Why do color variations occur in anodized aluminum alloy shells from the same batch?

In the aluminum profile industry, anodizing is a common surface treatment process, which can form a uniform and dense oxide film on the surface of aluminum.

However, sometimes we find that the same batch of aluminum alloy shells will have color difference after anodizing. So, what exactly causes this phenomenon? This article will give you a detailed answer.

1. Raw material factors

1. The aluminum alloy material is impure

The composition of aluminum alloy materials contains a variety of elements, such as copper, manganese, magnesium and so on. The different proportions of these elements in the aluminum alloy melting process will affect the color difference after anodizing. When the content of certain elements in aluminum alloy materials is high, the surface color may be biased to the color of these elements after anodizing treatment.

2. Inclusions during alloy smelting

Aluminum alloy in the smelting process, may include some impurities, such as silicon, iron and so on. These impurities will react with the oxide film during the anodizing process, resulting in a difference in surface color.

2. Production process factors

1. Unstable electrolyte concentration

The anodizing process requires the use of an electrolyte containing sulfuric and nitric acid. The proportion of sulfuric acid and nitric acid in the electrolyte will affect the formation speed and quality of the oxide film. If the electrolyte concentration is not stable, it may cause the formation of oxide film in some areas to be slow, resulting in color difference.

2. Current density mismatch

In the anodizing process, it is necessary to control the appropriate current density. Too high or too low current density may lead to uneven formation of oxide film, resulting in color difference. In addition, the mismatch of current density may also lead to the occurrence of local corrosion phenomenon, which further affects the consistency of surface color.

3. Inconsistent processing time

The time of anodizing also has a great influence on the surface color. If the treatment time is not long enough or too long, it may lead to the formation of an uneven oxide film, resulting in color difference. In addition, the inconsistency of the treatment time may also lead to different degrees of corrosion in some areas, further affecting the consistency of the surface color.