The Stovebolt Site Forums The Shop Area General Truck Talk What is that metal?

Working on various old trucks now, I've noticed there can be a big difference between what type of metal trim is used outside a vehicle as well as inside.

So, how can one tell the difference between aluminum and stainless parts? I'm no metalurgist by far, and I have seen some pieces off my '72s that I couldn't decide what they were made of?

Dull stainless can look like aluminum to me. Polished aluminum looks far different than dull. How do you tell whether or not a piece is just chromed pot metal or not if it's 60 years old without pitting and it's non magnetic?

There are various clues that are pretty easy to see, but I've ran into some odd ones with one person telling me it's aluminum and another stainless. Obviously corrosion damage, pitting, staining and patinas are indicators depending on the how and whats involved.

What about the stuff your not sure of?

Thanks, Jeff

Boy, I thought I could answer that. And, the more I thought about it, it's not that easy. I can tell the difference, but it is not easily described. A few clues: Stamped aluminum parts are soft, check an edge. Easily burned with hard buffing. Cast aluminum will have casting marks on back. Stainless is tough, and you can buff it easily (you can overheat it, and damage it, but not like aluminum.) It's rarely cast, will be stamped. Pot metal parts will be die cast, not stamped. And mostly chrome plated, but I'm sure there exceptions. Usually used for decorative emblems, ornaments, etc. Newer cars used anodized aluminum trim (thinking my '62 Chevy) and little, if any stainless. Emblems were chrome plated die cast pot metal.

You can tell aluminum by putting a flat file to an edge. Aluminum will file very easily, stainless will not.

another way would be to touch a magnet to it. a magnet won't stick to alumimim.

Stainless can go both ways according to alloy, magnetic or not.

As a metallurgist and a car guy, you asked a really tough question to explain.

It's always a good idea to touch it with a magnet, that can rule out aluminum and many stainless steels if it isn't magnetic.

As was already mentioned, you can tell the difference in the way the parts are formed. A stamped part on these trucks will most likely (although not always) be stainless.

As far as pitting, Aluminum is very resistant to corrosion damage, so if the part has corrosion or pitting it's more likely it's stainless steel or pot metal.

It won't stick to higher quality stainless either.

It depends on the specific stainless steel alloy as well. And if an austenitic stainless (say 316) is cold worked (like stamping, for instance), it can become magnetic.