| Copper is a metal material with excellent thermal and electrical properties,however copper is scarce and expensive.Aluminum is a good conductive material,which is abundant and cheap.Therefore,the method of "replacing copper with aluminum" was put forward.However,the single pure aluminum structure has low strength,poor corrosion resistance and great constraints on the service environment,so it can not completely replace copper with aluminum.Using aluminum and copper composite structure instead of single copper,not only can integrate the characteristics of the two materials,but also can save copper resources,reduce production costs,so that it has a broad prospect in cable,refrigeration,electronic appliances,new energy vehicles and other industries.However,in the welding process of Al/Cu dissimilar metals,a large number of brittle and hard intermetallic compounds will be produced at the interface,which will greatly affect the performance of the joint.Using ultrasonic-assisted method for the joint of aluminum and copper,the intermetallic compound layer can be broken under the action of ultrasonic vibration,and the grain size of the weld zone is obviously refined under the action of ultrasonic cavitation,so as to achieve the purpose of improving the joint performance.In this paper,a new method of assisting plasma arc welding by ultrasonic vibration.The effects of ultrasonic vibration assistance on the microstructure,mechanical properties and electrical conductivity of Al/Cu lap joints are studied,and the interface reaction process of ultrasonic-assisted Al/Cu fusion brazing joints is discussed.In this paper,the ultrasonic-assisted plasma arc welding process is used to realize dissimilar metal joining between 5052 aluminum alloy and T2 copper with a lap width of 3 mm,and a well-formed aluminum and copper lap joint is obtained through adjusting the welding parameters.The effects of ultrasonic vibration on the surface formation,the spreading of aluminum on the copper,the weld grain size,the microstructure and mechanical properties of the joint interface are studied by means of SEM,EDS,XRD and shear test.The results show that a 55 μm thick intermetallic compound layer is formed at the interface without ultrasonic vibration,some dendrites and coarsely equiaxed crystals appear in the Al-Cu eutectic zone,and the shear strength of the welded joint is 51.37 MPa.After the application of ultrasonic vibration assistance,the wetting ability of aluminum on the copper increases,the thickness of the intermetallic compound layer decreases to 29 μm,the grain size of the Al-Cu eutectic zone decreases significantly,and the shear strength of the welded joint from 51.37 MPa increases to 84.93 MPa.The fracture morphology of the joint is observed by SEM,and it is found that the fracture mode of the joint is brittle fracture.Then,in order to study the conductivity of the Al/Cu joint in the later stage,the ultrasonic-assisted plasma arc welding process test of 1060 pure aluminum and T2 copper with a lap width of 10 mm is carried out.The effects of ultrasonic power,welding current and welding speed on the macro morphology,micro morphology,interface structure and shear strength of Al/Cu lap joints by plasma arc welding are analyzed.The results show that the joint spreads well,and the joint has no obvious welding defects such as cracks and pores.Using SEM to observe the lap joints show that the entire interface transition area and weld zone can be roughly divided into Al-Cu intermetallic compound layers,Al-Cu bulk eutectic zone,and α-Al and network Al-Cu eutectic structure zone;The Al-Cu eutectic structure zone is composed of a-Al and CuAl2 intermetallic compound.With the increase of ultrasonic power,the degree of fracture of the intermetallic compound at the interface increases,the thickness decreases,and the thickness of Al-Cu eutectic zone increases.As the welding current increases and the welding speed decreases,the welding heat input increases,and the thickness of the intermetallic compound layer at the interface increases obviously.The shear test results show that the shear strength of the joint first increases and then decreases with the increase of ultrasonic power,welding current and speed.When the ultrasonic power is 700 W,the welding current is 75 A,the welding speed is 190 mm/min,the ion gas is 2 L/min,and the shielding gas is 15 L/min,the maximum shear strength of 1060 pure aluminum and T2 copper lap joint is 86.31 MPa;the fracture mode of the joint is cleavage fracture,the fracture site occur on the CuAl2 intermetallic compound.Finally,the effects of process parameters on the resistivity and conductivity of pure aluminum and copper plasma arc welding lap joint are studied.The research results show that with increase of ultrasonic power,welding current and welding speed,the resistivity of the joint firstly decreases and then increases,while the conductivity firstly increases and then decreases.When the ultrasonic power is 700 W,the welding current is 75 A,and the welding speed is 190 mm/min,the minimum resistivity of the joint is 2.18 μΩ·cm,and the maximum conductivity of the joint is 79.09%IACS. |
