First of all, chromic acid anodizing can effectively improve the performance of aluminum profiles. A dense aluminum oxide film will form on the surface of the oxidized aluminum profile, which can enhance the corrosion resistance, hardness and wear resistance of the aluminum profile, and is particularly suitable for use in aviation and fields with high requirements for material fatigue strength.
Chromic acid anodizing can also improve the electrical insulation of aluminum profiles, which is suitable for the electronics and electrical industries. It can also give aluminum profiles a metallic luster and provide decorative properties. Due to the strong adhesion of the film layer, the coating is not easy to fall off, so the excellent performance of the aluminum profile can be maintained for a long time.
The color of the chromic acid anodized film is generally off-white, dark gray or rainbow, and it is not easy to dye due to the low porosity of the film. Although the film is thin (usually only 2~5μm), it has good elasticity and is relatively dense, and can be used normally even if it is not sealed. Chromic acid anodizing is particularly suitable for aluminum profiles with small dimensional tolerances and high surface gloss, especially aluminum profile castings, aluminum profiles with large porosity and welded parts, etc. It is difficult to achieve ideal results for these workpieces using ordinary sulfuric acid anodizing methods.
However, chromic acid anodizing also has some disadvantages. First, the hexavalent chromium in the chromic acid electrolyte is highly toxic and harmful to the environment. Therefore, the cost of using chromic acid anodizing is high, and its application range is limited. It is mainly used for aluminum profiles with special requirements. Secondly, chromic acid has a large solubility in copper, so it is not suitable for aluminum profiles with a high copper content. In addition, temperature changes have a great influence on the quality of the chromic acid anodizing film, which needs to be controlled within the range of (36±2)℃. It is best to install a temperature control device.
Regarding the use of the electrolytic cell, the area ratio of the cathode to the anode also affects the treatment effect. It is usually best between (2:1) and (6:1). Too large a ratio will reduce the reduction reaction of trivalent chromium in the electrolyte. When the oxidized workpiece area is small and the electrolytic cell is used as the cathode, the effect can be optimized by shielding part of the cathode area.
In general, chromic acid anodizing is mainly used in the aviation field and special occasions with high requirements for material fatigue strength. Although there are certain environmental and cost restrictions, its advantages in improving corrosion resistance, hardness, wear resistance and electrical insulation make it a very effective treatment method.
