Friction Stir Welding (FSW) has great potential over fusion welding for joining dissimilar alloys. However, formation of intermetallic compounds (IMCs) Al₁₂Mg₁₇ and Al₃Mg₂ in FSW of Al/Mg alloys is almost unavoidable and problematic for the research community. Such IMCs in the form of continuous layer provide easy crack propagation path which increases brittleness and reduces the joint strength of the weld. To improve the material flow behavior and reducing brittleness, accurate and precise attempts were taken to join two dissimilar alloys i.e. Al 7075 and Mg AZ31 with the incorporation of cadmium interlayer first time. Tool rotational speed of 1300 rpm and traverse speed of 20 mm/min were maintained throughout the welding process. Various phase formation and their distribution in the nugget zone has been studied in details by using optical microscopy, SEM–EDS and XRD. The supersaturated solid solution (SSSS) of Mg in Al, and a thin layer of Al₃Mg₂ and small particles (~ 1 µm) of Al₁₂Mg₁₇ have been observed in the stir zone. During processing Cd reacted with Mg and formed CdMg and CdMg₃ which have been distributed in the upper-middle portion of Mg region as intercalated lamellar structure. Formation of these compound provided micro-mechanical interlocking. Further, Al material has been found to be deposited into the Mg region in the form of elongated balloon which provided anchoring effect due to mechanical interlocking. The maximum tensile strength achieved is 129 MPa which is higher than the previously reported dissimilar FSW of Al 7xxx series alloy with Mg alloy. Fractographic study of the dissimilar FSW tensile sample was carried out to understand crack propagation path and scope for further improvement in the weld joint strength.

Graphic abstract

中文翻译：

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使用 Cd 夹层的异种摩擦搅拌焊接 Al 7075 和 Mg AZ31 合金的材料流动行为和机械性能

搅拌摩擦焊 (FSW) 在连接异种合金方面比熔焊具有更大的潜力。然而，在铝/镁合金的 FSW 中形成金属间化合物 (IMC) Al ₁₂ Mg ₁₇和 Al ₃ Mg ₂几乎是不可避免的，并且对研究界来说是个问题。这种连续层形式的 IMC 提供了容易的裂纹扩展路径，这增加了脆性并降低了焊缝的接头强度。为了改善材料流动行为并降低脆性，我们尝试准确而精确地连接两种不同的合金，即首次加入镉夹层的 Al 7075 和 Mg AZ31。在整个焊接过程中保持 1300 rpm 的工具转速和 20 毫米/分钟的横向速度。已经通过使用光学显微镜、SEM-EDS 和 XRD 详细研究了熔核区的各种相形成及其分布。在搅拌区观察到Mg 在 Al 中的过饱和固溶体 (SSSS)、Al ₃ Mg ₂薄层和 Al ₁₂ Mg ₁₇小颗粒 (~ 1 µm) 。在加工过程中，Cd 与 Mg 反应形成 CdMg 和 CdMg ₃以层状层状结构分布在 Mg 区的中上部。这些化合物的形成提供了微机械互锁。此外，已发现 Al 材料以细长气球的形式沉积到 Mg 区域中，由于机械互锁而提供锚固效果。达到的最大拉伸强度为 129 MPa，高于先前报道的 Al 7xxx 系列合金与 Mg 合金的不同 FSW。对不同的 FSW 拉伸样品进行断口研究，以了解裂纹扩展路径和进一步提高焊接接头强度的范围。

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