(Digital Presentation) Effect of Mg2si on Trenching Formation Around Al6(Fe, Mn) on AA5083 in Diluted Synthetic Seawater

Abstract

In chloride containing solutions like atmospheric environments, an interface between intermetallic particles (IMPs) and Al-matrix is mainly one of the initiation sites in localized corrosion of Al alloys. It has been widely reported that Al-matrix around IMPs containing Fe and/or Cu was dissolved like trenching due to the oxygen reduction reaction on the IMPs and the subsequent alkalization on and around the IMPs. The trenching is precursory stage of localized corrosion on Al alloys. In the case of AA5083, Al6(Fe, Mn) was known to become the initiation site of localized corrosion1). In addition to Al6(Fe, Mn), Mg2Si is precipitated in AA5083 to increase the mechanical strength. Mg in Mg2Si is easily dissolved to solutions immediately after immersion. Therefore, Mg2Si is less possible to become the initiation site of localized corrosion compared with Al6(Fe, Mn). For the reason, few previous research has clearly shown the effect of the Mg dissolution in Mg2Si on the trenching formation around Al6(Fe, Mn). In this study, the effect of Mg2Si on trenching formation around Al6(Fe, Mn) by immersion tests of microelectrode containing single or double IMPs.A5083 (Al-Mg alloy) were prepared as specimen in this research. The four types of AA5083 electrodes (1. only Al6(Fe, Mn), 2. only Mg2Si, 3. both of Al6(Fe, Mn) and Mg2Si, 4. neither Al6(Fe, Mn) nor Mg2Si (Al-matrix on AA5083)) were prepared. Diluted synthetic seawater (200 mg/L Cl-, pH 8.2) was used as the electrolyte for immersion tests. Ag/AgCl (3.33 M KCl) was used as the reference electrode. The immersion time was 1 h.After the immersion tests, trenching was generated around Al6(Fe, Mn) on microelectrode containing both of Al6(Fe, Mn) and Mg2Si. On the other hand, no trenching was observed around Al6(Fe, Mn) on microelectrode containing only Al6(Fe, Mn). The results suggested that the formation of trenching around Al6(Fe, Mn) was affected to Mg2Si.1) T. Kosaba, I. Muto, and Y. Sugawara, J. Electrochem. Soc., 169, 020550 (2022). https://doi.org/10.1149/1945-7111/ac5301