Metal finishing Q&As since 1989

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Incomplete Anodizing Coverage

September 21, 2009

I'm having a problem anodizing.

Parts are machined from AMS4027M material and then all the required NDT testing (FPI)is completed and the part are sent to be anodized.

The anodize source then pre-cleans non etch), this is producing a residue "white streaks" on the parts. This residue then acts as a mask during the anodize process.

If the residue is not removed the parts have incomplete coverage. If the residue is removed (by polishing)the parts anodize fine.

   

Testing has been done for a acid based pre-clean and the results are the same, incomplete coverage. The only thing that appears to work is hand polishing with scotch brite or media blasting as a surface preparation.

Tech info:
Material - AMS4027M
Processing Specs:
ANODIZE PARTS PER AMS2471
PROCESS COMPLETION PERMITTED PER MIL-DTL-5541 [on DLA] CL-1A OR AMS2473 .

Scott Haenel
Manufacturing Engineer - Ohio

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September 22, 2009

Interesting problem. I will guess that the problem is generated by the FPI chemicals.
I would try vapor degreasing noting that aluminum fines are very bad for most common halogen solvents.
Second, I would look into a tumbling process trying several different additives and possibly a higher liquid overflow.

James Watts
- Navarre, Florida

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If you mean a wrought 4000 series alloy, it is not commonly anodized because it is about 8.9 % NON-aluminum of which 7.5 % is silicon.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

October 16, 2009

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Three possibles 1- the cleaners may not be "etch" but high concentrations and or temperatures will cause etching 2- poor rinsing and drying of the part will cause a residue to form prior to anodizing 3- try a nitric and fluoride dip to remove this and see the results.

Drew Nosti, CEF
Anodize USA

Ladson, South Carolina

October 21, 2009

Thanks for all the suggestions. I'll look into them and post back my findings.

Scott Haenel
- Ohio
October 26, 2009