Influence of α-Al(Mn,Fe)Si Dispersoids and Microalloying on the Localized Corrosion Behavior of Aluminum Alloys

Microstructural heterogeneity plays an important role in the localized corrosion behavior of aluminum alloys. However, the contribution of fine α-Al(Mn,Fe)Si dispersoids remains insufficiently understood. This study investigates how dispersoid characteristics and Cr, Er, and Zr microalloying relate to localized corrosion in industrial-purity Al-based model alloys. Decreasing the total Mn + Si content increased the average dispersoid size by 146% and reduced the number density by 46%, accompanied by a 77% decrease in corrosion current density and a 411% increase in charge-transfer resistance relative to the base alloy. In the studied alloys, surface and cross-sectional observations together with in situ atomic force microscopy (AFM) were qualitatively consistent with suppression of localized corrosion development. Cr, Er, and Zr microalloying further modified dispersoid characteristics and corrosion response, with Cr producing the greatest improvement in electrochemical resistance. The different responses of the Er- and Zr-containing alloys indicate that dispersoid size and number density alone cannot account for the microalloying effect. A two-level interpretation involving dispersoid/matrix interface density and element-dependent interfacial responses is proposed as a working framework, providing a basis for controlling localized corrosion through dispersoid regulation and microalloying.