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darryl
04-11-2012, 11:33 PM
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
04-11-2012, 11:51 PM
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
04-12-2012, 07:53 AM
Many times when I order in 6061 it comes covered on one side.

Ian B
04-12-2012, 08:18 AM
Darryl,

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

Ian

macona
04-12-2012, 08:23 AM
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
04-12-2012, 09:15 AM
6061 with the film pulled off. I also haven't noticed any gulling up when working with 6061.

http://img859.imageshack.us/img859/4088/porsche003.jpg

sasquatch
04-12-2012, 09:40 AM
Nice piece of work there Andy!!

winchman
04-12-2012, 12:20 PM
Seems like ground aluminum tooling plate comes with a protective film.

George Bulliss
04-12-2012, 12:33 PM
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 donít recall milling any of it.

George

Tait
04-12-2012, 02:05 PM
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.

bborr01
04-12-2012, 02:27 PM
Seems like ground aluminum tooling plate comes with a protective film.

Sounds like tooling plate to me too. It is cast to size and ground to finish thickness.

Brian

Evan
04-12-2012, 02:57 PM
It's the "crisp" bacon frying sound that makes me think it is a harder material than 6061. You don't get that with the softer alloys so that limits it to something harder than 6061. That will normally be the 2000 or 7000 series for anything found in an ordinary shop. It is also unlikely to find a ground finish in something that thin so that argues for alclad. Darryl is also near the coast where alclad is used a lot for corrosion resistance.

It is possible to identify the material series with a simple lye test.

Here is an image from a previous post:

http://ixian.ca/pics9/aluminum_id.jpg

The link to this page is:

http://bbs.homeshopmachinist.net/showthread.php?p=267965#post267965

George,

While looking for this post in the forum I found this image on another web site. It is obviously a screen capture from this forum and includes enough identifying features to confirm that. That makes it a copyright violation not only of lbender, the member that posted the image, but also of Village Press.

The location is:

http://inventorsgarage.com/blog4/2011/02/07/identification-of-aluminum-alloys/

It is attributed including a link to the appropriate web page so I wouldn't be upset but it is common to ask for permission. When I posted a link on my site to this forum I asked for permission first. I also only post other peoples images or work with explicit permission unless in the public domain. Material posted here is NOT in the public domain unless explicitly stated otherwise.

George Bulliss
04-12-2012, 03:46 PM
While looking for this post in the forum I found this image on another web site. It is obviously a screen capture from this forum and includes enough identifying features to confirm that. That makes it a copyright violation not only of lbender, the member that posted the image, but also of Village Press.



Thanks for letting me know about this. Obviously, copyright is important for us but for some reason most people think that just because itís on the web, it somehow isnít covered. This guy appears to be simply trying to help, so itís not that big a deal, but I will contact him, as I always do.

Interesting coincidence regarding the author of this test and copyright: I spoke with him yesterday in regards to granting a second use permission for an article he wrote for us a few years back. In this case, a Canadian group wanted to reprint the article in their newsletter. The editor of the newsletter was kind enough to ask before copying Ė something I really appreciate.

The author and Village Press both gave permission to the group to use the article and I passed along a pdf and some hi-res photos to help out. It was agreed that the author and the magazine would receive credit in the newsletter. Village Press often gives permission to hobby groups and schools for reprinting material, but both the author and Village Press need to agree to the use, which can be difficult and time consuming for the older articles.

George