Brass (an alloy of mainly zinc and copper but can also incorporate other elements such as lead and magnesium) has excellent mechanical properties, possesses good machinability and is resistant to corrosion. These among other properties makes it an ideal candidate for utilization in pipes, valves and other fittings necessary for water transport. To enhance machinability, lead (Pb) is usually added. Unfortunately, lead is a neurotoxic substance and an undesirable heavy metal environmental pollutant. Especially, corrosion of brass may release large amounts of Pb ions, which are dissolved in drinking water, and are thus harmful to humans. Therefore, alternative substitutes have overtime been proposed such as bismuth, magnesium and graphite. However, these lead replacements have inherent drawbacks such as, the extremely low solid-solubility of bismuth into copper causes hot and cold embrittlement in bismuth brass due to reticulation and membranous distributions of the bismuth along grain boundaries. To this note, there is urgent need to further explore on other potential lead metal candidate substitute and related composition design rules.
South China University of Technology researchers led by Professor Chao Yang in collaboration with Dr. Yanfei Ding at Guangdong Huayi Plumbing Fittings Industry Co., Ltd. developed high-strength and free-cutting silicon brasses designed via the zinc equivalent rule by adding lead replacers, specifically Silicone and Aluminum elements. They anticipated that the resultant silicon brasses adjusted with a relatively low zinc equivalent would exhibit inhomogeneous microstructures and an α+β matrix with abundant nanoscale intermetallic compound (IMC) particles distributed along the grain boundaries. Their work is currently published in the research journal, Materials Science & Engineering A.
The research technique employed commenced with the designing of the high-strength and free-cutting silicon brasses using the zinc equivalent rule. Next, silicone brasses were prepared via casting in an induction furnace. The researchers then examined the phase components and microstructures of the brass samples by X-ray diffraction and scanning electron microscopy. Later, they processed dog-bone specimens using varying parameters which were then tested under tensile conditions. Lastly, they undertook cutting tests on a lathe machine where the resultant cutting-chips morphologies were observed using scanning electron microscopy.
The authors observed that when the zinc equivalent was below 43%, 43–47%, and 47–49%, corresponding phase components of the resultant silicon brasses were of α+β brass, β brass, and β+γ brass, respectively. Additionally, they noted that the inhomogeneous microstructure of the resultant α+β silicon brasses was composed of granulate and needle α phase embedded into the β matrix with profuse ultrafine IMC particles distributed along the grain boundaries of the α and β phases and high densities of nanoscale IMC grains distributed in the β-phase matrix near grain boundaries.
Professor Chao Yang and his research team successfully presented an alternative strategy involving controlling the zinc equivalent by adjusting Silicone and Aluminum contents so as to fabricate high-strength and free-cutting silicon brasses. Generally, from chip-breaking performance and roughness of the machine surface evaluation, the machinability of the resultant silicon brasses was seen to be improved as desired therefore rubberstamping this work as a step in the right direction with regard to brass alloys. Altogether, the results obtained here provide significant insight into the microstructural design of high-strength and free-cutting brass alloys.
This work was supported by the Guangdong Application-oriented Special Fund Major Project for Science and Technology R&D (No. 2016B090931002), entitled by “Key Technology Development and Industrialization Application of New-generation Environment-friendly Brass Faucet”. The performance indexes, specifically the lead release limit of the developed silicon brass meet national standards of China, America, European, Australia, etc. The developed silicon brass and its design method has been authorized a China patent (ZL 2015 1 0714013.X) and published a PCT (US-2018-0148813-A1). So far, Guangdong Huayi Plumbing Fittings Industry Co., Ltd. has produced 18 types and 500 thousand sets of faucets and achieved sales income of 150 million RMB.
C. Yang, Z. Ding, Q.C. Tao, L. Liang, Y.F. Ding, W.W. Zhang, Q.L. Zhu. High-strength and free-cutting silicon brasses designed via the zinc equivalent rule. Materials Science & Engineering A, volume 723 (2018) page 296–305Go To Materials Science & Engineering A