Composite films of aluminum nitride and alumina were fabricated on aluminum 6061 alloys in a DC plasma chamber. Samples were treated by three main processes. These were : (1) Ar plasma etching, (2) NH3/Ar plasma with low pressure and low current density, and (3) NH3 plasma with high pressure and high current density. The oxygen-free Al surface was obtained after 10 min 2.8 keV Ar+ sputtering in an ultrahigh vacuum analysis chamber after the sample was treated by processes 1 and 2. Composite films of aluminum nitride and alumina were obtained on samples treated by processes 1, 2 and 3. The surface compositions and bonding environments of the composite films were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. The thicknesses of the films were determined by argon sputtering in the ultra-high vacuum chamber. The surface morphologies of samples after fabrication processing in DC plasma were investigated by scanning electron microscopy. Al with the composite film not only shows a much better corrosion resistance in 1N HCl solution but also exhibits six times higher hardness than that of untreated Al. A possible formation mechanism of the composite film is proposed.