An appropriate friction stir welding (FSW) tool has been developed to perform high-quality joining of 12 mm thick Al-Li alloy plates. Threads and triple facets were machined on the stirring pin to improve the material flow. The differences in microstructure characteristics, recrystallization mechanisms, and precipitate evolution along the stir zone (SZ) thickness were systematically clarified. The results indicated that microstructures in SZ were refined by dynamic recrystallization (DRX) and showed an apparent top-to-bottom gradient distribution in grain size. The geometric topology of the stirring pin results in periodic ultrafine-grained bands throughout SZ. At the top and middle regions of SZ, high-density vacancies and dislocations were formed due to elevated temperature and strain rate, facilitating the precipitation of T (AlCuLi) phases through a dislocation-induced heterogeneous nucleation mechanism. In comparison, icosahedral quasi-crystalline T (AlCu(Li, Mg)) phases, which can be attributed to the segregation of atoms and high cooling rate, were detected along grain boundaries at SZ-bottom. Furthermore, the ultimate strength values of tensile specimens sectioned from the top, middle, and bottom parts of SZ are 452, 457, and 406 MPa, respectively. Studying the inhomogeneous microstructure and properties of welded joints provides a theoretical basis for manufacturing high-load components.

中文翻译：

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2195Al厚板FSW接头搅拌区微观组织演化的不均匀性

我们开发了一种合适的搅拌摩擦焊 (FSW) 工具，可以对 12 毫米厚的铝锂合金板进行高质量连接。在搅拌销上加工螺纹和三面，以改善材料流动。系统地阐明了沿搅拌区 (SZ) 厚度的微观结构特征、再结晶机制和析出物演变的差异。结果表明，SZ 中的显微组织通过动态再结晶（DRX）得到细化，并且晶粒尺寸呈现出明显的从上到下的梯度分布。搅拌销的几何拓扑结构在整个 SZ 中产生周期性的超细粒度带。在SZ的顶部和中部区域，由于温度和应变速率的升高，形成了高密度的空位和位错，通过位错诱导的异质成核机制促进T（AlCuLi）相的析出。相比之下，在 SZ 底部的晶界处检测到了二十面体准晶 T (AlCu(Li, Mg)) 相，这可归因于原子偏聚和高冷却速率。此外，从SZ顶部、中部和底部截取的拉伸试样的极限强度值分别为452、457和406 MPa。研究焊接接头的不均匀组织和性能，为制造高载荷构件提供理论基础。