Effect of grain size distribution on mechanical properties of ultrafine grained Al severely deformed by ARB process and subsequently annealed

A commercial purity aluminum was highly deformed by the accumulative roll-bonding (ARB) process and subsequently annealed. The specimens having various grain size distributions were obtained. In case of the specimen ARB-processed with lubrication, the specimens with mean grain size larger than 3μm showed continuous yielding. On the other hand, in case of the specimen ARB-processed without lubrication, the specimens with mean grain size larger than 3μm showed discontinuous yielding. It suggests that appearance of the yield-drop phenomena can not be decided by the mean grain size. In order to consider effect of grain size distribution, the volume fraction of grains was summed from coarser grains, and the grain size when the summed volume fraction reached 70%, d 70% was estimated from the grain size distribution. it was found that d 70% of specimens which showed continuous yielding were larger than 8 μm while the specimens which showed discontinuous yielding were smaller than 6 μm, regardless of the lubrication condition in the ARB process. The result suggests that the appearance of the yield-drop phenomena depend on d 70% .