Microstructure and Mechanical Properties of Ultra Fine Grained (α+β′) Dual-Phase Brass

To obtain a high strength copper alloy with ultra fine grain size, a brass with β′ precipitates was investigated. A Cu-37.3 mass%Zn brass was 95% cold rolled and annealed at 180°C to 300°C. It was confirmed by SEM, TEM, SAD, and X-ray analysis that the alloy was sub-micron grained (α+β′) dual-phase. The proof stress of this alloy was 400 to 500 MPa, and was higher than double of ordinarily annealed α brass. The relationship between proof stress and grain size of this alloy was on the extrapolated line of the Hall-Petch relation of α brass. A high strength due to ultra fine grain, 680 MPa in proof stress and 220 MPa in fatigue strength, was obtained by cold rolling and low temperature annealing after the recrystallization annealing. The Portevin-LeChatelier effect and increase of stress relaxation due to ultra fine grain sizes were observed.