mysterinum

[darryl]

I went into a shop today and asked for some aluminum scraps, a few thicknesses just for projects as they arise. One thing I got was some 3/16 aluminum plate, which has a protective sheet on one side. Not knowing what alloy it was, I milled an edge and drilled a hole. Nothing stuck to either the drill bit or the endmill.

When drilling, it gave a crisp sound like maybe there's some temper in it.

Now that I know it's not gummy, I'm wondering what alloy it might be. Is there some alloy that's commonly protected on one side that a (non-aerospace) shop might be likely to have on hand?

This piece has been sheared, not sawn, though in this thickness I think 6061 is also sheared.

I suppose I could saw off a test piece and do a bend test on it- I know 6061 doesn't like to bend well, so that would tell me right away if it is or isn't 6061.

I've given it the dimple comparison test to a known piece of 6061T6, and it's very much the same- possibly a tad softer.

Anyway, no big deal. Just wondering what it might be.

[Evan]

At that thickness it will be difficult to do a meaningful bend test. Since it has a protective sheet it sounds like it is alclad. The protective sheet prevents scratches in the cladding. The cladding is a couple of thou of pure aluminum to prevent oxidation of the alloy. If it is scratched that breaks the protection. When making skins for aircraft a scratch is enough to scrap the part.

2024 is the most common alclad alloy and it is between 6061 and 7075 in strength. It is about the same strength as mild steel in the same thickness. It machines beautifully, nice and crisp with no burr even without coolant.

[vpt]

Many times when I order in 6061 it comes covered on one side.

[Ian B]

Darryl,

We have a very similar material in the UK. Here, it's called mysterinium

Ian

[macona]

What does the shop normally make? That is always a good clue to what the material is.

Might be 7075. It machines a lot like steel in some ways.

[vpt]

6061 with the film pulled off. I also haven't noticed any gulling up when working with 6061.

[sasquatch]

Nice piece of work there Andy!!

[winchman]

Seems like ground aluminum tooling plate comes with a protective film.

[George Bulliss]

Seems like ground aluminum tooling plate comes with a protective film.

Fixture plate (or tooling plate) was the first thing I thought of. A quick check on Speedy Metals reveals that it is not a standard alloy such as 6061, 2024, etc. The stuff I used in the past drilled and tapped very cleanly but I don’t recall milling any of it.

George

[Tait]

There's a similar thread here.

Fixture plate (or tooling plate) was the first thing I thought of. George

Me too. I was just reading the specs at my local metal supply on Mic-6 vs 6061 - the Mic-6, if I recall correctly, had a slightly lower density than 6061.