The influence of rotary swaging and subsequent annealing on the structure and mechanical properties of L68 single-phase brass

Copper alloys based on the Cu–Zn system, in particular L68 brass, are promising structural materials. However, to improve their reliability and expand the scope of application, it is necessary to enhance their strength characteristics. In this work, the influence of a combination of rotary swaging (RS) and subsequent annealing on the structure, strength and ductility of L68 brass was studied. For this purpose, the alloy microstructure was studied in the quenched and deformed states, mechanical tests for uniaxial tension, a Brinell hardness study, and an assessment of structural and phase transitions using differential scanning calorimetry were carried out. It was found that during rotary swaging, both α-phase grains elongated along the deformation direction and an ultrafine-grained structure inside them consisting of subgrains, deformation twins and shear bands are formed. Subsequent annealing at 450 °C leads to an increase in the grain size to 3–5 μm due to static recrystallization. After rotary swaging, an increase in the offset yield strength (σ0.2) and ultimate tensile stress limit (σB) by ~10 and ~3.5 times, respectively, is observed with a decrease in the relative elongation value by more than 6 times. Subsequent annealing at 450 °C, which caused the formation of a recrystallised structure, led to a decrease in the strength characteristics of L68 brass relative to the deformed state with a simultaneous increase in the relative elongation value compared to both the deformed and the initial state of the alloy. However, it is worth noting that σ0.2 and σB of L68 brass after rotary swaging and subsequent annealing at 450 °C exceed the values for the quenched alloy by an average of ~2.5 and ~1.7 times, respectively, and exceed the values regulated by GOST 494-90, GOST 1066-2015, GOST 931-90, and GOST 5362-78.