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Anodizing process to match silver matte

January 16, 2009

I am aluminium anodizer from India. We get enquiries of anodizing from overseas and also from local market. Many times a customer comes with a sample of his desired finish which is generally been anodized in european nation. After our many trial and error method we have failed to achieve that finish.
Does anodizing process and technique varies from region to region. Do the method of anodizing in European nation and India is different, or am I going wrong somewhere?
I am specifically asking about silver matte finish.

Sumit Lodha
aluminium anodizer - Ahmednagar, Maharashtra, India

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First of two simultaneous responses -- January 20, 2009

Hi Sumit,

Particularly when we are talking about Cosmetic Finishes, it depends on your alloy, the pre-treatments chosen, the basic component condition like pressed,its shape, buffed, etc..

To the large extent we can play with the pre-treatments.
I would like to share my experience in developing a matte silver finish. Components were of 3XXX alloy, (Mn - based). We etched the components using Ammonium bifluoride solution (2-3 min) and then chemically polished for about 30 sec to 1 min, we could get the desired finish. I hope this helps, Good luck!

Keshava Prasad M
- Chennai, Tamil nadu, India

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Second of two simultaneous responses -- January 20, 2009

Sumit,

The actual anodising process varies very little the world over, but there are many variables that can affect the colour you get from your anodising.

The alloy type will go a long way to getting a clear coat. If you want it matt then a quick dip in a caustic etch or a wet blast will dull the surface sufficiently.

Do you have temperature control on your bath? Most commonly seen is a temperature of 18-22C, although on occasion I have seen other temperatures used, but not much different.

Your bath chemistry may also be a factor. Try raising or lowering your acid content to see what effect that has.

You could also do with getting hold of a couple of reference books that will be able to talk you through the process more constructively than an open forum such as this. Try "Aluminum How To" by Robert Probert and/or "Surface Treatment of Aluminium" by Sheasby and Pinner.

If you are still struggling you want to consider getting in the services of a consultant, who will be able to see exactly what is happening on site and may therefore be able to suggest cetain changes to obtain the colours you require.

Brian Terry
Aerospace - Yeovil, Somerset, UK

This does sound very much like a special type of etch. It is a common issue among competitive anodizers to produce a special finish. It's impossible to say how to produce a particular finish without seeing the part.

Leo Herringon
- Grand Rapids, MI, USA
February 3, 2009

Simple answer for your problem is ammonium bifluoride etch and anodize for short time with solution temperature at 60-70. degree. hot

Mohammed Shamsi
- San Diego, California, U.S.A.
February 5, 2009

Tell me your sequence of processing and parameter to get silver matte or polished finish.

ABOOBAKER CHUDESARA
ANODIZING/POWDER COATING CHEMIST - Lagos, Nigeria
May 14, 2011