Different strategies of secondary phase incorporation into metallic sheets by friction stir processing in developing surface composites

Abstract

Friction stir processing (FSP) is a solid-state processing method, which recently gained wide popularity to modify the microstructure of metallic surfaces and to produce surface composites. For the past decade, composites of different materials such as aluminum, copper, magnesium, titanium, and their alloys were successfully produced by FSP. The amount of secondary phase that is dispersed at the surface of the workpiece during FSP and the level of dispersion depend on many factors such as tool design, processing parameters, and type of material. Recently, the method of secondary phase incorporation into the surface metals was also considered as an important factor in developing surface composites by FSP. A few strategies such as groove filling, holes filling, sandwich method, direct method, and surface coating followed by FSP methods have been developed as promising ways of secondary phase incorporation into the surface of the materials during FSP. The aim of this review paper is to give a comprehensive summary of different methods developed to disperse the secondary phase into the surface of the workpiece during FSP to produce surface composites. The strategies have been explained, compared, and discussed to suggest an appropriate method based on the requirement to adopt in developing surface composites.