Friction Stir Welding Process For 2014 Aluminum Alloy Thin Sheets

2014 aluminum alloy is widely used in aviation,energy,transportation and other industries.It has the characteristics of high strength,good thermal strength and poor welding performance.It is difficult to avoid the problems of cracks,pores and distortion of thin sheets in the traditional welding process.According to the characteristics and problems of thin Aluminum Alloy welding,the high rotation speed friction stir welding process was used to weld the 1mm thick Aluminum Alloy sheets.The process exploration,feature parameters acquisition and analysis,and the performance test and numerical simulation were all carried out.The process test results show that the friction stir welding process of high speed can be achieved by using a small size welding tool.The welding process is: rotation speed10000rpm-16500 rpm,welding speed: 50mm/min-170mm/min.When the rotation speed is less than 15000 rpm,the plunge depth is difficult to control,the welding efficiency is low and the distortion is serious.When the speed reaches 15000 rpm,small plunge depth is required,the degree of thinning is relatively small and the whole process is easy to control.Assisted by high pressure mist cooling,the weld can be formed and welded without distortion.The axial force detection and analysis results show that when the rotation speed is in the range of 10000 rpm to 16500 rpm,the axial force stage are lower than 200 N which is conducive to the realization of lightweight friction stir welding with less requirements of machine body bearing and cost.The variation law of axial force is similar to that of traditional friction stir welding,and the axial force increases first and then decreases,and tends to be stable.The higher the rotation speed is,the smaller the peak axial force is.In addition,the stability of the axial force is the guarantee of the uniform longitudinal performance of the joint,and water mist cooling also plays an important role in the change of axial force.The weld performance test results show that the morphology of joint has obvious NZ,TMAZ and BM,and the HAZ is not obvious.The grains of the BM are elongated along the rolling direction.In the nugget zone,there is dynamic recovery and recrystallization under the stirring condition.The grains of the TMAZ are obviously deformed on the retreating side.The results show that the tensile strength of the weld increases and then decreases withthe increase of welding speed.With the increase of rotation speed,the peak value of tensile strength increases first and then decreases.The rate of elongation is improved with the increase of rotation speed.When the welding speed is 16000 rpm,the welding speed is110mm/min;the tensile strength is about 75% of the base metal.When the tensile strength is low,the fracture is usually at the center of the weld.When the tensile strength is higher,the fracture is at the advancing side or retreating side.The test results show that hardness distribution is not an obvious "W" shape.The corrosion resistance of the weld research results show that the corrosion resistance of the weld slightly reduced,the corrosion potential decreased and the corrosion current increased after welding.Electrochemical impedance spectroscopy is composed of inductance and capacitance at low frequency.The results of numerical simulation show that: with the process conditions of p<200N and W>15000rpm,weld metal can reach welding temperature.The lightweight friction welding process can produce enough heat and stirring but cause less distortion.Water mist cooling can accelerate cooling rate to reduce weld distortion degree and it is a necessary condition for high rotation speed friction stir welding.The simulation results verify the feasibility of the process,which is consistent with the test results.