高强铝合金厚板变摩擦系数双轴肩FSW焊缝组织性能均匀性研究

To solve the problems of nonhomogeneity of microstructure and properties along thickness direction by the single side friction stir welded (FSW), which has become a trouble for lightweight aerospace manufacturing and need to solve the key scientific and technological issues. Double shoulder friction stir welding, which presents relatively uniform thermal cycle and mechanical stir, was performed on high strength aluminum alloy thick plate for aerospace using the telescopic welding tool with the variable friction coefficient, different screw thread direction of pin and double shoulder. In the present research, microstructure evolution, macro and micro texture, second phase particles along thickness direction were investigated. Tensile testing of the whole joint as well as three slices through the plate thickness was also conducted. Texture analysis was calculated using the results of the orientation distribution function and Schmid factor, revealing the start of the weld material and quantitative analysis of tensile failure location and fracture mechanism. The systematic study was able to charify microstructure evolution law, recrystallization mechanisms, distribution of second phase particles and strengthening mechanisms, and also establish change laws for tensile properties, joint efficiency, strain hardening behavior and strain-rate sensitivity at different temperature and strain rates. The interaction relation mechanism between microstructure or mechanical properties and double-side friction stir welding were also obtained. An attempt was made to develop the associated control technology and the mechanism of homogenization of microstructure and mechanical properties through the plate thickness. These results may provide the supporting technology and fundamentals for the homogenization of microstructure and properties along thick direction of friction stir welded thick plate. The theoretical result is also helpful for expanding the applied range of FSW in the modern equipment manufacturing.

当前高强铝合金厚板单面搅拌摩擦焊（FSW）焊缝组织性能的不均匀性，已成为困扰航空航天领域轻量化复杂构件连接制造发展的难题和亟待解决的关键科学技术问题。为此，本项目提出采用变摩擦系数、不同螺纹旋向和双轴肩可伸缩搅拌头，开展沿板厚方向热力耦合相对均匀的双轴肩FSW研究。通过研究焊接工艺参数对焊缝成形的影响机制，沿板厚方向晶粒尺寸、第二相粒子形貌分布特征和织构演变，接头整体和分层切片拉伸性能以及断裂失效的定量分析。阐明双轴肩FSW焊缝沿板厚方向组织演变规律、再结晶机制、第二相粒子强化机制；揭示不同温度和应变速率时接头拉伸性能、硬化行为、应变速率敏感性的变化规律；获得双轴肩FSW工艺与焊缝组织结构分布特征、力学行为之间的内在相关性，及焊缝组织性能沿板厚方向均匀化机制，探索实现焊缝组织性能均匀化的控制技术途径。相关研究成果可为铝合金厚板FSW接头的均匀化制备提供理论依据、技术支撑，并拓展其应用范围。