Effect of iron and manganese on the corrosion resistance of contaminated secondary Al-Si-Mg cast alloys

Abstract It is well established that micro-galvanic corrosion induced by impurity phases during metallurgical processing limits the application of recycled aluminum. This study investigates the corrosion behavior of AlSi 7 Mg 0.3 alloy with two varying Mn/Fe ratios. A combined approach involving electrochemical testing, salt spray exposure, and finite element modeling was employed to clarify the roles of Fe-rich and Mn-rich intermetallic phases in corrosion progression. The appropriate addition of Fe and Mn promoted the formation of “Chinese-script” α -Al(FeMn)Si phases and improved alloy corrosion resistance by refining the dendritic structure and lowering galvanic activity. Accelerated exposure experiments revealed that the β -AlFeSi phase exhibited strong cathodic activity and facilitated phase-selective dissolution adjacent to the α -Al matrix. In contrast, the Chinese-script α -Al(FeMn)Si phase presented partial dissolution at peripheries, marking the initiation of localized attack. However, the phase is electrochemically inert and retains the original morphology, which has little effect on the corrosion propagation by reducing micro-galvanic coupling with the matrix. Complementary to a finite element corrosion model successfully captured the selective dissolution of the Al-Si and predicted the transient corrosion front progression as found in experiments. The integrated approach applied in this work offers theoretical guidance for corrosion-related impurity assessment of recycled aluminum alloys.