Metal finishing Q&As since 1989

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Hard anodize replacement

dear friend

my alloy is AL7075 AND surface coated by hard anodize, and I want stripping and to add new coating by another method, for example HVOF. this is possible or impossible? process guidance me.what is your offer?

Omran Karami
student - Tehran, Iran
May 12, 2009

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May 19, 2009

Hi

You can strip the HC of your parts by dipping in an alkaline etch for a minute or two, so bubbles start to show. Then rinse and go to the desmut tank. Depending on how good the layer is the part will have to stay there from several minutes to hours :o) You could go back to the alkaline etch just be careful with this solution because it will dissolve your aluminum too.

You have to be aware of your parts dimension will change depending again on the thickness of the layer.

Hope this helps, good luck

Sunny regards
Anne

Anne Deacon Juhl
- - Trustrup Denmark

Alkaline etch is too aggressive to aluminium,try to use a description in "ASM METAL HANDBOOK VOL 5 page 579 solution 5", using a solution of Phosphoric acid 70 ml (9 fluid oz), Chromic acid 20 g (2,75 oz)Water to make 4 L (1 gal) and Temperature of 43 to 65°C (110 to 150 °F) immersion time must be enough to remove all anodic coat, This solution does not attack the aluminium, only remove the oxide layer, in sequence desmut and good luck.

Franz R Wagner
- Blumenau, Santa Catarina, Brazil
June 9, 2009

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June 12, 2009

Hi

If your hard coat is well done, then you need a short time in the alkaline etch or else it can take days to start the process in the desmut tank.

You can go for the suggested solution with chromic acid if you have that in house.

Sunny regards
Anne

Anne Deacon Juhl
- - Trustrup Denmark