Effect of alkaline etching on microstructure and anticorrosion performance of anodic film on Al-Mg-Si alloy

Abstract

Alkaline etching as an anodization pretreatment process is critical to structure and anticorrosion performance of the anodic film. The effects of modification by alkaline etching on AA6061 surface microstructure and corresponding film growth behaviors have been investigated in this work. The in-situ characteristics of grain boundaries, intermetallic particles and film structure were investigated. It is found that a suitable etching time can effectively remove a number of intermetallic particles and reduce the roughness from the matrix surface. For 60s etching, as the microstructures (e.g. cathodic Al-Fe-Si-Mn phase, grain boundary and anodic Al-Mg-Si phase) with different local potential from the matrix are modified, the growth rate can reach 0.39μm min−1 and the integrity of the anodic film are all increased. Extending etching time up to 120s will significantly disturb the regularity of pore order and reduce film growth rate because of the excessive corrosion at grain boundary.