This paper studies the process, properties, morphology, composition and structure of ceramic-like amorphous composite conversion coatings formed on aluminum and aluminum alloys via anodic oxidation and deposition in neutral electrolyte systems. The film formation process and mechanism are also preliminarily discussed.

Process tests indicate that in the neutral mixed solution containing sodium tungstate (Na₂WO₄), a complete, uniform and glossy grey inorganic non-metallic coating can be obtained under the following conditions: accelerator concentration 2.5~3.0 g/L, complex film-forming agent concentration 1.5~3.0 g/L, Na₂WO₄ concentration 0.5~0.8 g/L, peak current density 6~12 A/dm² and mild stirring. The coating has a thickness of 5~10 μm, microhardness of 300~540 HV and excellent corrosion resistance. This neutral system is highly adaptable and can form qualified coatings on various aluminum alloys including anti-rust aluminum and wrought aluminum.