Study On Surface Properties Of SiC_p/Al Composite By EDM And Process Of Electroless Plating

In this work, three kinds of SiCp/Al-Si composites were fabricated by liquidinfiltration squeeze casting. SiC volume fractions of the composites are45%,55%and65%, respectively. All of the materials were incised by electrical dischargemachining (EDM) with the same process parameters. By means of microstructureobservation, phase analysis and performance test, the microstructure and phasetransformation of machined surface and powders which produced by EDM wereanalyzed, so as the machining mechanism of EDM process. In addition, the methodof electroless plating on the machined surface were also studied.The machined surface of composite is unsmooth with holes, cracks and otherdefects.The Profile of composite incised by EDM is consisted of recasting layer,heat-affected zone and internal structural. The depth of recasting layer is between2~5μm, which of heat-affected zone is about100μm with rich area of SiC particles.EDM has made a series of changes on the composite, which including melting,gasification, the decomposition and abscission of the SiC particles, oxidation ofvarious components. Materials incision is mainly depends on those reactions.The researches of property indicate that: the roughness of machined surface isbetween3~5μm, of which the composite with55%vol. SiC has the highest value.The residual stress, which increases with the volume fraction of SiC, is between30~60MPa. After machined by EDM, the BH increases by4%; the nano-hardnessand elastic modulus of re-cast layer are between29~42GPa、0.6~0.8GPa,respectively. Influenced by the Machined Surface, the electrical resistivity increasesby5%; thermal conductivity decreases by10%and the bending strength ofSiCp/Al-Si composites has a decline of6%~13%, which are in consistent withsurface roughness. Compared with two different surface state of composite materials,the friction coefficient of machined surface is lower and the friction wearmechanism is different from the other one.The studies on coating experiments shows that: a Ni-P coating was obtained onthe surface of SiCp/Al-Si composite machined by EDM. The whole surface iscovered with a pure nickel coating. And the coating is bright, compact with a highbinding force.