Materials for engineering, 3rd Edition - (Malestrom)

Metals and alloys 97
At% Zn
0 10 20 30 40 50 60 70 80 90 100
1100
1000
Liquid
900
902
800
834
Temperature (°C)
700
600
500
400
300
α
454
β
β′
γ
468
560
700
600
δ
ε
423
η
200
0 10 20 30 40 50 60 70 80 90 100
Wt% Zn
3.15 The Cu–Zn phase diagram.
progressively increasing tensile strength due to solute hardening. The zinc
also confers resistance to atmospheric and marine corrosion, as well as
increasing the work hardening rate. The α-brasses are thus particularly suited
to cold working into wire, sheet and tube.
At higher Zn contents, the β-phase appears in the microstructure, which
increases the tensile strength of the alloy but is associated with an appreciable
loss in room temperature ductility. These effects are summarized in Fig.
3.16. At 800°C, the β-phase is readily worked, however, the high Zn α/β
brasses, such as the 60% Cu 40% Zn alloy (‘60/40 brass’, or Muntz metal)
are well suited for shaping by extrusion and hot stamping.
The ‘high tensile brasses’ are formed from the 60/40 brasses by the addition
of solution-hardening elements such as Al, Fe, Mn, Sn and Ni. These may be
used for forgings as well as castings, notable among the latter being marine
propellers. The single-phase α-‘nickel-silvers’ contain no silver, but 18–
20% Ni has a decolorising effect on brass and confers good corrosion resistance.
‘Nickel-brass’ usually refers to the α/β alloy with about 45% Cu, 45% Zn
and 10% Ni which is available as extruded sections.
Copper–nickel alloys form a continuous series of solid solutions, as shown
in Fig. 1.11, so have essentially similar microstructures. The copper-rich
alloys are used as condenser tubes: the higher the Ni-content the higher their