Synergistic Effects of High-Pressure Torsion and Heat Treatment on the Microstructure Evolution and Mechanical Properties of B4C/7075Al Composites

In this study, B₄C/7075Al composites were fabricated via high-pressure torsion (HPT) and subsequent heat treatment. The HPT process refined the average B₄C particle size to 6.89 μm and achieved a dislocation density of 7.83×10¹⁴ m^-2, while promoting uniform particle dispersion. Heat treatment further enhanced mechanical properties, with peak-aged samples exhibiting a 54% increase in hardness (223 HB) and a yield strength of 658 MPa. Key microstructural evolutions included the formation of coherent GP zones and semi-coherent η′ phases in the matrix, alongside incoherent η phases near B₄C interfaces. A critical finding was the development of a sandwich-like B₄C/Oxide/Al interface, which reduced lattice mismatch from 25.74% to 3.86–6.61%, significantly improving interfacial coherence. However, excessive Oxide layer thickness consumed solute atoms, inhibiting precipitate formation. These results demonstrate the synergistic effects of severe deformation and heat treatment in optimizing microstructure and mechanical performance, offering insights for high-strength composite design.