Microstructures and mechanical properties of 6061 aluminum alloy processed by accumulative roll-bonding

Accumulative roll-bonding (ARB) process is an intense plastic deformation process that has been performed for a 6061 aluminum alloy to develop ultra-fine grains below I pm. in diameter and to improve mechanical properties. The ARB process up to eight cycles is performed at ambient temperature under unlubricated conditions. The ultra-fine grains surrounded by clear boundaries begin to appear at the third cycle, and the specimen after eight cycles shows a microstructure covered with ultra-fine grains with an average diameter of 310 nm, The tensile strength of the ARB processed 6061 alloy increases with the number of ARB cycles (equivalent total strain), and after eight cycles it reaches the maximum of 363 MPa, which is about three times of the initial. On the other hand, the elongation drops abruptly at the first cycle, above which it decreases progressively with the number of ARB cycles. The hardness of the specimens ARBed by one, three and five cycles varies inhomogeneously in the thickness direction; having peak values near the surface and the center. This is due to the redundant shear strain and wire brushing. The results show that the ARB process is effective for grain refinement and strengthening of 6061 alloy. (C) 2002 Elsevier Science B.V. All rights reserved.