Research On Microstructure And Mechanical Properities Of SiCp/6061 Composites Prepared By Stirring Technology

Particulate-reinforced aluminum matrix composites(PAMCs) produced by stirring casting method exhibit many advantages, including low producing cost, simple fabrication process and highly isotropic properties, and are quite promising in practical application. Squeeze casting process combines the advantages of casting and forming methods having characteristic of near net shape, and hence is one of the most important processes for composite forming. In this paper, stirring preparation, microstructure, mechanical properties and kinetics of precipitation of Si Cp/6061 composites prepared by squeeze casting method were investigated.Based on the analysis of the limitations of current stirring preparation of particle reinforced Al matrix composites(PAMCs), an experiemental apparatus for PAMCs was designed. The particulate transportation sub-system, stirring sub-system and other appendix parts for the apparatus were designed and made. Then, the apparatus were fabricated and applied to actual preparation. The results show the advantages of controlled velocity of particulate transportation, gas protection, and automatical handle.The Si Cp/6061 composite castings were produced by squeeze casting processes to study the effects of squeeze pressure, particle volume and particle size on microstructure and mechanical properties. It is found that defects of particle-porosity clusters can be clearly observed in the gravity castings, and the defects and porosities drastically reduce as the applied pressures increased. With the increase of squeeze pressure, the tensile properties, hardness and elongation of the castings increase due to reduce of the particle-porosity clusters and grain refine. With the increase of particle volume fraction, the yield strength and hardness of Si Cp/6061 composites are enhanced wheras the elongation decrease, and the tensile properties increase at first and decrease later. With the decrease of particle size, the tensile properties, yield strength, elongation and hardness of Si Cp/6061 composites are improved.The kinetics of precipitation during aging of Si Cp/6061 composites and 6061 alloys were investigated by differential scanning calorimetric analyses(DSC). The influence of Si C particulate on the precipitation kinetics of 6061 matrix and the effect of particle volume fraction on the precipitation kinetics of β″ phases in Si Cp/6061 composites were analyzed. The kinetic parameters, TTT curves and kinetic expresses of metastable phases in the composites and alloys were obtained by using Avrami-Johnson-Mehl(AJM) equation, and so β″ phases in Si Cp/6061 with different particle volume fraction were. The calculation results were compared and validated with hardness measurement, showing good agreement between the calculation and experiment results. The results have shown that GP zone formation is significantly suppressed with the addition of Si Cp; the precipitation of β″, β′ and Q′, β and Q phases are enhanced; the acceleration of β″ phases on precipitation increase at first and decrease later with the increase of particle volume fraction in Si Cp/6061.