人工対流により結晶微細化したアルミニウム合金鋳塊の機械的性質

Abstract

Artificial convection flow caused by Lorentz-interaction between a magnetic field and a direct current created wide equiaxed zones in aluminum alloy ingots. Mechanical properties were examined for these ingots by tensile and Charpy impact test. The results obtained were as follows.In hypo-eutectic specimens, Al-Cu and Al-Si alloys solidified with artificial convection flow exhibited higher tensile strength and 0.2% proof stress than without convection flow, whereas lower elongation and reduction of area were obtained in the former case than the latter. It was postulated that the strength increased by the grain-refinement but the ductility decreased by micro-shrinkage cavities caused by violent convection flow.In Al-CuAl2 and Al-Al3Ni eutectic alloys, the tensile specimens from the ingot solidified with no convection flow exhibited higher tensile strength than the specimen with artificial convection flow when loaded parallel to the growth direction. It was suggested that this behavior was due to the presence of lamellar or rod-type intermetallic compound with reinforcement in the former but the presence of degenerated structures caused by flowing melts in the latter.In Al-Si eutectic alloys, the tensile properties were improved by artificial convection flow. It was correlated with uniform refinement of eutectic silicon phase in solidification with convection flow.Charpy impact values of the hypo-eutectic specimens depended strongly on the direction and configuration of primary aluminum-rich dendrites. In the case of eutectic specimens, it was postulated that the continuous aluminum-rich matrix resulted in higher impact values when the impact direction was parallel to the direction of solidification.