先进高强钢板材复杂构件准静态冲压-动态电液成形复合加工增塑机制及变形协调控制

The technical bottlenecks, such as low formability and unmanageable forming precision at room temperature, have greatly impeded the application of advanced high strength steel (AHSS) sheets using for car body. Based on the applicant’s research on the high speed forming of sheets for many years, a new compound forming technology, the quasi-static stamping-dynamic electrohydraulic forming (EHF), is proposed to solve these problems of AHSS sheet forming at room temperature. In this project, the combined methods among theoretical analysis, experiment and numerical simulation will be used to investigate the plasticity improved mechanism and the deformation coordination control of the quasi-static stamping-dynamic EHF compound forming process of AHSS sheets. This project mainly focuses on the compound deformation behavior, deformation coordination control and microstructure evolution during quasi-static-dynamic compound forming process. The aims include to reveal the plasticity improved mechanism and the deformation coordination mechanism of AHSS sheets within the compound forming process, to establish the association relationship between the improved plasticity effect and the microstructure evolution, to propose the method used to evaluate forming limit of the compound forming and to break through the key technology to precisely control compound deformation. After the project completed, the theoretical and practical foundation to investigate the quasi-static stamping-dynamic EHF compound forming technology would be laid and an effective way to precisely fabricate AHSS sheet metal parts at room temperature would be presented.

针对制约车身用先进高强钢板材推广应用上的技术瓶颈问题（如室温成形性能差、成形精度难以控制），在多年板材高速率成形研究的基础上，申请人提出室温下车身用先进高强钢板材准静态冲压-动态电液成形复合加工新方法。本项目拟采用理论分析、试验和数值模拟相结合的方法对先进高强钢板材准静态冲压-动态电液成形复合加工过程的增塑机制和变形协调控制展开研究。通过深入研究准静态-动态复合成形过程的变形行为、变形协调控制及微观组织结构演变等基础问题，揭示复合成形条件下先进高强钢板材增塑机制和变形协调机制，建立先进高强钢板材复合成形增塑效应与微观组织结构演变的关联关系，提出准确评价复合成形极限的试验方法，突破复合成形过程中变形协调控制技术。课题研究结果将为先进高强钢板材准静态-动态复合成形技术研究与应用奠定理论和实践基础，为车身用先进高强钢板材室温精确成形提供一条有效技术途径。

近年来，以双相钢（DP）为代表的先进高强钢（AHSS）已成为车身轻量化的主要材料。DP钢板材室温成形性差，传统冲压成形极限偏低，成形精度难以保证。本项目提出了复杂曲面构件准静态冲压-动态电液成形复合加工技术，通过准静态冲压成形和动态电液成形的技术优势融合，提高室温下AHSS板材成形性能，为复杂曲面构件生产提供有效方法。.本项目从工艺试验、数值模拟、力学响应、微组织演变等方面对DP600板材的成形性能进行了研究。相对于准静态成形极限，动态电液成形条件下单向拉伸、平面应变、双等拉条件下的极限应变分别提高了27.8%、70%和17.5%。电液成形过程中的惯性效应对被测试样塑性变形的贡献率为87.1%，其可沿试样伸长方向产生额外的主应力，减缓了危险质点附近区域的速度变化梯度，抑制了不均匀塑性变形，从而协调了整体变形，此为宏观增塑机制。电液成形过程中，高应变速率下铁素体中形核产生新位错，导致位错密度增加，抵消了由准静态预变形引起的位错堆积、缠结和不均匀分布；马氏体中被诱导出现[01-1]MT形变孪晶，提高了铁素体相和马氏体相的塑性相容性，优化了应变梯度，降低了脱粘和微孔洞形核的风险，此为微观增塑机制。经准静态预变形后，板坯的动态材料本构行为发生显著变化，使典型应变路径下准静态预变形板材在后续的电液成形中展现出了良好的塑性；复合成形极限应变与初始板的动态电液成形极限应变处于同一水平，且准静态预变形水平对终极极限应变的影响不明显。弯曲件复合成形过程中，实现了弯曲试样圆角段与直壁段的协调变形，缓解了两段交界处的材料堆积现象，保证了弯曲试样的表面质量。通过调整放电电压，获得了满足贴模精度的R10、R8、R5、R3和R0系列弯曲圆角条件下的复合弯曲件。.通过本项目的研究，将为AHSS板材室温精确成形提供一条有效途径，对拓展AHSS板材的工业化应用具有重要实践意义。