Numerical Simulation Of Macro-Segregation In Cu-Cr Alloy

Cu-Cr system is a kind of Cu matrix with good comprehensive properties.When the second phase is dispersed in the matrix,the copper alloy can keep high strength while maintaining good conductivity.Due to the existence of liquid-solid phase transition,the liquid phase of Cu is easy to accumulate in the bottom of the matrix and the liquid phase of Cr is easy to float up,so that the distribution of Cr in the matrix is very easy to produce segregation.This paper is based on the Eulerian numerical simulation and fluid technology,simulating the segregation phenomenon in the solidification process of Cu-Cr alloy,and the influence of the temperature field and the third elements on the segregation pattern is obtained.(1)According to the changing rules and the diffusion of Cu-Cr6.5% alloy during solidification process of Cr in the matrix distribution area with the changing of time and location,in the initial stage of solidification,Cr is uniformly dispersed in the alloy matrix.Due to the high melting point of Cr phase,Cr phase firstly is lateral solidification leading to the formation of mushy zone;in the later stage of solidification,Cr phase at the top of the matrix will gather in large numbers,forming the top segregation.The formation of the wall segregation of the Cr phase is affected by the lateral solidification.(2)The change of the solute concentration in the surface of the alloy and the morphology of columnar crystal growth were analyzed.The flow direction of the liquid alloy was basically the same as that of the crystal.With columnar crystal growing,solute gradually enriches into the interior,when the solute concentration of mushy zonereaches a certain level,owing to the turbulent flow and gravity,the fracture of columnar crystal becomes the center of nucleation of equiaxed grains.(3)The formation of channel segregation was studied.The results show that the particle size range from 5 to 25?m can lead to the formation of particle aggregation,and ultimately the formation of channel segregation;When the particle size is less than5?m or greater than 25?m,the interaction between the particles in the mushy zone does not last long and therefore does not cause channel segregation.(4)The mechanism of phase segregation of Mo particles on Cr was studied.The results show: The influence of the flotation of particles on the formation of channel segregation is divided into two stages,segregation initiation and segregation growth.The increase of the local velocity near the mushy zone will change the solute movement and subsequent solidification,which results in the separation of the local solute and the suppression of local solidification.The formation of channel segregation depends not only on the particle size of the Mo phase,but also on the number of them.For the influence of the number of Mo phase particles,when the particle diameter becomes larger,the segregation band decreases gradually.The increase in the number of initial particles also increases the instability of the mushy zone.At the same time,the instability of the mushy zone also leads to more segregation bands.