This study aims to elucidate the mechanical properties and fracture mechanisms of cast Mg-6Gd-3Y-0.4Zr (wt.%) (GW63) alloy in the presence of geometrical discontinuities induced by notches. Notch strength is evaluated by room-temperature tensile tests using circumferentially notched bars of different notch acuity. Finite element calculations suggest that notch fracture is controlled by the von Mises stress and effective plastic strain at the notch tip. Through fractographic observations and EBSD analysis on samples subjected to interrupted tests, a cleavage micro-cracking behavior uncommon for conventional Mg alloys is found to dominate notch fracture. Grain-sized cleavage microcracks tend to occur along the basal plane of grains favorably oriented for basal slip, which is explained by crack nucleation at co-planar slip bands blocked by the grain boundary according to Smith and Barnby's theory. Failure is initiated by the accumulation and coalescence of such microcracks in the notch vicinity. The unexpected cleavage micro-cracking behavior is mainly ascribed to the RE solutes that suppress {10–12} twinning, and is responsible for the limited deformation capacity and notch strength of the cast-T6 GW63 alloy with coarse grains and significant strengthening due to precipitation.

本研究旨在阐明铸造 Mg-6Gd-3Y-0.4Zr (wt.%) (GW63) 合金在存在由缺口引起的几何不连续性的情况下的力学性能和断裂机制。缺口强度是通过室温拉伸试验使用不同缺口锐度的圆周缺口棒来评估的。有限元计算表明，缺口断裂受 von Mises 应力和缺口尖端的有效塑性应变控制。通过断口观察和对经过断续试验的样品进行 EBSD 分析，发现传统镁合金不常见的解理微裂纹行为主导了缺口断裂。晶粒尺寸的解理微裂纹往往沿着晶粒的基面发生，有利于基面滑移，根据 Smith 和 Barnby 的理论，这可以通过晶界阻挡的共面滑移带处的裂纹成核来解释。这种微裂纹在缺口附近的累积和聚结引发了失效。意外的解理微裂纹行为主要归因于抑制 {10-12} 孪晶的 RE 溶质，并导致铸态 T6 GW63 合金的变形能力和缺口强度受到限制，晶粒粗大并因析出而显着强化.