AZ31镁合金双向挤压变形的组织性能与工艺研究
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摘要
本文旨在研究DDE变形过程中AZ31系镁合金的微观组织演变和变形后的力学性能以及DDE变形工艺。重点讨论了DDE变形过程中的晶粒细化机制,变形后的室温力学性能及断裂机制,以及DDE变形过程中的挤压力和应力应变分布。以期对AZ31镁合金的DDE变形机理和DDE变形工艺本身进行初步研究和探讨。
论文选取了应用比较广泛的AZ31镁合金作为研究对象。采用金相显微分析(OM)、X射线衍射分析和电子背散射衍射分析(EBSD)等手段,对不同挤压温度下AZ31镁合金在DDE变形过程中的显微组织和织构的演变规律进行了分析;进行室温力学性能测试,探讨了DDE成型后AZ31镁合金的室温力学性能和室温下的断裂方式及断裂机理;采用透射电子显微技术(TEM),探讨了DDE变形过程中AZ31镁合金的晶粒细化机制;对经DDE变形后的AZ31镁合金进行了退火处理,探讨了经DDE变形后AZ31镁合金显微组织的变化及其力学性能;采用有限元软件对DDE变形工艺进行了模拟分析,对DDE变形过程中挤压力和应力应变分布进行了初步探讨。取得如下结果:
AZ31镁合金经DDE变形后,镁合金晶粒明显细化。变形后合金室温延伸率随晶粒细化而提高,屈服强度和硬度都随晶粒细化而提高,与Hall-Petch关系的趋势符合,由于受织构影响,250℃时与Hall-Petch关系相违背。在250~450℃温度范围内进行DDE变形,AZ31镁合金的晶粒随变形温度的降低而减小。AZ31镁合金经DDE热变形后,合金的室温强韧性得到综合改善。
随着挤压比的增大,合金的晶粒细化效果更显著。在挤压比为10.125时,晶粒变得更加致密细小,而且分布均匀,镁合金的屈服强度和延伸率都得到了提高。同时在挤压比为10.125,温度300℃,挤压后的AZ31镁合金,平均晶粒尺寸为3μm,屈服强度达到232MPa,延伸率达到了18.6%,说明在低温与大挤压比的共同作用下,镁合金的韧性能有效地得到提高。
DDE变形过程中AZ31镁合金的晶粒细化机制可以归结为模具转角的剪切作用和挤压比变形引起的晶粒破碎和整个DDE变形过程中发生的连续动态回复和再结晶(CDRR)。对于连续动态回复和再结晶,变形初期在粗晶粒内产生许多位错,位错会发生交互作用,重新排列形成位错界面以及亚晶界,而形成的位错界面以及亚晶界会进一步演化为小角度晶界和大角度晶界,镁合金得以细化。
利用有限元软件Deform-3D对DDE变形过程中的挤压力和应力应变分布进行了有限元模拟,发现模拟结果和实验结果基本吻合。
The purpose of this paper is to investigate the microstructure evolution, mechanical properties of AZ31 magnesium alloy by DDE, and placed an emphasis on the understanding of grain refinement mechanism during DDE, the mechanical properties and fracture mechanism at room temperature, the extrusion force and distribution of stress and strain of DDE, in order to provide a preliminary investigation and discussion for the DDE deformation mechanism and process.
In this paper, as-casted AZ31 magnesium alloy were elected as DDE deformation material for investigation. The AZ31 magnesium alloy microstructure and texture evolution were analyzed by Optical microscopy (OM), X-ray diffraction and electron backscatter diffraction(EBSD); the mechanical properties and fracture way and mechanism were discussed by mechanical test at room temperature, the grain refinement mechanism were explored by transmission electron microscopy (TEM), the properties and microstructure of annealing after DDE were discussed , and the extrusion force and distribution of stress and strain during DDE process were simulated by finite element analysis. The main results can be summarized as follows:
For AZ31 magnesium alloy, the grains were refined effectively after DDE. The ductility, strength and microhardness were improved with the grain refinement, which is consistent with Hall-Petch relationship. The effect of grain refinement was improved with lowering the DDE temperature. Both the ductility and synthetic mechanical properties of AZ31 magnesium alloy can be improved by DDE.
With the extrusion ratio increasing, alloy grain could be refined. When the extrusion ratio was 10.125, the grains become more compact and smaller, and distributed evenly. The tensile strength and prolongation rate of Magnesium Alloy got improvement. When the extrusion ratio was 10.125, temperature was 300℃, the average grain size was 3μm, yield stress got to 232MPa, prolongation rate reached 18.6%, it showed that with the low temperature and large extrusion ratio, the toughness of Magnesium Alloy could effectively improved.
Grain refinement mechanism of AZ31 alloy during DDE can be described as grain fragmentation in the shear zone and extrusion ratio zone for continuous dynamic recovery and recrystallization (CDRR). For the CDRR, at the initial stage of DDE deformation, dislocation density increases and then dislocations are arranged into dislocation boundaries and sub-grain boundaries. With further deformation, these sub-boundaries evolve to low angle grain boundaries (LAGBs) and high angle grain boundaries (HAGBs), therefore the grains can be refined.
