高周波誘導加熱による短時間溶体化処理がADC12高圧ダイカスト品のミクロ組織と硬さに及ぼす影響

抄録

  Solution treatment and age hardening normally cannot be applied to aluminum high pressure die castings, due to heating at high temperature leads to pores or blisters from entrapped air and hydrogen gases, and these defects cause the deterioration of mechanical properties and appearance quality. However, it can improve mechanical properties if the most effective solution treatment conditions for preventing pores by increasing solid solution amount such as Cu can be determined. This study focuses on rapid solution treatment until five minutes with the high temperature rising rate of 50℃/sec using high frequency induction heating. The effects of rapid solution treatment on the microstructure and hardness of JIS ADC12 high pressure die castings were investigated in terms of the formation of pores and progress of solid solution amount. The results were as follows. It was found that the area fraction of pores significantly increased when treated for more than five minutes at 490℃, three minutes at 500℃, and one minute at 510℃. The shape of the pores was round until 500℃, whereas crack shapes were observed at 510℃. Eutectic silicon was refined and spheroidized when solution treatment was carried out for one minute. However, treatment exceeding one minute resulted in eutectic silicon growth. Based on changes in the electric conductivity and Vickers hardness during solution treatment, the solid solution amount gradually increased till one minute and then saturated after that. From these results, the recommended solution treatment conditions for increasing hardness with reduced pores are treatment for one to three minutes at 490℃, or treatment within one minute at 500℃.