Study On Microstructures And Properties Of Unleaded Free-cutting Cu-Zn-Bi-Mn-RE Brass

In this paper, a new type of unleaded free-cutting brass which has goodproperties of mechanical, cutting and corrosion resistance was developed. Thefour composition factors of alloy compositions had been analysised by studyingthe microstructures, mechanical property, cutting property and corrosionresistance property of this brass. During the experiment process, the alloys wereproduced by casting in the induction furnace, and then hot extruding and finallyannealing treatment. The microstructures of specimen were characterized by thescanning electron microscope （SEM） and the phase composition was analyzed byX-ray diffraction （XRD）. The mechanical, cutting and corrosion resistanceproperties were also studied. The following conclusions were obtained:The phases of the brass which contain35%Zn were α phase (Cu_0.64Zn_0.36and a small amount of Bi simple substance. The Bi element distributes in the grainor phase boundaries by the form of simple substance. The Mn element dose notdistribute in the brass matrix by the form of simple substance, but as a solidsolution. The hardness of alloy supreme by the annealing of600℃, and thehardness increased slightly after hot extrusion. In the three alloy with different Zncontent, the alloy of Cu-35%Zn-1%Bi-1.5%Mn-0.1%RE have the best cuttingproperty, but it`s tensile strength is low.Addition of Bi element gives rise to a lessening of alloy hardness, and withthe Bi element increase, the hardness lower. When the alloy contain0.5%Bi, theshape of chip is short and small, which indicate the alloy`s cutting property isgood.Mn element play a role of solid solution strengthening, improve the hardnessof alloy. Mn content affect the plasticity of alloy, and the effect is clear. When thealloy contain0.5%Mn, it`s cutting property is best.RE element can fine grains, enhance the hardness of alloy. RE content affectthe tensile strength of alloy, and the effect is clear. And RE element can enhancethe cutting property.With the Zn element increase, the thickness of dezincification layer increase,the dezincification corrosion property lower. With the Zn element increase, thecorrosion potential lower, the corrosion current density increase, the corrosion resistance property lower. The dezincification corrosion property andelectrochemical property of the three alloys with different Bi content are similar.In the three alloys, the alloy of0.5%wtBi has the best dezincification corrosionand electrochemical properties, and it`s dezincification corrosion property isbetter than HPb59-1. The addition of Mn, RE element can increase thedezincification corrosion and electrochemical properties, but Mn element canimprove the property better than RE element.In this study, the most preferred components of unleaded free-cutting brass isCu-35%Zn-0.5%Bi-1.5%Mn-0.1%RE. This alloy has good mechanical, cutting andcorrosion resistance properties, can replace the leaded-brass in future.