Microstructures in an aluminum—silicon alloy analysed by means of a nuclear microprobe

An alloy consisting of a eutectic mix of aluminum and silicon to which traces of Sr and Mg have been added forms an important product of a major aluminum smelter (ALUSAF). Casts of this alloy, when cut and polished, display plate-like structures when viewed through an optical microscope. These structures are bound to have an effect on the physical properties of the alloy, for which strength is important. In this work we have used a nuclear microprobe to map areas of interest and determine the composition of the structures observed, using proton and alpha beams for proton-induced X-ray emission (PIXE) and Rutherford backscattering (RBS) analysis. The platelets were proved to be formed by the trace element strontium, a fact which has important metallurgical implications.