铝合金双轴肩搅拌摩擦焊过程材料流动行为

Material flow behavior during bobbin-tool friction stir welding of aluminum alloy

由于下轴肩的引入,双轴肩搅拌摩擦焊(BT-FSW)过程中的材料流动行为较常规搅拌摩擦焊更为剧烈和复杂,显著影响接头力学性能.以2219铝合金为研究对象,基于耦合欧拉-拉格朗日方法建立了BT-FSW过程三维热力耦合模型,并利用示踪粒子技术分析了焊接过程中材料的流动行为.结果表明,BT-FSW过程中的材料流动存在不同时性,靠近轴肩的材料先开始运动,且流动剧烈,随着逐渐远离轴肩位置,材料流动愈加滞后,但流动状态更加平稳;水平方向上前进侧材料作为剪切层内侧材料,绕搅拌针旋转后大部分沉积于搅拌头后方前进侧区域,而后退侧材料仅受到剪切层内侧材料的带动,进而被旋推至后方沉积;厚度方向上塑性材料在抵达搅拌头后方焊缝中心线前流动较弱,随后材料受到上、下轴肩挤压向板材中心流动.

Compared with friction stir welding(FSW),the material flow behavior during the bobbin-tool FSW(BT-FSW)process is more intense and complicated due to the presence of lower shoulder,which severely affects the mechanical properties of the joint.In this paper,a 3D thermo-mechanical coupling model of BT-FSW 2219 aluminum alloy was established based on the coupled Eulerian-Lagrangian(CEL)method and the material flow behavior during the BT-FSW process was investigated by using tracer particles.The results show that the material flow in the BT-FSW process is inconsistent.The material near both shoulders moves in advance,showing violent behavior.The farther away from the shoulder,the more lagging and stable material flow.As the inner material of the shear layer,the material on the advancing side of the weld rotates around the pin in the horizontal direction and most is deposited on the advancing side area behind the tool.While the material on the retreating side is only driven by the material in the inner layer of the shear layer,and most is pushed to deposit behind the weld.In the thickness direction,the plastic material shows weak flow before reaching the welding center line behind the tool.And the material is squeezed by both shoulders to flow toward the center of the plate after it enters the advancing side area behind the tool.