Mesoscopic origin of damage nucleation of Mg-RE-Zn alloys containing LPSO phase

Abstract

The role of the long-period stacking order (LPSO) phase in damage initiation within magnesium alloys remains inadequately understood. This study investigates the influence of the LPSO phase on damage nucleation and toughness in Mg-RE-Zn alloys, utilizing in-situ tensile testing combined with scanning electron microscopy and digital image correlation (SEM-DIC) to capture mesoscale strain distribution. Results identify the incoherent α-Mg/LPSO interface as the primary site of damage due to its inherent weakness. Damage nucleation is driven by strain gradients resulting from strain localization, which is governed by the strain compatibility factor (m_k value) and associated with high local stress from dislocation accumulation. Secondary damage occurs within LPSO blocks, where their higher elastic modulus prevents stress relief through plastic deformation. Thermo-mechanical processing offers strategies to mitigate these issues by enhancing intergranular strain compatibility (increasing m_k values through grain orientation adjustments) and refining LPSO blocks to improve dispersion strengthening. These measures help counteract the reduction in plasticity caused by damage at the α-Mg/LPSO interface. Furthermore, the main damage nucleation model provides a predictive framework for identifying potential decohesion sites at incoherent α-Mg/LPSO interfaces based on m_k values and grain orientation.