Aging Precipitation Behavior And Mechanical Properties Of B₄C/2024Al Composites Prepared By SPS

In this paper,B₄C/2024 Al composites with 15%,20% and 25% volume fraction and B₄ C of 4.5?m were prepared by spark plasma sintering?SPS?method.The microstructures of the composites were observed by metallographic microscope and scanning electron microscopy?SEM?.The distribution of the B₄ C was characterized by the synchrotron radiation CT imaging technique.The hardness of the composites was measured by Brinell hardness tester,and the optimum aging temperature and aging curves were determined.The thermal diffusion activation energy of the material was calculated by DSC experiment.The microstructures of the materials and the microstructures at different aging stages were analyzed by TEM electron microscopy.Three-point bending test and tensile test were performed on a universal electronic testing machine.The bending and tensile fracture of the material were analyzed and compared.The factors influencing the material performance were analyzed,and the strengthening mechanism of the material was discussed.?DIC?technique is used to study the distribution of strain and displacement field in the process of stretching.B₄C in the matrix distribution is uniform.During the preparation process,Al2 Cu phase was produced at the Al-B₄ C interface.In addition,there are a large number of B₄C/2024 Al composites prepared in the fine Al11Cu5Mn3 phase dispersed in the matrix.The composite material has been subjected to maximum aging hardness after solid solution at 495 °C then aging at 190 °C,and increased by more than 16% compared with no aging.In addition,the addition of B₄ C can reduce the thermal diffusion activation energy of the precipitated phase of the matrix,and the precipitation of the becomes easier.The aging mechanism of the composite material is the GPB region,and the matrix is coherent.The peak aging structure is S 'phase,semi-lattice with the matrix,the over-aged structure is S?Al2CuMg?phase,non-coherent with the matrix.The Al2 Cu phase disappears at the interface of the Al-B₄ C interface,and the S' phase appears in the crystal,and the S phase and the ? phase appear at the grain boundary.The maximum hardness of the original B₄C/2024 Al composite material reaches 149 HB.The maximum elastic modulus reaches 122 GPa and the elastic modulus is in accordance with the Halpin-Tsai formula.The bending properties of B₄C/2024 Al composites subjected to hot extrusion have been greatly improved.The bending strength of composites with the maximum increase of more than 20%,and the bending strength of 25 vol.% B₄C/2024 Al composite is more than 1100 MPa.B₄C/2024 Al composites with a volume fraction of 15% had a tensile strength of more than 500 MPa and an elongation of 6.6%.The specific modulus and specific strength of the materials were 44 GPa/?g/cm3?and 191 MPa/?g/cm3?,respectively.With the increase of the volume fraction of B₄ C,the hardness,elastic modulus,bending strength and tensile strength of B₄C/2024 Al composites increase.However,due to the uneven distribution of B₄ C in the material,not strictly follow this law.The uneven distribution of B₄ C in the matrix results in a strain concentration in the material stretching process.B₄ C can prevent the crack propagation during the crack propagation process and improve the tensile strength of the material.