Im a great fan of this technique. Seen countless $$ wasted identifying aluminum alloys with alternate means. Words of warning, there are other alloys that will result in false results. Avoid testing Aluminum leading edges, cowl skins, or aluminum alloys associated with high temperatures. (There is a higher probability these alloys are neither 2024 or 7075) Also need to ensure the clad material (alloy 1100) has been removed from the test sample (2024 or 7075). Note that this method will only identify the alloy and not the temper.

Cadmium Sulfate Soln: Mix 5 grams of cadmium sulfate (CdSO4),5 mL of concentrated Hydrochloric Acid (HCl) and 3 grams sodium Chloride (NaCl). Dissolve and dilute with distilled water to make 100ml of cadmium sulfate soln.

Sodium Hydroxide Soln: Disolve 25 grams of sodium hydroxide (NaOH) pellets in 100 mL of distilled water.

Use an eyedropper & place a few drops on bare (Alum) metal surface. If the soln remains clear then it is 2024. If the drops turn black (or black flecks form inside the drop) then it is 7075. You can confirm 2024 by adding a drop of Sodium Hydroxide soln on an adjacent bare location. If the clear drop turns black - then this confirms that this is 2024. A white color would indicate Clad (1100) series.

Last note: If this test is to be used in a Unionized environment, Keep the Health & Safety people updated. They get paranoid when the hear "concentrated HCl" or acid.

We use this test as an acceptable method for identification of items such as clips, gussets, smaller items not clearly identified in the IPC.

Quote (edmeister)

Last note: If this test is to be used in a Unionized environment, Keep the Health & Safety people updated after the test is finished.

Fixed that for ya
I am certain that edmeister knows, all too well, that the probability of a test being successful is inversely proportional to the number of people watching it.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

Wonderful !!
This is exactly what I was looking for... having a simple and easy way of identification for secondary structure parts.
Many thanks again edmeister for your clarification.

Sparweb .. appreciate the help ..
but just want to relate how difficult it was to have these solutions mixed (outside the company) and brought into use with the floor technicians.
I am not against safety; but i had to spend about 6 months emailing the H&S rep arguing that a couple of eye-dropper bottles will not endanger the entire company. Everything from storage, education, emergency procedures, reordering procedures had to be addressed for these small quantities of soln.

FYI for aluminum alloys...

Alloy ID is important... but so is temper ID...

DOD-HDBK-249, METALS AND ALLOYS, RAPID ON-SITE IDENTIFICATION OF (RECOMMENDED PROCEDURE FOR CHEMICAL SPOT TESTING AND ASSOCIATED PHYSICAL TESTS TO VERIFY METAL ALLOY CLASSIFICATION)

AMS2659 Hardness and Conductivity Inspection of Wrought Aluminum Alloy Parts

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

Great... I already checked that reference from your previous post.
Really helpful and lots of information.
Thanks again.