Molecular Dynamics Simulation Of Effect Of Melt Thermal History On The Solidification Behaviors Of Al Alloys

The melt thermal history of alloys has a direct and important influence on the structure and properties of materials.Currently,the study of solidification process has been extended to the liquid metal structure.It is great theoretical and practical significant to study the effect of melt thermal history on the solidification characteristics of Al alloys.In this thesis,the melting points of Al-Ni,Al-Cu and Al-Ti alloys were determined by molecular dynamics simulation,and the most suitable potential functions were obtained.The radial distribution functions(RDFs)at different cooling rates and the microstructures after solidification were compared and analyzed.The effect of thermal history on the diffusion coefficient of Al alloys was analyzed by changing the initial temperature and relaxation time.The main conclusions are as follows:The minimum error between simulated melting point and actual melting point of Al-Ni alloy is 39.12 K.The minimum error of Al-Ni alloy is 32.76K and the minimum error of Al-Ti alloy is 45.13K.The RDFs of Al-Ni alloys were obtained by molecular dynamic simulation calculation.Al0.25Ni0.75 melt obvious crystal characteristics after solidification at cooling rate of 1.0×1010K/s.and the fec after solidification accounts for 89%.Al0.8Ni0.2 melt obvious crystal characteristics after solidification at cooling rate of 1.0×1010K/s,and the fce and hcp after solidification accounts for 85.8%.In the RDFs of Al-Cu alloys,Al0.67Cu0.33 melt obvious crystal characteristics after solidification at cooling rate of 1.0×1010K/s,and the fcc and hcp after solidification accounts for 81.2%.Al0.96Cu0.04 melt obvious crystal characteristics after solidification at cooling rate of 1.0×1010K/s,and the fcc after solidification accounts for 90.9%.In the RDFs of Al-Ti alloys,Al0.5Ti0.5 melt obvious crystal characteristics after solidification at cooling rate of 1.0×1010K/s,and the fcc and hcp after solidification accounts for 95.1%.Al0.75Ti0.25 melt obvious crystal characteristics after solidification at cooling rate of 1.0×1011K/s,but the crystal structure analysis shows that the atomic structure arrangement is relatively scattered.And the hcp after solidification accounts for 54.5%.In the Al-Ni alloys,the diffusion coefficient of Al0.25N0.75 alloys is more affected with initial temperature change.The diffusion coefficient of Alo.67Cuo.33 alloys in Al-Cu alloys is more affected with initial temperature change.The diffusion coefficient of Al0.75Ti0.25 alloys in Al-Ti alloys is more affected with initial temperature change.The relaxation time and the alloy diffusion coefficient are not a simple linear relationship,but the diffusion coefficient tends to be stable when the relaxation time reaches the critical value,and does not continue to increase with the increase of relaxation time.Alo.67Cuo.33 alloys tends to be stable after relaxation for 10ps;Al0.96Cu0.04 alloys and Al0.75Ti0.25 alloys tend to be stable after relaxation for 15ps;Al0.5Ti0.5 alloys and Al0.25Ni0.75 alloys tends to be stable after relaxation for 20ps;Al0.8Ni0.2 alloys tends to be stable after relaxation for 25ps.