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 degrees C, 400 degrees C, 450 degrees C, 500 degrees C and 550 degrees 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 degrees C, the values of yield strength, ultimate tensile strength and the elongation ratio are 188 MPa, 266 MPa and 11%, respectively. At 400 degrees 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 degrees 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 degrees C and 400 degrees C, microcracks mainly initiate in the interior of Mg24Y5 particles. When the temperatures are 450 degrees C, 500 degrees C and 550 degrees C, the cracks preferentially initiate at the Mg24Y5/alpha-Mg interfaces.