MICRO-HARDNESS EVOLUTION OF Al-ALLOY AA 3004, PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING

Abstract

Equal Channel Angular Pressing (ECAP) is a very interesting method for modifying the microstructure in producing materials with ultrafine grain in sub-micrometer or nanometre range. Experiments demonstrate that these ultrafine structures may exhibit, by comparison with large - grained polycrystals, major differences in some fundamental properties. A nanostructured AA 3004 alloy was used to investigate the evolution of microhardness and microstructure on the cross-sectional plane X, after processing by ECAP at room temperature for up to six passes. The measurements show the average microhardness increases significantly after two passes with additional increases in subsequent passes. Microhardness values increase by more than two times after 6 passes. There is a reduction in grain size from of ~ 50μm in the initial condition to ~ 12 μm after 6 passes. The results also show that the microstructure and the microhardness evolve with increasing strain so that, after a total of 6 passes, the structure is almost homogenous throughout the cross-sectional plane of the billet.