Friction stir processing (FSP) is a severe plastic deformation (SPD) method that has been applied to as-cast NW bronze (NAB) materials, which are widely used for marine components. The thermomechanical cycle of FSP results in homogenization and refinements and the selective conversion of microstructures from a cast to a wrought condition. The physical metallurgy of NAB is complex and interpretation of the effects of FSP on microstructure has required detailed analysis by optical and electron microscopy methods. Annealing and isothermal hot rolling have been employed to confirm microstructure-based estimates of stir-zone peak temperatures. The variation of mechanical properties was assessed by use of miniature tensile samples and correlated with microstructure for samples from stir zones of single and multi-pass FSP. Exceptional improvement in strength - ductility combinations may be achieved by FSP of NAB materials.