Effects of hot rolling deformation on the microstructure and tensile properties of an in situ-generated ZrB2 nanoparticle-reinforced AA6111 composite

In this study, an in situ-generated ZrB2 nanoparticle-reinforced AA6111 composite was hot rolled to different reduction ratios in the range from 65% to 95% and characterized to observe the microstructural evolution associated with the different rolling states. With increasing rolling reduction, smaller clusters that consisted of many finer spherical ZrB2 nanoparticles were uniformly distributed along the rolling direction (RD). In addition, the uniform distribution and smaller ZrB2 particle accelerated the dynamic recrystallization (DRX) process to further refine the dynamically recrystallized (DRXed) grains. During the hot rolling process, the tensile properties increased with increasing reduction ratio. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation (El) increased to 356 MPa, 289 MPa and 28.1%, respectively, due to the uniform distribution of the particle clusters, the smaller size of the nanoparticles, and the refinement of the DRXed grains upon increasing the rolling reduction to 80%, in combination with T4 heat treatment and artificial ageing. In addition, the mechanisms of particle dispersion, recrystallization grain refinement and strengthening are also discussed.