Effect Of Forming Process Of Mg-Al Laminate On Interfacial Diffusion

During the preparation and forming of Mg-Al laminates,the quality of MgAl laminates is directly determined by the strong bonding between Mg-Al atoms at the interface,so it is necessary to study the diffusion behavior between Mg-Al atoms in the forming process.The traditional experimental research method can only obtain the static diffusion results,and it is difficult to conduct a fine analysis of the dynamic diffusion process,because this paper studies the diffusion behavior at the interface of the rolling process at the micro scale with the help of advanced molecular dynamics method.The diffusion behavior at the interface of the intermediate laminates during annealing is studied in order to obtain magnesia Al laminates with better interface bonding quality.The research work is as follows.(1)The diffusion behavior at the interface of Mg-Al laminates at different temperatures was studied,and the diffusion coefficient,diffusion constant and diffusion activation energy were obtained.The diffusion coefficients obtained by molecular dynamics simulation are:D300=1.26E-15m2/s,D325=3.20E-15m2/s,D350=5.30E-15m2/s,D375=7.41E-15m2/s,D400=4.43E-14m2/s,The diffusion constant D0=1.91E-6m2/s and the diffusion activation energy E=101195.41 J/mol were obtained.The diffusion coefficients at different temperatures were obtained as follows:D300=4.18E-14m2/s,D350=2.93E-13m2/s,D400=8.32E-13m2/s,and the diffusion constant D0=2.88E-5m2/s and the diffusion activation energy E=964660.92 J/mol.There is little difference between the experimental and simulated diffusion parameters,which indicates that the established diffusion model of Mg-Al laminates at different temperatures is feasible.(2)The diffusion behavior at the interface of Mg-Al laminates under different reduction rates was studied,and the diffusion law of Mg-Al atoms under different reduction rates was obtained.In the simulation,the reduction rate is 20%,23.5%,26.5%and 30%,and the diffusion coefficient is:D400-20=1.14E-12m2/s,D40023.5=1.34E-12m2/s,D400-26.5=1.47E-12m2/s,D400-30=1.51E-12m2/s.It was found that the diffusion coefficient increased with the increase of the reduction rate.Compared with the uncompressed diffusion coefficient(D400=8.32E-13m2/s),the diffusion coefficient after compression is significantly increased.It is found that the thickness of the diffusion layer increases from 26.67μm to 53.67μm with the increase of the reduction rate.The relationship between the diffusion coefficient and the reduction rate obtained in the simulation is analyzed,and combined with the experimental results,the linear relationship between the diffusion layer thickness and the reduction rate is finally obtained.(3)The diffusion behavior at the interface of the lower laminates at different annealing and cooling rates was studied,and the diffusion law of Mg-Al atoms at different annealing and cooling rates was obtained.In the simulation,the cooling rates are 0.0275℃/fs,0.015℃/fs,0.0092℃/fs and 0.0069℃/fs respectively.It is found that during the cooling process,the mean azimuth shift will first increase and then stop when the temperature decreases to about 180℃,and the mean azimuth shift decreases with the increase of the cooling rate.In the experiment,the cooling rate is 73.64℃/min,8.21℃/min,2.82℃/min,1.31℃/min.The diffusion layer thickness decreases from 28.57μm to 6.77μm with the increase of cooling rate,which is basically consistent with the law presented in the simulation.(4)The properties of Mg-Al laminates under different annealing processes are studied.It is found that:1)No phase change annealing,the strength of the laminate is basically unchanged,and the plasticity of the magnesium layer is improved to a certain extent;Recrystallization annealing,the plasticity of the magnesium layer is improved;Phase change annealing,the strength of the boundary plate is weakened.2)Annealing can improve the surface residual stress of magnesium aluminum laminate,so that the residual stress showing anisotropic distribution is more evenly distributed after annealing,and the residual stress is 3.97MPa when the annealing process is 300℃+0.5h.3)The average grain diameter and area of magnesium layer increase from 20.03μm to 22.69μm and from 746.92μm2 to 939.10μm2 with decreasing annealing cooling rate.The hardness decreases from 132.57HV to 116.65HV in rolling direction and from 127.42HV to 105.53HV in width direction.The tensile strength decreases from 191.07MPa to 176.32MPa in the rolling direction and from 188.55MPa to 182.78MPa in the width direction,but the ductility of the laminates increases.The interfacial diffusion behavior of Mg-Al laminates is studied by combining advanced molecular dynamics method with experimental method.The results show that the molecular dynamics simulation of interfacial diffusion behavior is feasible and has certain guiding significance for determining the forming process of Mg-Al laminates.