Brass is a copper-zinc alloy, which is ductile and easy to shape. The amount of zinc in the brass alloy can be varied from 5 to 45% to form different alloys with unique properties.
Two major types of brasses include alpha brasses and alpha-beta/duplex alloys. Brasses containing less than 35% of zinc and one solid solution termed alpha brasses, which are suitable for cold working.
Brasses containing zinc of more than 35% are known as alpha-beta/duplex alloys, which can be hot worked. Brass alloys are available in various colors and thus they are preferred for applications which require aesthetic appeal.
Nearly 3% of lead is added to alpha-beta brasses to ensure free-machining properties of brasses. Wrought alpha brasses do not contain lead as the addition of lead results in damage in the absence of adequate beta phase during hot working. Lead can provide pressure tightness and improve machinability of brasses by covering the shrinkage pores.
Lead brasses offer high corrosion resistance, good strength and excellent machinability. Low, medium and high-leaded brasses are three major types of lead brasses with maximum of 3.5% lead content.
Lead brasses have similar microstructure as that of the unleaded brasses. This microstructure has discrete lead particles present in the inter-dendritic regions or grain boundaries, and is formed as a result of zinc content.
The wrought lead brasses are named as UNS C31200 to C38500, and the cast lead brasses are designated as C83600 to C97300.
The alloys containing less zinc content have single-phase solid solution alpha dendrites with lead particles scattered all through the inter-dendritic regions. The alloys containing higher zinc content have a beta microstructure and alpha and beta structures. These higher zinc content alloys have alpha and beta phase mixture and lead particles that are present as discrete particles in the microstructure.
The composition of leaded brasses is outlined in the following table.
1Cu + sum of named elements, 99.6% min.
2For flat products, the iron shall be .10% max.
3Cu, 61.0% min. for rod.
4Cu + sum of named elements, 99.5% min.
5Pb may be reduced to 1.0% by agreement.
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