Research On Thickness Size Effect Of Interfacial Bonding Strength Of Steel/Aluminum Composite Plate Prepared By Rolling

Steel/aluminum composite plate is a typical layered metal composite material,which is widely used in ships,chemical industry,aerospace and other fields.Its thickness specifications range from 0.1mm?e.g.radiator fins?to 100mm?e.g.high-quality steel/aluminium composite joints for ships?and span three orders of magnitude.At present,the medium-thickness steel/aluminum composite plate is mainly prepared by the explosive composite method,and the technology is relatively mature,but there are still some limitations in dealing with extreme specifications such as severe weather,thinner coatings and wide format.The rolling composite method has the advantages of continuity and high efficiency,and has been successfully applied to the industrial preparation of stainless steel/carbon steel composite plate,aluminum alloy composite strip for brazing,thin specification steel/aluminum,copper/aluminum and other laminated composite materials.The technological and theoretical research has made considerable progress.However,in the existing literature investigations and rolling experimental studies of steel/aluminum composite plates,it has been found that the component thickness has a significant effect on the interface bond strength of rolled steel/aluminum composite plates.That is to say,it is easier to obtain relatively ideal interface bonding strength during thin strip rolling,but with the increase of thickness,the interface strength weakens or even cannot be welded.In order to clarify the flow behavior and interfacial stress state of the two component metals in the deformation zone,and to reveal the influence of component thickness on the bonding strength of the steel/aluminum composite plate rolling composite interface,based on numerical simulation and experimental research methods,this thesis carries out research on the thickness-size effect of the bonding strength at the rolling interface of steel/aluminum composite plates,explores the technological approaches to improve the interface quality of thick-gauge steel/aluminum composite plates,and strives to provide a theoretical basis for pilot production.Firstly,warm rolling composite experiments and interfacial shear strength tests of steel/aluminum composite plates with different thicknesses are carried out in the laboratory.In order to avoid the interface oxidation of steel/aluminum composite slab during preheating,aluminum foil is used to cover the slab under the protection of inert gas to achieve good results.The rolling experiments of steel/aluminium composite plates with four different thicknesses of 1.5mm,2mm,3mm and 4mmm,are carried out,under the conditions of 1:1original layer thickness ratio,400?rolling temperature,60mm/s rolling speed and 40%single pass reduction.The results show that the interface shear strength of the steel/aluminum composite plate decreases with the increase of the component thickness.When the initial single-sided component thickness is 1.5 mm,the average interface bonding strength of the composite plate is 62 MPa;when the initial single-sided component thickness is 4 mm,the average interface shear strength of the composite plate decreases to 21 MPa,and effective compounding cannot be achieved.At the same time,the scanning electron microscope?SEM?,energy spectrometer?EDS?and other advanced equipment are used to observe and to analyze the micro-morphology and element diffusion of the steel/aluminum composite interface under different working conditions.Secondly,in order to find out the deformation distribution and evolution rule of metal components in the deformation zone,the rolling samples in the whole deformation zone,including from the entrance to the exit of rolling,are cut through the rolling card experiment,and the thickness evolution of components is measured and analyzed by OM.The deformation of the steel/aluminum composite plate during the rolling process is mainly concentrated on the aluminum component.With the increase of the initial component thickness,the deformation coordination of the steel and aluminum components in the rolling deformation area further deteriorates.When the initial unilateral component thickness is4mm,the steel component only produces a reduction of about 0.2mm.Finally,based on the commercial finite element analysis software MSC.Marc,a thermo-mechanical coupling nonlinear finite element model for the steel/aluminum composite plate rolling process is established.By introducing the“life and death element”method,the interface contact behavior and welding state simulation of the two components of steel and aluminum in the rolling deformation zone are solved,and the component metal at the entrance side of the rolling can flow freely to ensure relevant behavior matched actual conditions.Through variable parameter simulation,the stress and strain states of the rolling deformation area are analyzed systematically.The results show that the direction of the thickness?reduction?of the aluminum components in the deformation zone is compressed;in the rolling direction,due to the initial welding of the steel/aluminum interface at the exit,the extended flow of the aluminum components in the front sliding zone is in a compressive stress state;In the direction of expansion,due to the frictional stress at the contact interface between the roll and the rolled product,the expansion resistance is also under compressive stress.That is,in the deformation zone,the aluminum component with lower deformation resistance is subjected to three-dimensional compressive stress,which makes it difficult to achieve the yield condition.Under this stress state,the normal contact stress of the steel/aluminum interface is greatly increased,and the principal compressive stress?₂provided to the surface of the steel plate is increased to a level where the steel plate can be plastically deformed.Extension deformation,fresh metal on the surface of the steel plate is exposed,and then the interface bonding strength is improved.The increase of initial component thickness will have an adverse effect on the establishment of three-dimensional compressive stress state in the deformation zone of aluminum component,which makes the steel plate enter into plastic deformation,resulting in the poor coordinated deformation of thick gauge steel/aluminum composite plate.The combination of numerical simulation and experimental phenomena better explains the thickness-size effect of the rolling interface strength of steel/aluminum composite plates.On this basis,the effects of roll diameter,friction,and reduction on the stress state in the deformation zone and the coordinated deformation of steel/aluminum are analyzed.