| The melting process is of the same importance as solidification, but was desolated for a long time because of its indirect relation with the materials performance. Recently, melting has gained more and more attention in the scientific community for its theoretical interest and practical applications with the development of technologies such as semi-solid metal process and melt treatment. In this work, we experimentally investigated the melting behavior and microstructural evolution of inhomogenous aluminum alloys during the controlled heating up process. Solute diffusion before melting, the dependence of the liquid volume on temperature during melting and the factors influencing morphology of the melting grains were theoretically analyzed. A new method to prepare semisolid slurry by means of controlling original solidification microstructure and melting process was proposed.DSC was employed to investigate the melting behavior of Al-5.8wt%Cu alloy with different solidification structures under the different heating sequences. During the heating process, most of the non-equilibrium eutectic in the solidification structure was dissolved controlled by the diffusion of the solute. The initial melting temperature was independent from the microstructure, but slightly rose with the increasing of the heating rate. The melting activation energy of the samples with slowly solidified structure was higher than that of the rapidly solidified one. The amount of dissolved non-equilibrium eutectic before melting was determined not only by the heating rate but also by its morphology, including its shape, distribution and diffusion interface area. The effect of heating rate on the temperature sensitivity of solid fraction was discussed. Fast heating is favorable for reducing the temperature sensitivity.The homogenization diffusion for inhomogenous materials plays an important role in the heating up process before melting. The diffusion-limited dissolution of the second phase during non-isothermal heating process was modeled resting on the constant heating rate for both plate-like and spherical second phases. The effects of heating rate and interface curvature on the concentration profiles in the matrix and the dissolution rate of the second phase were also discussed. A mathematical model for the effect was established and applied to calculate thedissolved fraction of the second phase before melting. The experimental results, well agreed with the calculated ones, clearly indicated the validity of the model.For solid solution phases, the equilibrium melting is usually difficult to achieve because of diffusion limitations in the solid. A diffusion controlled model for the melting between the solution phase was established based on solute and heat conservation. The relationship of theliquid fraction and temperature was derived setting on diffusion parameter β. The resultscalculated from the model were well agreed with the DSC experimental ones.By means of directional melting and quenching, we investigated the microstructure evolution during melting process for sphere-grain A357 alloy prepared by magnetohydrodynamic stirring and dendritic Al-5.8wt%Cu alloy through the normal solidification. Specifically, we examined the effects of heating rate and holding time on the grain morphology. The quenched microstructures revealed that the dendritic microstructure was able to evolve into equiaxed grains after proper annealing in the semi-solid state. Moreover, the smaller the heating rate is, the more spherical the grains will be.According to the new idea of preparation of semi-solid slurry from dendritic structure through controlled melting process, feasible techniques were given for the practice in industry, including grain refinement, low temperature pouring, rapid heating and annealing. In addition, the semi-solid slurry of A357 alloy consisting of equiaxed a-Al grains uniformly dispersed in the liquid was successfully obtained by means of the techniques mentioned above.In-situ observation of the microstruc...
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