Solid fraction analysis with DSC in semi-solid metal processing

Solid fraction at the forming temperature is a key parameter in semi-solid processing as it affects the slurry viscosity and the subsequent mould filling at the forming stage. The type as well as the rate of scanning in the DSC experiment impacts the solid fraction analysis. Hence, the DSC experiment for solid fraction analysis must be designed carefully to avoid over- or underestimation of the forming temperatures. Thixoforming involves heating into the semi-solid temperature range followed invariably by an isothermal step and uses a melting scan while the rheo route employs controlled cooling from the liquid state and must rely on a solidification scan. Isothermal as well as conventional scanning DSC experiments were performed in order to better approximate the heating and cooling routines employed in industrial scale semi-solid forming operations. Heating below 2.5 K min−1 and cooling at 0.5 K min−1 produced melting and solidification curves which are in reasonable agreement with the isothermal DSC experiments.