2018 Volume 90 Issue 12 Pages 703-709
In a previous article, rapid solution treatment until five minutes with the temperature rising rate of 50℃/sec using high frequency induction heating was applied to JIS ADC12 high pressure die castings. This heat treatment leads to the moderate increase in solid solution amount, preventing pores, and eutectic silicon refining, and spheroidizing. Especially, changing the eutectic silicon shape improves fracture toughness. In this article, the effect of rapid solution treatment on toughness improvement was evaluated from tensile strength and ductility. The results were as follows. It was found that elongation to fracture increased about 67% by solution treatment, moreover tensile strength increased by around 10% with aging treatment for four hours at 200℃, compared with as-cast specimens. Under-aging treatment was more effective than peak aging for toughness improvement in rapid solution treatment. The one hour aging treatment resulted in about 20% increase in elongation to fracture, while significant decrease was not found in tensile strength, in comparison to specimens treated by peak aging (200℃, 4hrs). In addition, it was assumed that the microstructure of as-cast specimens contained considerable solid solution amounts due to rapid cooling of castings, and also included fine precipitation formed during natural aging for a long-term period.
