The Effect of Heat Treatment on the Localized Corrosion Susceptibility of Extruded AA6063 Alloys With High Amount of Tramp Elements

ABSTRACT The growing use of secondary aluminium alloys requires understanding how trace amounts of Cu and Zn interact with heat treatment to affect corrosion. One primary and 3 secondary AA6063 variants were compared before and after T6 heat treatment using polarization, SEM‐EDS and SKPFM, with corrosion assessed in 0.1 M NaCl. Polarization alone did not resolve the localized corrosion responses associated with trace compositional differences. T6 treatment increased the size of Fe‐rich intermetallic particles while maintaining a similar area fraction. It also modified trace‐element partitioning and local electrochemical heterogeneity. In secondary variants, increased particle–matrix Volta potential contrast was associated with earlier trenching. T6 treatment increased the frequency of intergranular corrosion initiation, whereas untreated secondary variants generally developed fewer, larger affected regions during prolonged immersion. Thus, T6 heat treatment shifts the balance between trenching initiation and intergranular corrosion propagation rather than uniformly increasing or decreasing localized corrosion susceptibility.