【摘要】：隨著輕量化時代的到來,鎂合金越來越受到青睞,在航空航天、汽車、3C中都有較廣的應用前景。由于鎂合金密排六方的晶體結構,塑性變形能力較差,因此當前產(chǎn)品中壓鑄件比較常見。但壓鑄件有時無法滿足高性能零件的要求,塑性變形可獲得晶粒細小、綜合性能較好的組織,力學性能要優(yōu)于壓鑄件,因此鎂合金的塑性變形對鎂合金的發(fā)展和應用具有重要意義。金屬的宏觀力學性能由微觀組織決定,通過研究熱變形過程中微觀組織演變及動態(tài)再結晶行為,從而建立適當?shù)哪Ｐ蛯嶙冃芜^程中組織進行預報,是目前較常用的研究方法。元胞自動機作為交叉學科的出現(xiàn),引入了曲率驅動機制、熱力學驅動機制和能量耗散機制,能夠更真實地反映晶界遷移的物理過程,在現(xiàn)在模擬方法中是較受歡迎的一種。傳統(tǒng)的熱變形研究方法是通過應力應變曲線建立動態(tài)再結晶動力學模型和本構模型,這些是研究動態(tài)再結晶行為的基礎,可為模擬模型提供基礎性的材料參數(shù)。本文通過建立包含應變參量的流變應力應變模型,動態(tài)再結晶動力學模型,研究了擠壓態(tài)和鑄態(tài)的AZ61鎂合金的熱變形行為,通過引入晶粒拓撲變形機制,變化的激活能等,建立了動態(tài)再結晶CA模型,對擠壓態(tài)AZ61鎂合金進行了微觀組織演化模擬。確定合適的熱處理方法對AZ61鎂合金進行了優(yōu)化熱處理,獲得均勻組織后,進行熱擠壓,獲得擠壓態(tài)鎂合金。通過Gleeble-1500模擬試驗機,對鑄態(tài)和擠壓態(tài)的AZ61鎂合金進行熱壓縮實驗,獲得不同變形條件下的應力應變曲線。建立高溫應力應變模型,研究了應變對本構參數(shù)α、Q、n、lnA的影響。研究發(fā)現(xiàn)不同狀態(tài)下的AZ61鎂合金具有相同的熱變形行為規(guī)律,擠壓態(tài)鎂合金的動態(tài)軟化現(xiàn)象較明顯。通過動態(tài)再結晶動力學的研究發(fā)現(xiàn),擠壓態(tài)動態(tài)再結晶的發(fā)生要易于鑄態(tài),擠壓態(tài)的晶粒尺寸較小,更易發(fā)再結晶,鑄態(tài)鎂合金在變形初期會通過產(chǎn)生孿晶來協(xié)調(diào)變形。基于元胞自動機原理,結合曲率驅動機制、能量耗散機制建立了初始晶粒長大模型。結合動態(tài)再結晶理論建立了元胞自動機動態(tài)再結晶模型,引入了晶粒拓撲變形技術,考慮變形過程中晶粒形狀的變化,通過引入本構方程,考慮了激活能隨應變的變化。利用MATLAB完成了模型程序的編程,針對不同變形條件下的熱變形進行CA模擬。研究結果表明:初始晶粒生成模型的模擬結果能夠準確地反映晶粒長大過程的特點。動態(tài)再結晶CA模型可準確地再現(xiàn)變形參數(shù)對動態(tài)再結晶的影響規(guī)律。模擬獲得的微觀組織形貌與實驗獲得的金相組織也較相似,獲取的應力應變曲線、動態(tài)再結晶動力學曲線也能夠較準確地反映曲線的特點,獲得的峰值應力、穩(wěn)態(tài)應力、平均晶粒尺寸等都與實驗值吻合良好,因此所建立的元胞自動機模型可用于該材料動態(tài)再結晶過程的模擬。引入變化的激活能,通過影響動態(tài)再結晶形核率,進而影響再結晶行為,結果表明,引入變化的激活能后更貼合實際。
[Abstract]:With the advent of the age of light weight, the magnesium alloy is more and more popular, and has a wide application prospect in the aerospace, automobile and 3C. Due to the hexagonal crystal structure of the magnesium alloy, the plastic deformation ability is poor, so the pressure casting in the current product is more common. But the plastic deformation of the magnesium alloy is of great significance to the development and application of the magnesium alloy. The macroscopic mechanical properties of the metal are determined by the microstructure, and the microstructure evolution and the dynamic recrystallization behavior of the metal are studied by studying the microstructure evolution and the dynamic recrystallization behavior in the thermal deformation process, so that an appropriate model is established to forecast the tissue in the thermal deformation process, and the method is the most commonly used research method. Cellular Automata, as a cross-discipline, introduces the mechanism of curvature driving, the mechanism of thermodynamic driving and the mechanism of energy dissipation, and can more truly reflect the physical process of grain boundary migration, and it is a more popular one in the current simulation method. The traditional method of thermal deformation is to set up a dynamic recrystallization dynamic model and a constitutive model through the stress-strain curve, which is the basis of studying the dynamic recrystallization behavior, and can provide the basic material parameters for the simulation model. The thermal deformation behavior of the extruded and as-cast AZ61 magnesium alloy is studied by establishing a rheological stress-strain model and a dynamic recrystallization dynamic model which contain the strain parameters. The dynamic recrystallization CA model is established