汽车车身铝板等径角轧制成形机理及形/性一体化控制研究

Aluminum alloys have become the first choice material of automobile lightweight because of their excellent properties such as low density, high strength to weight ratio, good corrosion resistance and low cost recycling. However, it is easy to cause the phenomena of fracture due to its poor formability at room temperature, which often acts as the main obstacle for the wide application of aluminum alloys to automotive industry. The equal channel angular rolling is applied to the formation of 6xxx auto aluminum alloy sheets, and the mechanism of equal channel angular rolling of auto body aluminum sheet and its formation/performance integrated forming processes are discussed. Based on the crystal plasticity theory, the crystal plasticity constitutive equations of 6016 aluminum alloy and 3D crystal plasticity finite element model of equal channel angular rolling are created, and the effects of initial texture, roll parameters and heat treatments on the microstructure and properties of aluminum sheets are discussed by experimental observations and FEM simulations. To avoid mesh refinement in microcrack initiation and remesh in microcrack growth, the extended finite element method is introduced in the FEM simulation on the formability of auto aluminum sheets. Integrating the experiments of forming limit, the law of the effects of grain size, particle,texture and grain scale inhomogeneous deformation on the formability of aluminum sheets is analyzed at the macro-scale, meso-scale and micro-scale. Based on the above study, the equal channel angular rolling, heat treatments are to be optimizated to offer the basic theory and technical support for the formation of high performance auto aluminum sheets.

铝合金具有密度小，比强度高，耐蚀性能好、易回收等优点，成为汽车轻量化的首选材料。但由于铝合金室温成形性能差，易发生开裂现象，制约了铝合金在汽车工业中的广泛应用。本项目将等径角轧制工艺应用到6系汽车铝合金板材成形过程，探讨汽车车身铝板等径角轧制成形机理及形/性一体化成形工艺。项目以晶体塑性理论为基础，构建6016铝合金的晶体塑性本构方程和等径角轧制的3D晶体有限元模型，结合实验分析铝合金初始织构、轧制工艺、热处理等对板材组织与性能的影响。在汽车铝板成形性能分析的晶体有限元模型中引入扩展有限元，避免模拟过程中微裂纹萌生的网格细化和微裂纹扩展的网格重新划分的问题，同时结合成形极限实验，从宏、细、微观三个尺度揭示汽车铝合金中晶粒大小、第二相粒子、织构以及晶粒层次不均匀变形对铝板成形性能的影响规律。在此基础上，优化汽车铝合金等径角轧制、热处理工艺，为高性能汽车铝合金板材成形提供理论依据和技术支持。

铝合金具有密度小，比强度高，耐蚀性能好、易回收等优点，成为汽车轻量化的首选材料。但由于铝合金室温成形性能差，易发生开裂现象，制约了铝合金在汽车工业中的广泛应用。本项目将等径角轧制工艺、横轧和剪切挤压-轧制复合成形应用到汽车铝合金板材成形过程，探讨汽车车身铝板形/性一体化成形工艺。提出了一种金属板材强剪切轧制成形方法及装置，设计并制造了等径角轧制模具，研究了轧制路径、模具通道夹角、预热温度、横轧、换向轧制等对6016汽车铝合金组织与性能的影响。等径角轧制板材与普通轧制板材相比，T4P态板材具有较低的屈服强度、硬度、塑性应变比；较高的延伸率、平均塑性应变比、平均应变硬化指数、IE值，具有较好的成形性能。模具通道夹角为135°，板材预热温度为420℃时，制备的汽车铝合金板材成形性能较高。横轧和换向轧制弱化了强的形变织构，板材组织含有较多等轴晶粒，且晶粒大小分布更加均匀，从而提高了汽车铝合金板材的成形性能。在脆性断裂情况下，PFZ起减小应力集中的作用，软取向中的裂纹扩展最慢。在韧性断裂情况下，PFZ首先起减少应力集中的作用，软取向中的裂纹长大较快；但随着变形的进行，软的PFZ成为变形集中区，反而加速裂纹扩展，软取向的裂纹反而扩展最快。提出利用剪切挤压成形装置进行反复剪切成形，细化坯料晶粒；然后进行变薄剪切成形，制备具有强烈剪切织构的金属板材，从而提升汽车铝合金板材成形性能。在国内外重要刊物上发表论文21篇，其中SCI、EI论文16篇，授权国家发明专利5项，获湖南省自然科学三等奖1项；培养了5个研究生，承办2次国内会议。