Brass is a copper-zinc alloy. It is necessary to differentiate between binary brasses, made up only of copper and zinc and triples which contain a third element which characterises the alloy. Considering the binary brasses, one speaks of an α phase when the contents of the Zn is lower than 36% approximately, the crystalline structure of the alloy depends on the copper, or is a face-centred, cubic structure. These brasses have an excellent mallability in the cold (stretched and moulded) and are good in the cold. The brasses α-β (where the β phase is body centred cubic) have an oscillating zinc title between 36 and 45 %, which work well in heat.
In the machine tools, the binary alloys copper-zincs has a good mallability, but the hardness provokes the formation of very long metal shavings, so by adding lead which is insoluble and far removed from the crystalline structure, when dispersed in the grain borders, results in shorter or powdery shavings so the tools have to suffer less wear and less overheating which contribute to improving the quality and speed of the job. The brass lead is also known as leaded brasses.
The lead brasses (CuZn38Pb2, CuZn39Pb2 and CuZn40Pb2 are the most common) are used for parts which work with the lathe, such as valves and taps. The alloy CuZn36Pb3 (‘free-cutting brass’) is used as reference for the processing and extraction of valves, with a conventional index equivalent to 100; all the other copper alloys have a lower value.
The brasses are so widely used that it was only possible to make a short list.