Cast nickel-aluminum bronze (NAB) is specified for many marine applications due to its excellent corrosion resistance. Improved mechanical properties may be attainable using friction stir processing (FSP) to achieve localized microstructure modification in cast material, and convert an as-cast microstructure to a wrought condition in the absence of macroscopic shape change. In effect, FSP provides a means of surface hardening of castings. The complex physical metallurgy of cast NAB material will be reviewed and the effect of FSP on microstructure of an as-cast NAB material will be described.