【作者】 吴彤；

【导师】 呼咏；

【作者基本信息】 吉林大学 ， 机械制造及其自动化， 2021， 博士

【摘要】 颗粒增强铝基复合材料是应时代发展和科学进步需求而出现的极具生命力的材料,能适用于航空航天、轨道交通、国防工业、光学领域、信息通讯等众多领域对材料的特殊要求。颗粒增强铝基复合材料目前在前沿领域和一些典型关键零部件中有所应用,但其普及化和规模化的应用程度无法满足各领域的迫切需求,原因在于颗粒增强铝基复合材料的性能评价方法不够全面和系统,而且缺少对其微观组织和力学性能的全面掌控。自汽车等典型产品轻量化概念提出以后,颗粒增强铝基复合材料因为集高比强度、高比刚度、低热膨胀系数、经济可行等诸多优点,成为汽车等工业领域亟待推广的工程材料,在汽车制动盘、发动机活塞和连杆、发动机缸体和缸套、驱动杆等诸多关键零部件生产中有着巨大的发展潜力。针对部分汽车零部件材料的特殊性能需求,例如制动盘表面材料要求高强度、高耐磨性而里层材料要求高塑性、高韧性,汽车发动机活塞顶部材料要求耐高温、耐冲击、高强度而其余材料要求高塑性、高导热性,SiC颗粒增强的铝基均匀复合材料难以同时满足上述性能需求,而SiC颗粒增强的铝基梯度功能材料因为组成和性能的梯度变化对上述性能需求有更好的适用性。因此SiC颗粒增强的铝基均匀复合材料和铝基梯度功能材料有望在汽车等工业领域大规模推广和使用。针对建立颗粒增强铝基复合材料全面和系统性能评价方法的迫切需求,本文立足于推进颗粒增强铝基复合材料在汽车等工业领域的大规模普及应用,对SiC颗粒增强的6061Al基均匀复合材料和SiC颗粒增强的6061Al基梯度功能材料开展了组织与力学性能的深入研究,以期掌握其性能的变化规律和各种影响因素的作用机理,为其在汽车等工业领域及其他领域的推广应用奠定一定的基础。本文主要开展了以下研究工作:(1)设计并制备了SiC_p/6061Al均匀复合材料和梯度功能材料,并进行了物相组成分析和微观组织观察。选择真空热压烧结法制备了不同规格的SiC_p/6061Al复合材料,物相组成分析表明,在制备工艺和基体合金相的作用下,复合材料的不利界面反应得到了有效抑制。微观组织观察表明,SiC_p/6061Al均匀复合材料的SiC颗粒分布均匀;SiC_p/6061Al梯度功能材料的组成在宏观上呈梯度分布,在组成梯度功能材料的各层复合材料内部,SiC颗粒分布均匀,梯度功能材料的层间界面笔直、平行且完整。(2)深入研究了SiC_p/6061Al均匀复合材料和梯度功能材料的各项基本性能。相对密度分析表明,SiC_p/6061Al复合材料整体具有较高的相对密度,随SiC含量的增加相对密度减小;针对梯度功能材料,定义并考虑了层间差,即梯度功能材料相邻两层间的颗粒含量差异,较小的层间差有利于梯度功能材料获得更加致密的组织。硬度测试结果表明,SiC_p/6061Al均匀复合材料的硬度随SiC含量的增加而增大,SiC_p/6061Al梯度功能材料的硬度呈梯度变化,热处理显著提高了SiC_p/6061Al复合材料的硬度。文中验证了均匀复合材料等效弹性模量的计算模型,并构建了梯度功能材料等效弹性模量的计算模型,模型预测效果良好。(3)揭示了SiC_p/6061Al均匀复合材料和梯度功能材料的拉伸变形机理以及拉伸性能在各种影响因素下的变化规律。研究表明,SiC颗粒的直接强化和间接强化机制影响SiC_p/6061Al均匀复合材料的拉伸变形;除了受SiC颗粒的直接强化和间接强化机制影响,SiC_p/6061Al梯度功能材料的拉伸变形还受强度塑性协同强化机制和层间位错密度强化机制影响。SiC_p/6061Al复合材料的抗拉强度与SiC含量呈正相关,伸长率与SiC含量呈负相关,30 wt.%为SiC颗粒对复合材料性能提升作用的临界质量分数;热处理显著地提高了复合材料的抗拉强度,同时降低了其伸长率;复合材料的抗拉强度随温度的升高而减小,伸长率随温度的升高先增大后减小;使用均匀复合材料并承载拉应力的机械构件需选择适宜的材料参数以平衡其对强度和塑性的要求。SiC_p/6061Al双层复合材料的剪切试验表明,SiC含量的少量增加、较小的层间差和热处理对提高层间界面的强度有促进作用。层间差较小时SiC_p/6061Al梯度功能材料界面的结合强度高、强度塑性协同作用强,抗拉强度和伸长率比相应的SiC_p/6061Al均匀复合材料均有提高,适用于对强度和塑性均有较高要求的机械构件。(4)探究了各因素对SiC_p/6061Al均匀复合材料和梯度功能材料的弯曲强度、断裂韧性、裂纹扩展行为的影响以及SiC_p/6061Al复合材料的断裂失效机理。研究结果表明,SiC含量增加、热处理、层间差增大、FGM-A即载荷施加在高SiC层,都是提高SiC_p/6061Al复合材料弯曲强度的有利因素。SiC_p/6061Al复合材料的裂纹扩展形式主要有SiC颗粒断裂、SiC颗粒脱粘和基体断裂,主裂纹的扩展形式为微裂纹连接。SiC_p/6061Al均匀复合材料的断裂韧性与强度和塑性相关,SiC_p/6061Al梯度功能材料的断裂韧性受强度、塑性和层间协同作用的影响。梯度功能材料层间协同在提高位错密度、钝化裂纹、降低裂纹驱动力、吸收裂纹扩展能量等方面的促进作用,使FGM-A和层间差较大的SiC_p/6061Al梯度功能材料具有更加优异的断裂韧性,从而适用于承载弯曲应力和对材料韧性、安全性能有较高要求的机械构件。综上,本文主要从SiC含量、热处理、温度、层间差和加载方向等影响因素出发,经过多项试验测试,获得了SiC_p/6061Al均匀复合材料和梯度功能材料的微观组织结构和各项力学性能的变化规律,揭示了SiC_p/6061Al复合材料的拉伸变形机理和断裂失效机理。本文建立了SiC_p/6061Al均匀复合材料和梯度功能材料较为系统的性能评价方法,能够为颗粒增强铝基复合材料在工程实际中的应用和推广提供一定的技术支持和有力保障。更多还原

【Abstract】 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.更多还原