2099-T83/2060-T8异质铝锂合金搅拌摩擦焊搭接界面结构与力学性能INTERFACE STRUCTURE AND MECHANICAL PROPERTIES OF FRICTION STIR WELDING JOINT BETWEEN 2099-T83/2060-T8 ALLOYS

采用搅拌摩擦焊(FSW)对厚度为2 mm的2099-T83与2060-T8铝锂合金进行搭接。利用OM和SEM等分析技术探讨搅拌头转速和搅拌针长度对搭接接头界面结构与力学性能的影响。结果表明，2099-T83/2060-T8搭接接头焊缝区可观察到明显的结合界面，焊缝区显微硬度低于母材，且在热机影响区与焊核区的过渡区硬度值最低。当搅拌头转速由600 r/min增加到800 r/min，且搅拌针长度由3 mm减小至2.5 mm时，界面形貌由光滑界面转变成“锯齿状”咬合界面，焊缝区结合界面形貌主要受搅拌针长度影响。“锯齿状”咬合界面搭接接头平均破坏载荷为654 N，比光滑结合界面形貌的搭接接头承载能力提高了110%。搭接接头均断裂在底部母材2060-T8侧热机影响区与焊核区的过渡区，断裂特征为韧-脆混合断裂。“锯齿状”咬合界面搭接接头经150℃，保温20 h人工时效处理后，焊缝区显微硬度有所提升，接头承载能力较未经人工时效处理的降低了20%，断口呈现脆性断裂模式。

Aluminum-Lithium alloys are widely applied in aircraft structures owing to their unique properties, such as low density, high strength and stiffness, outstanding low temperature performance, corrosion resistance and superplasticity. 2099-T83 and 2060-T8 are two new aluminum-Lithium alloys which have great potential to fabricate the fuselage panels of aircraft. The application of traditional fusion welding on joining aluminum-Lithium alloys is limited by cavity, high thermal stress, high thermal strain and low joint strength produced during melting and solidification. Friction stir welding (FSW) is an innovative solid-state joining technology. Compared with traditional fusion welding, FSW is capable of achieving high-quality welded joint in similar or dissimilar high-strength aluminum alloys due to its excellent performance, such as low energy consumption, low stress and strain, fewer metallurgical defects and distortion under reasonable processing parameters. Weld nugget zone (WNZ), thermo-mechanically affected zone (TMAZ) and external heat affected zone (HAZ) will be produced in the FSW joint. The micromorphologies and bonding interface among WNZ, TMAZ and HAZ have a significant effect on mechanical properties of welding joint. In this research, lap joints of 2099-T83 and 2060-T8 aluminum-lithium alloy with 2 mm thickness were achieved by FSW. The interface microstructure of joints obtained by employing different tool rotation speeds and pin lengths was characterized by OM and SEM. The results showed that the obvious bonding interface was observed in the weld zone, and the bonding interface changed from smooth to zigzag with the rotation speed raising from 600 r/min to 800 r/min and pin length decreasing from 3 mm to 2.5 mm. In addition, micro-hardness of the weld zone was lower than the parent metal, and the lowest micro-hardness appeared in the transition region between the thermo mechanically affected zone and the weld zone (WZ). The results of peel tests showed that the average failure load of joint with serrated bonding interface was up to 654 N, which is 110 percent higher than that with the smooth bonding interface. The failure occurred in the transition zone between the TMAZ and WZ of the 2060-T8 side, and the toughness-brittleness fracture mode appeared. Furthermore, the microhardness of the weld zone improved, while the failure load of the FSW joint with serrated bonding interface decreased 20 percent under artificial aging treatment with the temperature of 150 ℃ and the holding time of 20 hours. The brittleness fracture mode existed in this condition. The pin length had a great effect on the morphology of bonding interface and mechanical property of welded joint.

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