アルミニウム合金ダイカストの超長寿命疲労強度特性

Abstract

To investigate the extra long life fatigue properties of aluminum die casting materials, fatigue tests were conducted on two type of aluminum die casting materials. One type is Al-Si-Cu die casting alloys ADC10-T5 and the other is Al-Si-Mg die casting alloys AC4C-T6. The main results obtained are as follows, (1) For ADC10-T5, the origin of fatigue crack is casting defect and the fracture surface at around the fatigue crack initiation portions were Mode I fracture surface. (2) For AC4C-T6, the origin of fatigue crack is the base matrix and the fracture surface at around the initiation portion changed from Mode I fracture surface to Mode II fracture surface along with the increase in the number of cycles. At the range of Nf 107, fracture surface were Mode II fracture surface. (3) The extra long life fatigue strength (107-109cycles) of AC4C-T6 decreased along with the increase in the number of cycles, while the extra long life fatigue strength (107-109cycles) of ADC10-T5 did not decrease along with the increase of the number of cycles. (4) The casting defect size in non-fracture specimen was much smaller than the allowable defect size predicted by the √area parameter model. It seems to be that the reason why no reduction was recognized in the fatigue strength of the ADC10-T5 in the life range beyond 107cycles.