Abstract: A method for testing and determining the alloy class of an aluminum alloy may be simply and easily carried out, for unequivocally determining the correct alloy class among the aluminum alloy classes 2XXX, 5XXX or 6XXX, and 7XXX, of the test sample. According to the method, the material sample is dissolved in hydrochloric acid (HCL) to prepare a first solution, then nitric acid (HNO.sub.3) is added drop-wise to the first solution in order to cause oxidation of any insoluble copper (Cu) therein and form a second solution, then a potassiumhexacyanoferrate (II) solution (K.sub.4 ?Fe(CN).sub.6 !) is added to the second solution to bring about a discoloration and precipitation reaction and form a final resulting solution. Finally, the applicable alloy class of the tested material sample is determined by visually categorizing the color and precipitation state of the resulting solution.