What is Gunmetal (Red Brass)

Gunmetal, occasionally called ‘red brass’ in the US, is an alloy made from copper, zinc, and tin ^{[1, 2]}. Aside from its basic constituents, modified forms may have nickel and lead, which are classified as ‘nickel gunmetal’ and ‘leaded gunmetal’ ^[2]. Because of good strength, corrosion resistance, and ease of casting, gunmetal has been widely used for thousands of years ^[2].

Composition

The chemical composition of gunmetal can be varied ^{[1, 2]}. Here we have shared the components of Admiralty Gunmetal:

Copper	88% [3]
Tin	10% [3]
Zinc	2% [3]

Modified gunmetal may contain up to 7 percent lead and up to 6 percent nickel ^[2] while the copper alloy C90300 or G Bronze comprises 8 percent tin and 4 percent zinc ^[4].

Properties and Characteristics of Gunmetal

Physical Properties

Color/appearance	Gray with bluish or purplish tinge [5]
Density	8.72 X 103 kg/m3 [6]
State of matter at room temperature	Solid [7]
Electric resistivity	15.6 X 10-8 Ohm-m [6]
Modulus of elasticity	103 GPa [6]
Thermal expansion (at 20 °C)	19.8 X 10-6 °C-1 [6]
Thermal conductivity	74.8 W/mK [6]
Specific heat capacity	377 J/kgK [6]
Yield strength	152 MPa [6]
Tensile strength	310 MPa [6]
Elongation	25% [6]
Fatigue strength	90 MPa [6]
Liquidus temperature	999 °C [6]
Solidus temperature	854 °C [6]
Hardness	75 HB(500) [6]

Uses

• Intricate, pressure-tight castings like pipe fittings, valves, and pumps are made from gunmetal ^[8].
• It is now commonly used for making statues ^[8].
• Bearings, where speeds and loads are moderate, are manufactured from gunmetal and used in machinery ^{[7, 8]}.

Cost

The scrap price is about $1.8 per pound of gunmetal ^[9]