Chemical polishing of aluminum and its alloys is based on 70% phosphoric acid. The mixture of phosphoric acid, nitric acid and sulfuric acid is commonly used. When the alloy composition changes, the sulfuric acid content is 9%. The content of nitric acid varied from 3% to 9%. Because the working temperature is about 105 ℃, a lot of nitrogen oxides are produced to pollute the environment. As a result, a yellow smoke free chemical polishing process was developed by using S-type Acid Copper brightener as additive on the base of the mixture of phosphoric acid and sulfuric acid. However, this kind of chemical polishing without yellow smoke is only suitable for pure aluminum or aluminum magnesium alloy, and has poor effect on other aluminum alloys. Later, only 2% nitric acid was added to the formulation, and similar additives were used, which did not extend the scope of application. However, the mixture of phosphoric acid, nitric acid and sulfuric acid is still the mainstream formula due to its strong compliance.
For aluminum alloy with high copper and zinc content, it is helpful to add 2-5g / L chromic anhydride during chemical polishing. There is a description in the manual. For aluminum alloy with high silicon content, 60-65ml / L nitric acid, 15-20ml / L hydrofluoric acid and 1-2ml / L glycerin are used for chemical polishing, and the mixture is immersed for 2S at room temperature. But this is more like erosion.
There is also a formula containing acetic acid, which is applicable to pure aluminum and 2A12 (lyl2): acetic acid has better effect on avoiding pitting corrosion.
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