How to test aluminum type

How To
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I have access to a decent scrap bin of aluminum from work. Nothing huge, but a lot of pieces I could use to make hold downs and small brackets for the mill. The trick is, all the off cuts are random and not labeled in any way. Is there any trick to determining if the aluminum is good for machining? I was thinking a hardness test, harder being better, but wasn’t sure how reliable that would be. Maybe just come up with a small slot mill procedure to do on all the pieces and grade them based on how it looks. Thoughts?

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I would try facing or squaring up the most ragged edge.

Do you know what types of aluminum are sourced by your company? For what purposes were the parts these off-cuts came from used for?

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1xxx series have an earthy taste.
2xxx series tastes tangy.
6xxx series are kind of sour.
7xxx series have a spicy kick.

I haven’t tasted any 5xxx series yet.

(please don’t lick the aluminum)

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Mostly aerospace and electronics, so I am guessing they are not cheese grade aluminum.

I was thinking that making some standard cut and taking a judgement call from that was the most reliable.

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Some notes from the (now off-line) Shapeoko wiki which may be of interest.

There is at least one company which colour-codes their aluminum:

http://www.westlakemetals.com/opencms/export/westlakemetals/downl/METAL_COLOR_CODESa.pdf

A further consideration is whether or no the material has been heat treated.[https://www.reddit.com/r/Machinists/comments/3k8lgj/are_there_material_pairs_where_one_is_inexpensive/cuxkc89]

Brinell Temper:

(Note that these denote a tempering ‘‘process’’ rather than a specific Rockwell hardness[2024-T3 Aluminum Cutting Question - #3 by DanoInTx])

  • 0 = Fully annealed (soft)
  • H## = Strain hardened (medium)
  • T# = Solution treated (hard)
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This is horribly subjective but I have observed working with different grades of Aluminium that I’ve purchased or found at the back of the garage that there are a some fairly discernible differences between

  • Type 1 - Aluminium that will machine OK on my Shapeoko
  • Type 2 - Aluminium that will gum up the cutter and be a pig if I don’t use lubricants

Which are

  • Thin sheet (3mm or less), bend a small piece around a sharp angle, (I use a small bender) if it is reasonably ductile and bends to somewhere near 90 degrees without fracturing like a hard cheese around the outside, it’s probably type 2 gooey
  • File the edge with a coarse file, if the file really digs in hard and you have to wire-brush the Aluminium goop back out of the teeth, the same is likely to happen on your CNC, if the file tends to skate a little and you get powdery filings it’s probably harder (a side note, I’ve found that using a tool wax on my files after cleaning and brushing helps get the Aluminium goop out later)
  • Pull a deburring tool along an edge, Type 1 harder stuff will tend to need sustained pressure, Type 2 goopy muck will dig in like a chisel in the grain.

Sorry, these are all really subjective, none of them are reliable indicators but if you’re just sorting through a scraps bin one of these might help before you put it on the machine and discover that you need lubricant or air blast to get a reliable cut. None of these methods tells you anything about the metallurgy, whether you can weld it, whether to anneal it for bending or anything else you’d know if you knew the alloy.

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This is really helpful, thanks. I was thinking about the file test you suggested and am glad you have had some success with it. I might need to find some known gummy aluminum and do some of these tests to calibrate myself.

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It’s also worth watching and listening to the machine pretty carefully at the start of a cut on unknown material, there’s a quite characteristic ‘thud thud’ sound that comes from a gummed up flute on a cutter (or gummed up tooth on the table saw). If you get to it quickly you can frequently save the cutter. The change from a happy ‘brrrrr’ cut to the thuddy lump of a clod of melted on Aluminium whipping round is quite distinct once you’ve heard it.

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