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.