Evolution of microstructure and mechanical properties of graphene nanoplates and ZrB2 nanoparticles reinforced AA6111 composites during hot rolling deformation

Abstract

Hot rolling deformation as a hot working process is commonly used to simultaneously improve the strength and toughness of aluminum matrix composites, owing to the excitation of the equiaxed recrystallized structure and the optimization of the distribution of the reinforcements. Therefore, the AA6111 composites reinforced by graphene nanoplates (GNPs) and in-situ ZrB 2 nanoparticles were prepared with the melt stirring casting technology and hot rolling. The evolution of the microstructure was characterized by electron backscatter diffraction (EBSD) technology. The results show that the clusters of GNPs and ZrB 2 particles were smaller and the grains were refined with the composites deformed from 75% to 92%. Besides, the textures of aluminum grains were transformed from simple to complex. The dynamic recrystallization (DRX) mechanisms of α-Al grains were explored through high-resolution transmission electron microscopes (HRTEM). It was found that the DRX was discovered to be caused by three dynamic recrystallization mechanisms: grain boundary bulging nucleation, mechanical fragmentation, and subgrain boundary coarsening. The role of ZrB 2 nanoparticles and GNPs for DRX revealed that GNPs and particle clusters have the combined effects of both promotion (larger than 1 µm) and hindering (smaller than 1 µm) on dynamic recrystallization. The strength of the composites was improved from 398 to 442 MPa by hot rolling deformation from 75% to 92%, and the elongation remained above 10%. The strengthening mechanism of the composites with increasing deformation was analyzed, providing a theoretical basis for the hot rolling deformation strengthening nanoparticles and GNPs reinforced aluminum matrix composites. • The Cu-GNPs and in situ ZrB2 nanoparticles synergistically reinforced composites. • The evolution of the size, orientation, and texture of α-Al grains was characterized. • Hot rolling deformation reduces the interlayer spacing and clusters of reinforcements. • Three dynamic recrystallization mechanisms of α-Al grains were analyzed. • The GNPs and particle clusters of different sizes can promote or hinder DRX.