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-----Pretreatment of 6061 aluminum
I am trying to get a even finish on aluminum parts made from 6061 bar stock that will be plated.
The part comes with the surface finished (jitterbugged to be even). the parts are cleaned in a hot 140 F soak for 30 min hot rinse and then etched in 10%HF 20%nitric 80%H20 for 30 seconds. this is where I am having a problem. I am getting marks on the surface that look like a tire tread pattern, not in the same area on each part and they seem random on the part. I have refinished the parts and repeated the process and get the same results is there a process I can add to stop of remove this or is this something in the aluminum and can this be changed.
thanks,
surface finishing - Charlton, Massachusetts
2006
First of three simultaneous responses -- 2006
Possibly, 'checking' from poor control of the extrusion process. Suggestions:
Try different etches (e.g., caustic) or mechanical finishing, as your present etching accentuates the problem.
Try a different batch of extruded 6061 stock.
Try rolled or cold-finished bar stock (ASTM B211), which has a better surface finish.
Also, Al 6063 gives a better appearance, although at lower strength for a given temper.
- Goleta, California
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Second of three simultaneous responses --
Do the parts ride on some sort of conveyor, or belt that has the same pattern? It is possible that the parts are picking up some kind of coolant/ oil that is not coming off in the soak cleaner. Titrate out the cleaner make sure its up to the correct concentration. and try it again. It sounds definitely like a surface prep problem.
Ryan Cook
Toccoa, Georgia
2006
Third of three simultaneous responses --
Perhaps there is a "weathered" oxide on the surface that is not uniform, then when you etch it builds a shelf. In order to get a uniform surface for the etch to start on, then try deoxidizing before etching. Otherwise, change aluminum company suppliers.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
2006
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