Study On Preparation Technology Of Al/Mg Bimetallic Isothermal Co-extrusion Composites

Bimetallic composite bar is composed of two different properties of metal materials combined with a higher than the strength of thermal conductivity,corrosion resistance,light and other excellent comprehensive performance.The use of aluminum-magnesium composite components can further reduce the weight of motor vehicles,rail vehicle structures and various components in the aircraft,thereby helping to reduce fuel consumption.This paper presents a method for preparing Al / Mg composite bar by isothermal extrusion process to exert the excellent performance of these two kinds of lightweight metal materials and expand the application field.This paper based on the rigid-viscoplastic finite element theory,the finite element model of Al / Mg bimetallic isothermal extrusion was established by using Deform-3D software.The flow phenomena,stress-strain state and temperature field evolution of 1100 aluminum and AZ31 magnesium alloy during isothermal extrusion was discussed.The effects of extrusion speed,extrusion temperature and die angle on the flow characteristics of bimetallic extruded materials were studied by orthogonal test.The optimum process parameters were as follows: extrusion speed 3mm/s,mold preheating temperature375℃,extrusion temperature 425℃,and extrusion die angle 45.According to the numerical simulation results,the results show that the composite bar has good uniformity and no obvious defects,the experimental results show that the forming load and die outlet temperature test data are in good agreement with the simulation results.It is shown that the basic constitutive relation and the friction characteristic of the introduced material describe the extrusion characteristics better.The bimetallic isothermal squeeze numerical model is accurate.In order to evaluate the quality of the composite bar,the microstructure,the element distribution,the phase structure and the microstructure of the interfaceand grain orientation,size of the composites during the extrusion process were analyzed by scanning electron microscopy(SEM),X-raydiffraction(XRD)and back scattering electron diffraction(EBSD).And the mechanical properties of the binding zone were tested.The results show:The thickness of the diffusion layer is about 315μm,and its phase structure is Mg + Mg17Al12 + Mg2Al3 + Al.The adjacent transition layer with AZ31 matrix is mainly composed of Mg17Al12,The intermediate diffusion regionis mainly Mg + Mg17Al12,while the transition layer 3 near the 1100 aluminum matrix contains a large amount of Mg2Al3.During the isothermal extrusion process,the outer layer aluminum is transformed from <111> to <001> in the single direction,in the isothermal extrusion process,the aluminum layer by a single direction of <111> texture conversion to the <001>,<111> dual texture,and the axial density ofmagnesium alloy reverse pole diagram is smaller and its texture is not obvious.The micro hardness of AZ31 magnesium alloy matrix is 55 HV,and the micro hardness increases gradually and reaches about 220 HV due to the increase of Mg17Al12 phase and Mg2Al3 phase in eutectic transition layer.To 1100 aluminum matrix micro hardness decreased significantly,its average value of 30 HV,it is shown that the change of micro hardness value at the interface junction is consistent with its microstructure.