アルミニウム合金ダイカスト中の破断チル層から発生する疲労き裂の超音波その場検出

抄録

  Aluminum alloy die-cast specimens (ADC12) containing cold flakes were subjected to fatigue test and broken at about 330 × 10³ cycles. During the fatigue test, ultrasonic measurement was carried out in synchronization with the loading cycle to obtain the intensity of reflection from the oxide layer of the cold flake without stopping the fatigue tester. With increasing number of fatigue cycles, the reflection intensity monotonically decreased with the number of cycles at 80 × 10³ cycles or larger, and then the phase of the reflection wave changed at about 220 × 10³ cycles. After the change in the phase of the reflection wave, the reflection intensity gradually increased with the number of cycles. From these results, it was found that the oxide layer of the cold flake detached from the matrix at 80 × 10³ cycles or less, namely less than 30 % of the fatigue life.