Influence of Mg and Si on the Oxidation of Aluminum

Test materials of pure Al, Al alloyed with 10,50, and 190 ppm Mg, and Al alloyed with 10 ppm Mg + 500ppm Si were oxidized at temperatures ranging from 250 to620°C. The composition and thickness of the oxide film were determined by electronspectroscopy for chemical analysis (ESCA) and Augerspectroscopy. Below the crystallization temperature(400°C) of Al₂O₃,Mg²⁺ is enriched in the interior portion of the oxide. The enrichment of Mg²⁺gives a somewhat thinner oxide compared with the oxideformed on pure Al. Above 400°C, MgO is formed as aseparate phase on the surface of theAl₂O₃. The Si-containing material showed Si⁴⁺ enrichment inthe surface oxide. Mg²⁺ species were notdetectable. Silicon is also strongly enriched in themetal phase just below the metal-oxideinterface.