The Effect of Different Heat Treatments on Stress Corrosion Cracking of ZK60 Magnesium Alloy

Magnesium alloys used as degradable biomaterials often experience failure due to the combined effects of corrosive environments and stress. In this study, ZK60 magnesium alloy in three different states, i.e., solution treatment (T4), T4 followed by artificial aging (T6), and deep cryogenic treatment followed by T6 (DT6), were subjected to slow strain rate tensile tests in both air and phosphate-buffered saline environments. Comprehensive microstructural characterization revealed that the T4 specimen exhibited fewer blocky second-phase particles, whereas the volume fraction of the second phase significantly increased after T6 treatment. Moreover, noteworthy is that the introduction of deep cryogenic treatment before T6 treatment led to a significant increase in the length and quantity of rod-shaped precipitates β1′. Slow strain rate tensile tests in PBS revealed that the T4 specimen exhibited better stress corrosion cracking resistance due to the lesser amount of the second phase in the matrix, which mitigated localized corrosion. Conversely, the T6 and DT6 specimens, having a higher volume fraction of nanoscale second-phase precipitates within the matrix, exhibited improved strength compared to the T4 specimen but exacerbated micro-galvanic corrosion, resulting in a faster corrosion rate and consequently poorer stress corrosion cracking resistance. In summary, controlling the distribution of second-phase precipitates is paramount for enhancing the stress corrosion cracking resistance of ZK60 magnesium alloy.