Applied Surface Science, Vol.254, No.2, 586-595, 2007
The effect of cerium and lanthanum surface treatments on early stages of oxidation of A361 aluminium alloy at high temperature
X-ray photoelectron spectroscopy analysis has been used to study the surface of A361 aluminium alloy after electrodeposition of cerium and lanthanum compounds followed by oxidation tests in air at 100-500 degrees C for 2 h. Cerium and lanthanum oxide deposits are found on the beta-AlFeSi second phase particles and to a lesser extent on the eutectic Al-Si areas, while the alpha-Al phase is covered with a thin aluminium oxide film. This uneven deposition may be related either to a preferential nucleation and growth process on active interfaces or to the differing electrical conductivity of the phases and intermetallic compounds of the alloy. Initial stages of oxidation of A361 alloy disclosed thickening of the aluminium oxide layer and Mg enrichment at the surface, especially above 400 degrees C. Rare earth deposits revealed two different effects: reduced Mg diffusion and enhanced thickening of the aluminium oxide film. A distinctive behaviour of Ce oxide appears at 300-500 degrees C related with Ce(III) to Ce(IV) transition. (c) 2007 Elsevier B.V. All rights reserved.