Effect of rare earth elements on high cycle fatigue behavior of AZ91 alloy

This article investigates effects of adding rare earth elements (RE) into a magnesium-aluminum-zinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of −1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al11RE3 intermetallic particles which is associated to the reduction of β-(Mg17Al12) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (S-N) shows an increase in the fatigue strength at 105 cycles, from 100±10 MPa to 135±10 MPa, when RE elements were added to the AZ91 alloy.