Papers by Author: J.S. Ha

Abstract: Coarse grains of commercial 5052 Al and 5083 Al alloys were refined by the accumulative roll bonding (ARB) process. Average grain size of the refined microstructure was 200 nm. The 5083 Al alloy that has higher Mg content required more deformation for the refinement. Dry sliding wear behavior of the ultra-fine grained (UFG) Al alloys was investigated using a pin-on-disk wear tester at room temperature. The UFG microstructure of the processed alloys hardly increased the wear resistance of the Al alloys in spite of the increased strength and hardness. Wear rate of the UFG Al alloys was higher than that of the non processed coarse-grained starting alloys. The SEM observation of worn surfaces revealed that surface deformation controlled the wear. The low wear resistance of the UFG Al alloys was attributed to non-equilibrium and unstable grain boundaries and low strain hardening capability of the alloys.

Abstract: Dry-sliding-wear behavior of ultra-fine grained 6061 Al alloy and AZ61 Mg alloy was investigated. The accumulative roll bonding (ARB) and the equal channel angular pressing (ECAP) processes were employed to obtain refined microstructures in the Al and Mg alloys, respectively. Pin-on-disk wear tests of the processed alloys were carried out with various applied load against a 304 stainless steel counterpart. In spite of the increased hardness and strength, wear resistance of the ultra-fine grained 6061 Al alloy was lower than that of the coarse-grained starting alloy. The strength and wear resistance of the ECAP processed AZ61 Mg alloy did not change appreciably despite the refined microstructure. Recrystallization was found to occur during the ECAP process of the Mg alloy. Worn surfaces and cross-sections of the wear-tested specimens were examined to investigate the wear mechanism of the ultra-fine grained Al and Mg alloys.