Thermodynamic Criteria for the Selection of Alloys Suitable for Semi‐Solid Processing

Abstract

In this work the suitability of alloys for semi‐solid processing was investigated using numeric simulation. The simulation was based on equilibrium calculations, Scheil‐Gulliver calculations and, when necessary, diffusion simulations. For this purpose a new parameter was introduced in addition to the commonly used selection criteria. With the new parameter, the thixo ranges Δ T 40–60 and Δ T 20–40 , the specific demands of the different semi‐solid processes thixocasting and thixoforging can be considered. On the basis of thermodynamic simulation, the conventional aluminium alloys A356, AA6082 and A319, the steels 100Cr6, HS6‐5‐2 and X210CrW12 and a number of experimental aluminium‐lithium based alloys were evaluated according to the selection criteria. The thermodynamic calculations showed a large sensitivity of the course of the solidification with respect to variations in the contents of the alloying elements. This shows the necessity of keeping a tight composition control on alloys for semi‐solid processing. For aluminium alloys in particular silicon has to be monitored closely and for steels carbon and chromium.