Creep behavior of Mg–9Gd–1Y–0.5Zr (wt.%) alloy piston by squeeze casting

The Mg–9Gd–1Y–0.5Zr (wt.%) alloy piston was produced by squeeze casting and further heat treated to peak-aged state. The tensile-creep behavior of the specimens taken from the piston top was investigated at temperatures of 200–300 °C (0.54–0.66Tm) and applied stresses of 50–120 MPa. The creep resistance decreases with increasing temperature and applied stress. When tested at 200 °C and 50 MPa, the specimen has a steady-state creep rate of 0.4 × 10− 9 s− 1 and creep strain of 0.014% after 100 h. The creep stress exponent and the activation energy are 1.66–4.47 and 115.9–174.2 kJ/mol, respectively, implying that dislocation creep is the rate-controlling mechanism. At 50–80 MPa the activation energy for creep indicates that dislocation climb is the creep mechanism. At 120 MPa the relatively high activation energy may be associated with the operation of cross slip. After test, the thermal stable β phase appears and its volume fraction increases with testing temperature. The steady-state creep rate and rupture time are modeled by the original and modified Monkman–Grant relationships. The microcracks and cavities preferentially nucleate at the grain boundaries, especially at triple points. Brittle rupture with few plastic tearing ridges is the dominant character of the creep fracture.