The Evaluation of Strain, Microstructural Aspects and Some Mechanical Properties of Nano-Grained Aluminum Processed by Accumulative Roll Bonding Using 2, 3 and 4 Initial Strips

The main objective of the paper is to present the refinement of grains when aluminum strips are exposed to Severe Plastic Deformation (SPD) by Accumulative Roll-Bonding (ARB). Also, the relationship between nano-grain size and the increase of some mechanical characteristics (yield stress, tensile strength) is investigated. The work presents a theoretical analysis of ARB process taking into account the effect of the initial number of strips stacked before rolling on the strain evolution. We proposed the ARB process analysis when the number of strips initially stacked is 2, 3 and 4 and the initial thickness of each strip before rolling is equal with the thickness of the laminated strip, so the thickness of initial strip is a multiple of thickness resulting from rolling. It is obvious that in the case of rolling with a multilayer initial stacked, each layer will be deformed with a bigger strain, so the bond will be realised easier, at lower working temperature and the grain refinement will be achieved by a smaller number of passes. For each case (2, 3 and 4 initial layers) the engineer and equivalent (von Mises) strain are calculated. From this analysis results that increasing the number of strips initially stacked increases the total strain and the grain size from the laminated strip achieve submicronic values after a smaller pass number. The micro-structural investigations, made with Atomic Force Microscope (AFM), show that nanometric grain appear at 5–6 equivalent strain for 2 initial stacked strips and at 3–4 equivalent strain for 4 initial stacked strips. The stress – strain curves for each case and evolution of yield stress, tensile strength and micro-hardness with the number of passes are presented.