铝合金搅拌摩擦焊管材液压成形机理及组织演变规律研究

Due to the increasingly urgent lightweight demand in the aerospace industry, the application of thin-walled aluminum alloy tube with variable cross section continues to expand in the aircraft and aerospace industry. Such tubes always have complex shape and large radius-to-thickness ratio. It is difficult to obtain such tubes by conventional manufacturing processes. In this project, large diameter thin-walled aluminum alloy tubes were produced using a hybrid process combining friction stir welding (FSW) and spinning, and the hydroforming mechanism and microstructural evolution of the aluminum alloy FSW tubes were studied by theoretical modeling, numerical simulation and experiments. The emphasis was put on the basic deformation law and wrinkling behavior of the FSW tube during hydroforming, and the regulation mechanism on microstructure and mechanical properties of FSW joints during thermomechanical treatment was also investigated in detail. The limiting corner radius of the FSW tubes was analyzed, and the theoretical value was verified. The formation of the geometric and mechanical conditions of the "beneficial wrinkles" for FSW tubes was clarified, and the constraining effect of weld on wrinkling behaviors of the FSW tubes during hydroforming was revealed by the classical theory of plasticity instability. The evolution of the mircrostructure and the toughening mechanism of the FSW joint under thermomechanical treatment were obtained. The aim of the project is to provide theory foundation and technology support to the application of hydroforming the FSW tubes.

航空航天领域轻量化的发展，对铝合金薄壁异型截面管件的需求不断增多。此类管件结构复杂、径厚比大，主要存在制坯困难，难以整体成形等问题。本项目提出搅拌摩擦焊(FSW)旋压复合制管工艺解决铝合金薄壁管材制备难题，结合液压成形技术，运用理论建模、数值模拟及工艺试验等方法研究铝合金FSW管材液压成形机理及组织演变规律。重点研究FSW管材液压成形中圆角充填规律、管材起皱行为，以及形变热处理对FSW接头组织及性能的调控机制等科学问题。揭示FSW管材极限圆角半径的变化机理，阐明FSW管材“有益皱”形成的几何和力学条件，主动控制多约束加载条件下焊缝所引入的不均匀变形特征，揭示FSW管材液压成形中的约束与变形协调机制，明晰FSW接头在变形及热处理协同作用下组织演变及其强韧化机理。为铝合金FSW管材液压成形技术在航空航天领域的应用提供理论基础和技术支撑。实现FSW与液压成形等研究领域广度和深度的同步扩展。

为了解决飞机进气道等铝合金异型截面管件整体成形的难题，提出铝合金FSW管材液压成形，运用理论建模、数值模拟与工艺试验等方法研究FSW管材成形机理和组织演变规律。取得的重要研究结果如下：.（1）阐明了铝合金FSW接头塑性变形规律及组织性能调控机制。根据金相与硬度实验，将焊缝分区，通过铝合金材料强度与硬度的关系公式，计算焊缝各个分区对应的材料特性，建立了准确的有限元模型。主应力和Mises等效应力及等效应变在试样长度方向上是非均匀分布的，应力在屈服应力最小的区域最低，在屈服应力较大的区域相应升高，各分区的应变存在相互协调与约束，并且在搅拌摩擦焊接头中存在失配比差的交界处应力与应变都会发生突变。对2024-O铝合金进行FSW后，通过采用降低温度固溶+冷变形+时效的方法，显著降低了FSW接头焊后热处理AGG的程度，同时保证了接头的力学性能。.（2）揭示了铝合金FSW管材液压成形圆角充填规律。分析圆角充填过程中，焊缝强度及形状对FSW管材的应力、应变状态的影响规律，发现焊缝的存在给管坯的圆角充填变形带了困难。贴膜后有焊缝一侧管坯贴膜长度明显小于无焊缝一侧；焊缝发生塑性变形的条件为形变强化效果大于摩擦力的阻碍作用。焊缝附近的壁厚明显大于其它部位，在一定程度上降低了成形件的壁厚均匀性。.（3）建立了铝合金FSW管材液压成形起皱行为及控制方法。揭示了铝合金FSW变径管液压成形起皱行为及成形规律。焊缝有抑制管材液压成形过程中皱纹产生以及减少皱纹数量的效果，在补料内压较低时，这种抑制效果很明显。提出了利用和控制FSW管材液压成形过程中起皱行为的方法。由于焊缝的存在，管材液压成形的合适成形压力区间会减小，成形时需要综合考虑焊缝强度及形状和加载路径的合理匹配关系，尽量提供高的成形内压，以改善管材的成形性能。