Effects of B₄C content on the microstructure and mechanical properties of B₄C/7075Al composites fabricated by...

Conventional stir-cast B₄C-reinforced aluminum matrix composites, especially those with high B₄C contents and 7xxx series matrices, suffer from poor wettability, particle agglomeration, pore formation, detrimental interfacial reactions, and a severe strength-ductility trade-off, while a systematic understanding of how reinforcement content affects microstructure and properties is still lacking. In this work, B₄C/7075Al composites with 10-40 vol% B₄C were fabricated by semi-solid stir casting combined with B₄C preheating and rapid casting, and the influence of B₄C volume fraction on the microstructure, interface characteristics, and mechanical properties was systematically investigated. The results show that preheating eliminates free carbon impurities and suppresses the formation of brittle Al-B-C reaction products, leading to clean interfaces with only a nanoscale Mg-O-enriched transition zone and short-range semi-coherent B₄C/Al interfaces. Both hardness and tensile strength increase with rising B₄C content, while elongation gradually decreases. The composite with 20 vol% B₄C exhibits the best strength-ductility balance, achieving a Vickers hardness of 258.2 ± 6.4 HV, an ultimate tensile strength of 418 MPa, and an elongation of 5.6%. These findings provide practical guidance for tailoring the microstructure and optimizing the properties of high-volume-fraction B₄C/7075Al composites.