Microstructures and mechanical properties of Aluminum matrix / Carbon Nanotubes (CNTs) reinforced composites produced through Accumulative Roll Bonding (ARB) or Cross Accumulative Roll Bonding (CARB)

The microstructural aspects and the mechanical properties of Aluminum matrix AA1200 / CNTs (Carbon Nanotubes) reinforced metal matrix composites (MMCs), obtained through Accumulative Roll Bonding (ARB) or Cross Accumulative Roll Bonding (CARB), were analyzed. Six ARB/CARB cycles were applied to the material, with and without the introduction of CNTs reinforcements. All produced specimens displayed remarkable increases in their tensile strength in relation to the strength of the annealed Aluminum sheets. CARB led to a higher strength than ARB for materials without CNTs, but the opposite was observed when CNTs were added. CNTs accelerated Dynamic recovery (DRV) processes especially during CARB. The size of subgrains/cells bounded by High Angle Grain boundaries (HAGBs) was similar for both CARB + CNTs and ARB + CNTs and it was considered that the strength of both materials is controlled by the fraction of High Angle Grain boundaries (HAGBs). This fraction was higher after ARB + CNTs than after CARB + CNTs processing; without CNTs, this situation was inverted. This was directly reflected in the strength of the material. The addition of CNTs in both ARB and CARB led to a marked lowering of the uniform tensile elongation in relation to material manufactured without CNTs. The fracture surface analysis revealed decohesions between the individual sheet layers and the presence of ductile dimples where such decohesions did not occur. The thin unbonded individual sheets undergo lower elongation than the thicker bonded regions and thus the bulk material elongation is partly controlled by the fraction of unbonded material layers, which in turn depends on the processing variables during ARB and CARB.