In this study, A7204-T4 aluminum alloy sheet with a thickness of 6 mm was welded using fiber laser variable polarity tungsten inert gas (VPTIG) hybrid welding with ER5356 filler wire, during which Nb (niobium) foils with different thicknesses (10 μm, 25 μm, 35 μm, and 50 μm) were preset between the butt joint faces. The joint microstructure and properties with different Nb content were investigated in detail. According to the results of this study, the welds after Nb micro-alloying exhibited significantly reduced pores, while Nb-concentrating phases and the NbAl₃ precipitated phase gradually appeared and acted as heterogeneous nucleation particles, which can refine the grains. Therefore, columnar crystals and secondary dendritic crystals at the weld center disappeared and fine equiaxed crystals appeared. After the addition of 10 μm Nb foil in the hybrid welding, the micro-hardness of weld metals was significantly enhanced, heat-affected zone in the weld joint became narrower, and the softening phenomenon reduced significantly. However, as the added Nb content increased, the micro-hardness was enhanced less significantly. After Nb micro-alloying, the tensile strength, yield strength, and elongation rate were enhanced significantly. The mechanical performance of the weld joint reached the optimum after 10 μm Nb was added in the welding process; specifically, the mean tensile strength, mean yield strength, and mean elongation rate reached 344 MPa, 269 MPa, and 6.2%, respectively, which were 91.5%, 89.4%, and 61.4% of those of base metal, respectively. The significant enhancement of weld micro-structure and mechanical properties can be attributed to the formation of effective nucleation particles during the solid solution of Nb in the Al matrix, thereby leading to grain refinement and a change in the corresponding precipitated phase.

中文翻译：

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铌微合金化对光纤激光-VP​​TIG混合焊接A7204-T4铝合金接头组织和性能的影响

在这项研究中，使用ER5356填充丝的光纤激光可变极性钨极惰性气体（VPTIG）混合焊接技术焊接了厚度为6 mm的A7204-T4铝合金薄板，在此期间，Nb（铌）箔的厚度不同（10μm，在对接面之间预设25μm，35μm和50μm）。详细研究了不同Nb含量的接头组织和性能。根据这项研究的结果，Nb微合金化后的焊缝显示出明显减少的气孔，而Nb集中相和NbAl ₃析出相逐渐出现并充当异相形核颗粒，可细化晶粒。因此，在焊接中心的柱状晶体和二次树枝状晶体消失，并且出现了细等轴晶体。在混合焊接中添加10μmNb箔后，焊接金属的显微硬度显着提高，焊接接头的热影响区变窄，软化现象明显减少。然而，随着添加的Nb含量的增加，显微硬度的提高不明显。Nb微合金化后，抗拉强度，屈服强度和伸长率显着提高。在焊接过程中添加10μmNb后，焊接接头的机械性能达到最佳；具体来说，平均抗拉强度，平均屈服强度，平均伸长率分别为344 MPa，269 MPa和6.2％，分别是母材的91.5％，89.4％和61.4％。焊缝微观结构和机械性能的显着提高可归因于Nb在Al基体中固溶期间形成有效的形核颗粒，从而导致晶粒细化和相应的析出相发生变化。