6061-T4铝合金单双道搅拌摩擦焊T型接头组织及性能

采用静止轴肩搅拌摩擦焊方法实现了10 mm厚5A06铝合金T形接头的焊接. 通过低主轴转速匹配高焊接速度与高主轴转速匹配低焊接速度两组不同的焊接参数，结合拉伸试验、宏观与微观金相分析、电子背散射衍射(electron backscattered diffraction，EBSD)分析与扫描电镜(scanning electron microscope，SEM)断口分析，研究了热输入对焊接接头力学性能与组织的影响. 结果表明，在两组焊接参数下均可获得无孔洞缺陷的全焊透T形接头，焊缝表面光滑平整，几乎无减薄发生；热输入不同会改变搅拌针与周围材料的摩擦形式，引起焊缝出现弱结合缺陷，并影响接头抗拉强度； 在高主轴转速匹配低焊接速度时，焊缝中心重叠区顶部易产生弱结合缺陷，导致接头抗拉强度较低，为198 MPa，拉伸试样断裂在筋板. 在低主轴转速匹配高焊接速度时，焊缝无缺陷存在，接头抗拉强度为287 MPa, 拉伸试样断裂在底板.

Microstructure and property of 6061-T4 aluminum alloy T-joints by friction stir welding under single pass and double passes

The 5A06 aluminum alloy T-joints with 10 mm thick were welded by stationary shoulder friction stir welding. Through different welding parameter selection of low rotation speed matching high welding speed and high rotation speed matching low welding speed, combined with tensile testing, macroscopic and microscopic metallographic analysis, electron backscatter diffraction analysis and fracture analysis by scanning electron microscopy, the effect of heat input on mechanical properties and microstructures of T-joints was studied. The results show that the two sets of welding parameters can both obtain full penetration T-joints without any cavity defects, the weld surfaces are smooth and flat without weld-thinning. The different heat input changes the friction mode between the stir pin and the surrounding materials and then cause kissing-bonding defects in the welding joint, consequently affect the tensile strength of the joint. Under the parameter of high rotation speed matching low welding speed, the top center of the weld overlap zone is prone to cause weak bonding defects, resulting in a lower tensile strength of 198 MPa, tensile specimen fracture in the middle plate. Under the parameter of low rotation speed matching high welding speed, the weld is free of defects and the tensile strength of the joint is 287 MPa, with the tensile specimen fractured at the bottom plate.