A novel method involving twin-wire pulsed VPPA (P-VPPA) welding was combined with Ti–Zr microalloying to improve the mechanical properties of AA2195-T8 Al–Cu–Li alloy variable polarity plasma arc (VPPA) welded joints. This method aimed to increase the width of the equiaxial cellular grain zone (ECZ) by adding higher content of Ti–Zr and reducing heat input. The microstructure evolution process was established to understand the formation and strengthening mechanism of the ECZ. The results showed that the strength of the ECZ was higher than that of the dendrite in the weld zone (WZ). The twin-wire VPPA welding led to the formation of a wider ECZ near the fusion zone (FZ). This ECZ was continuously distributed throughout the thickness direction of the welded joint. Combined with higher Ti–Zr microalloying, the maximum width of ECZ increased to 2.5 mm and extended to the WZ. Consequently, the proportion of cracks passing through the ECZ during tensile fracture increased from 27.6% to 88.7%. Moreover, the ultimate tensile strength (UTS) of the welded joint exhibited a notable improvement, rising from 328 MPa to 370 MPa, while the elongation also increased to 5%. The UTS of the welded joint achieved 66% of the base metal. Additionally, the average grain size in the ECZ was 14 μm. The formation of the ECZ was primarily attributed to the nucleation precursors of Al(Ti, Zr) and β′ phase, as well as less welding heat input near the FZ. The widening of the ECZ was mainly due to the presence of more Al(Ti, Zr) phases. Moreover, the grain boundary of the ECZ exhibited the distribution of Al–Cu eutectic, θ(AlCu), Ω, T2(AlCuLi), and ω(AlCuFe) phases, while a small amount of T1(AlCuLi) phase precipitated within the grain. The strengthening mechanism of ECZ is the result of multiple strengthening effects, including the reduction of element segregation and microcracks, the precipitation of the T1 phase, and the fine grain strengthening.

中文翻译：

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Ti-Zr微合金化AA2195-T8 Al-Cu-Li合金双丝P-VPPA焊接接头等轴蜂窝晶区的形成及强化机制

将双丝脉冲 VPPA (P-VPPA) 焊接与 Ti-Zr 微合金化相结合的新方法提高了 AA2195-T8 Al-Cu-Li 合金变极性等离子弧 (VPPA​​) 焊接接头的机械性能。该方法旨在通过添加更高含量的 Ti-Zr 并减少热输入来增加等轴蜂窝晶区 (ECZ) 的宽度。建立微观结构演化过程以了解ECZ的形成和强化机制。结果表明，ECZ 的强度高于焊缝区（WZ）枝晶的强度。双丝 VPPA 焊接导致在熔合区 (FZ) 附近形成更宽的 ECZ。该ECZ在焊接接头的厚度方向上连续分布。结合更高的 Ti-Zr 微合金化，ECZ 的最大宽度增加到 2.5 mm 并延伸到 WZ。因此，拉伸断裂过程中穿过ECZ的裂纹比例从27.6%增加到88.7%。此外，焊接接头的极限抗拉强度（UTS）也有了显着的改善，从328 MPa上升到370 MPa，而延伸率也增加到5%。焊接接头的UTS达到母材的66%。另外，ECZ中的平均晶粒尺寸为14μm。ECZ 的形成主要归因于 Al(Ti, Zr) 和 β' 相的形核前驱体以及 FZ 附近较少的焊接热输入。ECZ 的加宽主要是由于更多 Al(Ti, Zr) 相的存在。此外，ECZ晶界分布有Al-Cu共晶、θ(AlCu)、Ω、T2(AlCuLi)和ω(AlCuFe)相，而晶粒内析出少量T1(AlCuLi)相。 。ECZ的强化机制是多种强化效应的结果，包括元素偏析和微裂纹的减少、T1相的析出以及细晶强化。