What Are Leaded Brass?

Copper and copper alloys, such as bronze, brass, leaded brass are commonly used in friction parts of machines, as bearing liners, bushings, and water with gas fittings. Properties such as high strength and ductility, fatigue strength, wear resistance and machinability are necessary for these materials. Obtaining such properties is possible by creating submicrocrystalline and nanocrystalline structures in the materials [1]. The most common copper alloys are the brasses for which zinc, as a substitutional impurity, is the superior alloying element. Some of the common brasses are yellow, naval, and cartridge brass and gilding metal. Some of the common uses for brass alloys include jewelry, cartridge parts, automotive radiators, musical instruments,

Many parts, for example, screws, nuts, bolts, and fittings, are produced by automatic turning operations [10]. Some alloying elements sometimes added to impart special characteristics to brass. Lead, which is insoluble in copper alloys, is used to improve machinability of leaded brass. However, Pb and Bi or other elements that are used to improve the machinability often deteriorate the low and high temperature ductility of brass [11]. The content of Pb element is varies between 2.5 and 3.5 %, which make the machining processes at high speed and good surface [12]. The solubility of lead in copper alloys is very low therefore, it is found in microstructure as dispersed globules all over the material. These globules lead act as a lubricant decreasing the friction coefficient between the tool and the material by creating discontinuities of chip fragmentation. Therefore, it makes reducing in cutting force and then, the tool wear rate is minimized [13]. Different alloying elements help to improving the machinability are usually added to brass. The most common element using in this situation is lead, which improving the machinability with regard to excellent chip breakage, low tool wear and high applicable cutting parameters. These aspects can be explained by two basic phenomena; first of all, the solubility of lead in brass is extremely low and lead segregates in the entire microstructure, particularly at the grain boundaries. Hence, shear strength is reduced, resulting in very good chip breakage. Secondly, lead exhibits a low melting temperature and during cutting process, a thin, semi-fluid lead film reduces friction with cutting forces