• Multidirectional forging (MDF) for six passes effectively refines α-Al grains and improves TiB2 particle distribution in in-situ TiB2/Al–Cu composites.
• Grain refinement is driven by mechanical fragmentation and dynamic recrystallization, including discontinuous, continuous, and particle-stimulated nucleation mechanisms.
• MDF significantly enhances tensile properties: ultimate tensile strength and yield strength increase by 51.2% and 54%, respectively, compared to as-cast composites.
• The strengthening is primarily attributed to grain refinement and dislocation strengthening, offering a scalable approach for high-performance aluminum matrix composites.