Dependence of fatigue life of low-pressure die-cast A356 aluminum alloy on microporosity variation

The aim of the present study was to investigate the dependence of the high cycle fatigue property on the microporosity variation of a low-pressure die-cast A356 alloy. Also, it aimed to describe quantitatively the relationship between the fatigue property and monotonic tensile strength using modified Basquin’s equation which takes into account the microporosity variation. The fatigue life of the A356 alloy can be described by an exponential dependence on the variation of the fractographic porosity, in terms of the modified Basquin’s equation which is composed of the defect susceptibility of fatigue life to microporosity variation and the maximum tensile strength achievable in the defect-free condition. Using a modified form of Basquin’s equation, the maximum values of the fatigue strength coefficient and exponent in the defect-free condition are 341.5 MPa and −0.076, respectively, even though the nominal values of fatigue strength coefficient and exponent without consideration of microporosity variation are 237.6MPa and −0.048, respectively. Also, the difference between the maximum tensile strength and the fatigue strength coefficient on modified Basquin’s equation is about 120MPa, and it arises from variation in the deformation behavior due to the difference of loading condition between the monotonic and cyclic test modes such as the strain rate, Bauschinger effect, cyclic work hardening and damage accumulation on loading condition.