Study On Laser–Arc Hybrid Butt Filling Welding Of Immiscible Magnesium Alloy And Steel

Magnesium alloy as the lightest metal engineering material has broad prospect inlightweight application market.Steel materials still occupy the leading position in the industrial production field by virtue of its series of excellent properties.Mg/steel dissimilar metal bonding structures will be an important application direction for future lightweight manufacturing.A large number of researches on Mg/steel dissimilar metal welding have been conducted at home and abroad.Mainly in the form of lap welding,the problems of large difference melting boiling point and miscibility are mainly solved by fusion brazing and by cladding or interlayer metal.This paper presents a new welding method for laser–arc hybrid butt filling welding of Mg/steel.The influence of the hybrid welding process on the formation of welded joints,interface microstructure and mechanical properties was systematically studied,which provides technical support for the development of Mg/steel dissimilar metal structures.Using 1.6mm thick AZ31 B and 1.0mm thick Q235 steel butting,the laser is in front,the arc is behind,and the forward side is filled with 1.6mm AZ61 wire.In a wide range of process parameters,good single–sided welding double–sided weld formation is obtained.The end of the steel is heated and melted into an arc shape,which is then wrapped by spreading magnesium alloy weld to form a Mg/steel butt–coating structural joint.Systematic study of laser power,defocus amount,and heat input parameters that have a great influence on the Mg/steel interface.With the increase of laser power,the reduction of laser defocus and the increase of heat input,steel melt penetration increased,the interface bonding reaction more intense and gradually become completely,strengthen the interface combination,so that the joint under the tensile load increases gradually.However,limited by the conditions,the heat input is increased to a certain extent will appear discontinuous welding joint damage leakage.With the combination of strength increase fracture morphology from brittle fracture pattern of smooth river,to smooth area gradually decreased and there were many mixed fracture tearing edge step,to a tear equiax ductile fracture characteristics of dimple magnesium alloys.High performance Mg/steel joints were obtained under three parameters of laser power 850 W,defocus +2mm and heat input 73.86J/mm.The tensile specimens were broken at the steel side base metal.The microscopic interface analysis of magnesium/steel shows that the high interfacial temperature promotes the diffusion and enrichment of Al and Mn elements at the interface to form two reaction layer Al11Mn4 intermetallic compounds and Fe(Al)solid solution.The weld of magnesium alloy is mainly composed of ?–Mg equiaxed dendrite and mixed eutectic phase of grain boundary.The Mg/steel butt joint is divided into four fracture modes: the high quality high strength joint in the best bonding state breaks in the steel side base metal,the high strength joint breaks in the weld position of magnesium alloy,the middle strength joint breaks in the weld or interface near the interface,The low strength joint is stripped completely along the interface.Through The reinforcement height of the joint is removed to obtain the strength state of the two parts of the interface and the reinforcement height.The bearing capacity of the joint was increased about 100N/mm by the existence of reinforcement height of magnesium alloy weld,and the maximum tensile strength of removing the reinforcement height joint was 238 MPa.