Microstructure Simulation And Experiment Validation Of Al-cu Eutectic Alloy Based On Thermodynamic Calculation With Thermo-calc

Al-Cu eutectic alloy is widely applied in the military industry of aviation, astronavigation and ship, as well as civil industry of autocar and building materials. It is one of the metal materiasl, which develop the most quickly and used the most. The typical character of this alloy is that two solid phases are born from liquid phase L around eutectic temperature, namely L→α+β. The key of alloy solidification study is controlling the final microstructure, included grain shape, grain degree, microsegregation and inside phase buildup and so on.Because the accurate free energy data and phase graph data of actual alloy is obtained difficulty, the nowadays phase-field model mainly aim at the alloy of simple liquor. In this paper, Thermo-Calc commercial software is used to calculate the free energy data and phase graph data ofαphase,θphase and L phase in the extension, temperature (791-841) K and component (0-35)Cu(at.%). Besides, Sub-regular solution model is used to build continuous free energy connection of each phase in the calculational extension. At the same time, the Thermo-Calc calculational free energy data in introduced to the controlling equation of phase field and concentration field. Adoptting the system free energy density constructional method based original alloy phase graph in KKS model, and reducing calculational quantitative method by ignoring solid and liquid phase component of interface point in WBM model, the improved phased-field model from KKS is builed, which can used for microstructure simulation of any alloy.Equiax cryatal microstructure of Al-Cu alloy in different state is calculated by improved phase-field model. It is known that with the condensate depression increasing, the growing velocity of equiax cryatal is also incremental gradually, and growing pattern changes from sparse secondary arms, thick secondary arms and"square"equiax cryatal to grainy equiax cryatal. Microsegregation variation has a critical temperature. When temperature is higher than the critical temperature, microsegregation increases gradually with the temperature reducing. When temperature is lower than the critical temperature, microsegregation reduces gradually with the temperature reducing, and approach to 1 gradually. In the non-isothermal simulation of equiax cryatal, the secondary arms is more sparse than the isothermal one, the high melting point liquid phase between the arms increases, and the arms became thinner than the isothermal one. Besides, the nucleation and growth model of multi-grain is builded by introducing orientation field, the the nucleation and growth of multi-grain is calculated under different conditions. Multi-grain hit, crystal grain degree and microsegregation of multi-grain are talked about. By multi-grain nucleation and growth course of small anisotropy, it is shown that the boundary between two grains is like a line, and the crystal grain is close to polygon in final solidification.The evolutions of interface morphology and microstructure are simulated for Al-4.5Cu(at.%) alloy during its liquid-solid transition in Bridgman directional solidification at high rates. When growth rates lower than the absolute stability rate maintaining the high-rate planar growth, there is a transformation of microstructure from cellular dendrite to fine cell with increase of growth rate, and simultaneously, the enrichment of solute at interface becomes low and the partition coefficient of solute increases and approximates one gradually. When growth rate reaches the absolute stability one, initial interface breaks down slightly, but recovers planar again afterwards. The complete solute trapping appears at interface, and a microstructure of nearly free segregation is formed. In the directional solidification of controlling heat flow, with the boundry heat flow increasing, microstructure pattern changes from fir-tree crystal, fir-tree crystal and columnar crystals and columnar crystals to thin columnar crystals.Nestler multi-phase field is corrected, and more applied multi-phase field model is builted by introducing free energy data of each phase. Symmetrical layered steady growth and section solute distributing in different place are reached. When the initial layer thickness ofα-Al phase andθ-Al2Cu phase is asymmetry, oscillating growth appears. In the growing course of eutectic phase, if initial layered thickness is irrationality, it comes out the layer annihilation and layered thickness readjusted. At the same time, the mechanism is also analysed. Besides, directional microstructure of hypoeutectic alloy is also simulated and analysed.Lastly, the simulant growing courses of equiax cryatal growth, directional solidification, multi-grain growth and eutectic growth under different conditions are validated. It is shown that simulant and experimental results are comparable in phase growing characteristic and microstructure shape.