Copper and Copper Alloys

Copper

Although copper has a relatively low strength, its electrical and thermal conductivity make it an appropriate material for some marine applications. Copper corrodes uniformly at a low corrosion rate in many environments. Copper is subject to metal ion concentration attack and the corrosion of this alloy is usually reduced within crevices. Copper and copper alloys are cathodic to steel and many other commonly used alloys.

Bronzes.

Bronzes are copper-tin, copper-aluminium, or copper-silicon alloys. Many of these alloys corrode uniformly at a relatively low rate. Some of the alloys, particularly the aluminium bronzes with aluminium contents in excess of 10%, are subject to dealloying and should not be used if this form of attack is functionally significant. Nickel- aluminium bronzes are widely used as casting alloys and, if properly heat treated, can give excellent service. Most bronzes are subject to metal ion concentration attack and the corrosion of this alloy is usually reduced within crevices.

Brasses.

Brass is a copper-zinc alloy. Unless the zinc content is below 10% or inhibitors are added to the alloy, brasses are subject to de-alloying in immersion service, particularly in seawater. The use of other copper alloys such as the aluminum bronzes or copper-nickel alloys in lieu of brass is recommended for most applications where resistance to corrosion in immersion conditions is important.

Copper-Nickel Alloys.

The nickel content of the most common copper-nickel alloys ranges from 10% to 30%. They are most commonly used for heat exchanger tubes. The resistance of the alloys to velocity attack is good with the limiting velocity for the 10% nickel alloy being about 8 feet per second and for the 30% nickel alloy being about 20 feet per second. They also have good resistance to low flow conditions. The alloys corrode uniformly below their limiting velocities. Both alloys are subject to metal ion concentration attack and the corrosion of this alloy is usually reduced within crevices.

Beryllium Copper.

Beryllium copper alloys can have very high strengths of up to 200 ksi. They corrode uniformly at a low rate. Beryllium copper is subject to metal ion concentration attack and the corrosion of this alloy is usually reduced within crevices. Beryllium copper is widely used as a spring and electrical contact material.