Microstructural and mechanical properties of friction stir welded Cu–30Zn brass alloy at various feed speeds: Influence of stir bands

In this study, the effect of various feed speeds on microstructure and mechanical properties of friction stir welded Cu–30Zn brass alloy is investigated. Rotation speed was fixed at 950 rpm and feed speed varied in the range of 190–375 mm/min. Examination of the microstructure showed very fine grains with some deformed grains in the stirred zone and some coarser grains in the thermo-mechanically affected zone and base metal. A unique deformation pattern, namely “stir band” in the stirred zone region was identified and its density increased by increase in feed speed. Results showed that the grain size profile was independent of feed speed and the hardness values decreased by increase in feed speed. Increase in feed speed led to a slight improvement of yield strength and ultimate tensile strength, associated to continuous spring-like morphology of stir bands acting as a strengthening structure. However, ductility reduces considerably from 57 to 27%. Moreover, it is observed that during tensile test, fracture cracks originate exactly adjacent to the stir bands.

Research highlights
► During FSW, grain size was affected by both heat input and plastic deformation.
► A spring-like deformation pattern namely “stir band” was observed in the SZ.
► By increase in feed speed, stir band density increases while its width decreases.
► Hardness is balanced by Hall–Petch mechanism and plastic deformation processes.
► During tensile test, fracture cracks originate exactly adjacent to the stir band.