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Is this hard coat look and feel okay?

Hi,

I have some 6061-T6 parts hard coated and they came out very dull, as 400-600 grit sandpaper.

The color is dark grey ans in not uniform, as is it was badly spray painted.

What arguments can I use or should I just accept the job?

Eric Girard
product designer - Montreal, Quebec, Canada
2007

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It's hard to tell from a verbal description, but when you make an analogy to sandpaper, I think of "burning". A picture would be a big help, although I can't guarantee that it be enough -- but my feeling is that the parts are probably burned and not satisfactory. This can be caused by a current interruption (especially if the anodizer is anodizing by voltage), too much current, or a localized failure to cool the area in question. It is evidenced by a granular look and feel in the area of the burning. That area will not wear properly, the burned area will wear or flake off.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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First of two simultaneous responses --

You send out hard coat to 5 job shops, you get back 5 different shades of light gray to dark gray depending on temperature, current density, acid concentration, thickness, dissolved aluminum and alloy.

Darkest gray comes from lowest temperature, highest current density, lowest acid but is influenced by dissolved aluminum and alloy.

Your description does not indicate any problem with the coating. It seems most top quality, the darker the harder and more abrasion resistant.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

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Second of two simultaneous responses -- 2007

Thank you for the investigation path.

Would burning also cause an un-uniform color?

The part with the most features, many faces measuring 3x3in, is very bad for color.

But a larger, 10in flat doughnut shape part does exhibit the problem to a lesser extent.

I was also suggested two other possibilities by someone:

Either the parts may have had a poor electrical contact. A large part, 6 to 9 in long, would need to have more than one electrode connected to it.

Or they were reworked by the plater.

I do not think the parts were glass bead blasted, the edges are not that dull and we can see some tool marks. But I am still investigating.

Eric Girard
- Montreal, Quebec, Canada