Uniaxial Ratcheting of Extruded Mg-10Gd-3Y Alloy under Stress-Controlled Cyclic Tension

Uniaxial ratcheting behavior of an extruded Mg-10Gd-3Y rare-earth magnesium alloy was studied by performing stress-controlled cyclic tension experiments in ambient air. The effects of mean stress and stress amplitude on the ratcheting response and the ratcheting lifetime were explored. As the mean stress or the stress amplitude was increased, the ratcheting strain multiplied, whereas the ratcheting lifetime was shortened. Compared to the conventional Mg alloys, the addition of rare-earth elements suppressed the twinning/de-twinning events and restricted the development of ratcheting strain. In addition, dynamic precipitations were developed during the ratcheting deformation of the Mg-10Gd-3Y alloy at room temperature. This cyclic stress-induced dynamic precipitation is thought to play a critical role in the strong cyclic hardening exhibited during the ratcheting deformation of the Mg-10Gd-3Y alloy. A modified fatigue parameter, which takes account for both the effects of mean stress and stress amplitude, was proposed to well predict the ratcheting lifetime of the Mg-10Gd-3Y alloy.