急冷凝固したAl-11%Si-2.5%Cu合金板の曲げ性に及ぼす共晶Si相形態の影響

抄録

  The morphology of eutectic Si particles in Al-11%Si-2.5%Cu alloy was changed by heat treatment and rapid solidification in the aim to study the influence of the morphology of eutectic Si particles on bendability. Eutectic Si particles were plate-like in the as-cast condition of permanent mold cast specimens. The rounding of the plate edges was observed by short heat treatment (500℃-0h). The morphology of the eutectic Si particles became rod-like and globular with increasing heat treatment time. On the other hand, in a twin-roll cast product, the eutectic Si particles were rod-like in the as-cast condition. The aspect ratio of eutectic Si particles in twin-roll cast product was almost the same as that obtained by heat treatment time of 0.5h, and the average eutectic Si particle diameter in twin-roll cast product was the smallest in all specimens. As a result of bending tests, the permanent mold cast specimen (as-cast) was fractured at a bending angle of 45°. On the other hand, heat treated and twin-roll cast specimens were bent to a bending angle of 180°. Broken eutectic Si particles were observed near the bending surface, and cracks in the broken eutectic Si particles were most perpendicular to the bending direction. The size distribution of broken eutectic Si particles was also investigated. When the chill layer was chosen as the bending surface, specimens fractured only at the bending angle of 80°. This is considered due to the dense distribution of fine eutectic Si particles and difficulty of deforming the matrix by the Cu solution.