Basics of aluminum anodizing treatment

In the acid electrolyte, aluminum is used as the anode, and the material protection technology that produces an oxide film on the aluminum surface through electrolysis. There are many electrolytes for the anodization of aluminum, but they are basically prepared with sulfuric acid, chromic acid, oxalic acid or boric acid as the main components. One of the most commonly used is sulfate-based. The power supply can be direct current, alternating current or alternating direct current. The voltage is between 5 and 25 volts, and the temperature is lower than 25°C.

In the electrolysis process, the anion of oxygen interacts with aluminum to produce an oxide film. The film is not dense enough when it is initially formed, and has a certain resistance, so that the negative oxygen ions in the electrolyte can still reach the aluminum surface to continue to form an oxide film. As the thickness of the film increases, the resistance increases and the electrolysis current decreases, and the outer oxide film in contact with the electrolyte is chemically dissolved at the same time. When the rate of oxide formation on the aluminum surface gradually balances with the rate of chemical dissolution, this The oxide film can reach the maximum thickness under this electrolysis parameter. The structure of aluminum anodic oxide film is different from other conversion films. Close to the base metal part is a dense layer of 0.01 to 0.1 microns, on which is a honeycomb layer composed of many hollow hexagonal cylinders, with a total thickness of 2 to 100. The micron varies. The anodic oxide film produced by various electrolytes has different tones. Some are integrally colored and are mostly used in the construction industry. Some can be dyed or used hydrolysis and metathesis methods to deposit the formed pigment on the hollow part of the hexagonal column. Beauty.

Finally, it needs to be sealed and dried. Aluminum with anodized aluminum film sometimes has better corrosion resistance than chromate-treated aluminum. In addition to being widely used in the construction industry and daily hardware products, this kind of aluminum is also used in airplanes, automobiles, and civil ships. Using low temperature, weak electrolyte and higher voltage (100-150 volts), it can form engineering hard anodized film for mechanical parts and hydraulic components in contact with fiber, paper and rubber. Filling PTFE in the hexagonal cylinder cavity of the ordinary anodized aluminum oxide layer can obtain parts with extremely low friction coefficient.