6000系铝合金板热冲压过程中微观组织演化与强化机制

With the ever-increasing concern about the energy and environment crises, the demand for the automotive weight reduction has been required more than usually expected. The widely use of aluminium alloy sheets with high specific strength in automotive bodies has become an important solution, but the relatively poor formability of aluminium alloy sheets retards this progress. This bottleneck is expected to be overcome by the employment of a new hot stamping technology named solid solution treatment, forming and cold-die quenching. However, due to the introduction of the hot deformation and additional thermal process into the original production flow, the existing superior mechanical properties of the material improved by the previous heat treatment are likely to be degraded. Thus, how to rapidly harden the hot stamped parts has become another difficulty. For this reason, the proposed project will investigate the structural characteristics of precipitated phases in the 6000 series aluminium alloys and their dynamic evolution laws during the hot stamping, analyse the effects of heat, deformation, electricity and magnetism on the microstructure evolution and mechanical properties, reveal the precipitation hardening mechanism, and establish the multi-field coupling models of the microstructure evolution and hardening. This project will also explore the feasibility of improving the efficiency of the solid solution treatment of materials before the hot stamping and enhancing the subsequent bake hardening by means of selecting specific initial temper of sheets, increasing the heating rate, applying the induction heating or static electric field. The effects of the pre-ageing parameters, the modes and degrees of the hot stamping deformation on the bake hardening and mechanical properties uniformity will be elucidated. Finally, an efficient heat treatment process will be optimized to match the hot stamping, resulting in obtaining the needed mechanical properties of the 6000 series aluminium alloy parts formed precisely by the hot stamping.

随着能源和环境问题日益严峻，对汽车轻量化的需求愈发强烈，高比强度铝合金板在车身中普及成为重要措施，但其较低的可成形性成为发展的瓶颈。固溶处理-成形-冷模具淬火，即热冲压这一新方法的应用有望解决这一问题，但因其在原生产流程中引入热变形和额外的热过程，材料原有经热处理获得的优异力学性能退化，如何快速强化热冲压件成为另一难题。为此，本项目将研究6000系铝合金板热冲压过程中析出相的结构特点及其动态演化规律，分析热、变形、电、磁对微观组织演化和力学性能的影响，揭示析出强化机制，建立多场耦合的微观组织演化与强化模型；探讨通过选择板材初始状态、提升加热速度、采用感应加热或施加静电场来提高热冲压前材料固溶处理效率和后续烘烤硬化性的可行性；阐明预时效参数和热冲压变形形式、大小对构件烘烤硬化性和力学性能均匀性的影响。最终，优化与热冲压成形相匹配的高效热处理工艺，实现6000系铝合金板热冲压控形同时的控性。

随着能源和环境问题日益严峻，对汽车轻量化的需求愈发强烈，高比强度铝合金板在车身中普及成为重要措施，但其较低的室温可成形性成为发展的瓶颈。固溶处理-成形-冷模具淬火，即热冲压这一新方法的应用有望解决这一问题，但因其在原生产流程中引入热变形和额外的热过程，材料原有经热处理获得的优异力学性能退化，如何快速强化热冲压件成为另一难题。为此，本项目研究了6000系铝合金板热冲压过程中析出相的结构特点及其演化规律，分析了热、变形、电、磁对微观组织演化和力学性能的影响，揭示了析出强化机制，建立了微观组织与力学性能的映射关系。结果表明，原始板材析出相细小利于其加热时溶解，加热速率快利于避免升温时析出相的转变而加速溶解，感应加热和自阻加热对固溶处理的作用表现为提高加热速率的热效应，热处理中静电场的施加提高了合金元素的固溶速度和程度而使析出相更细小弥散，这些因素有利于提高固溶效率和时效强化；高温短时预时效和低温储存有利于抑制自然时效；W态下冷变形形成大量位错，为强化相形核提供质点，从而增强时效强化；热变形由于位错增殖同时发生动态回复和再结晶，其对自然时效和人工时效的强化作用不明显，并表现出微弱的烘烤软化作用。最终，探明了影响热冲压件微观组织和力学性能的主要参数及其影响规律，为制定与热冲压成形相匹配的高效热处理工艺，实现6000系铝合金板热冲压控形同时的控性奠定了基础。