大断面大壁厚比铝合金型材加工及组织性能控制研究

Currently, the rail transit has a rapid development in China, and Liaoning is an important supplying province of aluminum profiles used in rail transit. Hence, this research is proposed to systematically study the main problems existing in the fabrication and forming processes of aluminum profiles with large cross-section and large wall thickness ratio.. The controlling method of microstructure homogeneity and macro-segregation of large scaled aluminum ingot is one of the main research subjects. Moreover, the material flow behavior during extrusion process of aluminum profiles with large cross-section and large wall thickness ratio is studied, and the multi-objective optimization system for extrusion dies and process parameters is established, and then the equitable material distribution and profile distortion controlling methods are proposed. The formation of temperature field and rule of temperature rise during extrusion process of aluminum profiles with large cross-section and large wall thickness ratio is investigated, and it is aimed to control the temperature field and temperature rise through the coordination control of extrusion speed and billet gradient heating, and also the die with liquid nitrogen cooling. Meanwhile, this research will study the microstructure dynamic evolution during extrusion process and the formation mechanism of microstructure inhomogeneity, and establish the microstructure and properties controlling methods for aluminum profiles with large cross-section and large wall thickness ratio. This research can greatly enhance the metallurgical quality of large scaled aluminum ingots and the synthetical properties of aluminum profiles with large cross-section and large wall thickness ratio, which has important theoreticalsignificance and application value.

本项目针对我国轨道交通快速发展的迫切需求，结合辽宁省作为轨道交通用铝合金型材供应大省的现状，围绕大断面大壁厚比铝合金型材组织性能均匀性调控这一关键问题开展研究内容。. 重点研究：大规格铝合金铸锭组织均匀性与宏观偏析的调控方法，揭示外场及工艺参数调控下的凝固组织及成分均匀性演变机理；研究大断面大壁厚比铝型材挤压流变行为，建立挤压模具与工艺的多目标优化体系，提出材料合理分配和型材变形控制的方法；研究大断面大壁厚比铝型材挤压温度场的形成机理和温升规律，通过挤压速度和梯温加热的协调控制以及模具液氮冷却技术，实现对挤压温度场和温升的合理调控；研究挤压过程铝合金材料微观组织的动态演化规律，揭示不均匀速度场和温度场条件下组织不均匀性的形成机理，建立大断面大壁厚比铝型材组织性能的控制方法。本项目的顺利实施，将在提升大断面大壁厚比铝型材的综合性能及性能均匀性方面，具有重要的理论意义和应用价值。

本项目针对我国轨道交通快速发展的迫切需求，结合辽宁省作为轨道交通用铝合金型材供应大省的现状，围绕大断面大壁厚比铝合金型材组织性能均匀性调控这一关键问题开展了系统研究工作。.重点研究了大规格铝合金铸锭组织均匀性与宏观偏析的调控方法，获得了电磁场作用下对凝固前沿/固液界面处传质、传热的影响规律，揭示了外场及工艺参数调控下的大规格铝合金铸锭铸造过程温度场、流场调控下的凝固组织及成分均匀性演变机理。研究了大断面大壁厚比铝型材挤压流变行为，建立了挤压模具与工艺的多目标优化体系，提出了材料合理分配和型材变形控制的方法；构建了多种典型挤压用铝合金材料的本构方程和热加工图，实现了大断面大壁厚比铝型材挤压的高精度数模拟模。揭示了挤压过程的材料流动规律和变形机理，提出了关键模具结构和挤压工艺参数的优化设计方法；获得了多周期挤压过程的温度场变化规律，通过铸棒梯温加热等手段降低了挤压温升；明确了复杂材料流动和温度条件下挤压过程的微观组织演变规律，揭示了固态焊合机理及焊合质量对力学性能的影响规律；研究了挤压过程铝合金材料微观组织的动态演化规律，揭示了不均匀速度场和温度场条件下组织不均匀性的形成机理，阐明了铝合金型材时效强化相的析出序列及其强韧化机制，提出了型材力学性能和耐腐蚀性能协同提升的热处理手段，建立了大断面大壁厚比铝型材组织性能的控制方法。.制备了大规格6005A和7N01铝合金铸锭，铸锭直径规格达Φ784mm，6005A铸锭横截面偏析率≤5%，7N01铸锭横截面偏析率≤8%。挤压了最大外接圆直径1.1米的大断面大壁厚比铝合金型材。在型材性能方面，6005A和7N01铝型材综合性能提高10%以上，型材边部和心部的性能差异≤7%，在型材尺寸精度方面，宽度方向直线度<1mm/整个型材宽。.本项目的顺利实施，将在提升大规格铝合金铸锭冶金质量及大断面大壁厚比铝型材的综合性能方面，具有重要的理论意义和应用价值。