On the occurrence of Portevin-Le Chêtelier instabilities in ultrafine-grained 5083 aluminum alloys

Abstract

The Portevin-Le Chêtelier (PLC) instability is commonly observed in Al-Mg alloys and is manifested in serrated flow within the stress-strain response. We investigate the persistence of this instability with reduction in grain size by studying an ultrafine-grained (ufg) aluminum alloy (Al5083) and a conventional grain size Al5083. Micro-scale tensile tests combined with digital image correlation (DIC) reveal strength anisotropy and heterogeneity of the deformation in the three material directions (extrusion, rolled, and transverse). For the same applied displacement rate, the PLC effect in ufg-Al5083 is observed only over a small strain range immediately following the yield, while the coarse-grained Al5083 exhibits serrated flow over nearly the entire plastic strain range. These observations are explained using the stability analysis of Hähner (Acta Mater 45:3695-3707, 1997), and implications for nanocrystalline (nc) alloys are discussed. © Society for Experimental Mechanics 2009.