The present study aims to investigate the effect of Sn interlayer on the quality, microstructure and mechanical properties of 7075 T6-AZ31H24 dissimilar joints fabricated by friction stir lap welding. In this regard, various joints were fabricated by changing the interlayer thickness and the number of FSW passes. The microstructure of the joints was studied by optical, scanning and transmission electron microscopes linked to EDS and EBSD detectors. Shear-tensile test was utilized for evaluation of the mechanical properties of the joints. The results showed that the use of 40 μm-thick Sn interlayer was very effective on the improvement of joint quality and joint strength. In this case, the tunneling defect was eliminated and the lap shear fracture load improved by 10% with respect to conventional friction stir lap welding. This was attributed to the facilitated displacement and more proper mixing of dissimilar materials in the nugget due to the lubricating effect of molten tin. Although increase of interlayer thickness showed positive effects on dissimilar material mixing, width of nugget and thickness of mixed region, however, joint strength decreased due to the formation of Mg₂Sn intermetallic compound at the out part of the mixed region. Increasing the FSW passes from one to three led to spreading of Mg-Al mixed regions throughout the nugget, thereby the joint strength was deteriorated significantly by formation of various brittle intermetallic compounds (Mg₁₇Al₁₂, Mg₂Al₃ and Mg₂Sn) within the nugget.

本研究旨在研究 Sn 夹层对搅拌摩擦搭接焊制造的 7075 T6-AZ31H24 异种接头的质量、显微组织和力学性能的影响。在这方面，通过改变层间厚度和 FSW 遍数来制造各种接头。通过与 EDS 和 EBSD 探测器相连的光学、扫描和透射电子显微镜研究接头的微观结构。剪切拉伸试验用于评估接头的机械性能。结果表明，使用 40 μm 厚的 Sn 中间层对提高接头质量和接头强度非常有效。在这种情况下，隧道缺陷被消除，与传统的搅拌摩擦搭接焊相比，搭接剪切断裂载荷提高了 10%。这是由于熔融锡的润滑作用促进了不同材料在熔核中的置换和更适当的混合。虽然层间厚度的增加对异种材料混合、熔核宽度和混合区厚度有积极影响，但由于Mg的形成，接头强度降低₂ Sn 金属间化合物在混合区的外部。将 FSW 道次从 1 次增加到 3 次导致 Mg-Al 混合区域在整个熔核中扩散，从而由于形成各种脆性金属间化合物（Mg ₁₇ Al ₁₂、Mg ₂ Al ₃和 Mg ₂ Sn）而显着降低了接头强度金块内。