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Phase Field Simulation on AZ31 Mg Alloy Grain Growth during Recrystallization in Real Spatio-time Scale

Author: WangMingTao
Tutor: ZongYaPing
School: Northeastern University
Course: Materials Science
Keywords: Grain Growth Recrystallization Phase-field method Computer Simulation Free energy density AZ31 magnesium alloy Mixed crystal degree Stored energy
CLC: TG146.22
Type: PhD thesis
Year: 2009
Downloads: 296
Quote: 1
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Abstract


Phase-field method is based on the Ginzburg-Landau phenomenological theory based on the theory of classical thermodynamics and kinetics simulation method that is currently within the scope of computer processing power to achieve the most promising can be observed in the microstructure scale range Materials simulated temporal organization's way. However, due to the physical meaning of some parameters of the model is not clear, its true value can not be determined, it is most analog phenomenon or trend limited to qualitative or compared with each other simulations. This study established a single-phase recrystallization grain growth model, and determine all parameters in the model and the true value of the physical meaning, to achieve a single-phase polycrystalline material microstructure evolution of the real space-time simulation, in order to promote the phase-field method Solid State Microstructure simulations made important efforts into practical application. AZ31 magnesium alloy has good ductility and high strength, is currently the most widely used commercial wrought magnesium alloys. However, low room temperature ductility of the alloy, the element content is low, age hardening and solid solution strengthening effect is not ideal, so as to control the alloy recrystallization organization, an effective means of improving its performance. Therefore, this study selected AZ31 magnesium alloy, for example, the recrystallization process simulation are compared with the experimental results verify the proposed model in this study as well as the law of the model parameter values ??correctness, and on this basis to further Microstructure evolution of the study, in order to optimize the study of the alloy as a reference. In this study, the conventional phase-field model based on a modified single-phase recrystallization proposed system, local free energy density function expression, the introduction of component field variables, storage items, etc. In industrial applications built within a virtual reality temporal recrystallized microstructure evolution model. While for AZ31 magnesium alloy system to determine the values ??of parameters in the model law, and the law is also applicable to other single-phase grain growth phase-field model. Followed by additional storage can determine the size of stored energy associated with the free energy density function coefficients B 1 and B 2 values, while the recrystallization grain interior after The free energy density function and thermodynamic data software THERMOCALC calculated free energy of the alloy composition curve fitting to determine the entire function coefficients A, A 1 , A 2 of true value. Secondly, through the grain boundaries of the scope of known width and interfacial energy values ??determine the gradient coefficient K 2 and the coupling coefficient K 1 true value, the existing models can not be determined K 1 and K 2 , which is unable to complete the phase-field model of the real space-time simulation of the key. This paper studies the model parameter values ??for the characteristics of the interface, elaborated grain boundary phase field model is scoped at the interface range ordering of variables, its physical meaning is the interface energy distribution range and corresponds to the component interface segregation range. Finally the mobility of the interface can be expressed as a coefficient L form Arrhenius equation and determine the activation of which can be in the system and the substrate is the biggest difference Zn atomic size segregation atom activation energy. 400 ℃, by comparing the values ??of experimental methods to determine the expression of the interface with the activity independent of the temperature coefficient L 0 values. Models and parameters in determining this simulated AZ31 magnesium alloy at 250 ℃ -400 ℃ range of recrystallization grain growth process, with the experimental results in the microstructure, the evolution of a single grain, grain size and the degree of mixed crystals other aspects of the comparison demonstrate that the proposed phase-field model is correct and effective. Found: at 250 ℃ alloy interface mechanism for migration activation energy changes, while Zn atoms at the interface description of the interface segregation migration initiative plays a major role, while the proportion of Al in the system, but the interface although larger initiative the role of small; analog set after completion of nucleation comparable with the experimental results into the recrystallization phase coincides immediately with the measured values, indicating that this model is a random set of nucleation one minute fast grown nucleation model reasonable and consistent with recrystallization nucleation time is short, rapid release of stored energy characteristics of the grain growth process is then stored energy and interfacial energy and jointly promote the results. The alloy is mixed crystals is very serious, mainly due to the thermodynamic properties of alloy own decisions, and its degree of mixed crystals increases with increasing temperature, the same temperature, degree of mixed crystal aging time increases gradually increased. This study further simulation of the stored energy and interfacial energy of the recrystallization grain growth effects, the study found: a certain temperature, the average grain size, grain growth rate and degree of organization were mixed crystal with stored energy decreases with an increase; alloy system has a value equal to 0.33J / m 2 The critical energy value of the interface, when the interfacial energy is less than the critical value, the interfacial energy of the average grain size of recrystallized little effect , when the interface is greater than the threshold value to the average grain size, grain growth rate, degree of tissue were mixed crystal with the increase of the interfacial energy increases significantly.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Magnesium
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