Description of the characteristics of the anodizing process of die-casting aluminum
Wed Jun 07 16:27:02 CST 2023
1. Introduction of natural color anodizing process
Both the natural color anodizing process and the black anodizing process are a kind of anodizing process, and there are only differences in some processes. Natural color anodizing means that the appearance shows the original color of the oxide film layer, and no additional dyeing process is required, while black anodizing is based on the natural color anodizing, adding a dyeing process (such as dyeing black) to make the film appear black. Generally, the choice is made according to the different appearance requirements. In particular, it should be noted that the natural color anodized film is not necessarily white or colorless, but will show different colors according to different materials and oxidation conditions. For example, the natural color oxide film of ADC12 material is grayish in brownish yellow.
Second, the characteristics of cast aluminum anodizing
1. The appearance color is uneven.
A) Impurity elements in cast aluminum. The substrate of this new product is die-casting aluminum ADC12, in which the silicon content is about 9.5-12%, and the copper content is 1.5-3.5%. The existence of these non-oxidizable elements causes the film structure of the oxide film on the aluminum substrate to be different. Single, these non-oxidizable elements will be included in the normal oxide film, resulting in a difference in color appearance from the surrounding normal oxide film, resulting in uneven color.
B) Release agent. During die-casting, a release agent will be added to the mold to promote demoulding. At high temperatures, the release agent will be strongly bonded and adsorbed on the surface of the material, and solidified on the surface after cooling. It is difficult to remove by conventional chemical methods. Even sandblasting, sometimes It cannot be completely removed. If the oxide film layer is formed on the aluminum surface containing the release agent, such a film layer is also abnormal and has an uneven appearance.
For the above two reasons, the film layer usually has flow marks and spots, such as macular, bluish or dark and other uneven appearance. Therefore, the oxidized appearance of the ADC12 material can only be kept as consistent as possible, but the local color will be uneven.
2. The film thickness measurement fluctuates greatly.
The thickness of the oxide film is usually measured using an eddy current thickness gauge, and the measured value of the thickness gauge is affected by factors such as the roughness, curvature, and electrical properties of the measurement point of the substrate surface. In practical operation, due to the large and uneven surface roughness of die-cast aluminum materials, the measured values are unstable and fluctuate greatly. If the surface of the product has a machined surface, and the area of the processed surface is larger than the area of the probe, the measured value will be much more stable. If there is no machined surface, you can only select a few points on the rough surface to measure and take the average value. If the average value is within the range, it can be judged qualified.
3. Salt spray performance.
Due to the special material and surface state of cast aluminum itself, its oxide film is loose, porous, non-dense, and high in impurity content compared to other extruded aluminum oxide films, so its corrosion resistance is also much worse. Referring to ISO9227:2006, the specific salt spray test time is determined according to the needs of both parties. At present, the similar products we are doing are generally 72H-120H NSST test. However, different customers, different materials, and different application places have different salt spray test requirements. Whether it can pass or not requires a sample test.