Towards high performance of degradable Mg-RE-Sr alloy obtained by friction stir processing in the urinary system: Corrosion behavior and related mechanisms

Mg-based alloys have emerged as promising candidates for biodegradable implants. In this study, a significant improvement in the anti-corrosion behavior of a Mg-RE-Sr alloy in the artificial urinary system, with high passivity and micro-galvanic corrosion resistance, was achieved through friction stir processing. The processed Mg-RE-Sr alloy exhibited an optimized microstructure characterized by refined grains, a highly supersaturated solid solution matrix, and uniformly distributed secondary phases. These features effectively mitigated localized corrosion damage and facilitated the formation of a dense passive surface film, thereby improving anti-corrosion performance by reducing the corrosion rate, enhancing corrosion uniformity, and decreasing the corrosion current density in the artificial urine solution by 52.3%. To further understand the corrosion behavior in the urinary system, comparative corrosion experiments were conducted in a 0.1 M NaCl solution containing the same chloride ion concentration as artificial urine. The higher corrosion rates observed in the urinary environment were primarily attributed to the natural buffer effect of artificial urine, which hindered surface film deposition and promoted rapid alloy dissolution. In contrast, in the 0.1 M NaCl solution, the alloy's surface alkalization promoted the formation of a denser protective film. In summary, this study provides valuable insights into Mg alloys for an in-depth understanding of their potential applications in biomedical and other engineering fields.