by introducing the grain topological deformation mechanism and the activation energy of the change. The microstructure evolution of the extruded AZ61 magnesium alloy was simulated. And a suitable heat treatment method is used for optimizing the heat treatment on the AZ61 magnesium alloy, and after the uniform tissue is obtained, the hot extrusion is carried out to obtain the extruded magnesium alloy. The stress-strain curves under different deformation conditions were obtained by the Gleeble-1500 simulation test machine, and the AZ61 magnesium alloy in the as-cast and extruded state was subjected to thermal compression experiments. In this paper, a high-temperature stress-strain model is established, and the effects of strain on the parameters, Q, n, and lnA, are studied. It is found that AZ61 magnesium alloy in different states has the same thermal deformation behavior, and the dynamic softening of the extruded magnesium alloy is more obvious. It is found that the dynamic recrystallization of the extrusion state is easy as cast, the grain size of the extruded state is small, and the recrystallization can be more easily, and the as-cast magnesium alloy can coordinate the deformation at the beginning of the deformation by generating twinning. Based on the cellular automaton principle, the initial grain growth model is established by combining the curvature driving mechanism and the energy dissipation mechanism. In this paper, the dynamic recrystallization model of the cellular automata is established in combination with the dynamic recrystallization theory, and the grain topological deformation technology is introduced, and the change of the grain shape in the deformation process is considered, and the change of the activation energy with the strain is taken into account by the introduction of the constitutive equation. The programming of the model program is accomplished by using MATLAB, and the CA simulation is carried out for the thermal deformation under different deformation conditions. The results show that the simulation results of the initial grain generation model can accurately reflect the characteristics of the grain growth process. The dynamic recrystallization CA model can accurately reproduce the influence of the deformation parameters on the dynamic recrystallization. The microstructure of the obtained microstructure and the metallographic structure obtained by the experiment are also similar, the obtained stress-strain curve and the dynamic recrystallization dynamic curve can accurately reflect the characteristics of the curve, the obtained peak stress and the steady-state stress, The average grain size and the like are in good agreement with the experimental values, so the established cellular automaton model can be used to simulate the dynamic recrystallization process of the material. The activation energy of the change is introduced, and the recrystallization behavior is influenced by the influence of the dynamic recrystallization nucleation rate, and the results show that the activation energy of the introduced change is more practical after the activation energy is introduced.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.22

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