抄録
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 < 105 or about Nf = 105, fracture surface were Mode I fracture surface, about Nf = 106, fracture surface were mixture of Mode I and Mode II fracture surface, and 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.
