6061-T4铝合金搅拌摩擦焊T型接头拉伸断裂实验研究

Experimental Investigation on Tensile Fracture Behavior of Friction Stir Welded T-Joints of 6061-T4 Aluminum Alloy

针对6061-T4铝合金搅拌摩擦焊T型接头力学性能开展了实验研究,首先通过显微观测分析了T型接头的缺陷特征,随后进行了沿蒙皮板方向和沿支撑板方向的宏观拉伸实验,利用数字图像相关(DIC)方法研究了接头的拉伸断裂行为.实验结果表明,焊接接头中均存在弱连接缺陷,且弱连接缺陷是导致接头沿筋板断裂的主要原因.沿蒙皮板方向拉伸时,接头的强度受焊接参数的影响不大,且其断裂主要是由热影响区(HAZ)材料软化且两侧材料强度差异较大所引起;沿支撑板方向拉伸时,试件首先在弱连接缺陷处萌生裂纹,裂纹在载荷作用下沿弱连接所在的方向扩展,并在试件另一侧靠近筋板处产生明显的应力集中区域,最终试件发生剪切断裂失效.此外,接头沿筋板方向抗拉强度随焊接转速的增加有增大趋势.

The mechanical properties of 6061-T4 aluminum alloy T-joints fabricated by friction stir welding have been experimentally investigated. The flaw characterization of T-joints was first observed by microscope,then two groups of tension experiments stretching respectively along skin plate and support plate were conducted,and the fracture behavior of T-joints under tension was analyzed by digital image correlation（DIC）method. The experimental results show that,weak-bonding defects,which lead to the joint failure along the reinforcement plate,always exist in the welded joints. When stretching along the skin plate direction,the strength of joint is hardly affected by welding pa-rameters,and the fracture is mainly caused by softening and the strength difference between the materials on the two sides of the heat affect zone（HAZ）;when stretching along the support plate,crack generates at the region of weak-bonding defect,then grows along the direction of defect under tension,and a stress concentration region appears in the place near skin on the other side of the plate,the joint finally ruptures due to the shear fracture. In addition,the ultimate tensile strength（UTS）of the joints under tension along the support plate increases with the acceleration of welding rotation speed.