Application of Electromagnetic Force to Fabrication of Aluminum-matrix Composites Locally Reinforced with Particles

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Electromagnetic separation technique of nonconductive particles from liquid metal was applied to fabricate a partially reinforced MMC of aluminum by ceramic particles, which has a high wear resistance and a good deformability. To separate particles, a high frequency magnetic field was imposed on an aluminum melt suspending silicon carbide (SiC) particles of which mean diameter was about 20μm. Suspended SiC particles were found to be transferred to the vicinity of the crucible wall in several ten seconds. The thickness of the particle accumulated layer (PAR) and the particle density could be changed by frequency (30-200 kHz) and current (42-163 A) in the ranges from 0.6 to 1.5mm in thickness and from 0.05 to 0.22 in particle density. The thickness of PAR was large in the middle of the aluminum cylinder, however it was very thin near the free surface and the bottom where the existence of strong liquid flows were predicted by the numerical simulation of turbulent flows in liquid aluminum. … More In order to obtain thicker PAR needed for brake materials, e.g.4mm, a 3-kHz generator was applied, which was expected to achieve thicker PAR because of its large skin depth, 4.7mm. However, intensive electromagnetic stirring prohibited particle separation. Numerical simulation revealed that the lift force generated in a velocity gradient near the wall prevented particle accumulation. By this simulation, the vertical distributions of the PAR thickness at different frequencies were well reproduced and the PAR formation was predicted for the case of 3kHz if the vertical profile of electromagnetic force was reformed to be uniform. Based on such prediction, molybdenum rings were placed near the free surface and the bottom to reduce flow strength there. However, improvement was not enough, though thin PAR was observed partly. A pulse imposition of magnetic field was tested aiming the reduction of flow strength without change in electromagnetic separation force. As a result, homogeneous PAR was obtained though the thickness was about 1mm. It should be noted that the particle density in PAR was more than 50 %, which was extraordinary comparing with the other results, less than 20%. Finally, the deformability and the strength of wear resistance were measured and the applicability of the present particle-reinforced MMC was confirmed. Less