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Finishing ALMAG-535

We are Casting Aluminum-Magnesium Alloy-535. After casting we are to surface finish the product as it looks like Zinc Plated. But in vibratory polishing machine finish turns to Grey tone instead of whitish. Need to know what process to be adopted to get whitish tone like Zinc Plated smooth surface.

Thanks,

Garin Gujral
Casting - Exton, Pennsylvania, USA
2003

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First of two simultaneous responses --

It sounds as if you have a liquid problem. Meaning the chemical compound may be having a reaction to the metal. Normally I recommend a plastic media preform shape and a slightly acidic compound; however, this can be done with ceramic and a basic compound. The most important factor is to have a good flow through system to flush the media mass.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2003

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Second of two simultaneous responses --

Magnesium is gray. Aluminum is a "whiter" gray. Most 835 castings are of non-homogenious mix and spots of magnesium interfere with the final cosmetic appearance. If you want a "zinc look" here is an idea I have cherished for 20 years but have never found a commercial application, perhaps you have. Note that the matrix of the alkaline zinc plating processes sold by the many supporters of finishing.com is the same as the matrix for a zincate immersion plating on aluminum system. A process for a "zinc look" then would be to prepare the surface of the aluminum as: Clean, CWR, ETch, CWR, Deox, CWRx2, Now dip in any proprietary alkaline zinc plating solution and wait 45 seconds before turning on the d.c. power, turn it on at the very lowest voltage and very slowly raise the current up to about 10 or 20 ASF. Now you have bright zinc plated aluminum. Let us all know if this idea suits your needs.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003