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The Microstructure Evolution and Melting Behavior of Inhomogenous Materials during Controlled Heating Process

Author: WangXiaoYing
Tutor: JieWanQi
School: Northwestern Polytechnical University
Course: Materials Processing Engineering
Keywords: Non - homogeneous materials Melt Proliferation Microstructure evolution Heating rate Semi-solid Organization of genetic
Type: PhD thesis
Year: 2003
Downloads: 309
Quote: 5
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Melting, equally important scientific significance and solidification, but unduly overlooked. Has become increasingly evident in recent years, with the theoretical value and application of new materials, new technology development, melting background. Melting process of the non-homogeneous materials commonly used in the research and production practice, semi-solid processing, melt processing of new technologies has important guiding significance. In this paper, semi-solid processing technology for the application background, proposed the concept of controlled melting, through the DSC experimental and directional melt quenching experiments to study the melting behavior and microstructure evolution of the heterogeneous Al alloy in control the heating process, analyzed theoretically before melting solute diffusion, the solid-phase volume fraction in the melting process and the temperature dependence of factors affect the melting tissue morphology. Semisolid slurry prepared by controlling the original organization and the melting process of the new ideas, and to provide a low-cost, simple and feasible prepared a new way of semi-solid slurry. DSC analytical tools to study the melting behavior of Al-5.8wt% Cu alloys with different solidification structure under different heating conditions. Experimental results show that the heating method and the state of the original organization to influence Al-5.8wt% Cu alloy melting behavior of the main factors. The onset of melting temperature with increasing heating rate slightly increased. Eutectic melting activation energy associated with the organization of the state, the rapid solidification of the organization due to the density of defects, caused by the crystal structure of the degree of disorder increases, thereby melting activate small. Nonequilibrium eutectics diffusion during the heating process due to different degrees of dissolution, heating method, the diffusion surface area, non-equilibrium eutectic morphology and distribution of the combined effect of the extent of the proliferation of non-equilibrium eutectic dissolved. Heating rate, the temperature sensitivity of the solid fraction of semi-solid impact are discussed, and the results show that the rapid heating process control helps reduce the temperature sensitivity coefficient, in favor of semi-solid processing. In the heating process before melting, homogenization diffusion of major changes in the organization of a non-homogeneous material. \expressions. The use of the model, for example, calculate the Al-5.8wt% Cu alloy before melting heating solute distribution in the cell forming operation of the cell body and the second phase dissolution rate, intuitively reflect the heating rate, the second phase morphology of solute distribution The second phase, the dissolution rate and dissolution extent. At the same time, the calculation of the Al-5.8wt% Cu alloy unbalanced common crystal melting proportion DSC experimental results and the calculated results are in good agreement with different heating rates, further illustrate the rationality of the model. For non-homogeneous material, has great significance to study the melting of a solid solution of the understanding of the melting process of the alloy material and semi-solid material processing control. Through analysis of the solid solution during the melting process, emphasizes the important role of solute diffusion in the solid solution melts. Solute conservation and heat conservation in the melting process, the establishment of a solid solution melting dynamics model. Given a summary of the liquid volume fraction and temperature in the melting process through the introduction of the diffusion parameter β, ie, / _, Rainbow 1, the 1st cloth T0} 'a} J B' twenty-one to two million Japanese Guang eleven twenty thousand I cry I l a fan of L 'material a' less] analyzed according to different melting conditions to calculate the diffusion parameters knife. calculation results are very close DsC experimental results with the same heating methods, proved built a model of rationality. use of the directional melting process liquid quenching method study the electromagnetic stirring prepared the semi-solid A357 alloy morphological evolution of organizations in the melting process, as well as the heating rate of tissue morphology was found, the slower the heating rate solid-phase grain roundness the better, the greater the solid phase grain size and the degree of aggregation. use the same method to study Al the one 5.swt% Cu alloy with dendritic structure in the process of melting and holding tissue morphology evolution, as well as the heating rate and holding time on the morphological evolution. Experimental results show that the appropriate insulation, semi-solid dendritic structure can evolve into spherulites. proposed obtained through the analysis of melt morphology ideal semi-solid slurry, control original organizations and heating parameters, from an engineering point of view feasible given the specific measures. example, grain refinement hypothermia A357 alloy casting with the rapid heating process short holding successfully by dendrite solidification structure prepared by solid-phase particles rounded, smaller size, qualified semi-solid slurry evenly distributed. evolution in order to truly reflect the organization of the alloy under high temperature using high temperature metallurgical microscope records Sn of 5% wtPb alloy situ melting and solidification process of organizational change. melted by the grain boundaries, advancing to the interior of the grains; grew up in different nuclei in the solidification process at different rates, leading to the final grain size of different sizes. visually for the first time observed in 5% Sn states Pb alloy genetic phenomenon and the organization of Genetics and superheat temperature contact. genetic causes of the organization is to melt the microscopic uneven structure, this microscopic uneven structure the genetic phenomenon related to the melt superheat temperature in a certain temperature range.

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