The effect of precipitates on the fracture behavior and tensile properties of Mg–14Gd–0.5Zr (wt.%) alloy

The effect of precipitation aging on the fracture behavior of cast Mg–14.23Gd–0.45Zr (wt.%) alloy at room temperature has been studied in this work. Uniaxial tensile and three-point bending tests were conducted on samples peak-aged at 175, 200, 225, and 250 ℃. Notably, samples aged at 175 ℃ and 200 ℃ exhibited premature fracture during the uniaxial tensile test. Through fractographic observations of the tensile test samples and electron backscattered diffraction (EBSD) analysis on the samples subjected to three-point bending tests, a preferential formation of cleavage cracks in samples aged at 175 ℃ and 200 ℃ was identified as the reason for their premature fracture. The X-ray diffraction (XRD) results and transmission electron microscopy (TEM) observations of precipitates indicate that the dominant strengthening precipitates in all peak-aged samples are of the β' phase, and their size significantly influences the formation of cleavage cracks. This phenomenon is attributed to the shearing mechanism of precipitates. Specifically, the smaller β' precipitates formed under the aging temperature of 175–200 ℃ are susceptible to dislocation shearing, leading to the formation of cleavage cracks. In contrast, the larger size of β' precipitates formed under the aging temperature of 225–250 ℃ provides resistance to shearing, resulting in the restrained formation of cleavage cracks and ultimately contributing to the enhancement of the ultimate tensile strength.