The influence of rolling on the microstructure, mechanical properties, and in vitro degradation of biomedical Zn-2Cu alloy treated by ultrasound

Abstract

Zn alloys are considered ideal materials for in vivo implants owing to their moderate degradation rates. The addition of Cu significantly enhances the antibacterial properties of Zn-Cu alloys, making them suitable for degradable implants such as orthopedic bone plates and bone screws. However, cast Zn-Cu alloys exhibit a poor strength-plasticity balance, which limits their ability to meet the mechanical performance requirements of bone implants. This study combined ultrasonic treatment with rolling processes to systematically investigate the microstructural evolution, mechanical properties, and degradation behavior of Zn-2Cu alloys prepared under different rolling conditions. The results revealed that after rolling, the α-Zn grains was significant refined into equiaxed grains with average sizes of 474 nm, 613 nm, and 591 nm. Additionally, sub-micron fine CuZn₅ precipitates formed, with average sizes of 610.7 nm, 503.9 nm, and 568.8 nm. Tensile tests revealed that 5-pass rolling at 200 °C significantly improved the mechanical properties of Zn-2Cu alloys compared with the unrolled condition. The ultimate tensile strength (UTS), yield strength (YS), and elongation (El) were increased from 178 MPa, 161 MPa, and 3.01% to 378 MPa, 367 MPa, and 58.1%, respectively. Electrochemical polarization tests indicated that the 5-pass heat-rolled (HR-5), 5-pass cold-rolled (CR-5), and 2-pass heat-rolled (HR-2) alloys in Hank's solution exhibited degradation rates of 1.865 mm/year, 0.418 mm/year, and 1.207 mm/year, respectively. After 7 days of immersion corrosion in Hank's solution, the degradation rates followed the order of HR-5 (35.94 μm/year) > HR-2 (20.06 μm/year) > CR-5 (25.08 μm/year). These results suggested that multi-process composite regulation can achieve an optimal balance between alloy strength and plasticity. This study provides a theoretical and technical basis for designing and fabricating next-generation biodegradable Zn alloy implants and highlights their potential applications in orthopedic medical devices.