| Characteristics of aluminum alloy, including small density and high specific strength, is gradually used in the automotive lightweight design, but the traditional fusion welding welding of aluminum alloy thin plate welding prone to deformation, burn through and joint strength is not high. Friction stir welding is a solid state bonding technology, which has obvious advantages in welding aluminum, magnesium and other non-ferrous metals. However, the use of friction stir welding technology is rarely reported in China. This paper studies welding problems of the 0.5mm thick and ultra-thin 6061-T4 aluminum alloy, using FSW to butt weld and analyzing welding characteristics of aluminum alloy plate, designing shoulder tools fit for ultra-thin plate welding based on its characteristics, through the experiment to explore suitable welding parameters and analyze the impact of welding parameters on the joint surface forming, microstructure, mechanical properties and fracture characteristics and the characteristics of materia flow.FSW technology used in thin plate welding is a new field, the problems of welding thin plate including the follows: parent material is easy to tear, weld forming is difficult and joint strength is difficult to guarantee clamping precision and the high requirements. To solve the problems of thin plate welding and obtain good quality joint, we design shoulder welding tool for thin plate welding in different needle shape, of which shoulder diameter is 6mm, concave corner for 3 degrees, stirring pin is in a conical shape, and in order to enhance the mixing effect we equidistantly cut out three edges in the conical base to weld 0.5mm thick 6061-T4 aluminum.The research shows that the welding parameters have great influence in the surface forming of the joint, and the joint with the reduction of the amount of less than 2% can be obtained under the proper welding parameters. When the rotating speed is higher than 1500 rpm, the surface forming good joint can be obtained, and the welding speed of the joint surface formed by the welding speed on the 1500 rpm is better than that of the conical stirring head when the welding speed is 500-800mm/min. Based on the analysis of the welding parameters and mechanical properties, fracture surface morphology and defect type, with a week to welding platform, at 1500 rpm and 500 mm under the condition, the tensile strength of the joint and elongation rate can reach 220.29 MPa and 11.65%, but compared to the conical pin, week to welding platform to expand the thin plate welding process window; welding parameters in the 1500-1750 rpm and 300-500mm/min changes, all can get good performance of joint; joint fracture morphology observation, no welding joint defects of the fracture mode is ductile fracture. When the welding speed is greater than 600mm/min or speed below 1250 rpm, joint is easy to have the holes and bottom bonding defects, this is mainly due to the heat input is not enough, metal mobility is poor and prone to defects.In order to study the metal flow behavior characteristics in thin plate welding joint, this experiment adopts the conical mixing head, welding 0.5mm, 1mm and 2mm thick aluminum alloy under the same welding parameters, three sections of the four positions were analyzed from the joint cross section, longitudinal section and horizontal plane is discussed. The metal flow characteristics of ultrathin plate welding, the plastic metal is restricted by the shoulder and the bottom plate in the thickness direction of flow, the metal flow is mainly horizontal flow; when welding heat input to the bottom of the weld, shoulder lower metal are at high temperature, viscous force of welding in the area of metal flow generated to drive the metal deformation range becoming larger, the shoulder deformation effect on the metal flow strengthening, the pin is weakened. |
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