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Simultaneous etch-passivation solution for aluminium pretreatment

Q. Hello!

I am in powder coating business. We used to coat ferrous metals only in the past and the standard pretreatment method prior to powder coating was either sandblasting or mechanical roughening.

Right now we're planning to dedicate one coating line fully to powder coating of aluminium extrusions. Having consumed a lot of information on this forum and elsewhere, I am aware that chromate conversion coating is the best way to go in terms of aluminium pretreatment.

Unfortunately, due to certain laws and restrictions it is very difficult to built a dipping pretreatment line that has anything to do with Chrome VI. At least in my area.

Recently I came across a Henkel solution called Bonderite MN-T 2040 R2. it is a chrome-free process which contains hexafluorotitanic acid. It is marketed as a solution that offers one step etching and passivation. Standard example of its use is "Alkaline Cleaning -- Rinse -- Demi Rinse [ed. note: presumably '2nd rinse'] -- Etch-Passivation with 2040 R2 -- Rinse -- Demi Rinse.

An alternative example of its use proposed by Henkel is "Cleaning and etch-passivation with 2040 R2 with the addition of a Henkel surfactant Bonderite C-AD D-4 -- Conversion coating seal with pure 2040 R2 solution -- Rinse -- Demi Rinse". Official Henkel representative stated that indeed it is possible and tested, although the first bath needs to be heated to 30-40 °C and should ideally have ebullition [ed. note: presumably 'air agitation']. Other baths can be at room temperature and without ebullition.

Of course I am more intrigued about the second scheme, because it cuts cost, has less stages, water consumption etc. The aluminium that is going to be coated comes pretty clean (no oil or grease whatsoever), just oxidized aluminium. I want to ask you how viable and realistic does this sound to you?

Before this I have not heard about solutions that can offer one stage etching and conversion coating. Furthermore, with a surfactant this magic solution is marketed as a mild degreasing/etching/conversion coating 1-2 stage process without the rinse in-between.

Henkel is big name in industrial chemistry but.... Should we be wary?

Waclaw Kazarnowicz
Shop employee - Rzeszów
November 7, 2024