Because the so-called oxidation blackening of aluminum alloy is actually that most of the surface of aluminum alloy is transformed into an oxide film, which has some functional characteristics such as protection and decoration. The pore size of the oxide film is between 100 nm and 200 nm, the thickness of the oxide film is about 10 micron, the porosity is about 20%, and the pore spacing is 300-500 nm. Such a thin thickness will not change the aluminum alloy itself.

Extended data:

What is the structure of anodic oxide film?

Anodized oxide film consists of two layers, the outer layer is called porous layer, which is thick, porous and has low resistance. The inner layer is called barrier layer (also called active layer), which is thin and dense and has high resistance. The porous outer layer is grown on the dense inner layer with dielectric properties.

Generally speaking, the anodic oxide film is an array of hexagonal cylinders, and each cylinder needs a star-shaped hole filled with solution, which looks like a honeycomb structure, and the thickness of the hole wall is twice the diameter of the hole.

The barrier layer is composed of anhydrous AI2O3, which is thin and dense with high hardness and has the function of preventing current from passing through.

The pore size of the oxide film is between 65438+300~500nm and 200 nm, the thickness is about 10 μm, the porosity is about 20%, and the pore spacing is between 300~500nm. The cross-sectional view of the oxide film shows that the holes of the oxide film are basically tubular structures, and the membrane dissolution reaction of the oxide film basically occurs at the bottom of the holes.

However, the pore size of the anodic oxide film of DC sulfate is about 20nm. If it is a 12 micron oxide film, what a deep thin tubular structure it is! Suppose this is a well with a diameter of 1m, and its depth will be 600m m.

Most excellent properties of oxide film, such as corrosion resistance, wear resistance, adsorption and insulation, are determined by the thickness and porosity of porous outer layer. However, they are closely related to anodizing conditions, so we can obtain thin films that meet different application requirements by changing anodizing conditions.

Film thickness is a very important performance index of anodic oxidation products, and its value directly affects the corrosion resistance, wear resistance, insulation and chemical coloring ability of the film. In the process of conventional anodic oxidation, the film thickness increases with time.

After reaching the maximum thickness, it gradually becomes thinner with the extension of treatment time, especially for some alloys, such as Al-Mg, Al-Mg-Zn alloy. Therefore, the oxidation time is generally controlled within the maximum film thickness time.

Baidu encyclopedia-aluminum anodic oxidation