Research On Ultrasonic Vibration Laser-MIG Hybrid Welding Technology Of Steel/Aluminum Dissimilar Metals

The steel/aluminum dissimilar metal joint is a widely used lightweight composite material that takes full advantage of the excellent properties of steel and aluminum.The fusion brazing technology has excellent performance in the connection of dissimilar metals,which can effectively control the formation of interfacial intermetallic compounds（IMCs）and improve the performance of the joint.Laser arc hybrid welding can precisely control the heat input during the welding process,and its introduction into steel/aluminum fusion brazing can ensure the stability of the welding process.In view of the fact that the traditional steel/aluminum dissimilar metal connection joints have thicker IMCs thickness and more hard and brittle Fe₄Al₁₃ phase content in the IMCs layer,which leads to the decrease of the mechanical properties of the joints,the experiment adopts the method of external mechanical ultrasonic welding to study the ultrasonic effect.The effects of application on the porosity,grains and i nterface IMCs of steel/aluminum brazing joints were investigated.The effect of power on these factors was explored by changing the applied power of ultrasonic waves.In this paper,an ultrasonic-assisted welding system with adjustable ultrasonic power was constructed,and the ultrasonic field of the system was observed through the ultrasonic powder laying verification experiment to observe the influence of the ultrasonic field on the different positions of the welded specimen,so that the flow state of the powder on the sample is not the same.Design 304 stainless steel surfacing experiments and ultrasonic-assisted aluminum alloy butt experiments to verify the ultrasonic-assisted welding system.In the ultrasonic-assisted aluminum alloy butt-joint experiments,it was found that the aspect ratio of the weld seam was increased,the grains were refined,and the porosity was also reduced.This is the main benefit for the four effects of ultrasound,the experimental results show that the ultrasonic-assisted welding system can meet the requirements of use.In the process of ultrasonic-assisted steel/aluminum dissimilar metal brazing,by changing the applied ultrasonic power,the macro-and micro-morphology of the joint,the grain size of the weld,the porosity,and the morphology and composition of the interface IMCs layer were investigated by the ultrasonic power.Impact.The results show that when the ultrasonic power is 200W,the grain size decreases to 3.4μm compared with 5.2μm when no ultrasonic is applied,and the grain refinement effect becomes more obvious with the increase of ultrasonic power,but the porosity of the joint increases with the increase of ultrasonic power.The increase of ultrasonic power shows a trend of first decreasing and then increasing gradually.When the ultrasonic power is 200W,the porosity increases to 0.93%.This is mainly because the stirring effect of ultrasonic increases the floating and overflowing speed of the pores of the molten pool at low power.The porosity decreased from 0.25%when without applied to 0.21%,but when the power continued to increase,a large number of keyhole-type pores appeared,which increased the porosity,and the large ultrasonic power also made the joint interface connection prone to cracks,which greatly increased the porosity,reduce the mechanical properties of the joint.By measuring the thickness and composition of IMCs at the steel/aluminum interface and observing the tensile fracture of the joint,it was found that with the increase of ultrasonic power,the thickness of the interface IMCs decreased,and the Fe ₄Al₁₃ phase content in the IMCs decreased.When the power reached 200W,the thickness of the IMCs decreased to 1～3μm,the experiment shows that when the ultrasonic power is 130～140W,the tensi le strength of the joint is increased by 12%compared with that when no ultrasonic is applied,and the joint performance is the best.Finally,the thermosdynamic conditions are used to analyze the formation process of IMCs at the steel/aluminum interface,and the reasons why the application of ultrasound has the above effects on the morphology and composition of the interface IMCs are analyzed.The flow field and temperature field change the thermodynamic conditions of the interface.The article also analyzes the pores of the joint,and explores the reason why the large ultrasonic power in the ultrasonic-assisted welding process increases the porosity.and the mechanism of its formation was analyzed.