Micro-macro modelling of thermal evolution during solidification of binary equiaxed alloys with experimental validation

Abstract

A micro-macro model based on deterministic continuum mechanics and the modified source term method has been used to study the solidification problems involving binary Al-4.0 wt% Cu eutectic system. The model is further tested with other equiaxed eutectic binary aluminium alloys that include Al-3.0 wt% Si, Al-6.0 wt% Mg and Al-3.0 wt% Zn. All the heat transfer regimes including convection and radiation at the open top surface of the mould are considered. The nucleation steps are accounted for by considering continuous nucleation and growth kinetics. Information such as undercooling, nucleation rate, recalescence, growth rate, solid fraction, cooling curve, grain size and volumetric grain density which directly link to mechanical properties of cast components are accurately predicted. The model result is validated against the experimental data obtained from the current study and others published in the literature. From the results predicted in the current work, it is observed that the model gives the actual cooling history instead of a rough estimation of cooling curves as obtained from previous models. Among the aluminium-based alloys analysed, the Al–Cu alloy has the fastest nucleation and solidification rates. The predicted volumetric grain density suggests that magnesium has a more grain refinement effect on the aluminium matrix than copper, zinc and silicon. The model results are in agreement with the physical metallurgy of alloy theory and can be used by alloy manufacturers to improve the mechanical properties of alloy castings.

Keywords

• Micro-macro coupling model
• Nucleation and growth kinetics
• Casting and solidification
• Eutectic alloys
• Microstructure