Notch strength and notch fracture mechanisms of a cast Mg-Gd-Y alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-02, Vol.835, p.142668, Article 142668
• Main Authors: Wei, J.X., Yan, H., Chen, R.S.
• Format: Article
• Language: English
• Subjects: Acuity; Alloys; Band theory; Basal plane; Cleavage; Crack initiation; Cracking (fracturing); EBSD; Edge dislocations; Finite element analysis; Fracture; Fracture mechanics; Gadolinium; Grain boundaries; Magnesium alloy; Magnesium base alloys; Mechanical properties; Microcracks; Notch strength; Notches; Nucleation; Plastic deformation; Room temperature; Tensile tests
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.142668

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. •Notch strength is controlled by plastic strain and von Mises stress.•Cleavage microcracks are initiated by incompatible basal slip.•Initiation of slip-induced cleavage microcracks dominates notch fracture.•Cleavage cracking leads to limited strength properties.