Research On The Characteristics Of Ultrasonic Assisted Laser-MIG Hybrid Welding Of Aluminum Alloy With Different Vibration Modes

Lightweight has important practical significance and engineering value for improving train speed and saving energy consumption.Aluminum alloy is considered to be one of the most effective materials to realize the lightweight of car body because of its excellent properties such as low density,high specific strength and good corrosion resistance,especially the continuous development of extrusion technology of large hollow thin-walled aluminum profile.As an advanced connection technology,laser-MIG welding can realize high-quality and high-efficiency welding of aluminum alloy,but there are still some problems,such as prominent porosity,coarse grains and so on.In view of the unique cavitation effect,acoustic flow effect,mechanical effect,thermal effect and other nonlinear effects of ultrasound in the metal molten pool,it can reduce the content of pores and refine the microstructure and grains,and help to improve the performance of composite welded joints.Therefore,in this paper,two ultrasonic assisted laser-MIG hybrid welded test platforms under different ultrasonic vibration modes are built,and ultrasonic vibration is introduced into the process of laser-MIG hybrid welded: one is that ultrasonic vibration acts on the workpiece;one is the ultrasonic vibration acting on the welding wire.Based on this platform,aiming at aluminum alloy plates and profiles for high-speed trains,the composite welding process characteristics under different ultrasonic vibration modes are studied respectively,the effects of different ultrasonic vibration modes on weld formation,porosity defects,microstructure characteristics and mechanical properties are analyzed,and the ultrasonic action mechanism of the two vibration modes is discussed.The test results show that for aluminum alloy sheet,when ultrasonic vibration acts on the workpiece,the weld surface forming has no obvious change;when ultrasonic vibration acts on the welding wire,the weld width increases and the reinforcement decreases;under the two ultrasonic vibration modes,the area of the main action area of the weld arc increases,the grain size of the weld area decreases and the distribution is more dense and uniform,and the microhardness of the weld area increases.Under the two ultrasonic vibration modes,with the increase of ultrasonic amplitude,the content of weld porosity decreases first and then increases;when the ultrasonic amplitude is 35μm,when the welding speed is 1.2m/min,the porosity content of the weld decreases from 9.3% to 3.5% and 1.5%respectively,and the average tensile strength of the joint increases from 181.4MPa to 220.3MPa and227.8MPa respectively;when ultrasonic vibration acts on welding wire,the stability of keyhole is improved by reducing the droplet size and increasing the droplet transition frequency,which is conducive to the escape of bubbles;the effect is more ideal when ultrasonic vibration acts on the welding wire vertically.For thin-walled hollow aluminum alloy profiles,compared with ultrasonic vibration acting on the workpiece,when ultrasonic acting on the welding wire,the content of weld porosity is reduced from 4.6% to 1.3%.The average tensile strength of the joint increased from 156.8MPa to 183.2MPa.Ultrasonic assisted laser-MIG welding with ultrasonic acting on welding wire mode has better process applicability.