Abstract: Effect of aging on the microstructure and properties of hot-extruded Mg-8Gd-4Y-1Sm-0.5Zr (GWS841) alloy was studied by means of scanning electron microscope (SEM), transmission electron microscope (TEM), electron backscatter diffraction (EBSD), hardness test and tensile test. The results show that the hardness of the hot extruded GWS841 alloy reaches the highest after aging at 200 ℃ for 96 h, 225 ℃ for 24 h, and 250 ℃ for 12 h, respectively. The peak hardness and tensile strength reach their maximum values after aging at 200 ℃ for 96 h. During the aging process at 200 ℃, rare earth atoms first precipitate along 〈12$\bar{1}$0〉_α crystal direction in α-Mg matrix to form a single black contrast stripe, β′ phase, which is in the under aged state. As the aging time increases, the β′ phase expands along 〈10$\bar{1}$0〉_α crystal direction, and the hardness of the alloy gradually increases. After aging for 96 h, β′ phase precipitates simultaneously in the (11$\bar{2}$0)_α、($\bar{1}$2$\bar{1}$0)_α and (2$\bar{11}$0)_α crystal planes, which is in the peak aged state. After aging for 120 h, the β′ phase in the matrix grows and forms a shuttle like shape, and sub-micron β phases are generated at grain boundaries, which is in the overaged state. The tensile fracture mechanism is quasi-cleavage fracture, and the fracture structure consists of cleavage planes, tearing edges, and dimples.

Key words: Mg-8Gd-4Y-1Sm-0.5Zr alloy, aging treatment, hardness, microstructure, strengthening mechanism