Characterization of aluminum based oxide layers formed by microwave plasma

Polycrystalline, commercially pure, aluminum (1100-Al) and an AlZnMgCu alloy (7075-Al) were plasma oxidized in a microwave 2.45 GHz glow discharge. The resulting surface oxide layers were characterized by Auger electron spectroscopy, by x-ray photoelectron spectroscopy, and by Fourier transform infrared spectroscopy. In 1100-Al the surface layer was γ-Al2O3 oxide, followed by an Al–O interdiffusion layer, while magnesium oxide was the dominant phase in Al-7075. Furthermore, the 200 nm layer of Mg–O acted as an oxygen diffusion barrier and reduced the Al–O interdiffusion layer thickness. The compositions and the structures of the oxide layers are presented and discussed further including the effect of microalloying on the layers’ properties, providing some rationale for the current results.