Study On The Microstructure And Properties Of SiC_p/Al-12Si Composites With Rare Earth Added

Owing to the excellent properties of light weight,low expansion,high strenth and good wear resistance for the SiC_p/Al-12 Si composites,they can be used in many fields such as aerospace,automobile industry and electronics.In this thesis,the SiC_p/Al-12 Si composites with added rare earth?CeO₂?were fabracated by powder metallurgy method and hot extrusion.Using the measures and mthods such as XRD,SEM,EDAX,TEM,density,Vickers hardness,coefficient of thermal expansion,tensile properties and wear tests,the effect of content of CeO₂ on the microstructure,physical and mechanical properties,the effect of content and applied loads on the wear resistance of the composites were investagated and technology of the heat treatment was optimized.The results show that:1.Appropriate amount of CeO₂ can make the Si particles smaller,the distribution of Si particles more uniform in the matrix of composites,while it can also improve the density,the hardness,the tensile strength and elongation,and reduce the coefficient of thermal expansion of the composites.when the volume fraction of CeO₂ is 0.2%,the properties of composites are the best,and the corresponding properties are 2.7477 g/mm3,176.6 HV0.3,376.9 MPa,4.09%,13.94×10-6/K.2.The precipitated phases of SiC_p/Al-12 Si composites with added CeO₂ are mainly CeCu₂Si₂,Al₄Cu₉,Al2 Cu,Al₁₉Mn₄,Al₅Cu₆Mg₂ and Mg₃₂Al₄₇Cu₇;The are CeO₂ particles in the grain bondary of the Al grains.3.There are three kinds of mechnism of action of rare earth in the SiC_p/Al-12 Si composites: firstly,CeO₂ can minish the size of Si particles as the nucleation basement of the Si particles;secondly,CeO₂ can react with elements of aluminum alloy in the matrix to generate new phase and CeCu₂Si₂,which have a function of dispersion strengthing,and CeCu₂Si₂ can also improve the bonding strength between Al and Si particles;thirdly,the grain can be refined by the CeO₂ and CeCu₂Si₂ particles' pinning effect of aluminum grain or phase boundaries.4.The fracture mechanism of the SiC_p/Al-12 Si composites is a mixed mode including the brittle cleavage fracture of the Si and SiC particles,the tearing of matrix near the interface bewteen the aluminum matrix and Si or SiC particles,and the dimple fracture far from the Si or SiC particles in alluminum matrix.5.Though the optimization of heat treatment,the optimun solution treatment process is 510?×2h,and the optimun aging treatment process is 170?×5h;using the process indicate the best mechnical properties,whose tensile strength and elongaton are 376.9MPa and 4.09%.6.Appropriate amount of CeO₂ can significantly improve the wear resitance of the composites.When the volume fraction of CeO₂ is 0.2%,the composites have the best wearability.The bigger the applied load is,the more seriously the composites wear.The main wear mechanism of composites is abrasive wear,adhesive wear,delamination wear and oxidation wear.The wear mechanism of composites has different effects under different rare earth content or applied load.The results of the thesis may be helpful to the research and application of highperformance SiC_p/Al-12 Si composites...