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.