Insight into the Ni microalloying effects on the corrosion characteristics and mechanism of Fe-21Mn-10Al-1.25C lightweight steels in chloride-containing solution

Lightweight alloys primarily composed of iron (Fe), manganese (Mn), aluminum (Al), and carbon (C) are considered promising structural materials due to their excellent mechanical properties and low weight. The corrosion resistance of FeMnAlC alloys has recently gained widespread attention due to their great potential for service in marine environments. This paper studied the impact of Ni addition on the microstructure and corrosion resistance of an austenitic Fe-21Mn-10Al-1.25 C alloy in 3.5 % NaCl solution by microstructural analysis, electrochemical and immersion tests. Results showed that Ni addition worsened the corrosion resistance of the alloy. Specifically, the formation of (Ni, Al)-enriched B2 phases along grain boundaries significantly enhanced micro galvanic corrosion effect, leading to rapid dissolution of the austenitic matrix. Moreover, localized corrosion was accelerated by the increase in the proportion of high-angle grain boundaries and local dislocation density. Consequently, an inhomogeneous product film with segregation of Al and Cl elements was formed, providing inadequate protection for Fe-21Mn-10Al-1.25 C alloy. •An adverse effect of Ni addition on the corrosion resistance of FeMnAlC lightweight alloy in 3.5 % NaCl solution is discovered.•The addition of Ni enhances the micro galvanic corrosion between the (Ni, Al)-rich B2 phase and the austenitic matrix.•The addition of Ni causes the formation of a nonuniform corrosion product film with segregation of Al and Cl elements.