| Particle reinforced aluminum matrix composite is a kind of extremely vital composite that emerges with the need of modern development and scientific progress.It can meet the special requirements of composites in many fields such as aerospace,rail transit,national defense,optics,and information communications.Particle reinforced aluminum matrix composite has been applied in cutting-edge fields and some typical key parts.However,its degree of popularization and large-scale cannot meet the urgent needs of various fields.The reason is that the performance evaluation system of particle reinforced aluminum matrix composites is not comprehensive and systematic,and there is a lack of comprehensive control over its microstructure and mechanical properties.Particle reinforced aluminum matrix composite has many advantages,such as high specific strength,high specific stiffness,low coefficient of thermal expansion,and economic feasibility.Since the concept of lightweight of typical products such as automobiles was proposed,it has become an engineering material that urgently needs to be promoted in the automotive and other industrial fields.It has great development potential in the production of many key parts such as automobile brake discs,engine pistons,connecting rods,engine blocks,cylinder liners,and drive rods.Some automotive parts have special property requirements.The surface material of the brake disc requires high strength and high wear resistance,while the inner material requires high plasticity and high toughness.The piston top material of the automobile engine requires high-temperature resistance,impact resistance,and high strength,while other materials require high plasticity and high thermal conductivity.SiC particles reinforced aluminum matrix uniform composites are difficult to satisfy the above property requirements at the same time,and SiC particles reinforced aluminum matrix functionally gradient materials have better applicability to the above property requirements due to the gradient changes in composition and properties.Therefore,SiC particles reinforced aluminum matrix uniform composites and functionally gradient materials are expected to be widely promoted and used in the automotive and other industrial fields.To urgently establish a systematic and comprehensive performance evaluation system for particle reinforced aluminum matrix composites and promote its large-scale popularization and application in the automotive and other industrial fields,the microstructure and mechanical properties of SiC particles reinforced 6061 Al matrix uniform composites and SiC particles reinforced 6061 Al matrix functionally gradient materials need to be studied.Studying the changing laws of composite properties and the effect mechanism of various influencing factors can lay the foundation for the popularization and application of composites in the automotive and other industrial fields.Therefore,the following research work has been carried out:(1)SiCp/6061 Al uniform composites and functionally gradient materials have been designed and prepared,and phase analysis and microstructure observation have been carried out.SiCp/6061 Al composites with different specifications were prepared by vacuum hot-pressing sintering.The phase analysis shows that the adverse interfacial reaction of composites has been effectively restrained by the preparation process and matrix alloy phases.Microstructure observation shows that SiC particles of the SiCp/6061 Al uniform composite are uniformly distributed.The composition of the SiCp/6061 Al functionally gradient material shows a gradient distribution in the macro,and SiC particles are uniformly distributed in each layer.The interlayer interface is straight,parallel,and complete.(2)The basic properties of SiCp/6061 Al uniform composites and functionally gradient materials were deeply studied.The relative density analysis shows that SiCp/6061 Al composites have a high relative density which decreases with the increase of SiC content.The interlayer difference is defined and considered for functionally gradient material,that is,the difference in the particle content between two adjacent layers.The smaller interlayer difference is conducive to the denser organization of functionally gradient materials.The hardness test results show that the hardness of SiCp/6061 Al uniform composites increases with the increase of the SiC content,and the hardness of SiCp/6061 Al functionally gradient materials changes gradually.The hardness of SiCp/6061 Al composites is significantly improved by heat treatment.The calculation model of equivalent elastic modulus of uniform composites has been verified,and the calculation model of functionally gradient materials has been constructed.(3)The tensile deformation mechanism of SiCp/6061 Al uniform composites and functionally gradient materials and the change law of tensile properties under various influencing factors were revealed.Results show that the direct and indirect strengthening mechanisms of SiC particles affect the tensile deformation of uniform composites.In addition to the direct and indirect strengthening mechanisms of SiC particles,the tensile deformation of functionally gradient materials is also affected by the strength-plastic synergistic strengthening mechanism and the interlayer dislocation density strengthening mechanism.The tensile strength of SiCp/6061 Al composites is positively correlated with SiC content,and the elongation is negatively correlated with SiC content.30 wt.% is the critical mass fraction of SiC particles to improve the properties of composites.Heat treatment significantly improves the tensile strength while reducing elongation.The tensile strength of the composites decreases with the increase of temperature,and the elongation first increases and then decreases with the increase of temperature.For mechanical parts using uniform composites and bearing tensile stress,appropriate material parameters should be selected to balance the requirements for strength and plasticity.The shear test of SiCp/6061 Al double-layer composites shows that a small increase in SiC content,a smaller interlayer difference,and heat treatment can promote the strength of the interlayer interface.When the interlayer difference is small,the bonding strength of the interface and the strengthplastic synergistic strengthening mechanism of functionally gradient materials have a good performance.At this time,functionally gradient materials have better tensile strength and elongation than corresponding uniform composites,and it is suitable for mechanical parts with high requirements for strength and plasticity.(4)The effects of various factors on the bending strength,fracture toughness,and crack propagation behavior of SiCp/6061 Al uniform composites and functionally gradient materials were explored,and the fracture failure mechanism of SiCp/6061 Al composites were revealed.The results show that the increase of SiC content,heat treatment,the increase of the interlayer difference,and FGM-A are all favorable factors for improving the bending strength of composites,wherein FGM-A means that the load is applied to the high SiC content layer.The crack propagation forms of composites mainly include SiC particle fracture,SiC particle debonding,and matrix fracture.The expanded form of the main crack is the microcrack connection.The fracture toughness of uniform composites is related to strength and plasticity.The fracture toughness of functionally gradient materials is affected by strength,plasticity,and interlayer synergy.The interlayer synergy of functionally gradient materials can promote the increase of dislocation density,blunt cracks,reduce crack driving force,and absorb crack growth energy.Functionally gradient materials with FGM-A and a large interlayer difference have better fracture toughness,so it is suitable for mechanical parts that bear bending stress and have higher requirements for material toughness and safety performance.In summary,a number of mechanical performance tests have been carried out in this paper based on the influencing factors such as SiC content,heat treatment,temperature,interlayer difference,and loading direction.The research obtains the variation law of microstructure and mechanical properties of SiCp/6061 Al uniform composites and functionally gradient materials and reveals the tensile deformation mechanism and fracture failure mechanism of SiCp/6061 Al composites.The systematic performance evaluation system of SiCp/6061 Al composites established in this research can provide certain technical support and a strong guarantee for the application and promotion of particle reinforced aluminum matrix composites in engineering practice. |
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