Due to excellent mechanical properties, corrosion resistance, casting properties and formability, brasses alloys are widely used in many industries such as sanitary ware, electronic product and equipment manufacturing. Generally, 3wt% Pb is added into brasses alloys to improve their cutting performance. As a soft and brittle phase with relative low melting point, Pb acts as a separate phase in the Cu-Zn binary alloy, which can play roles of chip breaking, lubrication and cooling, and thus improve the cutting performance of brasses alloys. However, Pb is a toxic element and can cause environmental pollution during its production, processing and usage processes. Especially, when lead brasses are used as products contacting with water environment, Pb ions are easily precipitated from the matrix. Lead poisoning can damage the blood, nerves, digestion and reproductive systems of the human body. On this account, the development of lead-free environmentally-friendly brasses becomes an urgent and significant problem. According to the easy-cutting mechanism of lead brasses, in order to obtain excellent cutting performance, new lead-free environmentally-friendly brasses alloys should have dispersed fine particles in the matrix, which can play a role of chip breaking like Pb particles during cutting processing. According to the existing modes of the particles, the elements beneficial to the cutting performance of brasses alloys can be classified into three types, minor solid-soluble ones in Cu that can form eutectics with Cu, insoluble ones in Cu that can form compounds with Cu, and partial solid-soluble ones in Cu that can form compounds with Cu. Currently, systematic researches have been carried out on the first type of substitute elements such as Bi. However, these elements are of limited resources and are mostly toxic. Some research results have been obtained on the second type of substitute elements, which are easily oxidized and formed harmful inclusions, thus increasing the difficulty in the preparation and processing of these materials. A large number of studies have been conducted to improve the cutting performance of brasses alloys by the third type of substitute elements, such as Pb replacer of Sb, Mg and Si. Unfortunately, Sb is a toxic element like Pb; lead-free magnesium brasses are easy to bring in inhaling, oxidizing and other casting defects, making its smelting process very complicated. The element Si has many advantages of large zinc equivalent coefficient, rich resource and non-toxic effect. Tailoring Si content is easy to regulate microstructures of lead-free silicon brasses with simple smelting process. As such, silicon brasses are expected to realize the complete lead-free in brasses products, which is of great significance in protecting human health, ecological environment and realizing green manufacturing. In summary, based on the selection characteristics of the third component elements and the zinc equivalent rule, this paper reviewed the research progress in lead-free environmentally-friendly free-cutting brasses, including microstructure, cutting performance and corrosion resistance. Meanwhile, the effects of Si and Al additions on microstructure and properties of developed brasses are analyzed. Particularly, the composition and microstructure design, cutting performance and production process of lead-free environmentally-friendly free-cutting silicon brasses are underlined. Finally, prospects for future research trends are pointed out. The progress reviewed herein may provide significant insight into the development and application of lead-free environmentally-friendly free-cutting brasses. © 2019, Materials Review Magazine. All right reserved.
