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Aluminum alloy hard anodic oxidation

Release time:

2021-10-14 15:00

1. Characteristics of hard oxide film

Aluminum alloy hard anodic oxidation and ordinary oxide film has the following characteristics: the oxide film is relatively thick (generally not less than 25um), the hardness is relatively high (greater than 350HV), good wear resistance, low porosity, high breakdown voltage, and the surface smoothness may appear slightly worse.

2. Process characteristics of hard anodic oxidation

There is no essential difference between the principle, equipment, process and detection of hard anodic oxidation and ordinary oxidation. Hard oxidation tries to reduce the solubility of the oxide film, the main features are:

A. bath liquid temperature is low (ordinary 20 degrees, hard 5 degrees below), under normal circumstances low temperature oxide film hardness is high

B the concentration of the bath solution is low (the concentration of common sulfuric acid is 20%, and the hardness is less than 15%), and the solubility of the film is small if the concentration is low.

C. adding organic acid sulfuric acid to the bath solution, adding oxalic acid or tartaric acid, etc.

D. applied voltage and current are relatively high (ordinary current 15A/dm2 voltage below 18V, hard current 2 ~ 5A/dm2, voltage above 25V. Up to 100V)

e. The applied voltage should adopt the method of increasing the voltage step by step. Because of its high voltage and large current, the processing time is long, so the energy consumption is large. At the same time, hard oxidation often uses pulse power supply or special waveform power supply.

3, cast aluminum alloy hard anodic oxidation

Cast aluminum alloys usually need hard anodization to improve their performance. Cast aluminum alloys are commonly used in aluminum/silicon alloys and aluminum/copper alloys. Aluminum silicon has good casting performance and wear resistance, and the amount is the largest. It is widely used in dry structural parts and parts. Sometimes copper and magnesium are added to improve mechanical properties and heat resistance.

Aluminum copper casting alloy is also commonly used, mainly used to withstand large dynamic load and shape is not complex sand castings. Casting aluminum alloy because of containing non-metallic elements need to improve the electrolyte and power waveform, electrolyte can generally add some metal salts or organic acids in sulfuric acid, sulfuric acid-oxalic acid-tartaric acid solution, sulfuric acid-dry oil solution; power supply form is generally changed to AC/DC superposition, asymmetric current, pulse current, etc., the pulse effect is better. Before oxidation of electric castings, water chestnut shall be guided and burrs shall be removed to prevent current concentration.