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 + 500 ppm Si were oxidized at temperatures ranging from 250 to 620 degrees C, The composition and thickness of the oxide film were determined by electron spectroscopy for chemical analysis (ESCA) and Auger spectroscopy. Below the crystallization temperature (400 degrees 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 oxide formed on pure Al. Above 400 degrees C, MgO is formed as a separate phase on the surface of the Al2O3. The Si-containing material showed Si4+ enrichment in the surface oxide. Mg2+ species were not detectable, Silicon is also strongly enriched in the metal phase just below the metal-oxide interface.