Effect of Frequency, Environment, and Temperature on Fatigue Behavior of E319 Cast Aluminum Alloy: Stress-Controlled Fatigue Life Response

Abstract

The fatigue stress-life (S-N) behavior of E319 cast aluminum alloy was studied by using both ultrasonic and conventional fatigue techniques in order to understand the potential effect of frequency on fatigue behavior of cast aluminum alloys. It was observed that, at the investigated temperature (20°C, 150°C, and 250°C), fatigue life in air at 20 kHz is 5 to 10 times longer than that at 75 Hz. The difference in fatigue life between 20 kHz and 75 Hz is attributable to an environmental effect on fatigue crack growth rate. The effect of frequency, environment, and temperature on S-N behavior of E319 cast aluminum alloy can be predicted by use of a general version of a modified environmental superposition model. Environmental effects need to be considered when ultrasonic fatigue is used for estimating fatigue lives of aluminum alloys that are under cyclic loading at lower frequencies in service. It is possible to extrapolate ultrasonic fatigue data to conventional fatigue behavior for an E319 cast aluminum alloy based on the environmental superposition model.

Onset Frequency of Fatigue Effects in Pure Aluminum and 7075 (AlZnMg) and 2024 (AlCuMg) Alloys

“…However, the effect of frequency on fatigue behavior was not statistically significant [15]. On the contrary, for E319 cast Al alloy at 293, 423 and 523 K, fatigue life at 20 kHz was 5-10-times longer than that at 75 Hz [14], but this author states that fatigue crack initiation is not influenced either by temperature or frequency. Rather, the observed difference in fatigue life is attributed to environmental effects on FCG rate.…”

“…The reasons supporting this assumption are explained herein. Namely, Zhu et al [14] observed that the fatigue strength of an Al alloy decreases with temperature, with a behavior that follows closely the temperature dependence of the yield and tensile strength. Furthermore, Liaw et al [16] suggested that the fatigue limits and fatigue lives of steels decrease due to the temperature increase caused by plastic deformation.…”

“…For E319 cast Al alloy tested at 293, 423 and 523 K, Zhu et al [14] observed that the fatigue strength decreases with temperature and that the temperature dependence of the fatigue resistance at 108 cycles follows the temperature dependence of the yield and tensile strength for this alloy closely. Furthermore, by integration of a universal version of a modified superposition model, the effects of temperature, frequency and the environment on the S-N curve of this alloy can be predicted, and it is possible also to extrapolate ultrasonic data to conventional fatigue behavior [14].…”

“…Zhu et al [14] state that environmental effects need to be considered, and Mayer et al [15] explain that this is so because the time-dependent interaction with the environment may cause an extrinsic frequency influence on fatigue properties, on top of the intrinsic strain rate effects. Furuya et al [12] state that frequency generally affects high frequency fatigue tests because: (1) fatigue limits and lives decrease due to the temperature increase caused by plastic deformation [16]; (2) dislocations may not match the applied frequency because dislocation movement is slow compared to sonic velocity [17]; and (3) provided that embrittlement by hydrogen diffusion had an effect [18], fatigue lives would depend on both the number of loading cycles and time.…”

“…Furthermore, by integration of a universal version of a modified superposition model, the effects of temperature, frequency and the environment on the S-N curve of this alloy can be predicted, and it is possible also to extrapolate ultrasonic data to conventional fatigue behavior [14]. Henaff et al [26] concluded that the temperature has almost no influence on FCG rates for AA 2650-T6, after conducting tests at 293, 403 and 448 K and frequencies of 0.05 and 20 Hz.…”