Chromating and Cr-free treatment of aluminium

1. Characteristics and properties

Average 1-2 µm thick coatings are produced on a cleaned aluminium surface.

Metoba offers 2 variants:

1. transparent, Cr-(VI)-free passivation of aluminium

The colour varies from silver white to milky white and depends on the layer thickness produced. The coating complies with DIN 50935-2, coating type A and meets all requirements of ELV (Directive 2000/53/EC), RoHS (Directive 2011/65/EU) and WEEE (Directive 2012/19/EU).

2. yellow chromating of aluminium

The colour varies from a pale yellow tone to a dark yellow tone with strong iridescence, which also depends on the layer thickness produced. This surface is not Cr(VI)-free and therefore not RoHS compliant. The chromate layers produced are conductive, which is not the case with anodising or anodising of aluminium. Since yellow chromating of aluminium is a purely chemical process, the layer structure is identical at all points of the workpiece. Of course, this also applies to recesses, bores and threads.

2. Benefits and areas of application

The chromating or passivation of aluminium is a predominantly technical process with subordinate optical significance. Yellow chromating of aluminium provides a very adhesive and absorbent primer for subsequent painting with both water- and solvent-based paints. A further advantage of this process is the preservation of the dimensional accuracy of the workpieces, as the layers produced are only very thin.

3. Basic material

For the yellow chromating or passivation of aluminium, almost all aluminium alloys are suitable, both from mechanical processing and from gravity die casting and die casting. In rare cases, pickling of the workpieces can be dispensed with in order not to alter the dimensional accuracy and surface quality.

4. Required delivery condition

The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with conventional aqueous alkaline degreasers. Oils containing silicone, alkali/alkaline earth and high-pressure additives must be avoided at all costs.