Research On Roll-bonding Processes,Microstructures And Properties Of Mg-Sn-Zn-Al/Al6061 Composite Plate

Multilayer metal composite plates combining two or more kinds of alloy can make up and improve the defects of one alloy plate and make use of the characteristics of component metals to obtain a new multifunctional alloy.These new materials have wide application areas in various industries such as automobile,aerospace,electronic equipment and other industries.The preparation of Mg/Al composite plate is expected to take advantage of the advantages of Mg and Al.As is well-known,Mg and its alloys are the lightest metal and have many advantages as structural materials,such as high specific strength,high specific stiffness and excellent damping capacity.In contrast,aluminum and its alloys have better corrosion resistance and formability.Therefore,Mg/Al or Al/Mg/Al composite plates are expected to be combined to broaden the advantages of magnesium and aluminum alloys.The Mg-Sn-based alloy has excellent high temperature strength and creep resistance,which can overcome the shortcomings of the regular ZK and AZ magnesium alloys,such as poor high temperature creep resistance and negative plasticity at room temperature.Adding Al and Zn elements can further improve the strength and plasticity,so Mg-Sn-Zn-Al alloys have great potential for use.To a certain extent,it can avoid the problems such as large residual stress of plate and inconsistency of deformation between component metals caused by conventional alloy composite plates.It is an ideal choice as the base material for composite plates.Based on the above considerations,the substrate Mg-7Sn-5Zn-Al and cladding plate Al6061 were selected in this paper to produce Mg/Al composite plate with good performance by single-pass rolling process and double-pass rolling.The single-pass rolling process is different temperature asymmetrical rolling,and the double-pass rolling process is differential temperature asymmetrical rolling+isothermal symmetrical rolling.The effect of different thickness ratios and different reduction rates under single-pass rolling process and different first-pass reduction rates under double-pass rolling process on the changes of interface morphology,microstructure,mechanical properties and residual stress of composite plate were studied.The results show that:（1）With the increasing rolling reduction,the interface morphology of single-pass rolled composite plate gradually becomes smooth,straight and compact from the initial rough and uneven.The diffusion interval at the interface increases gradually with the increase of reduction rates.When the reduction rate reaches 45%of the plate blank thickness,the diffusion reaches a saturation state and the diffusion interval thickness is 7μm.Because of the same shearing action,the exposure of fresh metal on the surface is approximately equal to the rolling reduction rate.When the reduction rate is the same under different thickness ratios,the thickness of diffusion intervals of Mg/Al composite plate is the same.When the thickness ratio is 0.3,the deformation difference of component metals is smaller than that of other thickness ratios.（2）The binding strength and tensile properties of Mg-Al composite plate increased with the increase in the reduction rate.When the thickness ratio is0.3 and the composite plate is reduced to 3.25 mm,the composite plate has the best mechanical properties;the bond strength is 67.25 MPa,the tensile strength is 309 MPa,and the elongation is 14.4%.（3）The residual stress of Mg-Al composite plate alongside the rolling direction accelerated first and then reduced with the enlarge in reduction rate under different single-pass processes.When the reduction reaches 45%,the most residual stress value of composite plate is in the range of 45-80 MPa.When the reduction continued to increase,the residual stress decreased significantly due to the occurrence of dynamic recrystallization,which can effectively avoid the cracking phenomenon（4）The intermetallic compound layer is broken into chunks in the second-pass rolling,neatly distributed along the bonding interface,forming the gear-type 3D structure morphology.The thickness of the intermetallic compound layer formed by double-pass rolling is proportional to the reduction of the first-pass rolling.Moreover,as the Al side deformation is larger under the AS50%process in the first pass rolling process,Al element is rapidly diffused to form Mg₁₇Al₁₂,and Mg₂Al₃grows rapidly afterward.Therefore,the increase of intermetallic compound thickness is mainly concentrated on Mg₂Al₃on the Al side.（5）The main structure of the matrix is twins,and the grains in the cladding plates are deformed grains extending along the rolling direction.With the increase of the first-pass reduction,the proportion of twins increased,and the dislocation strength of clad plate is inversely proportional to the first-pass compression.（6）The average hardness value and elastic modulus of the cladding plate increased with the increase of the first-pass reduction,but the substrate is just the opposite.The shear fracture occurred at the interface of composite plates,and the fractures all present neatly arranged fracture stripes.Fracture stripes distributed closely under the process of first-pass small reduction,and its binding strength is 94.2 MPa.The composite plate under this process has the best mechanical properties,tensile strength is 320.6 MPa,and the elongation is16.7%.