The similarity in external appearance of the various alloys, along with the different combinations of elements used when making each alloy, can lead to confusion when categorizing the different compositions. There are as many as 400 different Copper and Copper-alloy compositions loosely grouped into the categories: Copper, high Copper alloy, Brasses, Bronzes, Copper nickels, Copper–Nickel–zinc (nickel silver), leaded Copper, and special alloys. The following table lists the principal alloying element for four of the more common types, along with the name for each type.
A brass is an alloy of copper with zinc. Brasses are usually yellow in color. The zinc content can vary between few % to about 40%; as long as it is kept under 15%, it does not markedly decrease corrosion resistance of copper.
Brasses can be sensitive to selective leaching corrosion under certain conditions, when zinc is leached from the alloy (dezincification), leaving behind a spongy copper structure.
A bronze is an alloy of copper and other metals, most often tin, but also aluminium and silicon.
Aluminium bronzes are alloys of copper and aluminium. The content of aluminium ranges mostly between 5-11%. Iron, nickel, manganese and silicon are sometimes added. They have higher strength and corrosion resistance than other bronzes, especially in marine environment, and have low reactivity to sulfur compounds. Aluminium forms a thin passivation layer on the surface of the metal.