Research On Copper And Steel Dissimilar Materials Welding Under Co-Effect Of Laser And Magnetic Field

Now that energy and environmental problems are becoming more and more serious,automobile light-weighting has become more urgent.The use of aluminum-steel dissimilar structures is lighter than traditional steel structures and safer than all-aluminum structures.The physical properties of aluminum steel are very different,and it is difficult to connect with each other.At the same time,aluminum steel is extremely prone to metallurgical reactions during welding,producing iron-aluminum intermetallic compounds with a highly brittle hard phase,resulting in a decline in the mechanical properties of the component.So that its application is limited.Laser fusion brazing has the advantages of high controllability of heat input,high welding efficiency,and ease of automation.It is widely used in automobile plate welding.At the same time,a large number of studies have shown that the magnetic field has a significant regulation effect on the flow of conductive liquids.However,the effect of the magnetic field on the macro forming,microstructure,and mechanical properties of laser welding brazed joints of aluminum/steel dissimilar metals needs further study,and the mechanism of the magnetic field's effect on molten pool flow and element diffusion has yet to be elucidated.In this paper,the regulation behavior of the magnetic field on the macro forming,microstructure and element distribution of the weld joint is studied,and the specific role of the magnetic field is explained.As the strength of the magnetic field increases,the structure of the interface structure becomes simpler.The structure is transformed from the steel matrix,the free intermetallic compound,the acicular intermetallic compound,the lamellar structure(three layers),and the aluminum matrix when the magnetic field is not applied.The structure of the steel matrix,lamellar structure(no delamination phenomenon)and aluminum matrix.The average thickness and thickness fluctuation of the structure are reduced from 37?m and 70.99?m to 7.83?m and 2.63?m,especially when the external longitudinal magnetic field strength reaches at 120m T,the thickness of the interface structure is 7.83?m<10?m.At this time,the high brittle hardness of the intermetallic compound will no longer have a significant effect on the toughness of the joint.The element distribution becomes single,the element diffusion distance decreases,and the shape of the underlying layered structure gradually changes from a band shape to a continuous line shape,intermittent line shape,and intermittent point shape,and the number continues to decrease.And under the experimental conditions,the application of 60m T magnetic field can completely suppress the diffusion of Fe element into the aluminum matrix.However,under the action of the magnetic field,the heat input during welding and the geometry of the joint are basically unchanged.The wetting angle of the joint forming parameter fluctuates within the range of 20±1°,and the brazing width does not change much.By analyzing the influence of the magnetic field on the mechanical properties of the joint,it is found that under the action of the magnetic field,the microhardness uniformity of the intermetallic compound at the interface is improved,the tensile strength of the joint is enhanced,and the tensile strength increases with the increase of the magnetic field.Especially when a 120m T magnetic field is applied,the tensile strength is increased by 65.4%,the average diameter and depth of the ligament dimples in the joint fracture become larger and deeper,and the tissue defects are reduced,and the plasticity becomes better.In order to clarify the reasons for these effects of the magnetic field,the growth process of the main phases Fe₂Al₅and Fe Al₃in the interface structure is explained.Under the interaction of the Marangoni convection and the magnetic field,an ampere force that hinders the convection is generated.This braking force causes the Marangoni convection intensity to decrease.Based on the high-speed imaging results of the 0/60/120m T welding process,it was found that under the action of the magnetic field,the lateral velocity of the molten pool(along the direction of the weld)is suppressed,and as the strength of the magnetic field increases,the degree of suppression is gradually increased.The suppression of convection intensity leads to a decrease in the solute concentration in the solid-liquid interface,a decrease in solute mobility,and a reduction in the formation of intermetallic compounds.At the same time,when the Al atoms diffuse through the layered structure vacancies to their growth fronts and interact with the magnetic field,the Lorentz force is generated,Under the influence of the braking force Lorentz force,the diffusion rate is reduced,which leads to a further reduction in the concentration of solutes at the growth front and a further reduction in the formation of intermetallic compounds.Therefore,in this experiment,the effect of 120m T longitudinal magnetic field is the best.