Roles of Mn on corrosion resistance in Mg–Zn–Sn–Zr-xMn alloys

Although Mg alloys exhibit excellent biocompatibility and biodegradability, their relatively rapid corrosion rates limit their applications. Alloying is an effective method of enhancing the corrosion resistance of Mg alloys. This study investigated the corrosion behavior of Mg-1.5Zn-0.5Sn-0.3Zr-xMn (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5) alloys to understand the roles of Mn on corrosion resistance. The electrochemical and immersion tests revealed that the alloys containing an optimal level of Mn demonstrated a lower corrosion current density compared to the Mn-free alloy. Two mechanisms responsible for regulating the corrosion resistance of Mg-1.5Zn-0.5Sn-0.3Zr-xMn alloys are suggested with respect to the Mn roles: (1) the solid solution Mn atoms significantly reduce the potential difference between the Mg matrix and the Mg 7 Zn 3 phase, and the more stable and compact corrosion product film enriched the Mn oxide layer, which effectively retards the corrosion process of the alloy. (2) The overlap between a-Mn and the Mg 7 Zn 3 phase increases the potential difference between the second phase and the Mg matrix. Meanwhile, the presence of α-Mn at the grain boundaries leads to the formation of corrosion channels, which in turn exacerbates the corrosion of the alloy. The Mg-1.5Zn-0.5Sn-0.3Zr-0.9Mn alloy demonstrated an optimal corrosion rate of 0.03 mm/y, implying it can be used as a promising material for biomedical applications.