Mystery Grade of Aluminium

Hello all,

Bit of a vague one, this. I picked up a few sizeable aluminium plates out of my dad's shed a while back (and stripped another he had been using as the bed on a home-made table saw. Trust me - that thing is better off dismantled). 12mm thick, heavily patinated, had probably sat there since the late 70's/early 80's. My dad passed a few years back and probably couldn't have told me the grade with any certainty - but there was a story behind the metal: surplus material from a tank armour plate project that was cancelled.

The stuff cuts beautifully - I mean, like 120 brass. Barely gets warm, chips well etc. Just love working with it. It's strong too - not as hard as 7075, but very non-ductile.

I'm familiar with cutting other regular grades (6082, 2014, 7075) and none of 'em cut like this - so I'm curious. I've seen the term 'free machining' aluminium used somewhere before. I assumed this just meant 6082, but seeing the difference between the two materials has got me scratching my head.

I know that 6061 is a grade often seen as the US equivalent of 6082 (of course, it's not - it's a grade all of its own) and I think it might be that, but I've never managed to buy 6061 off my usual supplier (Smiths) - they don't stock it, and I've not found any UK suppliers that do.

Any other suggestions as to what this mystery metal might be? One day (still a long way off) I'll need more...

Wal.

Air portable tanks and armoured vehicles were still a thing back in the 80s when we were still galavanting around the world saving everybody

The scorpion tank for example

The military are always trying to make things lighter and better

(Apart from the guys who make Humvees)

From the link

Armour

Edited By Ady1 on 24/09/2022 10:36:18

Thanks for that Ady,

Very interesting - a likely candidate, I reckon. Thickness in the ball-park and it's heavy patina and non-ductile nature could be commensurate with the reference to SCC... Time frames would match, too. Great info, thanks again.

Wal.

A quick google will unearth a surprising amount of data on aluminium armour.

The CVRT (Scorpion, Scimitar, Sultan, Spartan, Striker et al) were made from 7059 an aluminium-zinc-magnesium alloy. But there are many others with widely different performance and machinability.

Generally aluminium armour materials are cold worked to stabilise and enhance the material properties. The big no-no is age hardening and at least acceptable welding properties are essential. The materials are usually not very responsive to heat treatment.

Clive

Edited By Clive Foster on 24/09/2022 11:53:58

Many thanks Clive,

Yep - I wasn't being lazy, I did peruse the google and found a few bits and pieces of interest, just thought I'd interrogate the ME hive-mind to enlighten me further. 👍

Wal.

I've got a few bits like that from Fokker planes its beautiful stuff to work with and I would presume plenty strong enough for any job in the model world. I made a 0.5 cc crankcase from one of my bits and works well.