Effect Of Hot Deformation On Microstructure And Mechanical Properties Of B₄C/2024Al Composites

In this paper,B₄C/2024 Al composites with a volume fraction of 15%were prepared by pressure sintering method.The Gleeble-3500 thermal simulation tester was used to perform high temperature compression experiments.The hot deformation behavior of the material during the high temperature compression process was studied and the composite was determined.The best hot deforming temperature and strain rate of the material were determined.The XRD method was used to analyze the orientation of the matrix.The distribution of particles in the composite,tensile fracture,the interface between the particles and the matrix,and the precipitated phase in the matrix were observed by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The tensile test of the material was completed using a tensile tester,and the influencing factors of the material properties and the corresponding strengthening mechanisms were discussed.The results of high temperature compression test of B₄C/2024 Al composites prepared by pressure sintering show that the flow stress increases with the decrease of temperature and with the increase of strain rate.The hyperbolic sine model can be used to describe the deformation behavior during hot deformation.According to the thermal processing map of the composite,it can be determined that the best hot deformation temperature ranges from 425°C to 500°C,and the optimum strain rate ranges from 0.08s^-1to 0.19s^-1.Combined with the microstructure observation,it was found that there was a layer of amorphous B₂O₃ at the interface of the obtained composite material,which was favorable for the hot deformation.Therefore,the maximum deformation resistance of the composite material at the temperature of 500°C.and 1s^-1was only 14 MPa.After hot extrusion,the（200）,（220）,（311）crystal planes of the B₄C/2024 Al composite have a preferred orientation along the extrusion direction.The hot extrusion process disintegrates the B₄C particles.The size of the particles is finer,and the distribution is more dispersed,and the average particle size is at least about 11μm.Due to different extrusion ratios,the corresponding extrusion conditions are also different,and the interface structure of the composite material is different.For the material without extruding,the interface has only two forms:no interface reaction and presence of amorphous B₂O₃ oxide layer;when the extrusion ratio is 10:1,the interfacial reaction product still has MgO;the extrusion ratio continues to increase,and Al₄SiC₄ is produced at the interface.At the same time,the interface precipitates are Al₂Cu and Cu-Mg-rich phases.The types of precipitates in the matrix before and after extrusion includeθ（Al₂Cu）,S’（Al₂Cu Mg）,and Fe-Mn phases.With the increase of extrusion ratio,the size of S’phase first increases and then decreases.The elastic modulus,tensile strength and elongation of unextended composites were 98 GPa,450MPa and 0.5%,respectively,while the elastic modulus and strength of 10:1 extruded composites were the highest,reaching 112 GPa and 550 MPa.The extruded material with extrusion ratio of 81:1 has the best plasticity,and its elongation is about 4.5%,which is 9 times of the unextruded state.