Cadmium-Sulphate solution testing method

Does anyone would know the composition or concentration of Cadmium-Sulphate solution for identification of 2024 or 7075 aluminum?


I’m 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: Dissolve 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.

Above is a snippet.