page_title: Brass
section_title: Properties
hierarchical_section_title: Brass / Properties
caption_attribution_description: English: Microstructure of rolled and annealed brass; magnification 400X
context_page_description: Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying mechanical and electrical properties. It is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure.
  Brass is similar to bronze, another alloy containing copper that uses tin in place of zinc; both bronze and brass may include small proportions of a range of other elements including arsenic, lead, phosphorus, aluminum, manganese, and silicon. The distinction between the two alloys is largely historical, and modern practice in museums and archaeology increasingly avoids both terms for historical objects in favor of the more general "copper alloy".
  Brass has long been a popular material for decoration for its bright gold-like appearance, e.g. for drawer pulls and doorknobs. It has also been widely used for all sorts of utensils due to many properties, such as low melting point, workability, durability, electrical and thermal conductivity.
context_section_description: Brass has higher malleability than bronze or zinc. The relatively low melting point of brass (900 to 940 °C, 1,650 to 1,720 °F, depending on composition) and its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard and soft brasses. The density of brass is 8.4 to 8.73 g/cm³ (0.303 to 0.315 lb/cu in).
  Today, almost 90% of all brass alloys are recycled. Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is collected and transported to the foundry, where it is melted and recast into billets. Billets are heated and extruded into the desired form and size.  The general softness of brass means that it can often be machined without the use of cutting fluid, though there are exceptions to this.
  Aluminium makes brass stronger and more corrosion-resistant. Aluminium also causes a highly beneficial hard layer of aluminium oxide (Al₂O₃) to be formed on the surface that is thin, transparent and self-healing. Tin has a similar effect and finds its use especially in seawater applications (naval brasses). Combinations of iron, aluminium, silicon and manganese make brass wear- and tear-resistant. Notably, the addition of as little as 1% iron to a brass alloy will result in an alloy with a noticeable magnetic attraction.
  Brass will corrode in the presence of moisture, chlorides, acetates, ammonia, and certain acids.  This often happens when the copper reacts with sulfur to form a brown and eventually black surface layer of copper sulfide which, if regularly exposed to slightly acidic water such as urban rainwater, can then oxidize in air to form a patina of green-blue copper sulfate. Depending on how the sulfide/ sulfate layer was formed, this layer may protect the underlying brass from further damage.
  Although copper and zinc have a large difference in electrical potential, the resulting brass alloy does not experience internalized galvanic corrosion because of the absence of a corrosive environment within the mixture.  However, if brass is placed in contact with a more noble metal such as silver or gold in such an environment, the brass will corrode galvanically; conversely, if brass is in contact with a less-noble metal such as zinc or iron, the less noble metal will corrode and the brass will be protected.
caption: Microstructure of rolled and annealed brass (400× magnification)
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