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Extrusion cosmetic issue crystallization after anodize

I have problem on extrusion which is extruded with AL6082 after anodize process it show shiny surface like crystal.My factory have to manufacture on Al6060,6061,6082 and 7003 the crystal was occur on AL6082 only sometime it's good some time is bad.

Somebody can please advise how we solve the problem.


Thank you

Nakaret.

Nakaret Ruksataya
Product - Thailand
November 23, 2009

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Extrusion causes enlargement of the grain size. Any operation that etches the surface will show the grain boundaries. I suggest that you do not etch at any time in the process. Or at least very mild etching if necessary.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
November 24, 2009

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Thank you very much, Don; at this moment our Anodize process do etching 8 mins can you please advise what is proper time which is can solve problem

Thank you.

Nakaret Ruksataya
- Thailand
November 29, 2009

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November 30, 2009

Coarse grain appearance may be unavoidable because of the grain structure of the aluminium. But it often arise from the presence zinc or other metals in the alloy. The effect is frequently called "galvanising" or "spangling". Possible cures include:-

1) Shorter immersion times in the etch followed by desmutting and reimmersing in the etch until the desired degree of etching is achieved.

2) Adding 10 to 50 g/l sodium nitrate ⇦ this on Amazon [affil link] or nitrite to the etch.
Note: this will result in the evolution of ammonia ⇦ this on eBay or Amazon [affil links] during processing.

3)Adding 1 g/l sodium sulfide.
Note: there will be a distinct smell of hydrogen sulfide.

4) Some proprietary etchants contain sulfur compounds which decompose to form sulfides which do the same job as (3). There is less smell, sulfide is only produced during etching, but in my experience are not as effective.

Harry Parkes
- Birmingham, UK

8 min is a long etch for most Al cleaners. Concentration and temperature are the other factors. Unless you have a customer that needs the heavy etch to hide surface blemishes, I would try different times, concentrations and temperatures in the lab to see if there was a better option for the same chemical.

James Watts
- Navarre, Florida
December 1, 2009