泡沫铝夹芯三明治复合板制备及形/性协同控制机理研究

Aluminum-foam sandwich (AFS), which combines the advantages of lightweight and high stiffness to weight ratio, is a typical lightweight, high-strength structural materials and has a clear demand and urgent application in the automotive and aerospace field. However, traditional preparation methods always lead to poor density and uniformity of the foam, and low bonding strength between the panel and core layer. In response to these problems, the project proposed a new preparation process to produce the AFS plate based on friction stir welding. Combined the tailor-welding technology, the cooperative control mechanism of the forming and microstructural evolution of the AFS were studied in order to solve the problem of fabrication and forming of the large AFS plate. The emphasis was put on the formation mechanism of the friction stir welding and the control mechanism of the mechanical properties and microstructure, as well as the constraints and deformation coordination mechanism of the AFS plate during forming was also investigated in detail. Thermal coupling flow model during welding AFS plate was built to clarify the microscopic mechanism of heat transfer and material flow. The control mechanisms and methods for the foam stability and uniformity were clarified. The failure mechanisms and deformation mechanism of the AFS plate were revealed, and the constraint and deformation coordination mechanism of the AFS plate during forming was also clarified. The aim of the project was to provide theory foundation and technology support to the application of preparing and forming the AFS plate.

泡沫铝夹芯三明治板(AFS,Aluminum Foam Sandwich)兼具比强及比刚度高等特点是一种典型轻质高强材料，在汽车及航空航天领域具有明确需求牵引和应用前景。但传统制备方法面临预制体致密性、均匀性以及板/芯结合强度差等问题。本项目提出基于搅拌摩擦焊的AFS复合板制备新工艺，解决大面积AFS复合板制备成形难题；结合拼焊成形技术研究AFS复合板制备及形/性协同控制机理。重点研究AFS复合板搅拌摩擦焊焊缝形成机理及组织性能调控机制，以及AFS拼焊板成形中的约束与变形协调机制等科学问题。建立AFS复合板焊接时的热力耦合模型，阐明传热与材料流动转移微观机制，揭示焊缝形成机理，给出泡孔稳定性与均匀性的控制方法和机制，实现控性目标；揭示AFS拼焊板失效机制及变形不均匀机理，阐明AFS拼焊板成形中的约束与变形协调机制，实现控形目标。为AFS技术在汽车及航空航天领域的应用提供理论基础和技术支撑。

为了满足汽车及航空航天领域零部件的轻量化，减少燃料消耗，本项目打破传统粉末冶金发泡工艺束缚，提出基于搅拌摩擦焊技术制备泡沫铝夹芯三明治结构复合板(AFS)工艺。运用工艺试验、理论分析、数值模拟等方法研究AFS制备工艺及形/性协同控制机理。取得的重要研究结果如下：. (1) 阐明了不同搅拌摩擦焊工艺条件下AFS组织形貌，确定最佳制备工艺条件：搅拌头旋转速度1000rpm，焊接速度300mm/min。利用搅拌头高速旋转，TiH2和CNTs粉末在铝基体中混合均匀可以获得高致密度的发泡预制体。AFS预制体发泡过程大致分为三个阶段：快速膨胀阶段、气孔长大合并阶段、泡沫坍塌阶段。同时，随着发泡温度升高，孔径尺寸先增大后降低，最终孔壁破裂，出现无泡层。最佳发泡温度为680℃发泡15min后，整个泡沫体孔隙率达到最大值，泡孔结构均匀趋于圆形，气孔数量多。并且，复合泡沫中CNTs结构较完整，Al基体与CNTs结合良好。. (2) 建立焊接过程中AFS热源输入模型及三维流动物理模型。对AFS搅拌摩擦焊温度场、流场进行模拟分析。搅拌摩擦焊AFS表面温度场随着焊接时间的不断延长，轴肩与工件的摩擦产热增加，温度场呈半圆形，且随搅拌头中心距离的增加温度逐渐降低；当搅拌焊时间t=300s时，搅拌头呈现最高温度值567℃，此时材料达到塑化状态，可实现良好的固态连接。AFS焊缝横截面温度场中，横截面焊缝温度分布呈“V”型，焊核区上宽下窄，沿着工件厚度方向温度分布逐渐降低。搅拌摩擦焊AFS流场分析中焊缝区域流场受到搅拌头旋转带动作用，流动区域主要集中在搅拌区，离轴肩距离近的位置，流速高；搅拌摩擦焊接过程中搅拌头的旋转速度与材料流场的速度成正比，随着旋转速度从 1000rpm 增加到 1300rpm，最高速度从0.41m/s增加到0.48m/s。. (3) 揭示AFS失效机制及变形不均匀机理。对不同孔隙率AFS力学性能进行研究，表明：AFS应力-应变曲线表现出脆性与韧性相结合的变形特征，AFS屈服强度随着孔隙率的增加而减少，最大屈服强度和平台应力值分别为11.1MPa和8.5MPa，最高的吸能性能为10.85MJ/m3。孔隙率45.8%的AFS最大冲压力32.8KN，杯突值达到7.2mm。