Enhanced mechanical properties of an Mg-Zn-Ca alloy via high pressure torsion and annealing for use in bone implantation

ABSTRACT The use of degradable magnesium alloy as a bone implant material has gained much research attention. However, its mechanical properties cannot meet the clinical requirements of bone implantation. In the present work, the microhardness, strength and plasticity of biological Mg-Zn-Ca alloy are evaluated before and after high pressure torsion (HPT) processing. The results demonstrate an obvious increase in the microhardness of the HPT-processed Mg-Zn-Ca alloy, with higher values distributed along the edge of the sample and low values in the center. After annealing, however, the microhardness value of the HPT Mg-Zn-Ca alloy decreases, but the distribution of microhardness values becomes significantly more uniform. The tensile test results show that the HPT processing increases the tensile strength of the Mg-Zn-Ca alloy, but decreases the toughness. When the HPT Mg-Zn-Ca alloy is annealed, however, the tensile strength decreases, while the plasticity noticeably increases, with increased annealing tempera-ture. The improvements in the strength and microhardness of the HPT Mg-Zn-Ca alloy are attributed to a combination of dislocation strengthening, fine grain strengthening, and precipitation strengthening. In conclusion, the Mg-Zn-Ca alloy has excellent comprehensive mechanical properties after 5 turns of HPT processing, followed by annealing at 210 ℃ for 30 min.