Thermodynamic modelling of growth-restriction effects in aluminium alloys

The amount and type of alloying elements in aluminium affect the as-cast microstructure through the dependence of solidified fraction on undercooling. This can be quantified by the growth-restriction parameter Q. Phase-diagram calculations using the CALPHAD method show the effects of thermodynamic parameters on Q. In binary systems, the deviation from linear dependence of Q on solute concentration is assessed. In ternary alloys, model systems elucidate the role of solute interaction in the liquid and solid, and can be used to interpret the behaviour in actual systems. Growth restriction is discussed in relation to solidification modelling and the attainment of a fine, equiaxed microstructure in wrought and shape-casting alloys.