What is eloxal?

The operation of eloxal (with the abbreviation: electricity oxidation of aluminium), it is a technically method of surface engineering to generation of oxidic coating though anodic oxidation.

In the galvanic overdrawing-process will not the coating to thump the workpart. Though a conversion, at uppermost metal-zone to generates oxide or hydroxide.

It develops a thickness coating, with 5-25 mm. The coating protect against corrosions. The aluminium-oxide-coating is only a few nm.

Pre-treatment:

The aluminium-parts (blank sheets or pre-cut-parts)to be defatted and bated. This process happened in a natron-base-dip (electrolyte) and the thickness, natural oxide-coating will be deleted. 

After the pre-treatment it begins the anodization.

To customer wishes, will the blank sheets and coatings to eloxadize in silver and different colours.Afterwards it begins the compaction with hot water.

The electrolytically treatment will by direct current in or oxal-sulphuric-electrolyte. By the variant of direct current will switch the aluminium as anode. This treatment is called “anodization“. 

The backplate electrode from a material, that will not attacked by electrolyte.

Compaction:

The pores must be to compacted, about inclusion of corrosion-promoting substances to avoid.

The anodized and coloured aluminium will compact in demineralized water. The water will compact though digestion simply.

Thereby it comes to a reaction between aluminium-oxide and water. It develops aluminium-oxide-hydrate.

furthermore, it comes to  volumetric expansion, though the absorption of water and the pores (pores-neck)will be contract and then will be close.

Lamination-Procedures:

The lamination-Procedures will be influence by: 

• Choice of electrolyte; the concentration and temperature
• kind of current (direct current/alternating current)
• Current density
• Tension and continuance of conditioning 

An extreme influence has modification of temperature. The period of time at the treatment is dependent on a coat thickness. 

Sometime it will be mixed additives into the electrolytes. The additives influenced the composition of oxide-coating.

All the time the base-material of the coating   remains by aluminium oxide. The thickness is out aluminium oxide, therefore will not conduct the electricity current – in contrast to the aluminium.

Depth of layer growth:

The coating is microcrystalline, with a lot of pores. 

Therefore the coating is able to aspirate liquids. That is important for growth of the oxide-coating. The electrolyte must to expand into internal interface, between aluminium-oxide and aluminium, about to perform the oxidation there.

The oxide-coating grow form the surface in the metal, therefore the adhesion of the coating is excellent. The coating developed itself to put the metal.

Hardness:

The hardness by the eloxal-thickness is 8-9, after the hardness scale by Mohs., between quartz and corundum.

Very hard eloxal-coating  is refractory, that hairline cracks is developing by the bending. The result is the termination of the material, when  hairline cracks are desired. The process of the material must end, before the anodization – them the coating are not damaged.