in fatigue lives both before and after pre-corrosion. When the stress amplitude is 120 MPa, the fatigue lives for specimens without pre-torsion treatment are 54,275 cycles and 4324 cycles before and after pre-corrosion, while they increased significantly to 92,015 cycles and 5050 cycles with the 30% shear strain, respectively. Additionally, the 30% shear strain specimens show a significant reduction in corrosion rates. In conclusion, pre-torsion treatment can effectively modify the microstructure of Mg-3Zn-0.2Ca alloy, enhancing both mechanical properties and corrosion resistance. The optimal shear strain for this improvement is 30%. This study provides a practical method to enhance the mechanical properties and corrosion resistance of Mg-3Zn-0.2Ca alloy, making it more suitable for biomedical implant applications.