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<p>Magnesium alloys, as critical lightweight structural materials, exhibit crack propagation behavior that is significantly regulated by the second phase. However, the underlying atomic-scale mechanisms remain unclear. This study employs molecular dynamics simulations to establish models of pure magnesium and magnesium containing MgZn<sub>2</sub> phase magnesium matrix. The influence mechanisms of the size and angle of the second phase on the crack propagation behavior of magnesium single crystals were systematically investigated. Through analysis of stress responses, dislocation density, and the evolution of crystal structures, combined with the Orowan bypass mechanism, this study explores the formation of dislocation loops and their role in shielding at the crack tip. The results show that as second-phase size increases, the crack fracture mode transitions from shear fracture dominated by along the 45°maximum shear stress to ductile fracture characterized by interface debonding induced void nucleation at both poles of the second phase, which drives crack path deflection. When the size of the MgZn₂ phase exceeds 2.0&#xa0;nm, dislocations bypass the second phase via the Orowan mechanism, leading to a sharp increase in dislocation density. Moreover, the 90° angle significantly promotes the multiplication of basal dislocations due to its maximum Schmid factor. The MgZn₂ phase stabilizes the 1/3 &lt; 1–100 &gt; and 1/3 &lt; 1–210 &gt; dislocation loops through pinning effects, enabling their accumulation into high-density dislocation networks at crack tips. Meanwhile, they inhibit the HCP → BCC structural transformation, thereby significantly enhancing the dislocation shielding effect. The research results provide an atomic-scale solution to the persistent bottleneck of rolling edge cracks in magnesium alloys, supporting the design of high-reliability lightweight structural components.</p>

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Atomic mechanisms of MgZn2 phase effects on crack propagation and dislocation shielding in magnesium alloys

  • 期刊论文

  • 发表日期：

    2025年11月19日

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  • Min Wang,
  • Jinbao Lin,
  • Xun Chen,
  • Yihao Li,
  • Xiaohua Zheng

摘要

Magnesium alloys, as critical lightweight structural materials, exhibit crack propagation behavior that is significantly regulated by the second phase. However, the underlying atomic-scale mechanisms remain unclear. This study employs molecular dynamics simulations to establish models of pure magnesium and magnesium containing MgZn2 phase magnesium matrix. The influence mechanisms of the size and angle of the second phase on the crack propagation behavior of magnesium single crystals were systematically investigated. Through analysis of stress responses, dislocation density, and the evolution of crystal structures, combined with the Orowan bypass mechanism, this study explores the formation of dislocation loops and their role in shielding at the crack tip. The results show that as second-phase size increases, the crack fracture mode transitions from shear fracture dominated by along the 45°maximum shear stress to ductile fracture characterized by interface debonding induced void nucleation at both poles of the second phase, which drives crack path deflection. When the size of the MgZn₂ phase exceeds 2.0 nm, dislocations bypass the second phase via the Orowan mechanism, leading to a sharp increase in dislocation density. Moreover, the 90° angle significantly promotes the multiplication of basal dislocations due to its maximum Schmid factor. The MgZn₂ phase stabilizes the 1/3 < 1–100 > and 1/3 < 1–210 > dislocation loops through pinning effects, enabling their accumulation into high-density dislocation networks at crack tips. Meanwhile, they inhibit the HCP → BCC structural transformation, thereby significantly enhancing the dislocation shielding effect. The research results provide an atomic-scale solution to the persistent bottleneck of rolling edge cracks in magnesium alloys, supporting the design of high-reliability lightweight structural components.