Effect of iron-containing intermetallic particles on film structure and corrosion resistance of anodized AA2099 alloy

The anodizing behavior of iron-containing intermetallic particles in AA2099 aluminum-lithium alloy and their effect on structure and corrosion resistance of the anodic film were investigated using electrochemical measurements and scanning electron microscopy. High-copper-containing Al-Fe-Mn-Cu particles (HCCPs) dissolved preferentially through dealloying at ∼ 0 V (vs. saturated calomel electrode) in a tartaric-sulfuric acid solution, at 22, 37 and 42^◦C, leading to formation of copper-rich nanoparticle of 50–200 nm diameters. They dissolved completely under normal anodizing conditions, resulting in cavity defects of micrometer dimensions in the anodic film and sunken regions in the alloy substrate immediately beneath the dissolved HCCPs. Immersion testing of the anodized alloy in 3.5% NaCl solution for 24 h indicated that localized corrosion of the anodized alloy predominantly developed at the site containing dissolved HCCPs at the film/alloy interface. It is suggested that HCCPs play a critical role in controlling the corrosion resistance of the anodic film formed on AA2099 aluminum-lithium alloy.