The effect of Zn content on tensile properties and fracture toughness of Al–Zn–Mg–Cu alloy

The trade-off between strength and fracture toughness in metallic alloys remains a longstanding challenge. This study investigates the effect of Zn content on the mechanical properties and fracture behavior of Al–Zn–Mg–Cu alloys. Increasing Zn content enhances yield and tensile strength due to precipitate strengthening, driven by increased η′ precipitate density. However, this improvement in strength is accompanied by reduced fracture toughness, as higher Zn content decreases the plastic zone size and promotes crack propagation. The high dislocation density induced by η′ precipitates contributes to this by creating a driving force for crack propagation, further influenced by the strain field generated by fine precipitates. These findings underscore the critical role of Zn content in managing the strength-toughness trade-off, offering insights for optimizing the mechanical performance of Al–Zn–Mg–Cu alloys.