Ａｌ合金鋳物の疲労特性に及ぼす溶体化時間の影響

概要

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Rotating bending fatigue tests were carried out for a squeeze cast Al alloy, AC4CH-T6, to investigate the effects of solution treatment time on microstructure, static mechanical properties and fatigue strength. The solution treatment conditions selected were treatment times of 15, 30, 70, 240 and 480min at the same temperature of 545 °C. With increase in the solution treatment time, a eutectic Si particle was spheroidized and dispersed. Although 0.2% proof strength and tensile strength were increased by change in the treatment time from 15min to 70min, the effects of solution treatment time over that time on these strengths were hardly observed. Fatigue strength was slightly increased with increase in the treatment time. That is, effect of the treatment time on fatigue strength was very small in comparison with the change in microstructure by the treatment time. A crack initiated in α phase or from a eutectic Si particle irrespective of the treatment time. The increase in fatigue strength was mainly caused by the increase in the crack initiation life which was related to changes in the hardness of α phase and the shape of a eutectic Si particle by the treatment time. The suitable treatment time at the temperature of 545°C was around 70min from the view points of mechanical properties and practical application.