1. Characteristics of hard oxide film
Compared with ordinary oxide film, aluminum alloy hard anodizing has the following characteristics: thicker oxide film (general thickness not less than 25um), relatively high hardness (greater than 350HV), better wear resistance, lower porosity, breakdown resistance The voltage is higher, and the surface flatness may appear slightly worse.
2. Process characteristics of hard anodizing
There is no essential difference between the principle, equipment, process and detection of hard anodizing and ordinary oxidation. Hard anodizing seeks to reduce the solubility of the oxide film. The main features are:
a. The temperature of the bath liquid is low (generally about 20 degrees, and the hardness is below 5 degrees), and the oxide film formed by the low temperature is generally high in hardness.
b. The concentration of the bath liquid is low (the concentration of ordinary sulfuric acid is 20%, and the hardness is less than 15%), and the solubility of the film is small when the concentration is low.
c. Organic acid is added to the bath, oxalic acid or tartaric acid is added to the sulfuric acid. d. The applied voltage and current are high (normal current 1.5A/dm2, voltage below 18V, hard current 2~5A/dm2, voltage above 25V. up to 100V).
e. The applied voltage should adopt the method of gradually increasing the voltage. Because of its high voltage and large current, the processing time is long and the energy consumption is large. At the same time, hard anodizing often adopts pulse power supply or special waveform power supply.
3. Cast aluminum alloy hard anodizing
Cast aluminum alloys usually require hard anodizing to improve their properties. Cast aluminum alloys are commonly used in aluminum / silicon alloys and aluminum / copper alloys. Parts and components, sometimes adding copper and magnesium to improve mechanical properties and heat resistance. Aluminum-copper series are also commonly used casting alloys, mainly used for sand castings with large dynamic and static loads and uncomplicated shapes. Casting aluminum alloys need to improve the electrolyte and power waveform due to the non-metallic elements. Generally, some metal salts or organic acids, sulfuric acid-oxalic acid-tartaric acid solution, sulfuric acid-dry oil solution can be added to the electrolyte solution in sulfuric acid; the power supply form Generally, it is changed to AC and DC superposition, asymmetric current, pulse current, etc., among which the pulse effect is better. Before the electroforming parts are oxidized, the water chestnut should be guided and the burrs should be removed to prevent the current concentration.
