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Metal Casting Technologies : September 2006
58 www.metals.rala.com.au TECHNICAL FEATURE wear during machining and this causes high machining costs. The cutting tool materials should be harder than the reinforcements. PCD tools (polycrystalline diamond) are used to machine MMC materials. For impact test samples were tested at room temperature and liquid nitrogen temperature. Samples were kept in liquid nitrogen can and removed very fast for the test. A pin on disk wear test was performed on both the materials. The tests were conducted at room temperature. The weights of pin were measured on an electronic balance. Figure 12 shows the micrographs of Al/SiC MMC. Figure 13 shows the spiral fluidity castings. PREPARATION OF ALUMINIUM FOAM The foam was prepared by melt route. Commercial pure aluminium was melted in a crucible at 7500C. The melt was stirred and calcium powder was added. This imparts high viscosity to the melt. 0.6% wt. titanium hydride (TiH2) powder was introduced in the melt and the slurry was stirred to disperse the powder homogeneously in the melt. The TiH2 decomposes to releases hydrogen gas. TiH2 powder was wrapped in aluminium foil and added in the melt. The crucible is removed from the furnace and cooled down. The foam produced was sectioned for further characterization. The relative density (RD) of foam is density of the foam/density of solid it is made from. Other characterization tests for foam like compression tests, cell wall diameter, and porosity % are under progress. They will be discussed later on. Figure 14 shows the aluminium foam prepared by casting route. Figure 15 are the sectioned pieces from the foam. RESULTS AND DISCUSSIONS The composites were successfully prepared by casting route. Base metal showed more fluidity compared to Al/Gr MMC. There is a decrease in the fluidity length of MMC due to increased viscosity. Base metal showed tensile strength of 70 MPa compared to 67 of Al/3Gr and 64 of Al/5Gr MMC. Results showed Al/5 Gr contains more porosity compared to Al/3Gr MMC. Porosity increased with increase in graphite %. Also the rockwell hardness values of Al/Gr are lower compared to the base matrix. With increase in graphite % the recovery decreased. With increase in graphite amount the tensile strength and hardness decreases. From the optical micrograph for Al/5 Gr it can be seen there is agglomeration of graphite particles in the matrix. The bimetallic casting was cut on a power saw and its Figure 14. Figure 15.