Simulation Of Interface Structure In Cu/Al Laminated Composite Plate By Molecular Dynamics

Copper aluminum layered composite is a kind of material which combines the advantages of copper such as "low resistance,high thermal conductivity" and aluminum such as "light weight,low price" to realize the double optimization of performance and cost.It has broad application prospects in the fields of transportation,communication and power,aerospace and national defense science and technology.Based on the supply and demand situation of "lack of copper and rich in aluminum"in China,the idea of "replacing copper with aluminum" is adopted to carry out the basic research on the preparation process and composite mechanism theory of copper aluminum layered composites,which is not only of positive significance for optimizing the distribution of copper and aluminum resources in China,promoting the industrial structure adjustment and transformation of non-ferrous metal industry,but also of great significance for the development of global non-ferrous metal industry" Energy conservation and environmental protection "and" sustainable development ".The casting rolling method combines the high temperature of casting and the pressure of rolling.The process is efficient and energy-saving.It is suitable for large-scale continuous production of large-scale copper aluminum laminated composite plate.The type and thickness of metal compounds at the interface of copper aluminum laminated composite plate directly affect the interface bonding strength and the application performance of the composite plate,which is the key problem in the production and processing process.Therefore,it has become a research hotspot to find out the diffusion law of interface atoms and the relationship between diffusion layer growth and process conditions.In this dissertation,molecular dynamics method was carried out to simulate the process of copper aluminum laminated composite plate produced with horizontal twin roll casting by designing Cu/Al solid-liquid interface model.The relationship between the diffusion depth of Cu and Al atoms and the surface structure characteristics of Cu was described.The mathematical expressions between the diffusion layer thickness and diffusion temperature,external pressure and diffusion time were fitted.The crystallization mode of liquid region and the composition of diffusion layer during solidification were analyzed.The interface normal tensile process of Cu/Al laminated composite plate model was simulated,and were compared with the tensile properties of single crystal model of Cu,Al and θ-Al2Cu.The crack location and propagation direction were analyzed,and the relationship between the interface normal tensile properties and the tensile properties of Cu,Al and θ-Al2Cu were summarized.The main conclusions and contents of the study are as follows:Firstly,by designing three low index ideal crystal planes of Cu(001),(111)and(110)as the surface of copper matrix,the Cu/Al solid-liquid interface models are composed of these copper matrices and liquid aluminum.The model of Cu/Al layered composite plate was obtained by simulating the atomic diffusion at the interface.The results show that the diffusion depth of Cu atom is obviously greater than that of Al atom,and the diffusion layer is mainly formed by the diffusion of Cu atom on the Al side.The reason is that the atoms in Al liquid are disorderly arranged,the metal bond energy is small,and the potential barrier of Cu atom diffusion is low.On the contrary,the diffusion of Al atom with relatively large radius on the Cu side of solid state,no matter vacancy diffusion or displacement diffusion,is in a inferior competitive position.The order of diffusion layer thickness in Cu/Al model is Cu(110)/Al,Cu(001)/Al and Cu(111)/Al,which is opposite to the order of binding energy of three crystal planes.The larger the binding energy of crystal surface,the more difficult it is for atoms to break away from surface binding and participate in diffusion.Through the analysis of the crystallization mode in the solidification process,it is found that the BCC and FCC structures begin to crystallize from the liquid region close to the copper matrix and extend to the Al side.With the decrease of temperature,the fcc structure is finally transformed.Secondly,the diffusion of interface atoms was systematically simulated in the temperature,pressure and time ranges of 800～950 K,1～7 bar and 0～2 ns,respectively,by taking the Cu(110)/Al interface model with the fastest diffusion among the three ideal surface models as the research object.The results show that the diffusion depth and thickness of diffusion layer of Cu atoms increase linearly with the diffusion temperature,and its mathematical expression is d=kdT*T,the corresponding kdT values are 0.45 (?)/K and 0.51 A/K,respectively.The diffusion depth and temperature of Al atom conform to Arrhenius formula,The diffusion depth of Cu and Al atoms decreases linearly with pressure,and the relationship with time is parabolic.Through the analysis of solidification process under different pressure,it is found that the solidification point increases linearly with the pressure,the expression is:Tn=702+20p.At lower pressure(1-5 bar)and higher temperature(850～950 K),θ-Al2Cu is formed at the interface.The diffusion layer is mainly composed of three substances from the bottom to the top,they are Al-Cu solid solution,θ-Al2Cu and Cu-Al solid solution,respectively.Then,the interface model of Cu/Al was formed by designing a symmetrical inclined grain boundary with different orientation difference on the surface of Cu matrix(001)crystal surface and contacting with liquid aluminum.The Cu/Al laminated composite plate model was obtained by simulating the diffusion of interface atoms.The observation of grain boundary migration shows that in GB1 model with the minimum in place deviation,the vacancy on the interface is filled with Cu and Al atoms quickly,which leads to the grain boundary disappearance.In the model with large differences in orientation,the interface of diffusion crystal gradually migrates and twists,and moves to the diffusion layer over the initial interface,and finally forms a boundary parallel to the interface in the diffusion layer.The orientation angle of newly formed grain boundary increases with the increase of orientation angle of grain boundary in Cu matrix,that is,the genetic effect of grain boundary is produced.The thickness of diffusion layer first increases and then decreases with the increase of grain boundary orientation angle,which is consistent with the law of surface energy caused by orientation angle.Finally,through the multi-directional tension of single crystal Cu,Al andθ-Al2Cu,the simulation results of the normal tension of Cu/Al laminated composite plate model along the interface show that the tensile modulus,elastic limit,tensile strength and elongation of single crystal Cu are greater than those of single crystal Al;the order of tensile modulus of Cu and Al is<111>,<110>,<100>,and the order of elastic limit,tensile strength and elongation is opposite;it is verified that the tensile properties of single crystal Cu and Al are anisotropic.The tensile modulus and tensile strength of single crystal θ-Al2Cu along[001]and[100]directions are between Cu and Al,the tensile modulus is close to Cu,the tensile strength is close to Al,and the elastic limit and elongation are less than Al.The fracture of each Cu/Al laminated composite plate model occurs in the pure Al region,which indicates that the bonding force of Al region is the weakest in the whole model.The results show that the tensile modulus of ideal surface Cu/Al laminate composite plate model is close to Cu,and the elastic limit is close to Al;the order of tensile strength is Cu(110)/Al,Cu(111)/Al and Cu(001)/Al,and the value is close to Al;the elongation is close to θ-Al2Cu.The results show that the tensile modulus of grain boundary surface Cu/Al laminate composite plate model increases with the increase of grain boundary misorientation;the elastic limit,tensile strength and elongation first decrease and then increase with the increase of grain boundary misorientation;the tensile strength and elongation are close to θ-Al2Cu.The tensile results of Cu(110)/Al laminated composite plate model by controlling the position of applied force end show that the fracture occurs at pure Al zone,at the junction of Cu-Al solid solution zone and θ-Al2Cu layer,and atθ-Al2Cu layer;the fracture at pure Al zone,the junction of Cu-Al solid solution zone and θ-Al2Cu layer belongs to brittle fracture,and the fracture at θ-Al2Cu layer shows certain toughness.This dissertation makes some attempts and provides some ideas for the simulation research of metal clad plate prepared by casting rolling method.Using molecular dynamics method,the interface diffusion,interface structure formation and interface mechanical properties are studied from the atomic scale,which provides a certain theoretical basis and technical support for the production and application of copper aluminum composite plate.