Research On Microstructure And Mechanical Properties Of A356/Q235 Clad Plates Fabricated By Cast Rolling

Bimetal clad plates are made of two metals with different physical and mechanical properties.Compared with the single metal plate,bimetal clad plate can meet the increasingly demanding demands of modern industry by integrating the best characteristics of the two metals.Aluminum and its alloys have many advantages,such as light weight,good corrosion resistance,good conductivity,good dimensional stability,rich reserves,etc.More and more attention has been paid to the development and utilization of aluminum and its alloys,but its low strength,poor wear resistance and other shortcomings also limit its application.Common low-carbon-steel has many advantages,such as good plastic toughness,good cold formability,suitable carbon equivalent,wide use and low price,but its poor corrosion resistance and high specific gravity also hinder its application.If these two materials are combined to make clad plate by some way,the weight of the clad plate is greatly reduced compared with that of steel plate in the same volume,and the disadvantages of low strength and poor wear resistance of aluminum alloy are overcome.In this study,Q235 cold-rolled steel plate and A356 aluminum alloy ingot were combined by liquid-solid casting rolling method to successfully prepare Al/low-carbon-steel clad plates.After that,clad plates were annealed,and then rolled down.The purpose is to strive to prepare the clad plate with the best mechanical properties and microstructure.With the help of thermal field emission scanning electron microscope（FEG-450,SEM）,energy spectrometer（EDS）,electron backscatter diffraction（EBSD）,optical microscope,X-ray diffractometer（D/max-2400X,XRD）,SEM in-situ tensile,microscope hardness tester（HV-100 type）and electronic universal material testing machine（WDW-100D type）were used to study effects of A356covering temperature,annealing process and reduction ratio on the microstructure and comprehensive mechanical properties of clad plates.It provides theoretical guidance for the rational control of the microstructure of Al/low-carbon-steel clad plates and types of intermetallic compounds in the interface,and systematically explores the internal relationship between the microstructure of Al/low-carbon-steel clad plates and mechanical properties.When studying the effect of A356 covering temperature on clad plates,the results show that with the increase of the covering temperature,the interface cracks of the clad plate disappears,and the thickness of the diffusion layer gradually increases in the overall trend.When the covering temperature is 710°C and above,Fe₃Al,FeAl,FeAl₂,Fe₂Al₅ and FeAl₃ phases will be formed at the interface.At the same covering temperature,the overall tendency of hardness is stable in Q235 and A356 matrix,but it continuously decreases from 100μm from the center of the interface of Q235 to 100μm from the center of the interface of A356.Both the tensile strength and the shear strength show a trend of increasing first and then decreasing.When the covering temperature is 710°C,the forming quality of the clad plate is the best,and the tensile strength and the shear strength are both the largest,336 MPa and 138 MPa.When studying the effect on the subsequent annealing process of as-cast clad plates,it is found that the diffusion layer thickness increases with the increase of annealing time or annealing temperature,and the influence of annealing temperature on the diffusion layer thickness is greater;the diffusion degree of aluminum and iron increases with the increase of annealing temperature,and the diffusion distance and flux of aluminum are always higher than that of iron.After annealing,the intermetallic compounds in the interface of the clad plate are FeAl₂,Fe₂Al₅ and FeAl₃,which are brittle aluminum rich phase and harmful to the interface.However,the shear strength and tensile strength of clad plates decreased with the increase of annealing time or annealing temperature.Among the annealed clad plates,the clad plate annealed at450°C for 1.5h has the best comprehensive mechanical properties,and its shear strength and tensile strength are 141 MPa and 316 MPa,respectively.When studying the effects of subsequent rolling reduction processes,it was found that the grain size,texture type,pressure state of the clad plate,and the thickness and morphology of the diffusion layer will all affect the mechanical properties of the clad plate.In the annealed condition and the rolling reduction 45%clad plates,there are a good interfacial bonding situation,while the reduced 25%and 35%clad plates have gaps and cracks in the interface area,and the bonding is poor.The in-situ tensile test on the clad plates found that the deformation of the annealed clad plates will continue to deform after the maximum pressure is reached,and the two materials are disconnected on the same plane after the clad plate is broken,indicating that the clad plates in this state have good plastic toughness and integrity;while the reduction clad plate is quickly broken after the maximum tensile stress is reached,except for the clad plate that can withstand the maximum tensile stress of 45%,the clad plates are reduced by 25%and 35%.The cross sections of the plates are not located on the same plane,indicating that the 45%clad plate has the highest tensile strength and good integrity,but the toughness and plasticity are poor.The 25%and 35%clad plates have poor integrity and plastic toughness.After the clad plate is rolled and reduced,the texture type of the A356 layer is changed from typical cubic texture and R texture to copper texture and brass texture,and the Q235 layer loses Gauss texture for{111}<110>and rotated cube texture.In addition,as the reduction ratio increased,the shear strength and tensile strength of the clad plates gradually increased,and the shear strength and tensile strength of the 45%clad plate were 161 MPa and 422 MPa,respectively.