過共晶Al-Si合金の高速回転撹拌凝固における粘性流動とミクロ組織

Abstract

An investigation was made on the viscous flow and microstructure in hypereutectic alloys by rheocasting with the rotation of a stirrer at a high speed in the range from 30 to 70 rev/s. The value of apparent viscosity in hypereutectic Al-Si alloys solidifying with the rotation of stirrer at a speed above 30 rev/s remained almost unchanged to a certain level except a rapid change in the initial stage of solidification. The average size of primary silicon was 66±19 μm in an Al-17%Si-4%Cu-0.5%Mg-0.3%Fe alloy ingot rheocast at 70 rev/s under the cooling condition of 0.6 K/s in the melt. The primary silicon size became finer by the modification of microstructure with an addition of 0.01%Na or 0.01 and 0.1%P in rheocast and conventionally cast hypereutectic Al-Si alloy ingots. A constant level of apparent viscosity was also observed during the high-speed rheocasting of an Al-17%Si-4%Cu-1.2%Fe-1%Mg-1%Ni-0.5%Mn-0.5%Zn-0.2%Ti-0.01%Na alloy ingot. It was depressed with the increase in stirrer speed from 30 to 50 rev/s. The primary silicon size of the alloy ingot was 101±27 μm at a rotation speed of 30 s−1, 96±25 μm at 40 s−1 and 93±25 μm at 50s−1.