Abstract: The present invention provides a simple, cost effective and hassle-free method and apparatus for modifying the surface grain structure of the material, thereby providing a material with multi-modal grain structure having high strength and good formability. The present invention uses a single step processing technique known as submerged static friction stir processing for modifying the surface grain structure of the material, thereby generating a multi-modal grain structure. In the present invention since the working material is completely immersed in the coolant, this maintains the working temperature of the system. Further the present invention does not involve long processing steps and do not need any specialized equipments.