Influence of Aging Treatment on Intergranular Corrosion and Exfoliation Corrosion Susceptibility of Super-high Strength Al Alloy Containing Sc

The influence of aging treatment on intergranular corrosion and exfoliation corrosion susceptibility of super-high strength Al alloy containing Sc was studied using optical microscopy (OM) and transmission election microscopy (TEM). It was found that intergranular corrosion and exfoliation corrosion of super-high strength Al alloy containing Sc were accelerated with prolonging the aging time, which were in accord with the results of polarization tests in 4.0 mol/L NaCl+ 0.1 mol/L HNO3+0.4 mol/L KNO3 (EXCO) solution. TEM observation shows that the size of precipitates at grain boundaries and the width of precipitate free zone (PFZ) at grain boundaries are the key factors responsible to the corrosion behavior of the alloy, As aging time was increased, η′ and S′ phases transformed into equilibrium η and S phases, and the size of η and S phases at grain boundaries and the width of PFZ were increased. The discontinuous distribution of the equilibrium phases at grain boundaries and the PFZ blocked the anodic tunnels of corrosion, which decreased the corrosion susceptibility of the alloys.