Metallographic study of a cast Al–Si–Cu alloy by means of a novel etchant

Samples from a heat treatable aluminium alloy were prepared from scrap and were cast in two different moulds to vary the solidification and cooling rates. These samples were subjected to solution heat treating at different temperatures for reduced time cycles, cooled in hot water and aged. The specimens were prepared for their metallographic study by etching them with a reagent that enhanced the contrast of copper-rich particles. The microstructures of the samples were studied by light optical microscopy and processed with the aid of an image analyzer. It was found that the size and shape of the particles depended on the solidification and cooling rates and on the solution heat treatment; it was also found that the amount of copper affected these changes in the samples that solidified within sand moulds, although the samples were cast within a narrow copper-content range. ► An etchant was developed to enhance the contrast of Cu-rich particles. ► The size and distribution of particles were evaluated in sand and metallic-mould castings. ► The effect of solution treatments on the particles was evaluated.