Effect of eutectic content on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys

• Increasing eutectic content thickens intergranular liquid films, which accommodate strain during solidification and reduce hot tearing susceptibility. • Prolonged solution treatment at 475 °C reduces residual eutectic fraction from 9.1% (10 h) to 0.35% (40 h) in Al-7Zn-3.5Mg-1.18Cu alloy. • Al-6Zn-3.0Mg-1.0Cu alloy achieves optimal mechanical properties after aging at 165 °C: tensile strength of 510 MPa and elongation of 6.4%. • Excess alloying elements beyond solubility limits form coarse residual intergranular phases, severely degrading mechanical properties; optimal addition levels are crucial.