EFFECT OF MECHANICAL VIBRATIONS ON MICROSTRUCTURE REFINEMENT OF Al-7 MASS Si ALLOYS

摘要

Mechanical vibration treatment is known to induce microstructure refinement. However, it is not completely understood which factor of vibrations is important for microstructure refinement. Factors of vibrations include frequency, acceleration, velocity and amplitude. In our study, it was found that velocity of mechanical vibrations, namely, the energy of vibrations is important factor for primary crystals refinement. This study aims to investigate effects of casting conditions with the mechanical vibrations on microstructure refinement of Al-7mass%Si alloys. Free space area for vibrating the melt affects the microstructure refinement. Moreover, primary crystal particles become rosette-like and fine when the mechanical vibrations are applied to the melt from about 923 K to 888 K (liquidus - 2 K). Thus, it was found that the mechanical vibrations promote heterogeneous nucleation just under the liquidus temperature.