• Extending furnace cooling time after solution treatment from 240 to 540 min increased impact toughness from 22.7 to 53.8 J/cm² by modifying αp lamella content and αs phase.
• Raising aging temperature from 500 to 700°C reduced αs phase content and increased αp lamella/αs thickness, significantly improving impact toughness.
• High αp lamellae content or large αs phase size leads to higher crack initiation and propagation energies.
• Severe kinking of αp lamellae and multidirectional arrangement of α colonies deflect crack propagation, enhancing plastic deformation coordination and uniformity.