超高强铝合金和镁合金同种/异种材料搅拌摩擦焊接技术及相关基础

In order to solve the technical problems of friction stir welding (FSW) similar thick plates of ultra-high strength aluminium and magnesium alloys, a new technique of differential double-shoulder FSW (DDS-FSW) is invented in this work. Several basic issues for DDS-FSW similar thick plates and traditional FSW dissimilar thin plates were systematically studied, including characterization of temperature, material flow, and stress-strain fields, reaction mechanism of precipitates and intermetallic compounds, and prediction and control of microstructure and properties of joints. In this study, the combination of experimental and numerical simulation methods is used. The relationship between friction coefficient and temperature is solved by the inverse solution algorithm, and the temperature, material flow and stress-strain fields are modeled by self-developed MSFESL software. Based on the characterization of grain size, grain orientation, precipitates and intermetallic compounds, the static tensile property, fatigue and stress corrosion behaviors are systematically evaluated. These investigations will clarify the evolutions of temperature, material flow, and stress-strain fields during FSW, indicate reaction mechanisms of precipitates and intermetallic compounds, elucidate the environmental response mechanism of the joints under complicated loading conditions, establish quantitative relations between grain orientation and mechanical properties, and thus achieve the effective prediction and control of the microstructure and mechanical properties of FSW joints.

为了解决超高强铝、镁合金厚板搅拌摩擦焊（FSW）技术难题，本项目提出了差动双轴肩自支撑FSW（DDS-FSW）新技术。针对铝、镁厚板同种材料DDS-FSW和薄板异种材料常规FSW，在温度场、塑性流场和应力应变场表征、沉淀强化相和金属间化合物反应机理、接头组织性能预测和控制等方面开展系统研究。拟采用实验和数值模拟相结合的方法，利用逆问题求解算法建立摩擦系数与温度的函数关系，并采用自主开发的MSFESL有限元软件高精度模拟仿真温度场、塑性流场和应力应变场。在表征晶粒尺寸、晶粒取向、沉淀强化相和金属间化合物等本征结构基础上，系统评价接头静态拉伸、疲劳和应力腐蚀行为。通过上述研究，掌握铝、镁合金同种/异种材料FSW温度场、塑性流变和应力应变演变规律；揭示沉淀强化相和金属间化合物反应机理；阐明接头多场服役环境响应机制；建立晶粒取向与力学性能量化关系，从而实现对FSW接头组织性能的理论预测和主动控制。

近年来国家重大工程项目建设对超高强铝合金和镁合金厚板焊接构件需求迅速增加。如何实现超高强铝合金和镁合金厚板同种/异种材料的高效优质连接成为关键技术问题。本项目针对超高强铝、镁合金厚板焊接，创新性提出了差动双轴肩自支撑搅拌摩擦焊（DDS-FSW）新技术，通过表征不同焊接条件下摩擦系数与温度的关系，建立了适用于超高强铝合金、镁合金厚板FSW温度场和塑性流场模型，阐明了铝合金厚板接头沉淀强化相快速溶解、析出的物理本质。基于轴肩与搅拌针的独立控制，实现了镁合金厚板接头晶粒尺寸和晶粒取向主动控制，提高了接头力学性能。通过研究沉淀强化相、晶粒尺寸和晶粒取向对接头力学性能的影响，建立了沉淀强化相、晶粒尺寸和晶粒取向与接头力学性能的定量关系。基于热力学反应原理和原子碰撞理论，阐明了铝、镁异种材料焊接接头金属间化合物快速扩散反应形成机制；阐明了滑移和孪生对铝、镁异种材料焊接接头高周疲劳裂纹萌生和扩展的作用机制，揭示了焊接接头腐蚀机制。基于上述研究，本项目实现了超高强铝合金和镁合金厚板同种/异种材料的高效优质连接。