强电磁脉冲载荷作用下铝合金塑性成形宏微观本构关系和断裂机制及其在大型复杂厚板件电磁成形中的应用

The forming for large and complex thick sheet metal parts of aluminium alloy have been an important and urgent light-weight demand with the development of aviation, aerospace and automobile industries. The plastic forming technology of aluminium alloy under high electromagnetic pulse loadings could highly enhance plastic deformation ability of aluminium alloy at room temperature, and has become a significant method for improving the forming ability and implementing the precise control for large and complex thick sheet metal parts of aluminium alloy. Macro/micro constitutive equations and fracture mechanism for plastic deformation of aluminium alloy under high electromagnetic pulse loadings based on the coupled multi-parameters and multi-physical fields are obviously changed, leading to an increase of strain hardening rate and/or rate sensitivity and influencing in electromagnetic forming and precise control of large and complex thick sheet metal parts of aluminium alloy, so become the key scientific problem which could be urgently solved. In the project, based on the integrated research methods of theoretical analysis, experiments and numerical simulation, the investigation of experimental technologies and numerical simulation methods for plastic deformation of aluminium alloy under high electromagnetic pulse loadings, the establishment of macro/micro constitutive equations for plastic deformation of aluminium alloy under high electromagnetic pulse loadings, the investigation of macro/micro fracture mechanism for plastic deformation of aluminium alloy under high electromagnetic pulse loadings and the investigation of forming mechanism and precise control for plastic deformation of large and complex thick sheet metal parts of aluminium alloy under high electromagnetic pulse loadings are performed. The results of the project show the significant scientific purpose and the extensive application foreground for the development of plastic deformation theory and technology of large and complex thick sheet metal parts of aluminium alloy under high electromagnetic pulse loadings.

随着我国航空、航天、汽车等领域的发展，铝合金大型复杂厚板件成形已成为实现轻量化的迫切需求。强电磁脉冲载荷作用下铝合金塑性成形技术能显著提高铝合金常温成形性能，是解决大型复杂厚板件成形能力不足、实现精确调控的重要方法。多参数多物理场耦合使强电磁脉冲载荷作用下铝合金塑性成形本构关系和断裂机制发生改变，导致加工硬化率和应变率敏感性提高，影响大型复杂厚板件电磁成形工艺及其精确调控，因此成为该技术发展亟需解决的关键科学问题。本项目综合采用理论、实验、数值模拟方法，研究强电磁脉冲载荷作用下铝合金塑性成形实验技术和数值模拟方法、建立强电磁脉冲载荷作用下铝合金塑性成形宏微观本构关系、揭示强电磁脉冲载荷作用下铝合金塑性成形宏微观断裂机制、研究强电磁脉冲载荷作用下铝合金大型复杂厚板件塑性成形机理和成形工艺精确调控。结果对发展强电磁脉冲载荷作用下铝合金大型复杂厚板件塑性成形理论和技术具有重要科学意义和应用前景。

在铝合金大型复杂厚板件电磁成形过程中，多参数多物理场耦合使强电磁脉冲载荷作用下铝合金塑性成形本构关系和断裂机制发生改变，进而影响铝合金大型复杂厚板件电磁成形工艺及其精确调控。针对该问题，本项目以铝合金电磁成形宏微观本构关系和断裂机制及大型复杂厚板件电磁成形技术为研究对象，开展了强电磁脉冲载荷作用下铝合金大型复杂厚板件精确塑性成形理论和技术的研究。主要研究结果包括：（1）基于虚速度原理构建铝合金在电磁力及惯性力作用下应力响应的表征方法，揭示了电磁成形下流动应力随着胀环应变率的提升而提升且相对较低，其原因是涡流效应带来的应力软化抵消了变形后期的应变硬化。（2）电磁胀环条件下，应变的均匀分布和颈缩失稳的分散，利于材料成形性能的提升；微观演变机制是位错消融与亚晶界逐渐旋转相结合的动态再结晶机制，变形机制是由晶界旋转和动态再结晶产生的晶间滑移机制。（3）动态变形时材料倾向于在多处同时发生失效，以及相似的惯性力演化规律，表明惯性效应对材料成形性能提高的主导作用；电磁动态单向拉伸在变形后期避免了载荷的持续作用，并且相应的应变率稍低。（4）由于电磁力分布特点，向下速度峰值首先产生于板材对应线圈半径中心处，速度峰值向板材中心传播时继续加速；对于电磁力作用区域和无电磁力作用区域内侧，塑性应变主要产生于电磁力作用阶段。（5）在电磁间接成形中，当驱动片厚度等于驱动片的趋肤深度时，工件的贴模程度最优；反弹效应被抑制，是因为板料下表面与模具的产生的碰撞压力与板料上表面受到的橡胶的压力相抵消。（6）放电电压与成形高度、最大/次应变近似成线性正相关；增加润滑和减小压边力可以提高成形高度，同时减小最大主应变，促进工件主体区域的材料流动至顶部和易破裂区。（7）针对大型构件提出了基于双线圈的分层多道次电磁渐进成形方法，获得表面光整的构件，且成形误差小于0.2%，材料减薄率小于10%。（8）针对电磁成形/电磁校形相组合的两步电磁成形新工艺，提出了斜向翻孔成形的几何设计方法；凸缘高度和板料厚度主要由成形决定，校形对其影响较小；变形区域分为单向拉伸、双向拉伸和平面应变等三个区域。研究结果对发展耦合宏微本构关系和断裂机制的铝合金大型复杂厚板件电磁精确成形理论和技术具有重要科学意义和工程价值。