Microstructural evolution during ARB process of Al-0.2 mass% Sc alloy containing Al 3Sc precipitates in starting structures

Abstract

Effect of pre-existing precipitates on microstructure evolution during severe plastic deformation was studied. An Al0.2 mass%Sc alloy was aged at 300 and 400°C for having different sizes of Al 3Sc precipitates. The mean precipitate size of Al 3Sc was 3.62 and 50nm for 300 and 400°C aging, respectively. In the as-aged specimens, Al 3Sc had coherency with the Al matrix. The three kinds of specimens that were solutiontreated (ST), aged at 300°C or aged at 400°C, were then heavily deformed by the accumulative roll bonding (ARB) process up to 10 cycles (corresponding to an equivalent strain of 8.0) at room temperature. After 10 cycles of the ARB process, the specimens showed a lamellar boundary structure having the mean lamellar interval of 0.37, 0.24 and 0.27μm in the ST, 300°C Aged and 400°C Aged specimens, respectively. Additionally, the fraction of high angle grain boundaries (HAGBs) and the average misorientation between boundaries in the Aged-specimens were both higher than those in the ST specimen ARB processed to the same strain. It indicated that grain refinement during the ARB process was accelerated by the pre-existing precipitates. The reasons for the acceleration in microstructural evolution are considered to be the introduction of shear bands, the enhancement of dislocation multiplication rate and the inhibition of grain boundary migration by the precipitates in the pre-aged specimens. © 2011 The Japan Institute of Metals.