I recently received an order of extruded aluminum strip 3/32" thick that supposed to be 6061 hardened to specification ASTM B221. However, when we tried to bend it, it broke and the interior looked like cast zinc coated with aluminum. Is 6061 supposed to look that way and be unable to bend 90-degrees?
How can I verify that I have solid aluminum and not some fake alloy with zinc in it?
I figured out a simple test.
Since the density of 6061 is 2.5 g/cm3 and the density of zinc is over 7 g/cm3, all I had to do was measure the density of the material.
This showed that indeed it was aluminum. So, its brittleness is probably just because it was hardened.
You can confirm the alloy and heat treating condition by measuring conductivity. It's like a fingerprint for any given combination of alloy composition and heat treatment. Reference values can be found here, for example: https://content.ndtsupply.com/media/Conductivity_Al%20Reference%20Chart.pdf
If you are faced with this task more often, you might want to get a eddy-current based conductance measuring device (eg. "Fischer Sigmascope"). As far as I remember, they are not exactly cheap (around $3000), but very reliable and can even measure through paint or metallic coatings
Unlikely you have anything except aluminum alloy. What is the heat treatment supposed to be ; what grades are offered in the spec? On the net, I see reference to T-5, that is- as extruded, then aged; lowest cost high strength option. I see elongations around 10% in ASM ( vol. 2, 8th ed.), so, depending on radius, it could easily fracture in a 90 degree bend. I expect a relatively rough grey, granular fracture surface at that limited ductility. Solution anneal and age T-6, should be slightly more ductile. You may need a larger bend radius and heating would help.
The standard simple test is to do vickers hardness testing, at a fixed load. the HV should be specified for the material and condition. I'm assuming you are using something like 6061 in the T6 condition. Random online papers suggest that the hardness should be 95HV (load not specified).
Your density test won't tell you too much about the Al grade, as the alloying elements are usually dilute, so don't change the overall weight to more than a few %.
The more complicated ways to confirm the material is to do either XRF, EDS or wet-chemical testing (in order of increasing cost), which can be used to confirm the chemistry, but not the mechanical properties. XRF and EDS are quick to do, but all these things require specialised equipment.
When you say that it wont bend 90*, you've not specified the important parameter, which is the bend-radius, and how it was bent. A two point bend-test and a three point bend-test will give different results for cracking, as will whether you do it at low or high temperature. If you do it at high temperature for any period of time (>150C) then you will likely invalidate the material condition by forcing ageing, and internal precipitation.
