The present study aims at investigating the effect of interaction between the process parameters of each weld pass (1st pass and 2nd pass) to improve the joint performance during the double-sided friction stir welded joints of AA6061-T6 aluminium alloy. Experimental designs were conducted following a design matrix developed using response surface methodology to investigate the impact on the microstructural changes and tensile properties. Pronounced interaction between the process parameters of each weld pass of the joint was observed and indicated a strong interdependency between them. The detailed microstructural study conducted through EBSD insights into the extent of homogenization, and abnormal grain refinement and reflects a vast transformation of low-angle grain boundaries into high-angle grain boundaries within the stir zone. The profound examination through scanning electron microscopy and transmission electron microscopy analysis validated the uniform homogeneous distribution of Al-Fe and Al-Si-rich precipitates. The significant improvement in the grain refinement and distribution of the strengthening precipitates within the stir zone led to a substantial enhancement in the microhardness, along with achieving a maximum ultimate tensile strength of 223 MPa and a percentage elongation of 14%. A study of the fracture morphology ensures the ductile fracture behavior of the tensile fracture specimen by observing the presence of numerous dimples within a well-bonded joint.

本研究旨在研究AA6061-T6铝合金双面搅拌摩擦焊接头中各焊道（第1道次和第2道次）工艺参数之间的相互作用对改善接头性能的影响。实验设计是按照使用响应面方法开发的设计矩阵进行的，以研究对微观结构变化和拉伸性能的影响。观察到接头的每个焊道的工艺参数之间存在明显的相互作用，并表明它们之间存在很强的相互依赖性。通过 EBSD 进行的详细微观结构研究深入了解了均匀化程度和异常晶粒细化，并反映了搅拌区内低角度晶界向高角度晶界的巨大转变。通过扫描电子显微镜和透射电子显微镜分析进行的深入检查证实了 Al-Fe 和富 Al-Si 沉淀物的均匀分布。搅拌区内晶粒细化和强化析出物分布的显着改善导致显微硬度显着提高，同时实现了 223 MPa 的最大极限拉伸强度和 14% 的伸长率。对断裂形态的研究通过观察粘合良好的接头内是否存在大量韧窝来确保拉伸断裂试样的延性断裂行为。