The extrusion force and distribution of stress and strain during DDE process were simulated by finite element software Deform-3D, and the result of simulation was well agree with the experiment result.
论文选取了应用比较广泛的AZ31镁合金作为研究对象。采用金相显微分析(OM)、X射线衍射分析和电子背散射衍射分析(EBSD)等手段,对不同挤压温度下AZ31镁合金在DDE变形过程中的显微组织和织构的演变规律进行了分析;进行室温力学性能测试,探讨了DDE成型后AZ31镁合金的室温力学性能和室温下的断裂方式及断裂机理;采用透射电子显微技术(TEM),探讨了DDE变形过程中AZ31镁合金的晶粒细化机制;对经DDE变形后的AZ31镁合金进行了退火处理,探讨了经DDE变形后AZ31镁合金显微组织的变化及其力学性能;采用有限元软件对DDE变形工艺进行了模拟分析,对DDE变形过程中挤压力和应力应变分布进行了初步探讨。取得如下结果:
AZ31镁合金经DDE变形后,镁合金晶粒明显细化。变形后合金室温延伸率随晶粒细化而提高,屈服强度和硬度都随晶粒细化而提高,与Hall-Petch关系的趋势符合,由于受织构影响,250℃时与Hall-Petch关系相违背。在250~450℃温度范围内进行DDE变形,AZ31镁合金的晶粒随变形温度的降低而减小。AZ31镁合金经DDE热变形后,合金的室温强韧性得到综合改善。
随着挤压比的增大,合金的晶粒细化效果更显著。在挤压比为10.125时,晶粒变得更加致密细小,而且分布均匀,镁合金的屈服强度和延伸率都得到了提高。同时在挤压比为10.125,温度300℃,挤压后的AZ31镁合金,平均晶粒尺寸为3μm,屈服强度达到232MPa,延伸率达到了18.6%,说明在低温与大挤压比的共同作用下,镁合金的韧性能有效地得到提高。
DDE变形过程中AZ31镁合金的晶粒细化机制可以归结为模具转角的剪切作用和挤压比变形引起的晶粒破碎和整个DDE变形过程中发生的连续动态回复和再结晶(CDRR)。对于连续动态回复和再结晶,变形初期在粗晶粒内产生许多位错,位错会发生交互作用,重新排列形成位错界面以及亚晶界,而形成的位错界面以及亚晶界会进一步演化为小角度晶界和大角度晶界,镁合金得以细化。
利用有限元软件Deform-3D对DDE变形过程中的挤压力和应力应变分布进行了有限元模拟,发现模拟结果和实验结果基本吻合。
The purpose of this paper is to investigate the microstructure evolution, mechanical properties of AZ31 magnesium alloy by DDE, and placed an emphasis on the understanding of grain refinement mechanism during DDE, the mechanical properties and fracture mechanism at room temperature, the extrusion force and distribution of stress and strain of DDE, in order to provide a preliminary investigation and discussion for the DDE deformation mechanism and process.
In this paper, as-casted AZ31 magnesium alloy were elected as DDE deformation material for investigation. The AZ31 magnesium alloy microstructure and texture evolution were analyzed by Optical microscopy (OM), X-ray diffraction and electron backscatter diffraction(EBSD); the mechanical properties and fracture way and mechanism were discussed by mechanical test at room temperature, the grain refinement mechanism were explored by transmission electron microscopy (TEM), the properties and microstructure of annealing after DDE were discussed , and the extrusion force and distribution of stress and strain during DDE process were simulated by finite element analysis. The main results can be summarized as follows:
For AZ31 magnesium alloy, the grains were refined effectively after DDE. The ductility, strength and microhardness were improved with the grain refinement, which is consistent with Hall-Petch relationship. The effect of grain refinement was improved with lowering the DDE temperature. Both the ductility and synthetic mechanical properties of AZ31 magnesium alloy can be improved by DDE.
With the extrusion ratio increasing, alloy grain could be refined. When the extrusion ratio was 10.125, the grains become more compact and smaller, and distributed evenly. The tensile strength and prolongation rate of Magnesium Alloy got improvement. When the extrusion ratio was 10.125, temperature was 300℃, the average grain size was 3μm, yield stress got to 232MPa, prolongation rate reached 18.6%, it showed that with the low temperature and large extrusion ratio, the toughness of Magnesium Alloy could effectively improved.
Grain refinement mechanism of AZ31 alloy during DDE can be described as grain fragmentation in the shear zone and extrusion ratio zone for continuous dynamic recovery and recrystallization (CDRR). For the CDRR, at the initial stage of DDE deformation, dislocation density increases and then dislocations are arranged into dislocation boundaries and sub-grain boundaries. With further deformation, these sub-boundaries evolve to low angle grain boundaries (LAGBs) and high angle grain boundaries (HAGBs), therefore the grains can be refined.
The extrusion force and distribution of stress and strain during DDE process were simulated by finite element software Deform-3D, and the result of simulation was well agree with the experiment result.
引文
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