[China Aluminum Network] Chemical polishing of aluminum and aluminum alloys is based on a 70% (mass percentage) phosphoric acid based solution. Commonly used is a mixture of phosphoric acid, nitric acid, and sulfuric acid. When the alloy composition changes, the sulfuric acid content (mass percentage) is 9%. Between 15%, the content of nitric acid (mass percentage) varies from 3% to 9%. As the operating temperature is around 105°C, a large amount of nitrogen oxides pollutes the environment. Therefore, on the basis of a mixture of phosphoric acid and sulfuric acid, the use of S-type copper brighteners as additives has resulted in a yellow-nosed chemical polishing process. However, such yellow-nosed chemical polishing is only applicable to pure aluminum or aluminum-magnesium alloys, and has a poor effect on other aluminum alloys. Later, there were formulas that only added 2% nitric acid, and similar additives were used, but the scope of application was not extended. However, since the phosphoric acid, nitric acid, and sulfuric acid mixture is adaptable, it is still the mainstream formulation.
Aluminum alloys containing higher amounts of copper and zinc are more likely to be chemically polished with 2-5 g/L of chromic anhydride. The manual states that aluminum alloys containing silicon are high, and a mixture of 60 to 65 mL/L nitric acid, 15 to 20 mL/L hydrofluoric acid, and 1 to 2 mL/L of glycerin is used for chemical polishing and immersed at room temperature for 2 seconds. However, this method is more like etching. The 7075 aluminum row also has an acetic acid-containing formulation for pure aluminum and 2A12 (LYl2):
Phosphoric acid 850ml/L
Glacial acetic acid 100ml/L
Nitric acid 50ml/L
Temperature 80-100°C
Time 2-5min
Acetic acid has a better effect on preventing pitting corrosion.
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