Fabrication of aluminum-matrix composites locally reinforced with SiC particles by using intermittent A.C. magnetic field

In our previous study, aluminum matrix composites partly reinforced by SiC particles were fabricated by the imposition of a high frequency magnetic field to molten aluminum suspending SiC particles. The thickness of particle-accumulated layer (PAL) was almost the same as the skin depth that depends on the frequency of the magnetic field. In the present study, a 3 kHz magnetic field is applied to realize thicker PAL. Although a 4.71 mm PAL is expected at 3 kHz, PAL is not formed because of a strong electromagnetic flow. Intermittent imposition of magnetic field is tested to increase PAL, which seems effective to reduce the electromagnetic flow. A 4 mm PAL with dense particle packing is realized by an intermittent magnetic field composed of 1 s imposition and 1 s pausing. Numerical calculation is performed to understand the behavior of metal flow with the intermittent magnetic field. It is found that 0.5 s is required for the development of metal flow. As the relaxation time of a single SiC particle in molten aluminum is far less than 0.5 s, PAL can be formed before the metal flow develops.