Anodyne Exempt Chromium
Chemical conversion of aluminium
This definition refers to aluminium chromium plating carried out with chromic solutions and to chemical oxidation of aluminium with non-chromic solutions.
The conversion layers take on different colour, depending on operating conditions.
Corrosion resistance is an inverse function of the iron and copper content.
The average electrical resistivity of a yellow film is low enough for earth-connections use in many applications.
The conductivity of the films for radio frequency currents is high enough, allowing use for waveguides and the like.
This ability of chromate films on aluminium to resist corrosion well without losing much conductivity allows them to be used in the field of electronics. When reporting the main data on chemical oxidation of aluminium published by I.S.M.L., we mainly refer to the M.B.V. process, which can be applied to pure aluminium and aluminium alloys that do not contain copper.
With reference to the Italian practice, therefore, alloys such as Aluman, Anticorodal, Peraluman and Silumin can be applied to the M.B.V. process.
A magnesium content higher than 2% in alloys, leads to some drawbacks in the practical application of this process, as well as to some irregularities in the characteristics of the obtainable oxide layers.
For alloys such as Peraluman 35, Peraluman 50, etc.., where the magnesium content is respectively 3.5%, 5%, etc.., a M.B.V. bath with a slightly different composition from normal can still be used, as we will see below.
When treated with the M.B.V. process, copper alloys such as Duralumin, Ergal, and Duralite, provide an excessively soft and not very consistent oxide layer that, even when subjected to further hardening, cannot offer the same protection that can be obtained with pure aluminium or with the previously mentioned copper-free aluminium alloys.
Some commercial names of products used for aluminium surface conversion and passivation are Surtec, Alodine and Iridite.
We carry out the surface conversion of aluminium and its alloys according to Directive 2002/95/EC (RoHS directive) which provides for the exemption of chromium, such as Fluorine zirconium plating and conversion based on titanium salts.