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

Abstract

Semi-solid metal (SSM) processing is a unique manufacturing method to produce near-net shape products for various industrial applications. The nature of the SSM slurry (with solid spherical grains suspended in a liquid), makes it susceptible to liquid segregation during forming processes such as high pressure die casting (HPDC). In this paper, the SLS phenomenon in SSM-HPDC plates of 7075, 2024, 6082 and A201 was investigated by means of 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. It is shown 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.