When using sulfuric acid hard anodic oxidation method, the factors affecting the oxide film should be considered.
(1) Concentration of sulfuric acid oxidation treatment: 200-250 g/L is usually used, and the relative density of bath solution (at room temperature) is 1.12-1.15.
(2) Water: Water is the main component of hard anodic oxidation treatment. Distilled water or cold boiled water is generally used instead of tap water, because there are chloride ions in tap water. When Cl 1 > 1%, its parts will corrode in the oxidation process and white spots will appear.
(3) Temperature of oxidation treatment: Temperature is one of the important factors affecting the quality of oxide film. Strictly controlling the temperature, the oxide film is thicker, the hardness is increased, and the film is smooth and compact.
(4) Current density: Current is also one of the important factors affecting the quality of the oxide film. It has a great relationship with the formation rate of the oxide film and the structure of the oxide film. When the current density is too low, the formation rate of oxide film is slow and the treatment time is increased. On the contrary, when the current density is too high, the solution and electrode will be overheated due to Joule effect, which will increase the dissolution rate of oxide film, decrease the hardness, and make the surface rough and loose.
(5) Initial voltage and treatment time: Initial voltage and time of hard anodic oxidation treatment also have great influence on the quality of oxide film. When the initial voltage is too high, the current will increase, the Joule heat and the heat of formation will increase sharply, and the dissolution rate will increase sharply. The oxide film will be soft, dull, powder and wear-resistant.
Warm reminder: For oxidation treatment time, generally with the extension of oxidation treatment time, the oxide film thickness increases, but after a certain time, if the applied voltage is not increased, the oxide film does not actually increase. If the time is prolonged, the hardness of the oxide film is low and the powder is loose. On the contrary, oxidation treatment time is too short, oxide film thickness is thin and wear-resistant.