Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism

The effects of Sm on the microstructure and mechanical properties of Mg-11Gd-2Y-0.6Al alloy were investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, energy dispersive spectrometry and high resolution transmission electron microscopy. Based on the theory of edge-edge matching and electronegativity theory, the mechanism of grain refinement is discussed. The strengthening mechanism is expounded conveniently from fine grain strengthening, coherent strengthening, precipitation strengthening and grain boundary strengthening. The results show that the microstructure of Mg-11Gd-2Y-0.6Al alloy is mainly composed of alpha-Mg matrix, Mg5Gd and Mg24Y5 phases. The addition of Sm forms Mg41Sm5 phase in the alloy and refines the alloy. The addition of Sm significantly improves the mechanical properties of the alloy at room and high temperatures. When the addition of Sm is 3 wt%, the tensile strengths of the alloy at room temperature and high temperature (200 degrees C) reach the maximum value 292 and 321 MPa, respectively. The fracture mode of the alloy at different temperatures is mainly brittle fracture and intercrystalline fracture. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.