friction stir welding/processing of metals and alloys

There is a growing interest in friction stir welding/processing (fsw/p) of metals and alloys because they have capacities to overcome some problems of the conventional fusion welding processes such as large distortions, solidification cracking, macro and micro segregations, dendritic structures, gas and shrinkage porosities, solid inclusions, color change, formation of brittle intermetallics between dissimilar materials, wide heat affected zone (haz), high energy consumption, environmental pollution, etc. on the other hand, it causes grain refinement by various deformation and restoration mechanisms due to the presence of both strain and heat. accordingly, efforts are underway to replace conventional fusion processes by fsw/p in different industrial sectors with great potential. therefore, studying the microstructural aspects of fswed/ped metals and alloys is essential to understanding the fundamentals of the processes, materials behavior, and associated properties. this presentation addresses recent research that has led to important advances in the field of microstructural evolution during fsw/p. it commences with a summary of the plausible microstructural mechanisms during fsw/p of metals and alloys and the method for texture analysis. we then provide a concise discussion of the most exciting new achievements, cutting-edge research topics, as well as some debatable issues in this field. the microstructural evolution during fsw of the metals and alloys is reviewed, including various ferrous and non-ferrous alloys. the influences of material compositions and fsw parameters on the evolution of microstructures and associated mechanisms are critically reviewed. recent results on the influence of fsw processes on the microstructure of dissimilar material combinations are also presented. finally, the article covers the microstructural evolution during fsp. particularly, the surface modification of wrought alloys, cast alloys, and metal matrix composites (mmcs) via fsp are discussed. moreover, the state-of-the-art in various mmcs produced by fsp is highlighted. the presentation outlines past and present trends in the field, summarizes apparent knowledge gaps, and discusses future developments/research directions in the field. it aims to build on the platform established by mishra and ma [1] and heidarzadeh et al. [2] to draw together our current understanding of, and gain a new perspective on, microstructural evolution during fsw/p. it will be of value for both beginners and experienced engineers and scientists interested in understanding the fundamentals of the microstructural evolution during fsw/fsp, and thus help to further improve and control the properties of assemblies and different metals and alloys.