Enhancing anti-corrosion performance of anodic film on aluminum-lithium alloy AA2099-T83 by post-treatment in lithium oxalate solutions near room temperature

Abstract

Anodic film formed on aluminum-lithium alloy AA2099-T83 is post-treated in various lithium oxalate (Li₂C₂O₄) solutions to enhance its corrosion resistance. The anodic film can be rapidly sealed near room temperature and there is an interaction between the sealing temperature and salt concentration. Particularly, the alloy specimens treated in 0.03 mol/L Li₂C₂O₄ solution at 40 or 50 °C for 30 min did not show any visible corrosion pits even after 1000 h of neutral salt spray tests. The sealed anodic film typically shows lamellar surface features and a dense top layer of a few hundred nanometers thickness. The sealing products are mainly composed of boehmite, layered double hydroxides (LDHs) and amorphous hydroxides. The high corrosion resistance of the treated alloy is ascribed to the formation of boehmite and LDHs (or amorphous hydroxides) in the anodic film and the self-healing characteristic of the coating system. The present work suggests that it is possible to achieve high corrosion resistance for anodized aluminum-lithium alloys by post-treatment in appropriate lithium oxalate solutions near room temperature.