Experimental Research On Process Param Eters Of Magnesium-aluminum Laminates Hot-rolled By Double Temperature Stage Process

Magnesium alloy is currently a key material for structural lightening of industrial equipment which is mainly prepared by rolling process.Aluminum alloy is one of the metal materials with the widest application range and the best processing plasticity.The magnesium and aluminum alloy plates can be composite formed to prepare a new kind of composite material which has both the advantages of two metal materials and named as magnesium/aluminum laminates through the rolling process.Magnesium-aluminum laminates are mostly compounded by hot rolling,while the traditional isothermal hot-rolling process has difficulty in temperature setting.At this time,too low the temperature will cause serious cracks formed in the magnesium alloy and too high the temperature will make the surface to be composited is prone to oxidation and ablation,or form the excessively thick brittle phases at the interface to weaken the bonding reliability because that the magnesium and aluminum plates have not yet formed a tight bond at the initial stage of deformation.For that,It’s difficult for the parameter setting of process to obtain a balance among plate shape and property,which makes the magnesium/aluminum laminates difficult to be prepared and applied.The double temperature stage hot rolling process can coordinate the deformation characteristics of aluminum and magnesium plates through the temperature difference between passes.In the early stage,a lower rolling temperature is used to make the soft aluminum plate deformed first.After the pre-composite is formed,the magnesium plate obtain the large deformation by increasing temperature,and the resistance of the aluminum plate caused by the cumulative deformation was reduced.In this paper,the magnesium/aluminum laminates was prepared by a double temperature stage hot rolling process,and the edge cracks,residual stress distribution,aluminum layer structure evolution,magnesium layer grains,interface formation process,tensile properties,the fracture characteristics and other aspects of laminates between rolling passes are studied.The planar distribution characteristic and the distribution law between passes of the surface residual stress are analyzed from the plastic deformation of the aluminum layer and the dynamic recovery and recrystallization behavior of the surface microstructure.The evolution of the interface bonding mode during the double temperature stage hot rolling process is more consistent to the N.Bay theory and the morphology evolution of the grains of the magnesium layer is used to explain the dynamic recrystallization behavior between passes.Through the tensile test,the tensile curves and fracture characteristics of magnesium,aluminum single plate and laminates are analyzed,and the relationship between the process parameters and the formation of hot-rolled defects which reduces the mechanical properties of the laminates is analyzed.Annealing treatment can usually eliminate the residual stress of the plate and promote the solid solution diffusion of heterogeneous metal elements.In order to study the annealing evolution mechanism of laminates,hot-rolled magnesium/aluminum laminates were annealed in the range of 150-350 ℃ for0.5-3 h,and the surface residual stress elimination law,the static crystallization of microstructure,the diffused evolution of the Mg/Al interface and the change characteristics of the tensile curve and properties of laminates were analyzed and studied.It was found that the residual stress of the laminates relieved better under high temperature and short time annealing process,and its recrystallization ratio and elimination ratio of dislocation density in surface microstructure of the aluminum layer was at a high rate.The recrystallization time of the magnesium layer grains drops as the increasing annealing temperature.The annealing phase transition at the interface is also related to the rolling deformation of the laminate: with a low degree of deformation,the R2 laminate does not undergo phase change during annealing,while the R3 laminate undergoes interfacial phase transition when annealed above 250 ℃,and the completion time of phase transition drops as the increasing temperature.The grains of the magnesium layer which is new recrystallized usually have grown at the annealing temperature required for the interfacial phase transition,so it is easy to form a coarse-grained structure resulting in a decrease in tensile strength.In addition,7 kinds of different processes divided into two sets are used to study the process parameters improve method of laminates in the double temperature process.It is found that both the two method which reducing the deformation in the low temperature stage and increasing the temperature in the high temperature stage can effectively improve the edge cracking and increase the diffusion distance of interface elements.With the rolling process of350 ℃+450 ℃ can control the interface oxidation and obtain a higher degree of interface diffusion and tensile properties.In addition,the hot rolling forming conditions of IMC at the interface of the laminates were studied,for which the more fully effect of thermo-mechanical coupling on the laminate at the appropriate reduction ratio and rolling temperature,the more likely it is to form IMC at the interface.