Electrical discharge machining and drilling of extruded (al/sic ) metal matrix composites

The fabrication, microstructure, micro-hardness and machinability of particulate metal matrix composite (Al / SiC) were investigated. The following conclusions can be drawn.Fabrication1. Range of particulate metal matrix composites of (0 - 26.5% SiC) were successfully fabricated using powder metallurgy technique followed by extrusion. 2. The mixed powders of aluminum (80 µm) and SiC (60 µm) were pressed under a pressure of 405 MPa and sintered at 723 ˚K for 6 hours.3. Extrusion process, using die of extrusion ratio = 2.37 was carried out on as secondary manufacturing process to consolidate the compacted (Al/SiC) composites under a pressure of 405 MPa and sintered at 773˚K Physical and Mechanical Properties4. The MMC densities and voids were found to increase as volume fractions of SiC were increased.5. SiC particles distribution within the aluminum matrix was improved by extrusion process.6. Micro-hardness has greatly increased with increase of SiC content. Micro-hardness in longitudinal direction has higher values than that in the transverse direction due to the density distribution of the specimens.Conventional Machining Properties7. The hard SiC particles in composite causes extremely rapid tool wear at all tested speeds and feeds. The higher the SiC content the larger is the tool wear.8. As cutting speed or feed is increased, the tool wear is increased and tool life is decreased. The effect of feed is not as great as speed.9. It was found that, as the SiC volume fractions increased both n and m of Taylor equation are increased but K is decreased. The exponent factor (n) is rather high 0.32.10. Surface roughness produced showed significant change as feed, speed or SiC% was changed. Increasing volume fractions of SiC increased surface roughness of machined surface.11. The chips formed in the presence of SiC particles have discontinuous type. As SiC is increased, chip size is decreased.Non-Conventional Machining Properties12. The metal removal rate and the tool wear rate were found to increase as discharge current is increased, but material removal rate decreased as SiC is increased.13. The metal removal rate and the tool wear rate obtained by using paraffin oil were higher than case of kerosene as dielectric fluid.14. Surface roughness of machined surface increased as discharge current is increased or as SiC content is increased. The discharge current has15. Common features of the re-cast layers are voids formed due to imperfect joining of the molten aluminum and fine spherical bubbles resulted from the trapped gas during re-solidification.16. Comparatively thick recast layer is formed on surface of electrical discharge machined surface, the higher the SiC the thicker is the recastlayer. SiC particles in recast layer seemed to be not damaged since it retains some of their sharp corners.17. EDX analysis confirmed the presence of precipitated carbide (Al4C3) on the machined surface when kerosene was used. This may be a reason for low material removal rate and low tool wear rate obtained when kerosene was used as dielectric fluid.5.2 Future Work1. Further investigation is suggested to optimize the effect of other machining parameters such as depth of cut and feed on machining characteristics of metal matrix composites.2. It was found that paraffin gave better material removal rate than kerosene. Other experimental and theoretical studies are required for other dielectric fluids.3. Further studies are suggested on effect of other extrusion parameters such as die angle, lubrication and extrusion speeds on mechanical characteristics of metal matrix composites4. Further investigations are required to understand the surface roughness deterioration and its relation to size of SiC particles.5. It is also suggested to study the cohesion, de-cohesion and fracture of the reinforcement particles as result of machining and their relation to surface finish and cutting tool wear.