What is Alodine Coating
The “Alodine” surface treatment process means that aluminum machining parts and aluminum alloys are treated with chromium phosphating technology. The phosphating solution is mainly composed of phosphate radicals and hexavalent chromium, and fluoride ions are generally added. The phosphating film formed is emerald green, which has good matching and corrosion resistance with the coating.
Aluminum Alloy Chemical Oxidation Alodine chemical oxidation was first used in the United States in 1945. Subsequently, France, Japan, and the Soviet Union all adopted it successively. The formulas they use vary, but they are basically chrome, phosphoric acid, fluoride, and various additives. In such a solution, a chemical conversion coating is formed on the surface of the aluminum alloy. Although the wear resistance of this film is only 20% of that of the anodized film, the former is more resistant to bending and torsion, especially with excellent paint adhesion.
The material used for chemical oxidation implements the US military standard MIL-C-81706. Colorless conversion film, namely CC film (Col.:-lessCon, ersionCoating) according to MIL-C-5541B class requirements, using Alodine 1500 (liquid); colored conversion film, namely MC film (Mu[tico sub oredConver- SionCoating) according to MIL-C-55 IBI class requirements, using Alodine 1200 (solid). The standard also stipulates: 6061-T6 (equivalent to LD2) uncoated aluminum test piece for CC oxidation; 2024-T3 (equivalent to LY12) uncoated test piece for MC oxidation. It can be seen that the requirements are very strict, which also shows that the corrosion resistance of the MC film is better than that of the CC film.
Secondly, it is clearly stipulated in the standard that a salt spray test of the conversion coating should be done once a month, and it is only allowed to be put into production if it is qualified. If it is not qualified, the reason should be found out, and the process can be adjusted until it is qualified before continuing production. We do not have such clear regulations and regular inspections.
Finally, it is also stipulated that different processes of dipping, brushing and spraying can be used as repair measures for the oxide film of aluminum parts. Brushing and spraying require special personnel to operate, and can only be produced after passing the examination.
Alodine anodizing treatment is a kind of aluminum alloy surface treatment, which is mainly used to improve the corrosion resistance of aluminum alloy structures and the adhesion with primers. Alodine is a trade name for the surface treatment of aluminum alloys, which can form a very thin (0.5~4 micron) anodic oxide film through chemical reactions on the surface of aluminum alloys. The principle of Alodine anodizing is the chemical reaction of chromate passivation. The main components of Alodine are mixed with chromic anhydride, methyl tetrafluoroborate, sodium fluoride and other substances in a certain proportion.