铝/钛异种合金回填式搅拌摩擦点焊接头的微观组织与力学性能

Microstructure and Mechanical Properties of Refill Friction Stir Spot Welded Al/Ti Dissimilar Alloys Joints

采用回填式搅拌摩擦点焊对厚度均为2 mm的5A02-O铝合金和TC4钛合金板材进行焊接。改变停留时间和回填速度,研究工艺参数对接头微观组织和力学性能的影响。结果表明,在选定工艺范围内(搅拌头旋转速度2000 r·min^(-1),搅拌套扎入深度1.9 mm),采用无螺纹搅拌头获得焊点成形良好,铝合金侧搅拌区晶粒细小,热影响区晶粒长大有限,停留时间6 s时获得界面原子扩散距离约2μm。随着回填速度提高,接头承载载荷总体呈现上升趋势,界面反应层变薄,晶粒更细。回填速度为0.5 mm/s,停留时间为6 s时获得接头拉剪载荷最低为4861 N,呈现纽扣断裂模式;回填速度为1.5 mm/s,停留时间为6 s时获得接头拉剪载荷最高为6617 N,拉剪后断面较为平整,呈现为界面断裂模式,微观断口由韧窝组成。

2 mm thick 5A02 aluminum and TC4 titanium dissimilar alloy plates were bonded by refill friction stir spot welding.The effects of different process parameters on the microstructure and mechanical properties were investigated by changing dwell time and refilling speed.Results show that within the selected process parameters,the sound joints are formed by the unthreaded stirring tool.The fine grains are produced in the stir zone and the grains in the heat affected zone are limited to satisfying extent.The atomic diffusion distance at the interface of the sleeve affected zone is larger than that in the pin affected zone.The atomic diffusion distance at the interface of the joint is about 2μm when dwell time is 6 s.With the increasing of the refilling speed,the tensile shear load of the joint increases basically.The thickness of interfacial reaction layer decreases and the grains in the joint are refined.The minimum tensile shear load is 4861 N at the refilling speed of 0.5 mm/s and dwell time of 6 s.The pull out fracture morphology is observed and dimples are found locally.When the refilling speed is 1.5 mm/s and dwell time is 6 s,the tensile shear load reaches the maximum of 6617 N.The interface fracture mode is observed while the macroscopic fracture surface is relatively flat.The microscopic fracture is consisted of dimples.