| Aluminium-copper composite components are widely used in electronics,chemical industry,manufacturing and energy industries.It is of great significance to realize the efficient and high quality welding of aluminium and copper.Laser welding-brazing is expected to solve the difficulties of copper-aluminum welding effectively because of its high energy density and good welding flexibility.This article adopts the way of laser molten brazing to docking tests of 5052 aluminum alloy and T2 copper,mainly studied the welding wire components,laser power,welding speed and quantity of the coke microstructure and mechanical properties of aluminum/copper joints,the influence of analyzing the forming mechanism of joint interface layer structure,to optimize the process parameters,to get good welding joint.Zn-02%Al,Zn-15%Al and Zn-22%Al flux cored wires were tested on T2 copper plates.In a certain range of technological parameters,the best wetting and spreading performance of Zn-22%Al flux cored wires was found through longitudinal comparison.In the following experiments,a Zn-22%Al flux cored wire with a diameter of 1.6mm was used to conduct the seamless laser fusion brazing experiment on 2mm thick 5052 aluminum alloy and T2 copper,and there was no groove on the copper side.Through the control variable method,the optimal process parameters were obtained as follows: laser power of 2400 W-2600 W,defocus of +6mm,welding speed of 6mm/s,wire feeding speed of 2 m/min.The laser beam was directly in the middle of the weld.At this time,the solder solder was fully spread and the weld was well formed.The microstructure of aluminum-copper joints was studied by metallographic,SEM,XRD and other test and analysis methods.The joint is composed of three areas: the aluminum side fusion welding interface area,the welding seam area and the copper side brazing interface area.The brazing interface area on the copper side is dominated by columnar crystals,which can be further divided into an Al-Cueutectic interface layer and an intermetallic compound layer whose main phase is Al4.2Cu3.2Zn0.7.The thickness will increase with the increase of the Al content in the welding wire and the increase of the welding heat input.The welding seam area is composed of CuZn5 phase and Zn-Al eutectic.The aluminum side fusion welding seam area has obvious fusion welding characteristics,and the columnar crystal area grows toward the center of the welding seam at the aluminum side interface.The effects of different process parameters on microhardness,tensile strength and fracture mechanism of aluminum/copper laser brazing welding joints were studied.The hardness of the weld zone is higher than that of aluminum and copper base metal.The regional hardness value of the intermetallic compound layer on the copper side is the highest,reaching about 225 HV.The hardness value of the heat-affected zone on the copper side is the lowest,reaching 50 HV.Under the optimum process parameters,the tensile strength of the joint increases gradually with the increase of Al content in the welding wire,and the maximum tensile strength reaches 212 MPa.Within a certain parameter range,the tensile strength of the joint increases first and then decreases with the increase of laser power,defocus and welding speed.The fracture behavior of the joint was analyzed.According to the difference of mechanical properties,the fracture of the aluminum/copper laser brazing joint mainly occurred in three areas,namely,the copper side brazing zone,the weld zone and the aluminum base metal.In the brazing zone on the copper side,the Al-Cueutectic zone and the hard and brittle Al4.2Cu3.2Zn0.7 intermetallic compound layer are the main factors leading to fracture,and the fracture mode is cleavage fracture.The fracture mode is quasi-cleavage fracture,which is between cleavage fracture and dimple fracture. |
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