Study On Preparation,Microstructure And Mechanical Properties Of SiC_p Reinforced 2024 Aluminum Matrix Composite Sheet

SiC particle reinforced aluminum matrix composites have the advantages of high elastic modulus,good wear resistance,high dimensional stability,and high specific strength.They are widely used in aerospace,automotive,sports equipment and other fields.In order to analyze and solve the problems existing in the preparation of particle-reinforced aluminum matrix composites by the stirring casting method,including uneven distribution of SiC particles,high porosity,serious segregation of solute elements,coarse grains,poor wettability of particles and matrix,etc.,the preparation of particle-reinforced aluminum matrix composites provides effective theoretical guidance.In this paper,ultrasonic-assisted semi-solid stirring casting is used,2024Al is used as the matrix,and 10μm SiC particles are used as reinforcements to prepare SiC_p/2024Al composites with volume fractions of 0%,5%,10%,15%and 20%.The method of step deformation（extrusion+rolling）finally obtained a SiCp/2024Al thin plate with a thickness of about 1 mm.Through the pressure solidification experiment of SiC_p/2024Al composite material,the influence of different mold temperature and ultrasonic treatment temperature on the microstructure and mechanical properties of aluminum matrix composite material was studied,and the uniform particle distribution,low porosity and second phase were successfully prepared.Uniformly distributed SiC_p/2024Al composite material.The as-cast SiC_p/2024Al composite material was subjected to two-step thermal deformation to prepare SiC_p/2024Al composite thin plates with different volume fractions.The two-step thermal deformation（extrusion+rolling）process was studied on the microstructure and microstructure of the as-cast composite material.The influence law of mechanical properties.By preparing SiCp/2024Al composite sheets with different volume fractions,the effect of SiC_p volume fraction on the microstructure and mechanical properties of SiC_p/2024Al composite sheets was studied.The research results show that the 10vol.%SiC_p/2024Al composite produced by ultrasonic-assisted semi-solid stirring casting has good mechanical properties,with the best ultimate tensile strength of 297 MPa and elongation of 2.21%.At a mold temperature of 450℃,the SiC particles in the SiC_p/2024Al composite have an obvious uneven distribution,the second phase of the particle barren zone has a network distribution,and the porosity inside the material is high.As the mold temperature rises from 450℃to 550℃,the porosity inside the composite material shows a downward trend,and the uniformity of SiC particle distribution increases,but the segregation of the second phase first weakens and then increases.At a mold temperature of 500℃,the composite material exhibits the best mechanical properties.With the decrease of the ultrasonic treatment temperature,the uneven distribution of SiC particles in the SiC_p/2024Al composite material intensified in the ultrasonic temperature range from 700℃to 640℃.Under the ultrasonic treatment higher than the liquidus temperature of 2024Al,with the increase of the ultrasonic treatment temperature,the pore content of the casting increases,and the mechanical properties of the SiC_p/2024Al composite material decrease.Under the ultrasonic treatment lower than the 2024Al liquidus temperature,the ultrasonic treatment temperature is lowered,the pore content inside the composite material increases,the second phase segregation is serious,and the mechanical properties of the composite material decrease.Under the ultrasonic treatment temperature of 670℃,the SiC_p/2024Al composite exhibits the best mechanical properties.The best solidification process is a process where the mold temperature is close to the 2024Al solidus temperature（500℃）,and the ultrasonic treatment temperature is close to the 2024Al liquidus temperature（670℃）.Under this solidification process,the as-cast SiC_p/2024Al composite exhibits uniform SiC distribution,low porosity（0.2%）and low second phase content（0.49%）.After the as-cast composite material undergoes two-step thermal deformation（extrusion+rolling）,the defects in the as-cast structure and the defects of the extruded specimen disappear.Two-step thermal deformation can significantly refine the average grain size of the aluminum matrix in the composite material.The agglomerated SiC particles in the extruded composite material hinder the refinement of the Cu Al₂ phase.After two-step thermal deformation,the size of SiC particles and Cu Al₂ phase decreases,and the distribution becomes more uniform.The two-step thermal deformation improves the bonding strength of the interface between the SiC particles and the aluminum matrix.The ultimate tensile strength and elongation of the 10vol.%SiC_p/2024Al composite after two-step thermal deformation are 489 MPa and 10.42%,respectively.The microstructure and mechanical properties of SiC_p/2024Al composite plates with different particle contents were analyzed.The study found that the average grain size of 2024aluminum alloy was 23.7μm.With the increase of SiC_p content,the average grain size of the composite material showed a downward trend,and the size of the second phase showed a downward trend,but the content of the second phase did not change.The uniformity of SiC_pdistribution increases first and then decreases with the increase of particle content.The 10vol.%SiC_p/2024Al composite sheet shows the best particle distribution.Solution treatment and aging treatment can significantly improve the mechanical properties of the rolled SiC_p/2024Al composite.After aging treatment,a large number of nano-scale second phases precipitated in the 2024Al matrix.After aging treatment,the yield strength,ultimate tensile strength and elongation of 10vol.%SiC_p/2024Al were 391 MPa,514 MPa and 7.2%,respectively.