Research On Friction Stir Welding Process Of AA6061 And Polypropylene Plastics

With the rapid growth of industrial modernization,lightweight technology has become a trend,and the use of lightweight materials is one of the effective methods of this technology.Lightweight materials include magnesium alloys,aluminum alloys,plastics and composites,etc.The wide application of these materials puts forward higher requirements for material bonding technology.Friction Stir Welding can weld a variety of materials,including dissimilar materials with great differences in physical and chemical properties.As well as,its applications are quite wide.And we can obtain good welding effect with good welding parameters.In this paper,AA6061 aluminum alloy and PP polypropylene plastic(lightweight metals)are the research object.Two different kinds of materials were joined through using Friction Stir Spot Welding(FSSW)without pin and Friction Stir Welding(FSW)without pin.Firstly,the influence of different shapes of prefabricated holes on the bonding properties of aluminum plates was studied by numerical simulation.According to the structure of the hole,the‘cylindrical structure'geometric model of the single hole was put forward,the functional relations among geometric parameters were established and a total of 335 groups of geometric parameter combinations were determined.Based on the geometric model,the tensile shear simulation model of single hole connection was established by ABAQUS software,and the mesh was optimized for the model.Then,parametric modeling technology was used to complete the establishment and analysis of all 335 groups of models.The optimal pore structure was obtained according to the tensile and shear loads of each group.Furthermore,data processing,such as variance analysis and regression analysis,was carried out to study the specific effects of geometric parameters on tensile and shear loads,and the expression which could effectively reflect its law was obtained.Based on the structure of optimized hole,FSSW and FSW experiments were carried out to study how welding process parameters affects the joint performance.The results of pore structure optimization show that the tensile shear load of2-cylindrical-structure pore structure is only related to the bottom diameter of aluminum plate D₁.The tensile shear load of 3-cylindrical-structure hole structure is related to all four geometrical parameters,and the influence of each parameter is D₁>D₃>D₂>h₁.It can be found that the tensile shear load increases when D₁increases,increases first and then decreases when D₂and D₃increase,increases first and becomes stable when the h₁increase from the trend chart.By regression analysis,the second-order polynomial regression equation of 2-cylindrical-structure structure is the best,and fourth-order polynomial regression equation with 3-cylindrical-structure structure is optimal.The results of FSSWed experiments show that the best schemes are rotation speed at 1000r/min,the depth of pressing at 0.1mm and residence time at 5s.Rotation speed has the greatest influence on the experimental results,followed by download and residence time.When rotation speed rises,the tensile shear load increases first and then decreases.And when residence time increases,results are shown as an increasing trend.To depth,results are shown as a decreasing function.The experimental results of FSW show that the welding effect is the best and holes are filled the most completely under the parameters of rotation speed at 1500r/min,welding speed at 50mm/min and the depth at 0.3mm.The affecting order of factors are the depth>welding speed>rotation speed.With the increase of rotation speed and depth,results are shown as a rising trend.However,with the increase welding speed,the results are shown as a subtractive form.Through measuring temperature,it is found that the temperature of advanced side is greater than that of retreated side.And it can be found that the temperature around the welding area is higher.The comparative experiments between the normal pore structure and the excellent pore structure show that the optimized pore structure can effectively improve the tensile shear load and bending load.The tensile and bending properties of the single-hole specimens are increased by 55.27%and 33.48%,the 2-hole specimens by 31.81%and25.11%,and the 4-hole specimens by 22.66% and 10.93%,respectively.