Numerical And Experimental Investigation On3A21Aluminium Alloy And20Steel Tube Magnetic Pulse Welding

Magnetic pulse welding (MPW) of pipe fittings made of dissimilar materials refersto high-speed solid-phase connection at room temperature using magnetic-pulse formingprinciple and under appropriate technical conditions, high-strength welding joints canbe obtained. The application of MPW to the welding of pipes made of such dissimilarmaterials as aluminum alloy-steel will help realize lightweight structural design of parts.Starting from the principle and characteristics of MPW, using the constitutive relation of3A21aluminum alloy at high strain rate, a method of combining numerical simulationand process tests is used to make a systematic study of the MPW procedure for Al-Fedissimilar pipe fittings. Through SEM tests and TEM tests, an analysis is made of theappearance and composition of MPW joints, with the formation mechanism of weldingwave involved in the MPW procedure and mechanism of MPW obtained.A loose coupling method is adopted to make an electromagnetic field analysis and adeformation field analysis of pipe fittings in the MPW process. A voltage drive-basedthree dimensional electromagnetic field coupling model is established using ANSYS-Multiphysics module to analyze the magnetic force in the MPW process and study theefect of such process parameters as discharge voltage, equipment capacitance, system re-sistance and pipe materials on the magnetic force. Through Hopkinson pressure bar test,a J-C model of3A21aluminum alloy at high strain rate is established. With the magneticforce involved the magnetic field analysis as boundary conditions, in the ANSYS/LS-DYNA module, the constitutive relation of materials at high strain rate is utilized to es-tablish a pipe deformation analysis model to make analysis of the deformation processof external pipes. The efect of such process parameters as discharge voltage, clearancebetween internal and external pipes and overlapping angle on collision velocity, with theoptimum process parameters in the MPW process determined to guide process tests.The movement process of aluminum pipes under diferent discharge voltage con-ditions is shot using a high-speed camera and through the analysis of shooting results,the displacement-time curve and velocity-time curve involved in the movement processof external pipes are obtained. Through process tests, the efect of such parameters asdischarge voltage, overlapping angle and clearance between pipes on the collision veloc-ity of MPW is studied, with the collision velocity of internal and external pipes under diferent process parameter conditions and the critical collision velocity for realizing themetallurgical bond of internal and external pipes. SEM is used to analyze the joints ofMPW obtained under diferent collision velocity conditions and study the efect of themovement speed of the collision point on the appearance of welding joints. The analysisof the macro-defects and microstructure defects of MPW joints is made, with methods foravoiding the formation of defects presented.Theoretical analysis, numeral simulation and process tests of internal pipe stifnessare conducted to obtain the minimum wall thickness value for meeting the internal pipestifness conditions under diferent voltage conditions. With internal pipes consideredequivalent to the force-deformation model of thick-walled cylinder parts without end clo-sure, equilibrium equations and coordination equations are used to obtain the displace-ment component of internal pipes under the action of magnetic force, with the pressureequation of plastic limit of internal pipes obtained based on Tresca yield criterion and thecritical wall thickness expression under diferent collision velocity conditions derived. Adeformation field model of pipes in the MPW process is established using the LS-DYNAmodule, the stifness conditions of internal pipes under diferent process parameter condi-tions are studied and the comparison with the result of theoretical analysis is conducted.Process tests are conducted under diferent conditions to verify theoretical calculation andsimulation results, with results showing these three have excellent goodness of fit.The mechanical properties of MPW joints are tested using uniaxial tension tests andtorsion tests. Through tension tests, the tensile strength of MPW joints and the base metalstrength are compared. A nano-hardness tester is adopted to test the hardness of weldedjoints and the metal on both sides of the joints. The hardness distribution law of themetal on both sides of MPW interface and the cause of increased hardness of the metalnear the interface are studied. The appearance in the transition area is observed througha metallurgical microscope and SEM, and the formation mechanism of Kelvin wavesformed around MPW joints is studied, with the expression of the width of the transitionarea obtained. The welding mechanism of the MPW process is obtained, using SEM andTEM to analyze the microstructure and composition of MPW joints, through comparisonwith the formation conditions of pressure welding and explosive welding.