Research On Process And Structure Of Magnetic Field Assisted Mg/Al Dissimilar Alloys CMT Welding

Magnesium alloy and aluminum alloy are excellent performance and lightweight metal widely used nowadays.The connector of magnesium and aluminum composite can combine the advantages of both.It can form complementary advantages,improve the applicability of the two metals.However,brittle inter-metallic compound usually easily generated in the magnesium/aluminum alloy welding process,and defects such as blowholes,deformations,and cracks could form in weld joint.Therefore,excellent welding joint are difficult to be gain through the conventional fusion welding method.Cold metal transition technology(CMT)is a new welding method own features such as low heat input and stable welding process.It can effectively reduce welding defects in the magnesium/aluminum welding process.Longitudinal magnetic field can regulate arc,change droplet transition,whirl molten pool,and modify the weakness in welding magnesium/aluminum welding.Therefore,magnesium/aluminum dissimilar metals were welded by the external longitudinal magnetic field hybrid CMT welding process.A new device for generating longitudinal magnetic field was designed in the first.Base on the element software of ANSYS,the distribution of the magnetic field generated was simulated,which generated by different magnetic pole structur(height,diameter and shape).Base on the simulation,we could select the scientific and suitable additional magnetic field.A platform magnetic pole structur has a better axial distribution magnetic field in the welding area.A lower height and a smaller diameter of the magnetic pole structur made magnetic field strength stronger.2mm thickness of AZ31 B magnesium alloy and 6061 aluminum alloy were welded by the external longitudinal magnetic field hybrid CMT welding process.The influence of welding wire type and process parameters on joint weld formation was studied.The molten metal wettability of ER4043 wire was better than ER5356 wire.Longitudinal magnetic field could improve the wettability of molten metal,reduce the number of blowholes,and reduce the melting amount of magnesium alloy.Then studied the mechanical properties and fracture mechanism of Mg/Al joints.The tensile load of joints indicated obvious improvements with the applied of magnetic field.And it can reach 1411 N.The fracture position was occurred at Mg base metal through the form of brittle fracture in general.However,the fracture position couled occurred at Al base metal with blowholes and intermetallic compounds.The microstructure and interfacial structure of Mg/Al dissimilar joint were investigated.A thicker continuous compound layer at the Mg-Al interface was produced,and the longitudinal magnetic field could suppress the formation of compounds.The thickness of the compound layer decrease of magnetic flux intensity.The distribution of Mg2 Si phase at the interface was wider and the particles were refined with the longitudinal magnetic field.Finally,the effects of the longitudinal magnetic on the transition of welding arc,droplet and weld pool was discussed.And its effects on formation mechanism of Mg/Al dissimilar joint were clarified.The longitudinal magnetic field mainly affected the interface temperature and the molten pool flow,which affected the microstructure of the joint interface.