Effects of humidity and temperature on the fatigue behaviour of an extruded AZ61 magnesium alloy

Load-controlled fatigue tests were performed at 20 and 50 degreesC using two relative humidity levels of 55 and 80% to characterize the influence of humidity and temperature on the fatigue behaviour of an extruded AZ61 magnesium alloy. Fatigue tests were also conducted at 150 degreesC. No significant variation in fatigue properties was noticed with respect to temperature over the range from 20 to 50 degreesC for both the humidity levels. Fatigue limits in the range 140-150 MPa were observed for relative humidity of 55%. Fatigue strength decreased significantly with increase in temperature to 150 degreesC. Further, a significant reduction in fatigue strength with a fatigue limit of similar to110 MPa was observed with increase in relative humidity to 80% at 20 and 50 degreesC. The crack initiation and propagation remained transgranular under all test conditions. The fatigue fracture at low stress amplitudes and high relative humidity of 80% results from the formation of corrosion pits at the surface and their growth to a critical size for fatigue-crack initiation and propagation. The observed reduction in fatigue strength at high humidity is ascribed to the effects associated with fatigue-environment interaction.