Microstructures and mechanical properties of friction stir welds of 60% Cu-40% Zn copper alloy

The characteristics of the microstructures and mechanical properties of friction stir welds of 60% Cu-40% Zn alloy (60/40 brass) were investigated. The defect-free welds were obtained in a relatively wide range of welding conditions; the tool rotation speed ranged from 1000 to 1500 rpm with a welding speed from 500 to 2000 mm/min, and 500 rpm-500 mm/min. The microstructures of the welds yielded extremely fine grains with some deformed grains in the stirred zone (SZ) and elongated grains in the thermo-mechanically affected zone. The hardness values within the SZ in all welding conditions were much higher than those of the base metal, increased with a decrease in heat input. The generation of refined grains in the SZ was a main factor which caused the hardness increase associated with decreasing heat input. The strengths of the all-SZ showed relative correspondence to the variation of the hardness values in the SZ.