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Dust-like Specks, Water-like Spots After Timesaving

April 30, 2012

Q. I recently took on a position running a very small shop which produces machined 6061 aluminum luxury goods, with a line of different time-saved and electroplated finishes. The plated colors are extremely reliable. The anodized colors.. are not.

Our gold will be tan one day, a dark brass the next.
Anodized hard grey will vary from a flat, dull color to something like salt and pepper.
Black and clear are our only reliable ones- and they're susceptible to their own special issues.

First is something we call spotting or 'water spotting'. We developed a process of surfacing our blanks with a 5" face-mill before anodizing or plating- it makes the spots in material very visible, so we can sort stock into piles for electroplating, which covers the defects, and anodizing, which requires stock free from the defects. I'd like to, instead of relying upon a hack, set up a supply of material free of this defect. Right now it's 6061 from Kaiser. I've heard ALCOA is a little more reliable, and that various other alloys are better for anodization, 6063, 5xxx series, etc- but an opinion from these forums would help me out a lot.

The second defect is more recent, and we haven't yet determined its source. It's light, small specks of dis-similar material, seemingly under the anodization, and only appears after anodization. A colleague thinks it's steel, stainless, or something other than 6061-t6 being embedded into our parts when they're run on the timesaving machine. I wonder why it reoccurs on the machined side of parts after stripping and re-anodization. Evidence points to both timesaving and anodizing; an expert opinion would be very helpful.

I suspect that a higher quality of aluminum will solve both of these issues. I also suspect that it'll be out of our price range, at least in the small quantities we need it in.

Water spotting


Michael Vroegop
machine shop employee - Fort Lauderdale, Florida, USA

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