The effect of cold rolling and annealing on the serrated yielding phenomenon of AA5182 aluminum alloy

Industrially produced DC AA5182 was cold-rolled to different reductions, and then annealed at 589K for 3h. The annealed and the cold-rolled samples were further heat-treated at 455 K for 100 h. Serration behavior during each stage of the process was investigated. It was found that a decrease in the grain size of recrystallized material results in an increase in both Luders elongation and serration frequency or the number of serrations within a fixed strain range. For differently treated materials, serration behavior is different. In the completely recrystallized materials, serration intensity is initially low and increases in magnitude with increase in strain. The increase is fast at first, then the rate of increase decreases until the magnitude becomes a plateau. For cold-rolled and recovered materials, serration starts abruptly and is high in magnitude when it first appears. For highly cold-rolled materials this behavior is more obvious and the magnitude is almost a constant during the whole serration process for the 80 and 90% cold-rolled materials. Both the dislocation density and Mg concentration in solid solution have an effect on serrated yielding and a decrease of each or both results in a decrease of the intensity of serrated yielding. Negative strain rate sensitivity is manifested with an increase in the ultimate tensile strength (UTS) when the strain rate decreases. The tensile elongation does not follow commonly accepted behavior and displays an increase when the serration intensity is most intense. (C) 2004 Elsevier B.V. All rights reserved.