Fracture-based prediction of high-cycle fatigue lifetime in heat-treated
AZ91/AZE911 magnesium alloys using striations spacing and Paris crack
growth rate
Abstract
The fractographic analysis of the fracture surface is one solution to
determine the kind of failures and predict the fatigue lifetime and
resistance of mechanical components under cyclic loading. In the present
research, the fracture behavior of the AZ91 magnesium alloy, under
stress-controlled high-cycle fatigue loading, was analyzed based on the
fatigue striations on the fracture surface. At first, equations and
relations were extracted with the Paris crack growth law and the space
of the fatigue striations. Then, striation spacing was measured by the
experimental results of the high-cycle fatigue (HCF) testing for
heat-treated Mg-Al-Zn alloys, containing and non-containing rare earth
elements. Finally, constants of the Paris law were calculated and
calibrated. Results showed that rare earth elements addition decreased
the space between the striations, and subsequently, the fatigue
resistance of the AZ91 alloy increased. The reasons are extreme grain
size reduction by heat-treating and formation of new Al
11RE 3 phase by rare earth elements
addition. The obtained results of the predicted fatigue lifetime, in
comparison to the experimental ones, the scatter band of ±1.5X
demonstrated the accuracy of the recommended model by a mean error of
33%.