Research On Extrusion Forming And Annealing Process Of Al-Mg Bimetallic Laminated Chamber

The cabin members belong to the cylindrical load-bearing members,which are widely used in aerospace,transportation and other fields.At present,aluminum alloy is the main material of the cabin.The new generation of equipment has higher and higher requirements for lightweight.As the lightest metal material,magnesium alloy has become the preferred material for lightweight,but its easy corrosion greatly limits the application range.Aluminum/magnesium composites,which overlay an aluminum layer on the magnesium alloy surface,improve corrosion resistance while being lightweight.Aiming at the problems of low bonding strength of traditional aluminum/magnesium bimetallic laminated materials and difficulty in forming laminated compartments by traditional process,this paper proposes to use rare earth magnesium alloys Mg-9Gd-4Y-2Zn-0.5Zr and aluminum alloy 2A12 with high strength to form bimetallic laminated compartments by circular channel Angle extrusion technology.Firstly,the microstructure mode of the rare earth magnesium alloy was regulated,and its constitutive equation and thermal working diagram were established through the hot compression test to explore its softening mechanism.Secondly,Deform-2D v11 simulation software was used to simulate and analyze the circular channel Angle extrusion forming laminates,to explore the influence of different billet thickness ratio and different extrusion process parameters on the travel load and the difference of the flow rate of two metals,and to obtain the best process parameters to guide the forming test.Finally,physical tests were carried out to verify the successful preparation of Al/Mg bimetallic laminated compartments,which provided a new direction for the lightweight of cabin members.The main conclusions of this paper are as follows:1.The Mg-9Gd-4Y-2Zn-0.5Zr alloy with lamellar LPSO phase has better thermoplasticity.The softening mechanism of the alloy under low strain rate is mainly DDRX,the softening mechanism under low temperature and high strain rate is mainly dynamic recovery,and the softening mechanism under high temperature and high strain rate is mainly dynamic recovery and DDRX.In addition to a small amount of DDRX at the grain boundary during deformation at low temperature,the intrachrystalline lamellar LPSO phase distortion induces CDRX and significantly improves the thermoplasticity of the alloy.Based on the dynamic material model,the hot working diagram was established.Combined with the microstructure analysis,the optimum forming temperature was 440℃and the strain rate was0.001～0.01 s^-1.2.The characteristics of stress,strain,temperature and metal flow in the deformation process were mastered through Deform-2D simulation of the Angle extrusion forming process of the annular passage in the aluminum/magnesium laminated cabin.Aiming at the small difference between the load and the flow velocity of the two metals,the billet thickness ratio and extrusion process parameters were optimized.The optimal parameters were obtained as extrusion speed of 0.1mm/s and friction coefficient of 0.1.Billet layer thickness ratio is 30/15.3.According to the optimum forming temperature obtained from the hot compression test and the optimum parameters obtained from the simulation,the forming test and annealing treatment of aluminum/magnesium bimetallic laminated chamber were carried out.The prepared laminated cabin has good surface quality and weight reduction≥18%compared with the aluminum alloy cabin.The extrusion chamber has a good bonding interface,and the width of the interface layer thickens obviously with the increase of annealing temperature and annealing time.At the interface,the extruded Al,Mg compound layer is transformed into Al,Mg,Gd compound layer and Al,Mg,Gd,Cu compound layer after annealing.4.The hardness of the interfacial layer of the bulkhead is greater than that of the matrix on both sides,and the difference between the hardness of the interfacial layer and the magnesium alloy matrix is small,while the difference between the hardness of the interfacial layer and the aluminum alloy matrix is large.After annealing at 200℃for 1h,the shear strength of the interface reaches the maximum value of 89MPa.With the extension of annealing time and the increase of temperature,the interface layer thickens and the shear strength decreases obviously.The interface cracking occurs on the aluminum side where the hardness gap between the matrix and the interface layer is large.