Brasses

Brasses comprise the major portion of copper-base alloy powders used for parts fabrication, in comparison with prealloyed bronze and nickel silver materials. Typical copper-zinc brass powders contain zinc contents ranging from 10 to 30%. Lead may be added in small amounts (1 to 2%) to improve machinability of the sintered compact. A photomicrograph of an 80%Cu-18%Zn-2%Pb alloy powder is shown in Fig. 2. The melting temperatures of these alloys range from 1045 °C (1910 °F) for 90%Cu-10%Zn to 960 °C (1760 °F) for 70%Cu-30%Zn. As zinc content increases, melting temperature is lowered.

Fig. 2 Scanning electron micrograph of prealloyed, air-atomized brass (80%Cu-18%Zn-2%Pb). 165x

Additional superheat, or the temperature in excess of the alloy melting temperature, depends on heat losses within the manufacturing system and the physical property requirements of the atomized powders. Typical physical properties of brass alloy compositions are given in Table 1.

Table 1 Physical properties of typical brass, bronze, and nickel silver alloy compositions

Property

Brass(a)

Bronze(a)

Nickel

Silver(a)(b)

Sieve analysis, %

+100 mesh

2.0 max

2.0 max

2.0 max

-100 + 200

15-35

15-35

15-35

-200 + 325

15-35

15-35

15-35

-325

60 max

60 max

60 max

Physical properties

Apparent density

3.0-3.2

3.3-3.5

3.0-3.2

Flow rate, s/50 g

24-26

Mechanical properties

Compressibility(c) at 414 MPa (300 tsi), g/cm3

7.6

7.4

7.6

Green strength(c) at 414 MPa (300 tsi), MPa (psi)

10-12 (1500-1700)

10-12 (1500-1700)

9.6-11 (1400-1600)

(a) Nominal mesh sizes; brass, -60 mesh; bronze, -60 mesh; nickel silver, -100 mesh.

(b) Contains no lead.

(c) Compressibility and green strength data of powders lubricated with 0.5% lithium stearate

(a) Nominal mesh sizes; brass, -60 mesh; bronze, -60 mesh; nickel silver, -100 mesh.

(b) Contains no lead.

(c) Compressibility and green strength data of powders lubricated with 0.5% lithium stearate

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