Development of Ultra High Strength and Nanocrystalline Materials by Accumulative Roll Bonding

Abstract

First developed by Saito et al., Accumulative Roll Bonding (ARB) process, is gaining popularity as one of the most promising methods of producing super metals (metals having ultra fine grains <1μm diameter) due to its many advantages including dimensional stability and an increase in strength of up to 200%. Commercially pure Aluminium sheets were heated at 2000C for 15 minutes, rolled for 50% reduction, then cut into two halves, joined together and, then rolled again for 50% reduction. Due to this, the thickness of individual layer decreased with each pass and a final reduction of 99.17% in thickness was achieved. The microhardness of the sheets tested in plane perpendicular to rolling direction showed an increase of 173% in the hardness. The SEM photographs showed the grain size decreasing from 20μm to 0.03μm. The non-destructive tensile tests showed that ductility decreased from 99.2% to 8.3% with increasing number of ARB passes. One peculiar observation was the decrease in the hardness for 99.17% reduction as compared to 96.67%.