PRECIPITATION AND RECRYSTALLIZATION DURING PROCESSING OF A SUPERPLASTIC AL-10MG-0.1ZR ALLOY

Microstructural evolution during thermomechanical processing (TMP) of a superplastic Al-10Mg-0.1Zr (weight per cent) alloy was studied. The TMP was carried out at 300-degrees-C and consisted of 12 rolling passe s corresponding to a total strain of 2.5. Superplastic elongations at 300-degrees-C exceeded 1 000% for an optimum processing schedule invol ving a 30 min interpass anneal (IPA) time. Precipitation of the interm etallic beta-phase (Al8Mg5) was complete at an accumulated strain of 1 .5 and the precipitate particle size and size distribution were found to be nearly constant for the remainder of the TMP. Particle stimulate d nucleation (PSN) of recrystallization associated with prolonged IPA times accounted for the grain refinement necessary to support superpla stic deformation. A model for PSN is applied to the data.