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How does Type 2, Class 2 change surface finish on aluminum?

I am a product specialist for a company that makes parts for the automotive aftermarket. I have a question about how the anodizing process affects the surface finish of aluminum parts. We have a 6061-T6 aluminum part are machined to a surface finish of 16 mu and then anodized with a Type 2, Class 2 dyed finish for decorative purpose.

In general terms would the finished surface be the same as the machined surface, smoother than the machined surface, or is there anything about the process that will cause the surface finish to be rougher than the machined surface?

I know it is easy enough for us to do our own tests to see, but right now I am trying to see if there is any general information about this topic and what your opinions may be.

Thanks in advance,

Gregg Nader
Product Designer - Libertyville, Illinois, USA
August 24, 2009

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All tiny imperfections on a polished surface will be very slightly magnified with a Type II 0.0008 inch thick coating.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

August 26, 2009

It is a rare part that does not get rougher during the typical anodize process. Some, but not many, anodizers will use a non etch acid cleaner and a very light acid etch/desmut which will give you a surface quite near that of what you started with. Not many shops have this process.

James Watts
- Navarre, Florida
August 28, 2009