MODELING THE MICROSTRUCTURAL CHANGES DURING HOT TANDEM ROLLING OF AA5XXX ALUMINUM-ALLOYS - PART I - MICROSTRUCTURAL EVOLUTION

A comprehensive mathematical model of the hot tandem rolling process f or aluminum alloys has been developed. Reflecting the complex thermome chanical and microstructural changes effected in the alloys during rol ling, the model incorporated heat flow, plastic deformation, kinetics of static recrystallization, final recrystallized grain size, and text ure evolution. The results of this microstructural engineering study, combining computer modeling, laboratory tests, and industrial measurem ents, are presented in three parts. In this Part I, laboratory measure ments of static recrystallization kinetics and final recrystallized gr ain size are described for AA5182 and AA5052 aluminum alloys and expre ssed quantitatively by semiempirical equations. In Part II, laboratory measurements of the texture evolution during static recrystallization are described for each of the alloys and expressed mathematically usi ng a modified form of the Avrami equation. Finally, Part III of this a rticle describes the development of an overall mathematical model for an industrial aluminum hot tandem rolling process which incorporates t he microstructure and texture equations developed and the model valida tion using industrial data. The laboratory measurements for the micros tructural evolution were carried out using industrially rolled materia l and a state-of-the-art plane strain compression tester at Alcan Inte rnational. Each sample was given a single deformation and heat treated in a salt bath at 400 degrees C for various lengths of time to effect different levels of recrystallization in the samples. The range of ho t-working conditions used for the laboratory study was chosen to repre sent conditions typically seen in industrial aluminum hot tandem rolli ng processes, i.e., deformation temperatures of 350 degrees C to 500 d egrees C, strain rates of 0.5 to 100 seconds and total strains of 0.5 to 2.0. The semiempirical equations developed indicated that both the recrystallization kinetics and the final recrystallized grain size wer e dependent on the deformation history of the material i.e., total str ain and Zener-Hollomon parameter (Z), where Z = (epsilon) over dot exp (Q(def)/RTdef) and lime ur the recrystallization temperature.