Research On Microstructures And Properties Of Lead Free And Free Cutting Brass

The traditional lead brass HPb59-1 has greatly satisfied the industrial needs because of its free-cutting property and good corrosion resistance,and it has been widely applied,especially in the field of bathroom and water system.As we konw,Pb is a poisonous element which is greatly harmful to human body and environment,so lead brass does gradually not meet the requirements of the increasingly improved environmental protection standards.lt has been the consensus of international scholars to exploit a lead free and free cutting brass to replace the traditional lead brass.The lead free brass was prepared by casting,as the Si element is cheap and has large storage,so the Si was used to replace Pb.At the same time,some Ni was added in the alloy.On the basis of the theory of zinc equivalence,the range of Si content which might get the brass of a+(3 phase was calculated out.The influence of Si content on the microstructure and properties of lead free brass was studied.The influence of Ni content on alloy's dezincification corrosion resistance property through experiment was also studied.The best compositon lead free and free cutting brass is Cu₅₈Zn_40.5Si_1.2Ni_0.3,which was prepared by composition design and study on alloy's properties.The samples of as-cast lead free brass was heat treated by solution and aging,and then the influence of heat treatment on microstructure and properties of the alloys was studied.By the means of scanning electron microscope?SEM?and energy dispersive spectrometer?EDS?,the morphology of tensile fracture was observed and the composition of ?and ? phase was analyzed.The phase of lead free brass was also analyzed by the mean of XRD.The main work and conclusions are presented as follows:?1?When the Si content is 1.2%;the grain size of lead free brass is small,? phase is also tiny,and the ratio of ? phase is more;The hardness and tensile strength are improved obviously compared with traditional HPb59-1,reached 164HB and 543.6Mpa;The fracture mechanisms of alloy is quasi-cleavage fracture.?2?The dezincification corrosion experiment results show that:The best Ni content is 0.3%,the average depth of dezincification layer is 403.36?m,and the maximum depth is 502.53 ?m.The dezincification corrosion property has improved compares to HPb59-1.?3?The results of the heat treatment for the best composition brass Cu₅₈Zn_40.5Si_1.2Ni_0.3 show that:The change of alloys' grain size is very small at the solution temperature is 400?and 600 ?,and the ratio of a phase change little compares to as-cast alloy.The hardness and tensile strength are increased,and elongation is decreased.When the solution temperature is 800?,the grain size become bigger,the a phase grow up and present thick reticulation that distribute on the base,at the same time the ratio of ? phase is decreased.The hardness and strength tend to a great decline,but elongation tend to improve.?4?The shape of breaking chip of lead free brass which Si content is 1.2%present helix coil that distribute randomly,the weighted average length of chip is 6.8mm.And the shape of breaking chip of HPb59-1 present small particle,the weighted average length is only 4.1mm.When the alloy was heat treated at the solution temperature was 600?,the weighted average length of chip was decreased obviously,is only 4.3mm,and the chip are segments.In general,the cutting property of lead free brass is similar to the cutting property of traditional lead brass HPb59-1.