Views:1 Author:Site Editor Publish Time: 2021-12-03 Origin:Site
The purpose of ash removal after alkali erosion is to remove the ‘stain’ left on the surface of the product after alkali erosion in order to obtain a bright and clean metal surface. These ‘spots’ are mainly formed by the deposition of elements such as silicon, iron, magnesium and copper in aluminium alloys. Generally can be removed with nitric acid or sulfuric acid solution. Ash at the same time there is the role of alkali neutralization, it can also be called neutralization and desmutting.
Generally, 10% ~ 25% (volume fraction) nitric acid is used to macerate at room temperature for 1 ~ 3 minutes, and 30% (volume fraction) nitric acid is used to remove ash There are 25% ~ 50% (by volume) of nitric acid after chemical polishing. In nitric acid solution, when its concentration is about 30% , the corrosion rate of aluminum is maximum. If the solution temperature increases, the corrosion rate increases.
The application of nitric acid ash removal process can meet the requirements of various aluminum alloy materials. For aluminum alloys with high silicon content, nitric acid alone can not meet the requirements, fluoride needs to be added. To combat the release of nitrogen oxide and acid droplets from the decomposition of nitric acid, some commercially available ash removal formulations use a combination of nitrate additives, including persulfate and bisulfate
In order to improve the effect of ash removal and enhance the light efficiency, some special auxiliaries are sold and added to the nitric acid solution of 100 ~ 150 g/L, and can remove high copper content of aluminum alloy surface difficult to remove the black ash layer, usually contains hydrofluoric acid, hydrogen peroxide, corrosion inhibitor, sodium sulfate, Surfactant, etc.
The content of sulfuric acid in sulfuric acid ash removal is approximately the same as that in anodic oxidation, usually 15% ~ 25% (by volume) sulfuric acid is used. For 6063 aluminum alloy building profiles can get satisfactory ash removal effect, but other aluminum alloys with high alloy composition are not necessarily suitable, that is, 6063 aluminum alloy must control the content of impurities. The operating temperature of sulfuric acid ash removal is room temperature, the operating time is longer than nitric acid, generally 3 ~ 5 minutes.、
The corrosion rate of aluminum increases rapidly when the concentration of aluminum exceeds 40% (volume fraction) in sulfuric acid solution, and the maximum corrosion rate is about 85% (volume fraction) .
Some commercial ash removal additives based on sulfuric acid, most of which add one or more additives, such as oxidants.