相场再结晶储能释放模型与显微组织演变的模拟研究

A model for releasing of stored energy and microstructure evolution during recrystallization by phase-field simulation

在相场再结晶模型中提出了形式为f(η_i^k,η_j^k)=E_s(η_i^(de))~2(1-(η_j^(re)~2)的冷变形储能项,并应用该模型模拟了AZ31镁合金的再结晶过程,模拟结果和实验观测结果符合很好.研究表明,引入储能释放模型可以实现再结晶形核物理过程的模拟;模拟结果可以把合金在冷变形后退火的过程按照机理分为再结晶和热晶粒长大两个阶段,模拟得出的理论再结晶时间是实验再结晶时间的2/3.考察了冷变形应变大小对形变金属的亚晶粒尺寸和储能的影响机理和试验结果,并将考察结果代入到改进后的再结晶模拟模型,成功地再现了一个经典实验结果:随预先应变量的增加,存在临界应变量对应的一个再结晶晶粒尺寸峰值.同时还给出了这一经典实验结果的理论解释.

A format of f（ηik,ηjk）= Es（ηide）2（1 - （ηjre）2） to express cold deformed stored energy is suggested in a phase-field model for simulating recrystallization in alloys. Using AZ31 magnesium alloy as an example, the recrystallization process is simulated by the new model, and the simulation results are in good agreement with experimental measurements. The nucleation process of recrystallization is realized for the first time by the model based on the physical background. The simulation results show that the grain growth of a cold deformed alloy in the annealing process indicates automatically two stages： recrystallization driven by the restored energy and thermal growth driven by boundary energy. A theoretical time spent in finishing recrystallization, obtained by simulation, is found to be 2/3 of that obtained by industrial practice. The mechanism and the experimental results about the influence of cold deformation on subgraln size and stored energy are examined, and the experimental results are introduced into the simulation. The common experimental phenomenon shows that there is a peak at the critical strain on the curve of recrystallized grain size versus cold strain. A theoretical explaination to the mechanism of the peak occurrence is also discussed.