Manufacturing Process、Microstructure And Properties Of Sulfide-Dispersed Lead-Free Brass

The machinability is often an important issue for many metallic materials needed to be solved in the application process, which directly affects the cost and production efficiency.Traditional free-cutting brasses usually contained lead and were called lead brasses. Due to the excellent mechanical properties and cutting performance, lead brasses were widely applied in various fields, such as components in water supply system, electronic connectors and so on. With the rapid development of environmental awareness, however, lead containing products were proved to be harmful to the environment. Although a lot of Significant progress has been achieved on the research of lead-free free-cutting brass in the past two decades, also many products had also been commercialized and put into industrial applications, the performance did not reach the level of the traditional leaded products. The purpose of this research is to develop a kind of unleaded free-cutting brass,which can replace traditional leaded brass.In this paper,the sulfide-dispersed brass was produced by adding copper sulfide into the H62 brass melt in situ synthesis reaction process,which have a good cutting performance.The effects of the way in which sulfide was added and the amount of the sulfide on the microstructure and properties of these brasses have been investigated.These lead to a very practical result.Besides,the effects of two elements Zn, Si additions on the microstructure and properties of these brasses have also been investigated.Experimental study turned out that CuS can be used as raw materials to get ZnS in H62-brass in the use of in situ synthesis process;with the preparation of prefabricated block we might get the desired machinability of brass. The results show that,the sulfide-dispersed brass has a good chip disposability where the prefabricated block was introduced into molten brass with copper powder and copper sulfide powder mass ratio of 1:2. As the addition of ZnS increases,the machinability of brass becomes better. With 1.5% ZnS introduced to the alloy,the H62 brass have a excellent cutting performance as good as H59-1.With the increasing of Zn content, microstructure of sulfide-dispersed brass prepared transforms from a single-phase field to (a+P) two-phase field and β single-phase field eventually,while the strength and hardness of alloys increases, elongation decreases. The stress corrosion resistance and cutting properties of the brasses prepared were overall worse. While sulfide particles cann’t be found in β-phase containing brass,therefore,the brass has a poor cutting performance.While we add Si to the sulfide-dispersed H62 brass which has 1.5wt.%of ZnS, the results showed that, With the increasing of Si content, microstructure of brass transforms from a single-phase field to α+β two-phase field and the volume fraction of the β-phase increases,this contribute to the increase of strength but the decrease of ductility.The stress corrosion resistance of the brass become better with the Si addition,the cutting performance become worse,as the number of ZnS particles in the brass decreases.All the brasses with silicon content higher than 1.5wt.%show excellent stress corrosion resistance.The appearance time of brass’s initial crack is about 510 minutes with 1.5wt.%silicon added, The appearance time of brass’s initial crack is up to 600 minutes with 2.0wt.%silicon added.The microstructures of 1.5ZnS-H72-1.5 and 1.5ZnS-H76-1.5 are both filled with a single-phases and a lot of dispersed sulfides,these sulfide particles have a large size(2-6um) and irregular shape,they can not improve the cutting performance,these two brasses both have a good stress corrosion resistance, The initial crack appearance time of 1.5ZnS-H72-1.5 is about 600 minutes,while the brass 1.5ZnS-H72-1.5 wouldn’t produce any crack in 24 hours.