Topic: Etching Aluminum

Can someone in the Finishing Talk Community help me understand why we use different products to etch aluminum.   Composition varies from sodium hydroxide to nitric acid plus ammonium bifluoride.... and I have seen other compositions.

My question is what are the differences and how do I know which are more suitable for a certain aluminum types?

Thank you


Re: Etching Aluminum

Hi Jack

Great question.

What we like to do during the pretreatment is to prepare our aluminum surface for the anodizing, plating or painting.

So what kind of etching to choose depends mostly on two things, the visual appearance you need on the end product and what kind of aluminum alloy you are processing.

Alkaline etch is right now the most common used and gives a matt finish, which depends on the process time, temperature and ratio between aluminum and hydroxide. This kind of etch creates a lot of sludge, due to the high dissolution of aluminum (10g/ft2).

Acid etch with fluoride gives an even more matt surface and it attacks all the alloying elements on the aluminum surface. The etch rate is 1 g/ft2 and you will have a reduction in etch time.

Two things to remember with Acid etch is; it doesn´t remove Al2O3 so you have to have an alkaline tank to clean your racks, and second Titanium racks are attacked by the flouride in the solution.

Both types of solution can be used for all kinds of alloys but the acid etch will do a better job with the heavy alloyed aluminum parts, specially the high silicon and copper alloys.

Please let me know if you need a more in-depth explanation about the etching process.

Sunny regards



Last edited by AluConsult (10/11/2009 - 02:31 PM)


Re: Etching Aluminum

Thank you Anne.

So if i understand, acid etching is used on alloyed aluminum because it removes the "contaminants" (Si, Cu, Mg...) like the 6000 series.

Alkaline etch would be more suitable for cast alloy's 100 series ?

what are the differences of using nitric acid or sulfuric acid ?

I would be very interested to have a more in-depth explanation on how the etching works or if you can reference a book i would be very grateful :)