Solid Soviet GOST 9.303-84 establishes requirements for the selection of metallic and non-metallic coatings. Here's what he writes about anodic oxide coating on aluminum. – aluminum anodizing.
Resizing during anodizing
When anodizing aluminum, the dimensions of the parts increase by about 0,5 coating thickness (per side).
Quality of the anode-oxide coating increases with the improvement of the surface treatment of parts purity.
Filling of anodic oxide coatings
Anodic oxide coating, which are used to protect against corrosion, filled in potassium dichromate solution, sodium dichromate or in hot water, depending on their purpose. These coatings provide a good basis for the application of coatings, adhesives, sealants, etc.. P.
To give the decorative details of the form of the anode-oxide coating prior to filling dye adsorption process in solutions of various dyes or electrochemically in a solution of metal salts.
To obtain a mirror-like luster on anodized aluminum alloy parts, their surface is pre-polished. The reflectivity of anodized aluminum and its alloys decreases in the following order: A99, A97, A7, a6, AD1, AMg1, AMg3, AD31, AD33.
Hard anodic oxide coatings
Solid anodic oxide coating having a thickness 20-100 microns are wear-resistant (especially when using lubricants), and also possess heat- and electrical insulation properties.
Details with hard anodic oxide coatings can be machined.
Properties of anodic oxide coatings
Anodic oxide coatings:
• have a porous structure;
• prone to cracking when heated above 100 ºS;
• prone to cracking during deformation.
Roughness of anodic oxide coating
at sulfate anodizing surface roughness increases by two classes. Chromic acid anodizing is less reflected in the surface roughness.
When appointing anodic oxide coatings, one should take into account their effect on the mechanical properties of the base metal.. Effect of the anode-oxide coating increases with increasing film thickness and depends on the alloy composition.
Anodizing in chromic acid is usually used for corrosion protection of aluminum alloy, containing not more than 5 % copper, mainly, for details 5-6 qualifications (1-2 classes of accuracy).
electrical insulating anodized
An.Oks.eiz coating is applied to make the surface of aluminum parts or aluminum alloy electrical insulation properties. When the insulating anodizing electrolyte recommended oxalate.
Anodic oxide coating provides stable electrical insulating properties after impregnation or application of appropriate paints and varnishes. After impregnation, the thickness of the material increases by 3-7 m, when applying paint - to 80 m.
Resist coating breakdown increases with its thickness, decrease the porosity and increase the quality of the original surface.
scratches, risks, dents, sharp edges reduces electrical properties of the coating.
After impregnation varnish coating insulating resistance the breakdown depends, mainly, thickness of the coating and little dependent on the composition of the aluminum alloy and process of anodization.
Anodizing aluminum alloys with copper
for details, made of alloys, containing more 5 % copper, not recommended for coating and An.Oks.hrom An.Oks.tv.
for details, made of alloys, containing more 3 % copper, not recommended for coating and An.Oks.emt An.Oks.eiz.
Mechanical properties of anodic oxide coatings
Anodic oxide coating has strong adhesion to the base metal; has a lower thermal conductivity, than the base metal; resistant to mechanical wear.
Microhardness on alloys:
- grades D1, D16, B95, Ak6, AK8: 1960-2450 MPa (200-250 kgf);
- grades A5, A7, A99, AD1, AMg2, AMg3, AMg5, AMg6, AMC, AB:
2940-4900 MPa (300-500 kgf).