SAO: Sulphuric anodic oxidation
This is generally implemented in a bath containing 150 to 250 g/l of sulphuric acid, at a temperature between 16 and 24°C, at a current density of 1.2 to 1.8 A/dm2.
Description of the process
he duration of treatment is 20 to 60 min, the thickness of the oxide film obtained depends on the chemical composition of the alloy and varies according to the application sought and the industrial sector concerned. It is usually 5 to 25 µm. The treatment leads to a swelling equivalent to 33% of the thickness of the film and a slight increase in the surface roughness. The oxide layer is mainly composed of a porous structure. Sealing treatment by hydration of the porous layer is necessary to achieve the maximum corrosion resistance, but paint adhesion decreases significantly. It is possible to colour the coating, a bright metallic colour is obtained by chemical colouration: black, red, blue or green.
Electrolytic colouring, by the deposit of a mixture of oxides and metals, produces shades of gold, bronze and black that are very solid under light. The colouring operation is located before the sealing.
All grades of aluminium alloys and for all modes of processing. However, the alloy greatly influences the level of performance obtained and the appearance.
Corrosion resistance, erosion or abrasive wear and good performance on scratching
Applications : automotive, building, navigation, household appliances, aerospace, cosmetics, food applications, etc.
Choice criteria - Limitations
The process used has no critical influence on the environment, it contains no heavy metals or chlorinated solvents. Consequently, so far there is no threat to the continuation of this process.