Effects of alloy modification and thermomechanical processing on recrystallization of Al-Mg-Mn alloys

The 5083 Al alloy (A1-4.75Mg-0.8Mn) holds potential for superplastic forming (SPF), but slow rates of forming limit its use for many applications. Higher strain rates are believed possible through the development of finer grained microstructures or stabilized subgrain structures. Grain sizes after recrystallization and recrystallization characteristics are known to be dependent on the amount and distribution of second-phase particles in the matrix. In this study, the concentration and sizes of such particles were varied by additions of particle-forming elements of Mn and Zr and by modifications of the rolling and aging schedules (thermomechanical processing (TMP)). The investigation involved studying recrystallization kinetics at different temperatures and correlating the grain sizes with particle sizes and volume fractions. The addition of Mn and Zr, for the composition ranges and TMP methods studied, resulted in a substantial reduction of the recrystallization kinetics, but complete suppression of static recrystallization (or subgrain stabilization) was not observed. However, statically recrystallized grain sizes as small as 6 mu m were achieved.