Characterization of surface liquid segregation in SSM-HPDC aluminium alloys 7075, 2024, 6082 and A201

The surface liquid segregation (SLS) phenomenon in semi-solid metal-high pressure die casting (SSM-HPDC) plates of 7075, 2024, 6082 and A201 was investigated by different techniques. Depth profiles were determined by firstly measuring the chemical composition of the surface of the plates using a Thermo Quantris optical emission spectrometer (OES). Material was then removed by a grinding process followed by measurement of the amount of material removed and chemical analysis. Chemical profiles of the main alloying elements were plotted for the cross-section of the plates in the as-cast and T6 (after solution treatment) temper conditions. Vickers hardness profiles from the surface to the centre of the plates were determined. Metallographic samples of cross-sections of the castings were prepared and evaluated using a scanning electron microscope. The results show that surface liquid segregation in SSM-HPDC alloys causes significant differences in properties between the surface and the bulk of these castings in both the F and T6 temper conditions.