轻合金搅拌摩擦焊接/加工中组织控制与力学行为研究

As a joining/processing technique by means of severe plastic deformation, friction stir welding and processing (FSW/P) has a wide application prospect. However, the key factors controlling the microstructure and mechanical behavior of FSW/P samples are still not well understood, and establishing effective controlling and predicting methods are highly desired. In this study, typical aluminum alloys, magnesium alloys and titanium alloys are subjected to FSW/P investigations under different conditions. The initial material flow and microstructural evolution during FSW/P of different-grained materials are analyzed in detail by using various tracers and tool extraction technology with rapid instant cooling. The relationship between friction coefficient and temperature is solved by the inverse solution method, and the temperature, residual stress and strain, and material flow during FSW/P are modeled by self-developed finite-element software. The mechanical properties and fracture behavior of the FSW joints are systematically investigated under complicated loading conditions. These investigations will clarify the mechanisms of the material flow, dynamic recrystallization, accelerated particle dissolution and element diffusion/reaction as well as the key influencing factors, and elucidate the response mechanism of the FSW joints under complicated loading conditions, thereby establishing the guide lines for the FSW tool design and parameter optimization, and achieving the effective control and prediction of the microstructure and mechanical properties of the joints. It is expected that this study will speed up the research/development and industrial applications of FSW/P in our country and enrich the classic theories of metal hot-working.

作为大塑性变形连接/加工技术，搅拌摩擦焊接与加工（FSW/P）应用前景广阔，但目前对控制组织与力学行为的关键因素仍缺乏深刻认识，急需建立有效的组织和性能的调控与预测手段。本项目选择典型铝、镁、钛合金作为研究对象，采用不同初始晶粒结构材料和多种流变示踪方法进行FSW/P并配合过程急停和急冷，以获得原始材料流动和微观结构演化信息并予以表征；采用逆问题求解摩擦系数与温度的函数关系并采用自主开发的有限元软件进行温度场、残余应力应变场和流变场模拟仿真；系统评价复杂工况下接头力学性能和断裂行为。通过这些研究，揭示材料流动、动态再结晶、第二相快速溶解、元素加速扩散/反应的机制及其关键影响因素，阐明FSW接头在复杂服役条件下的响应机制。从而建立搅拌工具设计和工艺参数优化的指导准则，实现接头组织和性能的有效调控与理论预测。促进FSW/P在我国的研发和工业化应用，丰富经典的金属材料热加工理论。

受制于对控制组织与力学行为的关键因素缺乏深入认识，我国搅拌摩擦焊（FSW）的工业应用步伐与国外相比明显滞后，而搅拌摩擦加工（FSP）的研究还处于起步阶段。本项目选取工业应用中常用的铝、镁、钛等多种轻合金为研究对象，对FSW/FSP过程中与微观组织演变和力学行为相关的关键科学问题进行了深入研究。采用对接面增厚氧化膜的方式对铝合金FSW过程中的材料流变进行了系统研究，阐明了特征微观组织和典型缺陷的形成机理；通过“急停+快速冷却”技术对焊核区的微观组织演化研究揭示了铝合金及钛合金FSW过程中的再结晶机理，并阐明了钛合金独特的热机影响区形成机制；通过对典型的2024铝合金FSW及后续时效过程中析出相演化的深入表征和FSP制备铝基复合材料中颗粒的破碎及分布特征分析，阐明了典型材料FSW/FSP过程中元素快速反应/扩散机理和第二相演化机制；通过自主研发的有限元模拟软件构建了温度场、流变场、残余应力场模型，率先实现了钛合金水下FSW过程的温度场和铝基复合材料FSW接头的残余应力场的精确表征；系统分析了影响FSW接头力学性能的关键因素，建立了不同材料体系的高质量FSW工艺；通过复杂应力条件下的力学行为表征揭示了FSW接头及FSP细晶/超细晶材料的高温超塑性变形和疲劳变形机制。通过上述研究，阐明了FSW/FSP过程的微观组织演化机制，建立了FSW焊接工具设计和工艺参数优化的指导准则，实现了接头/加工区组织和性能的有效调控与理论预测。基于本项目取得的研究结果，研制出复合材料及厚板FSW专用的高性能焊接工具，建立了核燃料贮运容器、高速列车车钩座板结构件的FSW制造工艺规范，成功实现了60 mm铜合金和40 mm铝-铜异种金属超厚板的FSW，利用FSP技术制备出高性能的碳纳米管增强铝基复合材料电枢，解决了我国核电、轨道交通、关键装备等领域的技术难题，实现了FSW/FSP的工业应用。通过本项目研究，丰富了经典的金属材料热加工理论，促进了FSW/FSP在我国的发展和工业化应用进程。