Numerical Simulation Of Friction Stir Welding With Thickness Difference Aluminum Alloy Plate

Friction stir welding is a new solid-phase connection technology.It has the advantages of ordinary welding technology.One of the important research field of friction stir welding technology is the heat transfer in welding process and the temperature field distribution,which has important influence on the study of residual stress and welding deformation.The residual stress after welding cooling is of great value to component reliability,especially fatigue life,dimensional stability and corrosion resistance.In this paper,numerical simulation and control variable method are used to study the temperature field and the distribution of residual stress field in friction stir welding of thickness difference aluminum alloy plate.Based on the characteristics of friction stir welding,considering the Mises yield criterion and the heat generated by shoulder and stir tool,the 6061-T6 aluminum alloy sheet with different thickness of 2mm and 4mm was used as the research object.Based on ABAQUS finite element analysis software,The three-dimensional heat source model of friction welding was used to simulate the temperature field and residual stress of friction stir welding.The results show that the peak temperature of 2mm thin plate is about 446 ?,the peak temperature of 4mm thin plate is about 441 ?,and the temperature field distribution is asymmetric elliptical.The residual stress of the thickness difference plate is the longitudinal residual stress,and in the vertical weld direction was M-shaped bimodal distribution.The longitudinal residual stress increases first and then decreases,and the longitudinal residual stress in the vicinity of the center line of the weld is tensile stress and gradually converted to compressive stress to the edge of the base metal.The transverse stress is expressed as tensile stress,but the value is much lower than the longitudinal stress.and the residual tensile stress peak and distribution range of 4mm thin plate are smaller than 2mm sheet.In addition,based on the above numerical model,use the control variable method,the temperature field and the residual stress of the friction stir welding were studied by changing separately the rotational speed,the welding speed and the diameter of the pin.The results show that under the control variable method,with the increase of the rotational speed,the peak temperature of the thickness difference aluminum alloy plate is increased,and the temperature field of the 4mm thin plate is larger than that of the2 mm thin plate.The residual stress of the thickness difference plate on both sides of the weld center is not the same.But both sides of them are inversely proportional to the rotational speed of the stirring head.The longitudinal residual stress of the 2mm sheet is greater than 4mm.The peak value of the longitudinal residual stress appears at the edge of the mixing area.The longitudinal residual stress of the thick plate is opposite increase with the increase of the welding speed.While the 2mm thin plate peak residual stress slightly larger than 4mm sheet.The temperature field of the thickness difference aluminum alloy plate is proportional to the diameter of the shoulder and the 4mm sheet is larger than the high temperature area of the 2mm sheet.With the increase of the diameter of the shoulder,the low temperature region of the thickness difference plate gradually increases,and same as the peak value of the longitudinal residual stress.It is of great significance that these studies guide the science formulation of friction stir welding process parameters of thickness difference aluminum alloy plate and for further experimental verification and saving of experimental cost.