Prediction of rheological behaviour and segregation susceptibility of semi-solid aluminium-silicon alloys by a simple back extrusion test

This paper studied the segregation susceptibility of a number of samples based on the Al-Si system and quenched from the semi-solid state. The work was performed on two compositions (A356 and A356 + 0.5Sn), characterized by spheroidal microstructures obtained by three different conditioning techniques. Viscosities were determined by a simple back-extrusion test and in order to obtain meaningful data a quantitative microstructural mapping of the extruded cups was carried out. From these measurements, a precise assessment of the segregation extent of the samples was compiled and the data was rationalized in terms of the D’Arcy law. Results showed a positive correlation associating segregation extent, microstructural permeability, liquid phase percolation velocity during extrusion and microstructural features such as the Al-(alpha) particle size and shape.