Simulation And Experimental Research On The Process Of Magnetic Pulse-Semisolid Hybrid Assisted Brazing Of Cu/Al Tubes

The Cu/Al composite structure not only can realize light weight of products,but also saves resources and reduces costs,and has broad application prospects.Brazing is often used for Cu/Al bonding.However,conventional brazing requires a flux to remove the oxidation film on the surface of the base metal.The residual halogen element after soldering reduces the corrosion resistance of the joint.Therefore,Cu/Al fluxless brazing has become the development direction in recent years.To this end,the research group proposed a new method of magnetic pulse-semisolid hybrid assisted brazing Cu/Al heterogeneous pipe fittings.The magnetic pulse force drives the outer tube to squeeze the semisolid brazing material at high speed.With the impact-shearing effects of the solid-phase particles on the wall,the oxidation film on the surface can be removed.In this paper,the commercial software LS-DYNA is used to simulate the multiphysics coupling of the whole process of magnetic pulse-semisolid hybrid assisted brazing,and the feasibility study of this new process is carried out in combination with the test.The research focuses on the influence of process parameters such as tube gap,lap length and discharge voltage of each process,and explores the mechanism of oxidation film removal,and analyzes the microstructure of the joint and the evolution mechanism of phase composition.For the solder clamping process,in the condition of the inner and outer tube gap is 1mm,the capacitance is 550?F,when the discharge voltage is less than 5kV,the deformation of outer tube is small,and it cannot be bonded to the solder;at 6kV and 7kV,the connection between the inner and outer tubes and the solder is loose;at 8kV,the connection is relatively tight,with a certain mechanical connection strength.When the inner and outer tube gap exceeds 1.5 mm,the outer tube?Al?may wrinkle.The preferred process parameters are discharge voltage 8kV,inner and outer tube gap 1mm?capacitance 550?F?.For solid-liquid composite forming process,the simulation results are obtained:the shear stress and velocity field inside the brazing filler metal are mainly distributed in the pipe end and the tail region of the brazed joint;wherein the velocity distribution is approximately parabolic,and the velocity at the wall surface of the Cu pipe is 0;the shear stress is the largest at the wall surface of the Cu tube;the internal pressure field distribution of the fluid is relatively uniform at the later stage;the shear stress,velocity and pressure are pulsed with time;under different discharge voltages,the thickness of the solder in the tube end region decreases as the voltage increases,and the compression amount slows down;the wall pressure amplitude,the shear stress amplitude and the tube end extrusion speed amplitude increase linearly with voltage;when the voltage reaches 8kV,the inner tube has a tendency to destabilize?capacitance 550?F?.Test results:under the condition of 550?F capacitor and 410°C solder temperature,the internal and external tubes are not connected to the solder at the discharge voltage of 5kV;the oxidation film on both sides of the base material is not effectively removed at 6kV;the oxidation film is effectively removed at 7kV,The joint is well connected;the oxidation film removal mechanism is attributed to the extrusion shearing action of the solid phase particles,the liquid phase intrusion and the secondary cracking of the oxidation film inside the fluid;the microstructure of the brazing layer is mainly?-Al,flower-like CuZn₅ and zinc-rich phase;the Al side is dominated by?-Al and CuZn₅;the Cu side is dominated by diffusion layer,flower-like CuZn₅,?-Al and serrated ternary phase Al_4.2Cu_3.2Zn_0.7;When the discharge voltage is7kV,lap length exceeds 2 mm,the joint strength is higher than that of the Al base metal,and the shear strength exceeds 60 MPa.