Study On Microstructure And Properties Of Laser-welded Joint Of Steel/aluminum Added Powder

Lightweighting of automobiles has become the frontier and hotspot of 21st century automobile technology.The use of lightweight materials on a large number of vehicles has become the development trend of the automotive industry,and dual-phase steel and aluminum alloy have been widely used as good lightweight materials.For the connection of dual-phase steels and aluminum alloys,it is difficult to obtain high-quality steel/aluminum joints because of obvious differences in physical and chemical properties between the two,and it is easy to form brittle Fe-Al compounds.In order to explore a new steel/aluminum connection method,DP590double-phase steel and 6016 aluminum alloys for automobile bodies were selected as research objects.Based on the first-principles calculation,the possible replacement of powder atoms in Fe-Al compound cells was studied.Sex and placeholder law,selection and design of powder elements,laser welding test of steel/aluminum underlap,addition of intermediate layer powder between steel/aluminum layers,use of metallographic microscope,environmental scanning electron microscope with EDS and EBSD probes,and Microcomputer controlled electronic universal testing machine etc.was used to study the formation of welds,phase composition of welds,grain size,interface elements and distribution,and shear resistance of joints.The role of intermediate layer powders in the laser lap welding of dual phase steel/aluminum alloys was explored.The mechanism for improving the performance of welded joints.The research results are expected to provide new research ideas for high-quality welding of dual-phase steel/aluminum alloy for vehicles,and provide important theoretical basis and experimental basis for advancing vehicle weight reduction.The powder atoms were used to replace the Fe or Al atoms in the FeAl compounds,respectively,and the binding energy,elastic constants,and electronic structures of the Fe₈Al₈ supercells were calculated.It was found that the Ti atoms preferentially replace the Al atoms in the FeAl compound,and the formed compound has ductility and can reduce Fe.For the brittleness of Al-compounds,Ti is selected as an additive powder element between the steel/aluminum layers.In order to obtain the best weld surface formability,the presence or absence of Ti-powder laser lap welding of 1.4mm dual-phase steel plates and 1.2mm-thick 6016aluminum alloys was investigated.It was found that the surface of welds was well-formed without obvious defects.Compared with the powder without Ti powder,the shear load of welded joints with Ti powder increased,and the elongation increased;the grain size of the weld zone was small,the additive elements were evenly distributed in the aluminum side melt pool,and the diffusion of the lower Al layer to the steel side of the upper layer was inhibited.Molten Al migrates to both sides of the melt.The mixing of Fe and Al inside the molten pool weakens.The layer thickness of the Fe-Al compound on the steel/aluminum interface decreases,and the type of intermetallic compound in the interface layer changes,resulting in a ductile Fe2Ti phase.Based on the numerical simulation of laser welding temperature field on aluminum under lap laser welding,it is found that the addition of Ti powder has no obvious effect on the temperature change of the upper dual-phase steel,while for the lower aluminum alloy,the addition of Ti powder increases the penetration depth of welded joints.Narrowing,the addition of Ti powder promotes heat transfer from the upper layer of steel to the lower layer of aluminum,reducing lateral heat transfer,due to the higher melting point of Ti,when the upper steel melts,the addition of Ti powder absorbs heat,and the upper steel rapidly solidifies,thereby increasing The depth of the Molten pool?...