Structural evolution and precipitation behavior of titanium diboride-reinforced 7075Al composites during multi-pass rolling

Abstract

In this study, titanium diboride (TiB₂)-reinforced 7075Al matrix composites with a bimodal structure were prepared by spark plasma sintering combined with multi-pass rolling. Structural evolution and precipitation behavior of interfacial micro-zones during multi-pass rolling were systematically studied. The results showed well bonding of the TiB₂/Al interfaces within sintered and rolled composites. After 50 % rolling deformation, the interfacial micro-zones mainly consisted of precipitated η′ and coarse η phases. The combined effect of mismatch dislocations, strain differences, and solute-rich atomic regions at the semi-coherent TiB₂/Al interface promoted local precipitation behavior of interfacial micro-zones during rolling, causing the density of the precipitated phases in the interfacial micro-zones to be higher than that in the matrix region. With the increase in rolling deformation, the strain in the interfacial micro-zone and the thickness of the solute-rich atomic region decreased continuously, while the density and homogeneity of the precipitated phases increased simultaneously. The composites exhibited bimodal structural features with the highest back stress and geometrically necessary dislocation density after 85 % deformation in multi-pass rolling, and the generation of bimodal structures was primarily related to the competition between the driving force of strain storage energy for grain growth and the inhibiting force of TiB₂ on grain boundary migration.