Studies On Preparation, Microstructures And Properties Of The SiC_p/Al Composites

The SiC_p/6066Al composites have been fabricated by a powder metallurgy route with the SiC surface modification techniques,the optimized forming temperatures of hot compression and hot extrusion and the optimized parameters of heat treatment to control the microstructures and the interracial cohesion in the composites.The microstructures,mechanical properties,fracture modes,dynamical modulus and internal friction in the composites were studied by OM, XRD,SEM,TEM,HREM,SAED,EDS,tensile tests and DMA.The laws of heat-treatment,the deformation behaviour,the damping mechanism and the interfacial effects in the SiC_p/6066Al composites have been explored by experiments combined with mathematical model. Some major conclusions can be drawn from the experimental studies and the theoretical analysis as follows:(1)It's the first time to adapt the SiC particle surface treatment techniques of oxidation,acid dipping and alkali washing as well as the optimized forming temperatures to explore the techniques to improve the interracial cohesion in the SiC_p/Al composites.The law of forming temperatures influencing the mechanical properties of the composites has been obtained and the cohesive mechanism of SiC/Al interface was also investigated,which has established the techeniques of particle surface modification,forming temperature and interracial control.The SiC_p/6066Al composites with good comprehensive properties have been fabricated through the optimized techeniques(â‘ 10%SiCp/6066Al:σ_0.2～387MPa,σ_b～484MPa,δ₅～7.2%,E～88.6 GPa;â‘¡12%SiCp/6066Al:σ_0.2～425MPa,σ_b～524MPa,δ₅～6.5%,E～92.7GPa;â‘¢15%SiCp/6066Al:σ_0.2～461MPa,σ_b～537MPa,δ₅～5.5%,E～96.8GPa。).(2)The mathematical statistical model with more factors and more levels has been set up to study the heat-treatment of the SiC_p/Al composites.The experimental and thereotical results combined with the micromechanism of heat treatment have established the law of mechanical properties depending on the parameters of heat treatment. The reasonable parameters of heat treatment for the 10%SiC_p/6066Al composites are solution at 535℃for 90 min,water quench and aged at 170℃for 7 h;the parameters of heat treatment for the 12%SiC_p/6066Al composites are solution at 530℃for 90 min,water quench and aged at 170℃for 6 h and those of the 15%SiC_p/6066Al composites are solution at 525℃for 90 min,water quench and aged at 170℃for 5h.(3)The dispersoid phase(Fe,Mn,Cu)₃Si₂Al₁₅(bcc structure with a lattice constant a≈12.8(?)and in size of 100～500 nm)in the SiC_p/6066Al composites have been found in the microstruetural solusion,which can pin up the dislocations.The interfacial structure and cohesive forms have been verified and the techeniques to get strong interfacial cohesion has been obtained.Studies on the effects of microstructures on the deformation behaviour in the composites through the modified EMA model have been proved the strengthening mechanisms and the fracture modes,which also confirmed that the optimized techeniques are beneficial to enhancing the strength and ductility of SiC_p/Al composites.(4)The dynamical experiments of the composites combined with the theoretical model have verified that,at low temperature,the dislocation damping is the primal damping mechanism in SiC_p/6066Alcomposites,while the sliding motion of interface and grain boundary plays major roles in internal friction at high temperature.All of these three mechanisms make up the main damping behavior in the composites.At the appearance of the internal friction platform,the dynamical modulus of the composites decreases rapidly.The temperature-and frequency-dependence of internal friction and the forming mechanism of damping peaks in the composites have been found.The activation energies of dislocation damping and grain boundary sliding are 1.2 eV and 1.57 eV,respectively.The damping capacity of the 12%SiC_p/6066Al can get the order of 10^-2as well as high elastic modulus at higher temperatures less than 400℃.(5)The equivalent representative element of particle reinforced metal matrix composites has been modified with different interface features to study the effects of interfacial parameters on the properties of the SiC_p/Al composites.The interface-denpendence of properties (including the elastic modulus,interracial damping and yielding strength) of the SiC_p/Al composites,compared with the experimental results,has been found.The studies can provide the manufacture of SiC_p/Al composites with scientific approaches.The studies on the effects of surface modification and forming temparatures on the properties and the interfacial structures of SiC_p/Al composites,the law of heat treatment and the microstructures,especially the interfacial features,can provide the industrialized production of SiC_p/Al composites with theoretical guidance and technical assistance, and promote the basic research in SiC_p/Al composites.