How can one distinguish between aluminum and aluminum alloy?

Distinguishing between aluminum and aluminum alloys can effectively be accomplished using a caustic soda solution. Aluminum alloys typically contain other metals such as copper, magnesium, or zinc, which can react differently to caustic soda compared to pure aluminum.

When a small sample of the material is tested with a 10 percent solution of caustic soda, a visible reaction will occur if the sample is an alloy made of metals that react. Pure aluminum tends to resist corrosion better and may show little to no reaction, making this method a clear indicator of the material’s composition. This allows for a straightforward and effective differentiation between pure aluminum and its various alloys based on their chemical reactivity.

Visual inspection may not show clear differences, as both forms can look quite similar, and weight comparison alone does not provide enough information since many alloys can be very close in density to pure aluminum. Magnetic testing is not applicable since neither pure aluminum nor aluminum alloys are magnetic. Thus, the use of caustic soda provides a practical and efficient means of distinction in a laboratory or field setting.