Influence of time-variant temperature gradients on resolidifying mushy zones

The influence of thermal diffusion in a stationary temperature gradient on the resolidification of a mushy zone is investigated. The temperature distribution in the sample is calculated by solving the heat diffusion equation numerically for the varying phase fractions, aiming at predicting the position of the liquid and solidus temperatures depending on the thermal diffusivities (heat conductivities and heat capacities Cp) in the different phases. Phase fractions and Cp values for thermal diffusivities are calculated using the thermochemical library ChemApp. Experimental investigations are performed using eutectic and peritectic alloys in the system Al-Cu. It is found that the solidus and peritectic isotherms migrate considerably during annealing. Micrographs of annealed samples show a more or less pronounced transition zone at the positions of the solidus and peritectic temperatures. The extension of the transition zone corresponds reasonably well with the experimentally determined migration distance of the solidus and peritectic isotherms.