A study of fatigue damage development in extruded Mg-Gd-Y magnesium alloy

Fatigue damage development through a surface crack observation of an extruded rare-earth Mg-8.0Gd-3.0Y-0.5Zr (GW83) magnesium (Mg) alloy was experimentally studied by conducting strain-controlled tension-compression experiments along the extrusion direction. Companion specimens were tested at three strain amplitudes of 1.2%, 0.75%, and 0.5%, correspondingly. The GW83 alloy has a weak texture and displays concave-down hysteresis stress-strain loops due to the slip dominant plastic deformation for all the three strain amplitudes studied. At a higher strain amplitude, cracks are mainly initiated at the grain boundaries (GBs) and propagate predominately intergranularly. Twin boundary (TB) cracks are seldom found although a few tension twins are detected. Final fatigue failure is due to both continuous crack initiation and microcrack coalescence. When the strain amplitude is low, cracks are found to initiate at the persistent slip bands (PSBs) as well as GBs, and early crack growth is mainly transgranular. Final fatigue failure is due to continuous accumulation of distributed microcracks. During a majority of the fatigue lives at the three strain amplitudes studied, the crack initiation and early crack growth do not significantly influence the cyclic stress-strain response of the material.