FATIGUE OF AZ91E-T6 CAST MAGNESIUM ALLOY

The purpose of this research was to obtain room temperature fatigue be havior of AZ91E-T6 cast magnesium alloy and to determine if commonly u sed models that depict fatigue behavior are applicable to this cast al loy. Axial strain-controlled fatigue behavior using cylindrical specim ens were employed to determine low cycle fatigue behavior with strain ratios R = epsilon(min)/epsilon(min) = 0, -1, and -2. The conventional log-log total strain low cycle fatigue model properly represented the R = -1 axial fatigue data. Significant mean stress relaxation occurre d for all R = 0 and -2 axial fatigue tests. However, for the smaller s train amplitude tests with R = 0, sufficient mean stresses were retain ed such that fatigue life was reduced. The mean strains/stresses had l ittle influence on the cyclic stress-strain curve which exhibited cycl ic strain hardening. Mean stress effects were analyzed using the Morro w, SWT and Lorenzo-Laird models and similar, but oftentimes nonconserv ative, calculations resulted. Region I and II fatigue crack growth beh avior was determined using C(T) specimens with load ratios R = P(min)/ P(max) = 0.05 and 0.5. Values of DELTAK(th) and (DELTAK(th)eff were le ss than 1.5 MPa square-root m and the Paris equation slopes were betwe en 3.3 and 3.9. Quasi-cleavage was predominant for both fatigue crack growth and final fracture regions. The commonly used low cycle fatigue and fatigue crack growth models appear to reasonably represent most o f the results with this AZ91E-T6 cast magnesium alloy.