Microstructure Formation Mechanism in a Composite Material during Friction Stir Welding of Dissimilar Components

Abstract—The problem of joint formation during friction treatment of composite materials based on immiscible components (ICs) is considered. The role of adiabatic shear bands (ASBs) in the interaction with the elements forming a composite material is demonstrated. The effects of heavy low-melting component migration along ASBs at rates significantly exceeding traditional diffusion rates are described. They offer a fresh perspective on friction stir welding (FSW) not only as an effective welding method, but also as the foundation for an alternative technology to produce bulk alloys from ICs. The stirring zone temperature is found to be high enough for the intensive formation of solid solutions and intermetallic phases. The structure of such particles is formed under heating and intense plastic deformation, with possible activation of two component migration mechanisms, namely, diffusion and migration along ASBs, which are reproduced during each tool rotation. An increase in the lead content in a composite material from 5 to 44% decreases the friction coefficient from 0.28 to 0.13. The main decrease in the friction coefficient of an Al–Pb composite material occurs within the lead content range 0–30 wt %. The development of the alternative technology for producing special-purpose composite materials (CM) discussed here involves two interrelated directions: expanding the range of new functional CMs using the unique capabilities of FSW technology and refining the mechanism of structural and phase transformations underlying this technology. In particular, further investigations are needed on the ASB formation mechanism and kinetics and the role of ASBs in the microstructure and properties of composites.