Hot and cold regions during accumulative roll bonding of Al/Al2O3 nanofibre composites

Abstract

Accumulative roll bonding (ARB) is a severe plastic deformation process invented in order to fabricate ultrafine- grained (UFG) materials. Having sub-micrometre sized or nano grains UFG materials generally have considerably higher strength than conventional materials with grains at micrometre length scale. Further increase in mechanical properties could be achieved by reinforcing UFG materials with nanoparticles or nanofibres. In this work two metal sheets were roll bonded to each other by inducing plastic deformation via the ARB process. The plates were then cut into two, stacked, and rolled again. Rolling was repeated multiple times. Observations and measurements were made in the hot and cold regions of the plate. In this study the aluminium matrix was reinforced with aligned and non-aligned Al2O3 nanofibres. The morphology of the reinforcement-matrix interphase and mechanical properties of the composites were studied. The microstructure of the material was investigated using scanning electron microscopy accompanied with quantitative microstructure analysis. It was demonstrated that the plastic deformation in the first cycle due to broken Al2O3 nanofibres continued in the second cycle. The Al2O3 nanofibres were embedded in the aluminium matrix surface area to improve the mechanical properties during the multiple cycle ARB process. In the cold regions micro-defects such as porosity and cracks were observed while in the hot regions no such defects were detected.