采用预置焊丝和偏心阶梯焊具实现高质量Al/Cu T-搭接FSW接头

Achieving High-Quality Al/Cu T-Lap FSW Joints Using Pre-set Wires and an Eccentric Progressive Pin

摘要:

通过搅拌摩擦焊（FSW）制备的Al/Cu T-搭接接头中，焊核区存在的钩状结构是裂纹的萌生源，严重影响接头性能。采用偏心阶梯焊具对6061铝合金与纯铜进行T-搭接FSW，通过在内角预置两种成分焊丝，试验了3种焊具对T-搭接接头的适用性，以期改善钩状结构与基体的结合质量，从而获得高质量的接头。优选两种焊具，观察其对Al/Cu交界面处晶粒形态及金属间化合物（IMCs）形貌影响，并评估了接头沿壁板和筋板方向的力学性能。结果表明，在减小界面IMC层厚度的同时，小针偏心的焊具减薄了Cu钩端部厚度，扩大了焊核区体积，且Cu钩外围与基体达到了冶金结合，提高了焊接质量。小针偏心加三切面的M800Al焊具，其周期性剪切作用促使形成涡流状互锁界面，且从Cu钩内刮擦的更多碎片混入整个焊核区，细化晶粒的同时有助于不连续动态再结晶和几何动态再结晶。采用偏心焊具制备的M800Al接头沿筋板方向的抗拉强度达176 MPa，与无偏心焊具制备的接头强度相比增加了23.9%，这为异种金属T-搭接接头性能改善提供了一种可行的解决方案。

Abstract:

In Al/Cu friction stir welding (FSW) T-lap joints, the hook-shaped structure present in the nugget zone (NZ) serves as a crack initiation site, which severely compromises the performance of the joints. In this study, FSW of 6061 aluminum alloy and pure copper in a T-lap configuration was performed employing an eccentric progressive pin. Two types of welding wires with different chemical composition were pre-set at the corner die, and the applicability of three tools for T-lap joints was examined. The research was intended to improve the bonding quality between the hook-shaped structure and the base material to obtain high-quality welded joints. Two optimal welding tools were selected. The influences of these tools on the grain morphology at the Al/Cu interface and the morphology of intermetallic compounds (IMCs) were analyzed, and the mechanical properties of the joints along the skin and stringer directions were evaluated. The results reveal that the tool with a small eccentric pin reduces the thickness of the interfacial IMC layer, simultaneously thinning the tip of the Cu hook and enlarging the volume of the NZ, and achieving metallurgical bonding between the periphery of the Cu hook and the matrix, thus improving the welding quality. For the M800Al welding tool equipped with a small eccentric pin and three cutting surfaces, its periodic shearing action facilitates the formation of a vortex-like interlocking interface. Meanwhile, more fragments scraped from the Cu hook are distributed throughout the NZ. This phenomenon not only refines the grain structure but also promotes discontinuous dynamic recrystallization and geometric dynamic recrystallization. The ultimate tensile strength of the M800Al joint along the stringer direction reaches 176 MPa, marking a 23.9% increment compared with that of the joint produced using a non-eccentric tool. This work provides a feasible solution for improving the performance of FSW T-lap joints of dissimilar metals.