Research On Continuous Extrusion Process Of Al/Mg Composite Materials

Magnesium alloy has a series of advantages such as low density,high specific strength,high specific stiffness,high elastic modulus,excellent thermal conductivity and so on,which are widely used in aerospace,automotive,3C electronic products and other fields.However,magnesium has a Hexagonal Close Packed（HCP）structure and poor plastic deformation ability at room temperature.In addition,application of magnesium alloys are largely limited due to its poor corrosion resistance and active chemical properties.However,with the continuous development of new technology,the metal composite materials composed of magnesium matrix may improve the performance of the material to a certain extent and make up for its inherent defects.Therefore,excellent performances of the Al/Mg composites have been widely concerned in recent years.In this paper,Al/Mg composites with two cross section shapes were prepared by continuous extrusion technology under different technological conditions,which could not only prepare magnesium alloy with high specific strength and high stiffness,but also compound a layer of aluminum alloy with corrosion resistance on the surface,exerting the"composite effect"of two metals.In this paper,the continuous extrusion finite element model of 6063 aluminum alloy/AZ31 magnesium alloy was established by Deform finite element（FE）software.The effects of preheating temperature,billet diameter and extrusion ratio on material flow,stress and strain,temperature field and velocity field in the continuous extrusion process were investigated.With the decrease of magnesium core diameter,the increase of preheating temperature and the decrease of extrusion ratio,the temperature difference between aluminum and magnesium decreased gradually,and the flow and deformation uniformity of the two metals also improved.When the diameter of magnesium core wasΦ3 mm,preheating temperature was 450℃and extrusion ratio was 1.78,the deformation uniformity of Al/Mg composite rod was better,and the deformation uniformity and composite quality of composite belt were the best when the extrusion ratio was 1.31.The Al/Mg composite bars and composite belt were prepared by continuous extrusion.The microstructure of the samples were analyzed by metallographic microscope,scanning electron microscope（SEM）,X-ray diffraction（XRD）and so on.The results show that the microstructure of magnesium core was refined by continuous extrusion.The minimum average size of grain was refined to 5.2μm with unpreheating.With the increase of preheating temperature,the grains grew up.In addition,the increase of magnesium core diameter and extrusion ratio also caused grain growth.The interface included the layer of AZ31 magnesium alloy,Mg₁₇Al₁₂,Mg₂Al₃and 6063 aluminum alloy.The preheating temperature had a significant effect on the thickness of the interface and the maximum thickness of the interface was 5.6μm when the preheating temperature was 450℃.The hardness,three-point bending,tensile and other mechanical properties of the Al/Mg composite bars and composite belt were tested.The results show that the hardness of the interface was higher than that of magnesium and aluminum.The highest interface hardness of the sample was 88.3 HV under the unpreheating condition and the lowest interface hardness of the sample was 66.3 HV under the preheating condition.On the other hand,the tensile strength of composite bar and composite belt were 141.4 MPa and 178.2 MPa respectively when the extrusions were conducted under the unpreheating condition.However,the bending property was very poor.Under the preheating condition,the elongation of the two materials increased to 10%and 16.2%and both showed good bending performances,with the bending displacement of 17.1 mm and the bending angle of 149°.The tensile strength and elongation decreased with the diameter of magnesium core increased.