铝合金差速双轴肩搅拌摩擦焊非对称成形机理及力学性能控制研究

With the rapid development of China's aerospace industry, bobbin tool friction stir welding (BT-FSW) has been expected to be a key technology in manufacturing of the large scale common bulkhead tank. However, it has been frequently reported that a bad-formation zone remains in the joint, which significantly intimidates the joint strength. In this study, the dual-rotational BT-FSW is proposed to introduce an asymmetrical effect on the weld formation, to enhance the material flow and improve the joint strength. To understand the nature of the weak flow zone, key features of the shape will be figured out based on the microstructure observation. Meanwhile, a coupled thermo-mechanical finite element model of BT-FSW is going to be established to visualize the plastic material flowing behavior. A thoroughly investigation on the evolution of grain size, precipitates and crystallographic texture will be carried out, for getting insight into the impact of dual-rotational BT-FSW on the joint microstructure. Moreover, a comparison study is proposed on global and local mechanical properties of the dual-rotation BT-FSW joint, to explore the relation between the inhomogeneous microstructure and the corresponding mechanical properties. At last, the welding parameter window will be figured out for future mechanical properties optimization. This work is not only expected to be a complement of the theory of the friction stir welding technology, but also an effectively theory guide for the future application of BT-FSW in aerospace industry.

随着我国航天事业持续快速发展，双轴肩搅拌摩擦焊被选为未来高性能大型共底贮箱制造的关键技术之一，但接头内部成形弱区问题严重影响了构件质量可靠性。针对成形弱区问题，本项目以铝合金双轴肩搅拌摩擦焊为研究对象，突破常规对称成形设计，提出并开展了主动差速控制非对称成形工艺理论与试验研究。以接头成形弱区为研究重点，分析提取接头形貌关键特征量，并建立其随工艺参数的演变模型。通过试验与数值模拟相结合的手段，研究焊接温度场及流场耦合演变规律，揭示接头成形弱区形成本质，阐明宏观塑性变形及微观界面消失协同作用下的非对称成形机理。研究接头晶粒、沉淀相和织构取向，揭示非对称成形对接头组织非均匀性的影响规律，结合接头整体与局部力学性能相关性分析，建立非对称成形条件下接头力学控制模型。研究成果将直接为铝合金差速双轴肩搅拌摩擦焊工艺规范设计提供参考，该项目的实施将有力推动搅拌摩擦焊的理论发展及其在航空航天等领域的应用。

本项目以航天贮箱铝合金双轴肩搅拌摩擦焊为研究对象，突破常规对称成形设计理念，提出并开展了铝合金差速双轴肩搅拌摩擦焊非对称成形机理及力学性能控制工艺理论与试验研究。以接头成形弱区为研究重点，通过试验与数值模拟相结合的手段，研究揭示了接头成形弱区形成本质，阐明了宏观塑性变形及微观界面消失协同作用下的非对称成形机理。结合接头整体与局部力学性能相关性分析，建立了非对称成形条件下接头力学控制模型。基于非对称成形理论的研究，开展了2195铝锂合金的焊接研究，实现了接头抗拉强度85%，延伸率8.4%，断裂位置全部位于HAZ/TMAZ的重要技术突破。推广技术研究在航天贮箱2219铝合金的试验应用研究，项目实现了中厚度2219铝合金双轴肩搅拌摩擦焊接工艺，接头抗拉强度超过330MPa，接头延伸率超过5%。研究成果直接支撑了双轴肩搅拌摩擦焊接技术在我国航天贮箱先进制造技术的升级换代，并顺利通过了我国某型号的应用论证与试验。