Fluidity of aluminum-silicon-alumina composite
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IN recent years there has been profound interest in the technology of cast metal-ceramic particle composites especially in their fabrication and engineering applications. Metal-ceramic particle composites such as Al_A1203,1-3 Al_graphite,4-10 Al_micall have been successfully made via the casting route by dispersing desired nonmetallic particles in liquid metal/alloy and casting the resultant composite melts in suitable molds. Generally it is known that the fluidity of molten metal/alloy is lowered by the presence of suspended secopd phase inclusions. However, quantitative information on the effect of second phase particles on the fluidity of molten metal/alloy is lacking. It is necessary to characterize the fluidity of the melts containing suspended particles, since this will determine the sizes and shapes of castings that can be made. Fluidity of these melts is also important from the point of view of compocasting of these materials. It has been reported that additions of hard ceramic particles/short fibres like AI203 in aluminum alloy could lead to improved hardness, wear resistance and strengthY 2 There are several reportsl-3describing the preparation and properties of A1-A1203 particles/short fiber composites. However, to date no work has been reported on the fluidity of aluminum alloy containing dispersed Al203 particles. In this investigation we have measured the fluidity of A1- l 1.8 pct Si alloy containing different wt pct of dispersed alumina particles and the results have been interpreted. EXPERIMENTAL PROCEDURE In this study AI-11.8 pct Si alloy was chosen as a base alloy. A1203 particles of spheroidal shape was obtained from M/s. Sarabhai Chemicals (India) and sieved into various fractions. For dispersion experiments sieve fractions of -200, + 300 (60#m), - 170, + 150 (90/tm), + 170, - 100 (120/tm), and + 100, - 6 0 (200#m) were chosen. Alumina particles of desired size M. K. SURAPPA, formerly with the Indian Institute of Science, Bangalore, India, is currently Scientist, and P. K. ROHATGI is Director at the Regional Research Laboratory (CSIR), Trivandrum695 019, India. Manuscript submitted April 30, 1980. METALLURGICAL TRANSACTIONS B
and amount were dispersed in molten AI- 11.8 pct Si alloy by the vortex method3 and the composite melts were poured into spiral fluidity mold) 2 The mold for the test piece~2made of cast iron was used to measure spiral fluidity. The spiral channel had a cross sectional area of 0.65 • 10-2 m 2 and the length of the channel was 1.5 m. The length of fluidity spiral was taken as a measure of fluidity. Measurements were made at melt temperatures of 680, 700 and 740 ~ Surface area of aluminium oxide particles used was measured by the EGME absorption method. 13All the spirals were machined on one side to observe the distribution of dispersed A1203 particles. RESULTS AND DISCUSSION Photograph of a typical machine cut surface (machined to a depth of 1 • 10 m -3) of fluidity spiral of A1-11.8 pct si-5.0 pct A1203 (200/t m) composite spiral is shown in Fig. l(a). A typical portion o
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