The Effects Of Surface Treatment Of SiC Particles And Preparation Process On The Microstructures And Properties Of SiCp/6066Al Composites

The effects of surface treatment of SiC particles and preparation process on the microstructures and properties of SiCp/6066Al composites were studied by means of optical microscopy, scanning electron microscopy (SEM), tensile testing and hardness testing. This thesis mainly focused on the following two areas.1) The effects of surface treatment of SiC particles on the microstructures and properties of SiCp/6066Al compositesTwo different surface treatments of SiC particles were used. The first one was the oxidation and acid treatment. Oxidation of SiC particles was carried out in an electric furnace in air at 1100℃ for 10 hours, then the oxidated SiC particles were dipped in 40% hydrofluoric acid for 3 hours, then baked. The other was that SiC particles were dipped in 100℃ saturated NaOH solution for 30 minutes and washed with pure water after ultrasonic cleanout, then treated by 80℃ saturated K₂ZrF₆ solution for 2 hours , then baked. The SiC particles treated by the two above surface treatments and the 6066A1 matrix composites reinforced by these SiC particles with the same volume fraction fabricated by powder metallurgy route, were analysed by metallography, scanning electron microscopy(SEM), tensile testing and hardness testing. The results showed that: â‘  SiC particles were apparently blunted by oxidation , and the sharp edges and angles were removed. The surface treatment of acidwashing after oxidation had completely removed granular heave on the SiC surface, which became clean and slippery;â‘¡ after the NaOH and K₂ZrF₆ solution treatment, the surfaces of SiC particles became rough and were coated with a thin layer of K₂ZrF₆ uniformly;â‘¢ Compared with the original SiC particles, the gather degree of reinforcements in the composites decreased by oxidation and acid treatment;there were hardly any holes and weak interface bonding in composites;the major fracture modes were ductile fracture of matrix and reinforcements being pulled out with matrix;by NaOH and K₂ZrF₆ solution treatment, the SiC particles with rough surfaces can pin and adhere to matrix particles easily and firmly;the K₂ZrF₆ film on SiC particle surfaces can remove the Al₂O₃ film on 6066A1 particle surfaces, sothe composites had good interface cohesion and uniform distribution of reinforcements in matrix, and the composites fabricated by this method had better properties than those of oxidation and acid treatment.2) The preparation process of SiCp/6066Al compositesThrough Brinell ball hardness testing, OM and SEM analysises, the effects of high energy ball milling and quick hot extrusion at low temperature on the SiC particle distribution were studied, the sintering mechanism and its effect on densification, microstructures and properties of SiCp/6066Al composites were studied too. The results indicated that: ? high energy ball milling is the most effective mixing method, which can remarkably improve the shape of reinforcements, reduce their sizes and lead to the homogeneous distribution of reinforcements in quantity at smaller micro-areas in matrix;by using the greatly plastic deformation of matrix, high-speed hot extrusion at low temperature can apparently reduce the reinforcement size and produce fine axial symmetrical reinforcements which can move easily and distribute homogeneously with the matrix's flow;it can also eliminate the cluster of reinforcements at micro-areas in the matrix or mostly reduce the cluster degree of reinforcements;high energy ball milling combined with high-speed hot extrusion at low temperature is the most effective method that leads to the uniform distribution of reinforcements in the matrix at micro-level. ? when sintered at high temperature for short time, the densification of composites increased greatly, but the matrix particles were badly oxidized , grains grew up and the liquid phase formed beads on the SiC particle surfaces;as will lead to composite hardness lower than those of long time sintering at low temperature;by high energy ball milling, small SiC particles had higher specific surfaces and more defects and crystal lattice deformation inside, which provided driving force for solid long time sintering at low temperature;with the sintering time prolonging, the sizes of pores became smaller and smeller and theirs amount became less and less, the composites had better densification and particle combination and the hardness of composites enhanced largely.