Mechanical Behavior and Failure Mechanism of an As-Extruded Mg–11wt%Y Alloy at Elevated Temperature

Through carrying out the high-temperature tensile experiments on an as-extruded Mg–11wt%Y alloy at 350 °C, 400 °C, 450 °C, 500 °C and 550 °C, the mechanical behavior and fracture mechanisms at elevated temperatures are investigated and compared. Tensile results show that with the increase of temperature, the yield strength and ultimate tensile strength of the alloy increase at first and then decrease, while that the elongation ratio decreases firstly and then increases. For the sample being tested at 350 °C, the values of yield strength, ultimate tensile strength and the elongation ratio are 188 MPa, 266 MPa and 11%, respectively. At 400 °C, the yield strength and ultimate tensile strength reach the maximum values of, respectively, 198 MPa and 277 MPa, but the elongation ratio is the lowest and its value is only 8%. When the applied temperature is increased to 550 °C, the values of yield strength and ultimate tensile strength, respectively, decrease to 140 MPa and 192 MPa and the elongation ratio increases to 38%. Failure analysis demonstrates that the fracture surfaces of different samples are mainly composed of plastic dimples and exhibit the typical characteristic of ductile fracture. The observation to the fracture side surfaces indicates that at the temperatures of 350 °C and 400 °C, microcracks mainly initiate in the interior of Mg₂₄Y₅ particles. When the temperatures are 450 °C, 500 °C and 550 °C, the cracks preferentially initiate at the Mg₂₄Y₅/α-Mg interfaces.