Study On The Process Of Hot-pressing Preparation Of Mg-Al Composite Plate In Atmospheric Environment

As the lightest metal structural materials,magnesium alloy and aluminum alloy have been widely used in the field of automobile lightweight and aviation.Mg-Al composite material is a new type of metal matrix composite material with excellent properties such as light weight,high strength,high thermal conductivity and high corrosion resistance.It can be widely used in aerospace,automobile,construction and furniture.In this paper,Mg-Al composite plates were successfully prepared by hot pressing in atmospheric environment,and the effects of hot pressing and annealing on the bonding interface structure and bonding strength were studied.The results show that the Mg-Al composite sheet with good bonding interface can be prepared at 350°C,40%deformation,hot pressing 1min,5min and 10min.The bonding strength of Mg-Al composite plate with hot pressing for 10 min is the highest,reaching～4.39MPa.The shear fracture of Mg-Al composite plates occurs at the Mg₂Al₃ interface.By annealing the Mg-Al composite sheet prepared by 1min rapid hot pressing at 350°C,the bonding strength can be greatly improved.The optimal annealing time is 60 min,and the shear strength can reach～5.58 MPa,which is 56.7%higher than that of unannealed Mg-Al composite sheet.The microstructure of the diffusion layer of Mg-Al composite plate from Mg side to Al side isα-Mg-Mg₁₇Al₁₂-Mg₂Al₃-α-Al.In addition,the effect of Zn interlayer on the bonding interface structure and bonding strength was also studied by hot pressing process.In this paper,Mg-Zn-Al composite sheets were prepared by adding pure Zn layer as the intermediate layer in Mg-Al composite sheets under hot pressing process.The effects of hot-pressing time on the bonding interface structure and bonding strength of Mg-Zn₃₀-Al composite plate with 30μm pure zinc layer were studied.The effect of different thickness of pure zinc layer on the bonding interface structure and bonding strength of Mg-Zn-Al composite plate.The effect of heat treatment process on the bonding interface structure and bonding strength of Mg-Zn₁₀₀-Al composite plate with 100μm pure zinc layer.The results show that the bonding strength of Mg-Zn₃₀-Al composite plates with hot pressing time of 1min,5min and 10min can be improved by bonding with Mg and Al respectively due to the diffusion barrier effect of Zn layer.However,Mg-Zn₃₀-Al after hot pressing for 30 min will form ternary intermetallic compound Mg₃₂Al₄₉Zn₄₉ due to the disappearance of diffusion barrier,which cannot improve the bonding strength.The increase of Zn layer thickness will not cause the change of Mg-Zn and Al-Zn diffusion layers,and the increase of pure Zn layer in the middle layer will reduce the bonding strength of Mg-Zn-Al composite sheet.Through heat treatment at 350°C for different time,the thickness of pure Zn layer is reduced by diffusion,which can effectively enhance the bonding strength of Mg-Zn₁₀₀-Al composite sheet.When the annealing time reaches 30min,the Mg and Al matrix will be bonded through the Mg Zn₂ layer.At this time,the shear strength of the Mg-Zn₁₀₀-Al composite sheet reaches the strongest～6.26MPa,which is 71%higher than that of the unannealed Mg-Zn₁₀₀-Al composite sheet.The diffusion barrier effect of the Zn layer disappears after annealing,and the Mg-Zn-Al ternary phase（φ,τ,γ）is formed.The Mg and Al matrix are bonded through these ternary phases.It shows that the structure of Mg-Zn-Al bonding interface can be enhanced by annealing.However,due to the different diffusion coefficients of Mg,Zn and Al and the appearance of Mg-Zn eutectic liquid phase,a large number of holes will appear at the Mg-Zn-Al interface.