局部循环变形对异种高强铝合金搅拌摩擦焊接头的强化机制研究

异种高强铝合金搅拌摩擦焊接在航空航天等领域具有重大的需求，但服役环境的苛刻性与复杂性对接头力学性能提出了更高要求，现有的接头性能调控方法存在较大局限，难以解决热影响区严重软化难题。基于前期研究结果，在循环变形作用下异种高强铝合金搅拌摩擦焊接头发生循环硬化现象，申请人发现并提出了焊后局部循环变形强化新方法，在室温下获得硬度分布均匀、强度显著提高的接头。本项目以接头非均匀组织与性能量化表征为切入点，揭示接头在拉伸和循环变形条件下的应力-应变响应行为，阐明局部循环变形参数（总应变幅、循环周次）对接头强化影响，获得其可控性规律。最后，基于量化的晶粒尺寸、晶界特性、强化相、位错组态等信息，建立接头拉伸过程中组织演化与非均匀硬化行为的相关性，阐明局部循环变形对接头强化的作用机制。该项目的实施将有力推动异种高强铝合金搅拌摩擦焊接头强化理论发展及在航空航天等领域的关键应用。

The welding of dissimilar high strength aluminum alloy is in a significant demands in aerospace field. But the greater requiremens is needed for the mechanical properties of joint because of the punitive and complexity in service. The present methods, controlling mechanical properties of joints, exist greater limitations, and induce the seriously softened heat affected zone which is very hard to solve. Based on the preliminary results, cyclic hardening phenomenon appeared when cyclic deformation was conducted on the friction stir welded dissimilar high strength aluminum alloy joints, the applicant has found and proposed a novel strengthening method, post weld local cyclic deformation, to achieve the joint with homogeneous hardness distribution and significant improvement of strength at room temperature. The quantified characterizations on the inhomogeneous microstructure and mechanical properties act as the pointcut in the present project, revealling the stress-strain response behavior when tension and cyclic deformation are performed, elucidating the effect of local cyclic deformation parameters, total strain amplitude and cycilc circles, on the joint strengthening and acquiring its controllability law. Finally, the correlation between microstructure evolution and inhomogeneous hardening behavior during tension process will be constructed based on the quantified grain size, grain boundary characteristics, precipates and dislocation state. The mechanisms of local cyclic deformation action on the joint strengthening will be revealed. Thus, the development of strengthening theory and key applications in the areospace filed for the friction stir welded dissimilar aluminum alloy joints will be promoted by the implement of the present project.