How are aluminum and aluminum alloys chemically polished?

Chemical polishing of aluminum and aluminum alloys is based on a 70%(mass percent) phosphoric acid solution. Commonly used is a mixture of phosphoric acid, nitric acid and sulfuric acid, when the alloy composition changes, the sulfuric acid content is 9%. The content of nitric acid varies between 3% and 9%. Because the working temperature is about 105℃, a large number of nitrogen oxides are produced to pollute the environment. Therefore, on the basis of phosphoric acid and sulfuric acid mixture, S class copper acid brightener is used as an additive to produce a chemical polishing process without yellow smoke. However, this kind of chemical polishing without yellow smoke is only applicable to pure aluminum or aluminum-magnesium alloy, and the effect of other aluminum alloys is poor. Later, a formula with only 2% nitric acid appeared, and similar additives were used, and the scope of application was not expanded. However, so far, phosphoric acid, nitric acid, sulfuric acid mixture because of strong adaptability, or the mainstream formula.

Aluminum alloy with higher copper and zinc, adding 2 ~ 5g/L chromium anhydride when chemical polishing is helpful. It is described in the manual that aluminum alloy with high silicon content is soaked for 2s at room temperature with a mixture of 60 ~ 65mL/L nitric acid, 15 ~ 20mL/L hydrofluoric acid and 1 ~ 2mL/L glycerol during chemical polishing. But this method is more like etching.

There is also a formula containing acetic acid, suitable for pure aluminum and 2A12(LYl2) : acetic acid has a better effect on preventing spot corrosion.

Analysis on the difference between casting and hot rolling process of aluminum alloy sheet

1. Casting and rolling process:

1. Melting casting 2. Crystallization cooling forming 3 cold rolling 4. Finish rolling

First, the aluminum ingot and the required alloy are directly fused and cast to form an aluminum alloy liquid. The caster blank of the desired width is then cooled through the crystallizer to form. Cold rolling and finishing rolling are actually completed in one process, the casting and rolling billet is cooled to a certain temperature with lubricant for rolling, and finally formed aluminum.

2. Hot rolling process:

1. Casting 2. Slag removal 3. Milling 4. Heating 5. Hot rolling 6 cold rolling 7 finishing rolling

After the process is cast into the alloy liquid, slag removal, about the total amount (1%-5%), and then form a cast block, because in the melting casting process under the action of high temperature, impurities are attached to the surface of the alloy, the slag removal process can not be completely removed, so after the formation of the cast block, to be milling, milling off the thickness of the cast block surface about 20mm, reduce the alloy impurities. Then the cast block is heated at high temperature, maintain a certain temperature, so that its internal structure recrystallization, after a long time of high constant temperature, the crystallization will be more uniform, the grain is more delicate, and then rolling under high temperature, forming hot rolled billet, and finally cold rolling, finishing rolling.

Compared with the casting and rolling billet, the hot rolling material has fewer impurities, so the corrosion resistance is much stronger, especially against sea water. At the same time, due to the recrystallization process, the internal structure is more stable and uniform, and the formed aluminum has better performance and ductility than the casting and rolling material.

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