These alloys contain zinc as the principal alloying element with or without other designated alloying elements such as iron, aluminum, nickel and silicon. The wrought alloys comprise three main families of brasses.

The cast alloys comprise five main families of brasses. Ingot for remelting for the manufacture of castings may vary slightly from the ranges shown.

In these alloys, zinc is added to copper in amounts ranging from about 5 to 45%. As a general rule, corrosion resistance decreases as zinc content increases. It is customary to distinguish between those alloys containing less than 15% zinc (better corrosion resistance), and those with higher amounts.

The main problems with the higher zinc alloys are dezincification and stress corrosion cracking (SCC). In dezincification, a porous layer of zinc free material is formed locally or in layers on the surface. Dezincification in the high-zinc alloys can occur in a wide variety of acid, neutral and alkaline media.

Dezincification

A tightly written valve specification that limits brass alloys to those containing no more than 15% zinc, or specification of proven dezincification-resistant yellow brass alloys, say the experts. Further, manufacturers must be required to provide alloy designations or chemistry for the materials used in their valves and fittings. Over the past decade, an evolution in alloys has occurred, and yellow brasses that are dezincification-resistant do exist. However, specifiers who simply accept inexpensive yellow brasses without regard to whether they are standard alloys-or even meet the performance requirements of standard alloys-are vulnerable to potential dezincification problems. (The right pic shows-Dezincification of a Brass Valve)

Dezincification can be avoided by maintaining the zinc content below about 15%, and minimized by adding 1% tin such as in Admiralty brass (C44300) and Naval brass (C46400). Adding less than 0.1% of arsenic, antimony or phosphorus gives further protection, provided the brass has the single a-phase structure.Again, a decrease in the zinc content to less than 15% is beneficial. Brasses containing less than 15% zinc can be used to handle many acid, alkaline and salt solutions, provided:

• There is a minimum of aeration
• Oxidizing materials, such as nitric acid and dichromates, and complexing agents, such as ammonia and cyanides, are absent
• There are no elements or compounds that react directly with copper such as sulfur, hydrogen sulfide, mercury, silver salts, and acetylene.