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 th
e oxide film were determined by electron spectroscopy for chemical ana
lysis (ESCA) and Auger spectroscopy. Below the crystallization tempera
ture (400 degrees C) of Al2O3, Mg2+ is enriched in the interior portio
n 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-contai
ning material showed Si4+ enrichment in the surface oxide. Mg2+ specie
s were not detectable, Silicon is also strongly enriched in the metal
phase just below the metal-oxide interface.