Hard Anodic Oxidation

What is Anodic Oxidation?

Aluminum anodic oxidation utilizes aluminum or aluminum alloy as anode, and lead plate as cathode to be electrolyzed in electrolyte, then form surface oxidation film, and thickness of which goes up to from several to several hundred microns. Its surface is porous honeycomb. Compared with the normal oxidation film of aluminum alloy, it has better corrosion resistance, abrasion resistance and appearance. Different electrolyte and process conditions result in anodic oxide film with different properties.

The Main Process

The main process: degreasing degreasing, alkali corrosion, polishing, anodic oxidation, dyeing, hole sealing.

Alkali corrosion aims at removing compact but uneven oxidation film on aluminum. Adopt the mix solution of HN03 and HF on high silicon aluminium alloy, and alkaline bath on other aluminium alloy.

The purpose of polishing is to get a smooth and bright surface, and it consists of mechanical polishing, electrolytic polishing and chemical polishing.

Dyeing is a process that utilize porous structure and perfect adsorption performance to absorb dyes on oxidation film.

Due to the oxide film has high porosity and adsorption, and is very easy to be polluted. Especially in the corrosive environment, corrosive medium easily goes into the membrane pore and cause corrosion. Therefore Oxide film should be subjected to hole sealing after dyeing processing, in order to improve sun resistance and corrosion resistance.

Hard Anodic Oxidation Advantages

Anodized film thickness is usually 5-20 microns, and the hard anodic oxidation film thickness can reach 60-250 microns, hardness is commonly HV240-500, and melting point goes up to 2050 ℃, which results in high temperature resistance of 1500-2000 ℃ in short time, and low thermal conductivity, good electrical resistivity and perfect insulation performance. However, normally anodic oxide film is very brittle, and worse with the increase of the thickness, so hard anodic oxidation film can't bear impact, bending and deformation. Corrosion resistance of hard anodic oxidation film is better than normal anodic oxide film.