Unveiling the Microstructure Evolution and Mechanical Strengthening Mechanisms in Mg–2Y–xZn Alloys

TL;DR

This study explores how varying zinc content affects the microstructure and strength of magnesium alloys, revealing new insights into improving their mechanical properties.

Contribution

The paper identifies synergistic strengthening and competitive fracture mechanisms among phases in Mg–RE–Zn alloys, offering a novel design strategy.

Findings

Optimal mechanical performance is achieved at 2 at.% Zn with 239 MPa UTS and 130 MPa YS.

X-phase provides significant strengthening through coherent orientation and kink band formation.

I-phase and W-phase exhibit competitive fracture, where I-phase preferentially fractures to preserve W-phase integrity.

Abstract

This work systematically investigates the Zn-content-dependent phase evolution (1–12 at.%) and its correlation with mechanical properties in as-cast Mg–2Y–xZn alloys. A sequential phase transformation is observed with the Zn content increasing: the microstructure evolves from X-phase dominance (1–2 at.% Zn) through W-phase formation (3–6 at.% Zn) to I-phase emergence (12 at.% Zn). Optimal mechanical performance is attained in the 2 at.% Zn-containing alloy, with measured tensile properties reaching 239 MPa UTS and 130 MPa YS, while maintaining an elongation of 12.62% prior to its gradual decline at higher Zn concentrations. Crystallographic analysis shows that the most significant strengthening effect of the X-phase originates from its coherent orientation relationship with the α-Mg matrix and the development of deformation-induced kink bands. Meanwhile, fine W-phase particles embedded within the X-phase further enhance alloy performance by suppressing X-phase deformation, revealing pronounced synergistic strengthening between the two phases. Notably, although both the I-phase and W-phase act as crack initiation sites during deformation, their coexistence triggers a competitive fracture mechanism: the I-phase preferentially fractures to preserve the structural integrity of the W-phase, effectively mitigating crack propagation. These dynamic interactions of second phases during plastic deformation—synergistic strengthening and competitive fracture—provide a novel strategy and insights for designing high-performance Mg–RE–Zn alloys.

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