Effect of Solution Treatment Time on Fatigue Properties of A Cast Alloy
Norio KAWAGOISHI, Shin-ichiro OHURA, Mitsuru ADACHI, Yoshikazu MAEDA and Eiji KONDO
Abstract: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 480 min at the same temperature of 545C. 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 15 min to 70 min, 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 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 phase and the shape of a eutectic Si particle by the treatment time. The suitable treatment time at the temperature of 545C was around 70 min from the view points of mechanical properties and practical application. Key Words:Squeeze cast Al alloy, AC4CH-T6, Solution treatment, Fatigue strength, Spheroidized eutectic Si particle, Crack initiation, Crack propagation