Advanced nano-particles anti-corrosion ceria based sol gel coatings for aluminum alloys

Chromate conversion coatings can be successfully used for the corrosion protection of aluminum alloys. However, the environmental laws in many countries have imposed severe restrictions on chromate use due to its high toxicity and consequent environmental hazards. Many attempts have been made to find alternatives to chromating such as cerate. In this work, the effect of surface preparation prior to ceria treatment was studied. A series of specimens was prepared under the following conditions: (a) as polished, (b) directly treated, (c) etched, (d) oxide thickened, and (e) etching followed by oxide thickening. After surface preparation, the specimens dipped in ceria solutions prepared by sol-gel method. Electrochemical Impedance Spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 3.5% NaCl. The optimum conditions under which ceria treatments can provide good corrosion protection to the aluminum substrate were determined. Generally, ceria treatments improve the corrosion resistance due to the formation of protective oxide films which act as a barrier to oxygen diffusion to the metal surface. According to the EIS and polarization measurements, a combination between etching and oxide thickening has a vital role on the corrosion protection performance of AA6061-T6 in NaCl. (c) 2006 Elsevier B.V All rights reserved.