铝-铜合金回填式搅拌摩擦点焊接头 连接机理与断裂模式分析

为了提高飞机蒙皮连接强度,采用回填式搅拌摩擦点焊(RFSSW)技术对飞机蒙皮材料2524-T3进行了焊接试验。采用体式显微镜和金相显微镜对接头组织进行观察,通过拉剪试验和拉脱试验对接头进行力学性能测试,对断口进行扫描分析。结果表明:接头成形良好,无明显缺陷,RFSSW接头在热机耦合作用下,焊点形成4个不同显微组织区域;RFSSW接头力学性能普遍高于铆接,焊接接头剪切性能达到7.233 kN,较铆接提高113.4%,焊接接头拉脱性能达到3.172 kN,较铆接提高6.16%;接头断裂呈现为焊核剥离断裂和塞型断裂两种模式,当接头下扎深度较浅,焊点内部搅拌不足时产生焊核剥离断裂,随着套筒下扎深度的增加,塞型断裂由上板塞型断裂转变为下板塞型断裂,拉剪和拉脱焊核剥离断裂均为韧性断裂,塞型断裂均为混合型断裂。通过对回填式搅拌摩擦点焊接头力学性能的分析,为搅拌摩擦点焊代替铆接在航空结构件上的应用提供理论和技术基础。

Research on joining mechanism and fracture mode of Al-Cu alloy joint by refill friction stir spot welding

In order to increase the joint strength, RFSSW is used to weld 2524-T3 aluminum alloys of aircraft skin. The joint Connection Mechanism is studied through the analysis of its appearance and microstructure by SM and metallographic microscope, The mechanical properties of the joint is investigated by tension-shear test and cross-tension test, and the fracture is analyzed by SEM. The experiment results show that the RFSSW joint has a good forming and defect-free on the surface, and with the action of thermo-mechanical, the cross-section of the joint can be divided into four zones in grain structure. The mechanical performance of RFSSW joints is generally higher than that of riveting joints. The tension-shear performance of welding joints reaches 7.233 kN, which is 113.4% higher than that of riveting joints. The tension-shear performance of welding joints reaches 3.172 kN, which is 6.16% higher than that of riveting joints. There are two types of joint fracture modes: nugget debonding fracture and plug fracture. When the plunge depth of sleeve is relatively small and the internal agitation of joint is insufficient enough, it can result in the nugget debonding fracture. With the increase of plunge depth of sleeve, plug fracture make gradually changes, the transition from plug fracture (fracture in the upper sheet) to plug fracture (fracture in the lower sheet). Ductile fracture is observed in both tension-shear test and cross-tension test with the nugget debonding fracture. The mechanical properties of refilled friction stir spot welding joints are analyzed, which provides theoretical and technical basis for the application of RFSSW in aerospace structural components.