An investigation into microstructural evolution during processing and superplastic deformation of an Al-10Mg-0.1Zr alloy was conducted. Processing schedules were modified to enhance particle-stimulated nucleation of recrystallization and refine subsequent gain size. Strain rates varying over three orders of magnitude were utilized in subsequent testing of processed material. At lower strain rates of about 10-4 sec-1 coarsening of the microstructure was apparent and elongations of 277% were obtained. A strain rate of 10-3 sec-1 resulted in lesser coarsening and elongations of 650%. A model of deformation by grain boundary sliding in association with microstructural coarsening is presented.