Abstract Triple-spiral micro-grooves on the tool-shoulder end-surface is a feature recently being used for improving material flow during micro-friction stir welding (µFSW). However, its effect on process responses in comparison to the plain tool-shoulder end-surface lacks recognition, which has been targeted in the present work. An additional contribution to the knowledge base of µFSW tools having such features is also made by investigating the effect of imparting different cross-sections (rectangular, circular, right-trapezoidal type I and right-trapezoidal type II) to the micro-grooves, on the process responses. Forces, temperature, and material flow pattern were mainly the process responses analyzed through experiment and FEA simulation of µFSW in 0.5 mm thick AA6061-T6 sheets at a tool rotation of 1900 rpm and welding speed 500 mm/min. Furthermore, the welds’ quality was assessed by its surface topography, microstructure, and tensile property. The physics of the interaction between shoulder end-surface and plasticized sheet material showed that besides the triple-spiral shape, it was the cross-section of micro-grooves (mainly the orientation angle and shape of micro-grooves’ wall) that crucially determined the mechanical, thermal, and flow characteristics of the plasticized sheet material, ultimately affecting the process responses. The possibility of low-temperature welding with enhanced material mixing had been achieved with the micro-grooved tools. A higher amount of plastic deformation was also seen, with these tools, through X-ray tomographic images of the deformed copper foils placed transverse to the welding direction. Moreover, a remarkable improvement in the weld surface finish was obtained using the micro-grooved tools. Among the four micro-grooved tools, the right-trapezoidal type II cross-section showed the best performance by yielding moderate process loads along with the best weld surface finish and tensile property.

中文翻译：

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AA6061-T6 µFSW 过程中在肩部端面三螺旋微槽影响下的工艺响应

摘要 工具台肩端面上的三螺旋微槽是最近用于改善微摩擦搅拌焊接 (µFSW) 过程中材料流动的一个特征。然而，与普通工具肩部端面相比，它对过程响应的影响缺乏识别，这是目前工作中的目标。通过研究将不同横截面（矩形、圆形、I 型直梯形 I 型和直梯形 II 型）赋予微凹槽的效果，还对具有此类特征的 µFSW 工具的知识库做出了额外贡献，过程响应。力、温度和材料流动模式主要是通过实验和 FEA 模拟在 0.5 毫米厚的 AA6061-T6 板材中以 1900 rpm 的工具旋转和 500 毫米/分钟的焊接速度对 µFSW 进行分析的过程响应。此外，焊缝的质量通过其表面形貌、微观结构和拉伸性能进行评估。台肩端面与塑化片材相互作用的物理学表明，除了三重螺旋形状外，微槽的横截面（主要是微槽壁的取向角和形状）是决定性的塑化片材的机械、热和流动特性，最终影响过程响应。使用微槽工具实现了低温焊接和增强材料混合的可能性。使用这些工具，通过横向于焊接方向放置的变形铜箔的 X 射线断层扫描图像，还可以看到更大的塑性变形量。而且，使用微槽工具获得了焊接表面光洁度的显着改善。在四种微槽工具中，右梯形 II 型横截面表现出最佳性能，产生适中的工艺载荷以及最佳的焊缝表面光洁度和拉伸性能。