Investigation On Preparation And Properties Of Micro/Nano Particles Reinforced Aluminium Metal Matrix Composite

Particle reinforced aluminum matrix composite has high specific strength and specific modulus, good thermal conductivity and electrical conductivity, excellent wear resistance and other properties. It was widely applied in aerospace, automotive, electronics, advanced weapons systems. Particle sizes and types are important for properties of particle reinforced aluminum matrix composites. The multiscale and multi-type particle reinforced aluminum composites have shown better mechanical properties than those with sole scale or single particles.In this thesis, the micron-level SiC particles were surface pretreated by a liquid coating method, where CuO nano-particles were coated on SiC particles. The composition and structure of composite powders were characterized by X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), Zeta potential instrument. SiC/Al2O3- micro/nano particles reinforced aluminum matrix composite materials were perparated by a stir casting in-situ reaction method. Their mechanical properties (bending strength, Brinell hardness), the friction and wear properties (friction coefficient, wear rate) and microstructure were carefully studied. The corresponding preparation parameters were optimized. Finally, the micro/nano particles reinforced aluminum matrix composites were heat treated by T6 method. The effects of heat treatment on the composite properties were studied and optimal heat treatment process was determined.The results were shown as follow. Micron-SiC particles with high temperature treatment were successfully coated by a uniform CuO layer with an average particle size of 50nm. The reaction temperature and surface state of SiC particles play a key role in the coating technique. The reaction between Al and composite powders beginning at 800℃and violent reaction at 815℃were determined by thermal analysis. Then, SiC/Al2O3-micro/nano particle reinforced aluminum matrix composites can be prepared by a stir casting-in situ reaction method. The composite prepared with optimized parameters (4wt% SiC, reaction temperature at 825℃for 20 min) show the best performances. Their bending strength and Brinell hardness are 486 MPa and 164.8 HB, respectively. The friction coefficient reduced by 25%, while the wear resistance reduced from 1.62 mg to 0.05 mg compared with aluminum matrix. These composites were strengthened by the dislocation strengthening, fine grain strengthening and Orowan joint action of dispersion strengthening. The abrasion cycles showed characteristic of oxidation wear, delamination wear and abrasive wear. Additionally, these composite materials have significantly enhanced effect by heat treatment. After a optimized T6 heat treatment process (solid solution treatment at 515℃for 5 h, followed with a aging treatment at 165℃for 6 h), their bending strength, Brinell hardness and friction coefficient are 584 MPa,181 HB and 0.3508, respectively.