High damping capacity of ultra-fine grained aluminum produced by accumulative roll bonding

Abstract

Accumulative rolling bonding (ARB) is a kind of severe plastic deformation process which can produce high strength metals with ultrafine (sub-micron) grained microstructure. Metals produced by this process are also expected to show excellent damping capacity since they contain significant amounts of lattice defects which give rise to internal friction. We examined the damping capacity of high purity (99.99% Al) and commercial purity (99% Al) aluminum sheets ARB processed to an equivalent strain of 4. Internal friction values ( Q −1) of the 99.99% Al and the 99% Al were as high as 12×10 −3 and 6×10 −3, respectively. Microstructures were observed to clarify the damping mechanism. The mean grain thickness of the pancake-like shaped ultrafine grains were 640 and 250 nm in 99.99% Al and 99% Al, respectively. A significant amount of dislocations was observed within the ultrafine grains in both of the ARB-processed aluminum sheets. The high damping capacity was attributed to vibration of the dislocations whose ends were tightly bound with the grain boundaries.