Table 2 Phosphoric acid-chromate treatment liquid composition and process conditions Phosphoric acid ml/L chromic anhydride, g/L ammonium bifluoride, g/L boric acid, g/L sodium fluoride, g/L Formula 1 and Formula 2 above Thick can be colorless to light blue, bean green oxide film is closed or coated with organic film can be used for decoration; Formula 3 film is thin, can be used to require conductive parts, the film is colorless. 4 Process flow and description 4.1 Process flow Water-based cleaning agent Degreasing - Alkali corrosion -> Hot water washing -> Washing -> Light-emitting water-washing - Chemical conversion film treatment - Water-washing hot deionized water washing (50-60°C) - Drying Self-drying or dry-up, water-washing, dry-up below 65°C Note: Suitable for chromate film; Suitable for phosphoric acid-chromate film 4.2 Process description Purpose To remove the oxide film on the surface of the workpiece and chemical conversion film. The matrix is ​​strongly bonded, and the alkaline solution generally contains NaOH 70~90g/L, and is soaked in 70~80° for 20~30s and then washed with hot and cold water. Mainly to remove the workpiece surface corrosion products, such as black film. The etching process is as follows: The conversion film obtained from the new anti-rust aluminum H2SO4 solution has a bright color and a moderate thickness. With the increase of the use time, the phosphoric acid-chromate film will appear light green or even colored, and it needs to be adjusted, such as adding chromic anhydride and Contains F compounds. If the accumulation of Al3+ is too high, the film can be discarded and part of the solution can be discarded, and H3PO4, Cr3, and other components can be added. H3PO4 and NaF content are too high, will make the film loose, and even difficult to film. The length of processing also varies with the temperature. Since the chromate passivation film has a thin film and low porosity, the chemical conversion film can be dried in a Cr-free deionized water (0~60°C), dried (50~60°C), or Do it yourself. Phosphate-chromate conversion film formed thick, high porosity, usually in the Na2Cn7 or K2Ci2730 ~ 50g / L, 90 ~ 95 ° immersed for 10min closed treatment, and finally dried by 50 ~ 60 °C, closed The rear part can be used for individual rust prevention. Aluminum rivets are usually H3BO320~30g/L, soaked for 10~15min, then cleaned and dried at low temperature.
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