High cycle fatigue properties of die-cast magnesium alloy AZ91D-1%MM

The high cycle fatigue properties of the die-cast magnesium alloy AZ91D containing 1% mischmetal (mass fraction) at a fatigue ratio of 0.1 were investigated. The difference in the microstructure between the skin and core region of the die-cast magnesium alloy was analyzed by optical microscopy. The mechanical property tests indicate that the values of the tensile strength, elongation and hardness are 185 MPa, 1.5% and HBS 70 +/- 3 at room temperature, respectively. The p-S-N curve (p=50%) of the die-cast magnesium alloy AZ91D-1%MM is determined and the mean fatigue strength corresponding to 3.8 X 10(5) cycles is 70 MPa. A linear relation between S and N-p in log scale between 10(3) and 10(6) cycles is written with a equation. The mechanical properties are influenced by the casting defects. The fatigue life of the samples with minor defects is near to the upper limit of the fatigue life data. The fatigue fracture surface of the samples with minor defects possesses the mixed characteristics of quasi-cleavage, lacerated ridge and dimple and it is brittle fracture mode as a whole.