Study On Ultrasonic-Assisted TIG Welding Process And Mechanism Of 7075 Aluminum Alloy

Super-hard aluminum alloy can reach the strength of medium-strength steel,and has broad application prospects in aerospace,rail vehicles and other fields.However,due to defects such as hot cracks,pores and deformation in the process of fusion welding,its application is limited.This subject is based on 7075 aluminum alloy,by designing the ultrasonic vibration-assisted welding fixture table,so as both to prevent welding deformation,can become a source of ultrasonic vibration emitted by the base material of the ultrasonic vibration energy into the weld puddle,the use of ultrasonic vibration to improve the effect of the metal melt tissue composition and mechanical properties of welded joints.In the non-filler fixed-point remelting,the effect of ultrasonic vibration increases the longitudinal depth by 4.8% and 27.1% respectively under high heat input conditions and low heat input conditions;ultrasonic vibration can suppress thermal cracking from metallurgical conditions and stress conditions.Ultrasonic vibration increases the penetration depth mainly in the melting stage,ultrasonic vibration can change the arc shape,increase the arc pressure,increase the degree of depression of the molten pool.Ultrasonic vibration can refine the structure,Its cavitation effect and mechanical effect can improve the fluidity of the molten pool,increase the cooling rate of the weld pool,and inhibit grain growth.The broken dendrites can increase the nucleation rate;the ultrasonic vibration makes the bath temperature uniform,lowers the bath high temperature residence time,and reduces the burning loss of low melting point strengthening elements such as Zn and Mg.In the surfacing experiment,the penetration depth and the toe angle increase with the increase of the ultrasonic power.The residual height decreases with the increase of the ultrasonic power.When the ultrasonic vibration is 400 W,the toe angle and the penetration depth increased by 32.4% and 15.3% respectively,and the weld residual height decreased by 31.7%;the application of ultrasonic vibration can make the equiaxed crystals in the center of the weld and the heat-affected zone refine,inhibit the growth of columnar crystals,and enlarge the equiaxed crystal regions,but have little effect on the parent metal structure;the ultrasonic vibration can accelerate the flow of the molten pool,promote the fusion of the base metal and the welding wire element in the molten pool,and improve the fusion ratio of the weld.In the flat butt welding experiment,as the welding current increases,the mechanical properties of the welded joint increase first and then decrease.When the welding current is 170 A,the tensile strength,average elongation and weld center Vickers hardness are respectively It is 281.76 MPa,4.28%,105.2HV;after applying ultrasonic vibration,the tensile strength increases with the increase of ultrasonic power.When the ultrasonic power is 400 W,the tensile strength,average elongation,and weld center are optimal.The Vickers hardness is 306.41 MPa,4.81%,and 108.8 HV,respectively,which is 8.75%,12.1%,and 3.4% higher than that without applying ultrasonic vibration.The mechanism of applying ultrasonic vibration to improve the mechanical properties of the weld makes the ultrasonic vibration strengthen the weld.