A Review of FSW Research on Dissimilar Metal and Alloy Systems

This review summarizes friction-stir welding (FSW) research over a period of a decade and a half, involving 18 different same materials FSW reference systems, and the FSW of 25 different, dissimilar materials systems. These are summarized in tables. The FSW of dissimilar materials systems is distinguished from same materials systems FSW by the formation of complex, intercalated vortex, and related flow patterns. These intercalated, lamellar-like patterns represent solid-state flow by dynamic recrystallization (DRX) which facilitates unrecrystallized, block flow in the DRX regime. A detailed characterization of representative systems involving optical and transmission electron microscopy is also presented. Residual microindentation hardness or other hardness measured across the weld face provides comparative performance signatures for the same material FSW systems in contrast to the dissimilar FSW systems. Hardness fluctuations or complex spikes occurring in the dissimilar systems are skewed from the weld centerline and are shifted when the tool rotation direction changes or the advancing side is reversed.