Super-long Life Fatigue Properties of Al-Si-Cu Die Casting Alloy by Using Ultrasonic Fatigue Tests

Abstract

Super long life Fatigue properties of Al-Si-Cu Die Casting Alloy were investigated by using ultrasonic fatigue tests at room temperature. The results were compared to fatigue data acquired from conventional fatigue tests, and the fatigue strength were stsudied quantitatively considering the casting defect that was the origin of fatigue crack. The main results obtained are as follows : (1) The S-N curves obtained by using ultrasonic fatigue tests broke in the regime around 107 cycles-as well as conventional fatigue tests. (2) The origin of fatigue crack is casting defect and the fracture surface at around the fatigue crack initiation portion was Mode I fracture surface as well as conventional fatigue tests. (3) From the S-N curve, the fracture mode and etc., ultrasonic fatigue tests seem to be the effective evaluation method of super-long life fatigue properties. (4) Below σ =100 MPa, some specimen were broke, some were not broke. tests seem to be the effective evaluation method of super-long life fatigue properties. (4) Below σ=100 MPa, some specimen were broke, some were not broke. The √area parameter model with casting defect size can explain whether a specimen breaks. but the fatigue limit predicted by the √area parameter model shows the upper level (5) The fatigue limit predicted by the relationship between the stress intensity factor range ΔKCD obtained from the casting defect size in the regime more than 107 cycles and casting defect size √area are in good agreement with the fatigue limit from the S-N curve.