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  for Metal Finishing since 1989
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Wear resistant coatings for A356 aluminum castings

I need a coating recommendation. I have an A356 aluminum casting that is being worn away by a mating thin plastic part (not fiber reinforced) due to vibration. The coating must have a good surface appearance, either black or easily painted black. Redesign of the plastic part may be necessary, but I was curious if anyone had a coating that is both wear resistant and not terribly expensive.

Kirk [last name deleted for privacy by Editor]
1996

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1996

Kirk: There are a number of options. Terribly expensive is a very relative term, virtually no one will agree on it.
1. Chrome plate it
2. Electroless nickel plate it
3. Flame (plasma) spray coating
4. Bright nickel plate it
5. Soft nickel (sulfamate) nickel plate it
These are listed in order of my personal preference with the top working better than the last. Any would probably do for your problem. Cost is going to be who you know or what you can get it done for in your area. If it is only one, you are going to believe that it is expensive. Can you machine it back and screw a piece of stainless steel sheet, at least .030 thick, to it?

James Watts
- Navarre, Florida

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Hardcoat anodize is commonly used as a wear and corrosion coating for aluminum and magnesium alloys. Hardcoating is not plating but rather an electrochemical conversion of the surface metal to a ceramic oxide. As such, it has virtually none of the adhesion problems sometimes associated with plating. On A356 castings a 2 mil thick Hardcoat is naturally dark gray. It can be dyed black for a darker appearance and/or PTFE impregnated for added lubricity. These coatings are also an excellent base for paints or dry film lubricant topcoats.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio

1996

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I think your best bet is still hard anodizing. Even so, A356 as a casting may be porous (is it?) and not very easy to work with, but the result will be exactly what you need: a slippery wear resistant surface.
Max

Max Stein
captive metal finisher - Montreal, Quebec, Canada
1996