Effects of defects on fatigue strength of aluminum cast alloys (AC4CH) and evaluation of fatigue limit

The effects of H2 gas content on fatigue strength of aluminum cast alloys (AC4CH) and improvement by atmosphric pressure casting, 1 MPa pressure casting and 773 K-100 MPa HIP treatment were investigated from the veiwpoint of defects, a method for evaluating the conservative fatigue limit was proposed. The main results obtained were ; (1) 1 MPa pressure casting and HIP treatment were effective in improving the fatigue limit of AC4CH, because the defect size in 1 MPa pressure casting and HIP treatment is smaller than that in atmospheric pressure casting. (2) The fracture origin proceeds from microshrinkage to adjoining blow holes as H2 gas content increases, but the size of each blow hole is the same as that of the microshrinkage. Consequently, H2 gas content has little effect on fatigue strength. (3) The conservative fatigue limit of aluminum cast alloys can be evaluated by substituting -areamax estimated by extreme statistics in the defined equation.