Aircraft skin and stringer elements are typically fabricated from 2xxx and 7xxx series high strength aluminum alloys. A single friction stir welding (FSW) pass using a specially designed tool with shoulder/pin diameter ratio (D/d) of 3.20 is used to produce dissimilar T-butt welds between AA2024-T4 and AA7075-T6 aluminum alloys at a constant travel speed of 50 mm/min and different rotational speeds of 400, 600 and 800 rpm. The AA2024-T4 is the skin and the AA7075-T6 is the stringer. Sound joints are produced without macro defects in both the weld top surfaces and the joint corners at all rotational speeds used (400, 600, and 800 rpm). The hardness value of the nugget zone increases by increasing the rotational speed from 150 ± 4 Hv at 400 rpm to 167 ± 3 Hv at 600 rpm, while decreases to reach the as-received AA2024-T4 hardness value (132 ± 3 Hv) at 800 rpm. Joint efficiency along the skin exhibits higher values than that along the stringer. Four morphologies of precipitates were detected in the stir zone (SZ); irregular, almost-spherical, spherical and rod-like. Investigations by electron back scattered diffraction (EBSD) technique showed significant grain refinement in the sir zone of the T-welds compared with the as-received aluminum alloys at 600 rpm due to dynamic recrystallization. The grain size reduction percentages reach 85 and 90 % for AA2024 and AA7075 regions in the mixed zone, respectively. Fracture surfaces along the skin and stringer of T-welds indicate that the joints failed through mixed modes of fracture.

中文翻译：

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异种搅拌摩擦焊接AA2024-T4 / AA7075-T6 T形对接接头的组织和力学性能

飞机蒙皮和桁条元件通常由2xxx和7xxx系列高强度铝合金制成。使用特殊设计的工具（肩/销直径比（D / d）为3.20）进行单摩擦搅拌焊（FSW）道次，以恒定的行程在AA2024-T4和AA7075-T6铝合金之间产生不同的T对接焊缝速度为50毫米/分钟，转速分别为400、600和800 rpm。AA2024-T4是皮肤，而AA7075-T6是纵梁。在所有使用的转速（400、600和800 rpm）下，在焊缝顶面和接头角处均产生无缺陷的稳固接头​​。通过将转速从400 rpm的150±4 Hv增加到600 rpm的167±3 Hv，可提高熔核区的硬度值，而降低到800 rpm时达到的AA2024-T4硬度值（132±3 Hv）。沿着皮肤的联合效率比沿着纵梁的联合效率更高。在搅拌区（SZ）中检测到四种形态的沉淀物。不规则，近球形，球形和棒状。通过电子反向散射衍射（EBSD）技术进行的研究表明，与600 rpm时的铝合金一样，由于动态再结晶，T焊缝的ir区域内的晶粒细化显着。对于混合区域中的AA2024和AA7075区域，晶粒尺寸减小的百分比分别达到85％和90％。沿T形焊缝的皮肤和纵梁的断裂表面表明，由于混合断裂方式导致关节断裂。沿着皮肤的联合效率比沿着纵梁的联合效率更高。在搅拌区（SZ）中检测到四种形态的沉淀物。不规则，近球形，球形和棒状。通过电子反向散射衍射（EBSD）技术进行的研究表明，与600 rpm时的铝合金一样，由于动态再结晶，T焊缝的ir区域内的晶粒细化显着。对于混合区域中的AA2024和AA7075区域，晶粒尺寸减小的百分比分别达到85％和90％。沿T形焊缝的皮肤和纵梁的断裂表面表明，由于混合断裂方式导致关节断裂。沿着皮肤的联合效率比沿着纵梁的联合效率更高。在搅拌区（SZ）中检测到四种形态的沉淀物。不规则，近球形，球形和棒状。通过电子反向散射衍射（EBSD）技术进行的研究表明，与600 rpm时的铝合金一样，由于动态再结晶，T焊缝的ir区域内的晶粒细化显着。对于混合区中的AA2024和AA7075区域，晶粒尺寸减小的百分比分别达到85％和90％。沿T形焊缝的皮肤和纵梁的断裂表面表明，由于混合断裂方式导致关节断裂。通过电子反向散射衍射（EBSD）技术进行的研究表明，与600 rpm时的铝合金一样，由于动态再结晶，T焊缝的ir区域内的晶粒细化显着。对于混合区域中的AA2024和AA7075区域，晶粒尺寸减小的百分比分别达到85％和90％。沿T形焊缝的皮肤和纵梁的断裂表面表明，由于混合断裂方式导致关节断裂。通过电子反向散射衍射（EBSD）技术进行的研究表明，与600 rpm时的铝合金一样，由于动态再结晶，T焊缝的ir区域内的晶粒细化显着。对于混合区中的AA2024和AA7075区域，晶粒尺寸减小的百分比分别达到85％和90％。沿T形焊缝的皮肤和纵梁的断裂表面表明，由于混合断裂方式导致关节断裂。