B₄C_p/A356 Composites Preparedby Semi Solid Stir Casting And Simulationofitsmixingand Dispersing Process

In this study,B₄C_P/A356 composites were prepared by semi-solid stirring and rolled into composite plates.This process has the advantages of low cost,good mechanical properties,simple preparation process and wide application prospect.The mechanical properties of the composite plate and ingot depend on the size and dispersion of B₄C reinforced particles.In this study,two kinds of semi-solid stirring composite process parameters were selected.B₄C particles with a size of 20?m were mixed with A356 alloy to prepare B₄Cp/A356 composites and rolled into plates.Firstly,a three-dimensional stirred tank was designed by UG NX7.0,and the effect of the stirring rod on the semi-solid stirred flow field was simulated by the fluid software of Fluent.The preparation process of semi-solid mixing flow field of B₄C_p/A356 composite was studied.B₄C_P/A356 composites were prepared by semi-solid mixing of B4C particles and A356 alloy particles after pickling and oxidation.The effect of semi-solid stirring parameters on Microstructure and properties of B₄C_P/A356 plates was studied.The mechanical properties and wear properties of rolled B₄C_P/A356 composite plates were tested.The influence of processing parameters on the B₄C particle size and the properties of B₄C_P/A356 composite plate was found.The main research results are as follows:The two-layer counter rotating impeller designed by ourselves and optimized by geometric parameters is used,it can produce three non-uniform converging vortices in semi-solid aluminum melt.Thus the melt in the crucible is all in irregular motion.The three layer non steady intersection vortex is suitable for semi solid stirred flow field.The irregular motion of the whole melt is beneficial to enhance the uniform dispersion of particles in the melt.The process of improving the semi-solid stirring flow field of B₄C_p/A356 composite was obtained.The inclination angle of the straight impeller is designed to be 60 degrees,which is beneficial to the complete contact between the blade and semi-solid aluminum melt.It also can increase the area of the aluminum melt wrapped on the blade,and the volume of the aluminum melt adhered to the blade is larger.The orthogonal blade arrangement is more suitable for the mixing of Semi-solid Aluminum Melt.The overall eddy current field force and sweep shear force are larger.The lower vortex basin has a wider range and faster flow.It greatly reduces the probability of forming"dead zone"in the lower flow zone when the semi-solid aluminum melt is combined.The influence of semi-solid stirring parameters on Microstructure of B₄C_p/A356composite and its sheet was obtained.It is found that with the decrease of semi-solid stirring temperature,the average grain size of the?-Al grains decrease gradually,and the distribution of B₄C particles is even more uniform.When the stirring temperature is 580?and the stirring time is 15min,the stirring speed is within 800r/min,the average grain size and roundness of the?-Al grains decrease with the increase of stirring speed.The distribution of B₄C particles is even more uniform.When the stirring temperature is 580?and the stirring speed is 800r/min,The average grain size and roundness of the alpha?-Al grains decrease with the increase of stirring times,the distribution of B₄C particles became uniform.The optimum technological parameters are as follows:The stirring temperature was 580?,stirring speed was 800r/min,stirring time was 35min.The influence of semi-solid stirring parameters on the microstructure and properties of B₄Cp/A356 composite and the plate was analyzed.The tensile strength and elongation of B₄C_P/A356 composite plate prepared by process parameter B?optimum process parameters?are higher.Because the process can make the B₄C particles more evenly dispersed,and in the process of rolling due to extrusion and friction between particles broken,thereby reducing the size of the enhanced particle B₄C,and the fracture probability of B₄C particles internal stress is reduced.The influence of semi-solid stirring parameters on the friction and wear properties of B₄Cp/A356 composite plate was found.The size of reinforced particle B₄C in B₄C_P/A356composite plate prepared by process parameter B becomes smaller after rolling and crushing,and the main form of wear failure is interface debonding.The dispersion of B₄C particles in the B₄C_P/A356 composite plate prepared by the process A is not uniform,it cannot be broken in the rolling process,When the distance between particles is large,resulting in the larger particle size.At this time,the main failure mode of B₄C_P/A356composite plate is the fracture of reinforced particle B₄C.