Please clarify the relationship between the density or/and porosity with the parameters wettability, stirrer position, rotational speed, stirring duration, relative density (density difference between reinforcement and matrix), rate of solidification, the treatment of the ceramic particles (preheating, use of a wetting agent), the nature of the alloy slurry, and the weight fraction of the reinforcement.
Dear Pradeep,
If wettability is not good obviously there will be porosity at the particle-matrix interface. Commonly, the stirrer position is kept at 2/3 of the melt but some stagnant zones are unavoidable. If rotational speed is high the vortex in the melt can suck air and increase porosity. The rotational speed is balanced to avoid settling of particles in the melt. Stirring duration is more then many undesirable intermetallic compounds are formed and oxidation of melt will also occur. Difference in relative density will tend to settle the particle due to gravity. Rate of solidification affects the microstructure, rapid cooling rate resulted in finer microstrucuture. Preheating of ceramic particles eliminates the adsorbed moisture and organic impurities. Wetting agent like magnesium in aluminum decreases the surface energy and hence increases the wettability. Alloy slurry viscosity depends on the operating temperature and it affects the particle settling. Commonly, 15 percent reinforcements were used. Higher volume fraction of reinforcement is associated with particle agglomeration and particle induced porosity.
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