Study On The Machinability Of Silicon Brasses With Different Zinc Equivalents

The traditional free-cutting lead-brass was applied widely in many fields such as mechanical manufacturing,electronic product,sanitary product,and so on.However,the Pb element is easy to separate out from the lead-brass in long-term usage,which is harmful to human's health and environment.Therefore,it becomes a common issue to develop the new lead-free brass to replace lead-brass.Zinc equivalent is of great significance for the development of new lead-free free-cutting silicon brass,Different zinc equivalents have great influence on the processing properties,mechanical properties and corrosion resistance of copper alloys.The silicon brasses,which were prepared via adjusting zinc equivalent by adding Si and Al in Cu-Zn alloy,possesses excellent combination of mechanical properties and corrosion resistance relative to lead brass.Moreover,the machinability of the prepared silicon brasses can reach up to 80%~90% of lead brass.Therefore,the silicon brasses are excellent substitute material for lead brass.In this paper,the silicon brasses with different(?+?),(?+?)and ? phase contents were prepared via the change of the zinc equivalent in the Cu-Zn alloy.The effect of phase component and phase content on the chip breaking performance and the machined surface quality of the silicon brasses were analyzed.The analyzed results were also compared with the traditional lead brass.Moreover,cutting tools with surface texture were also used to machine the prepared silicon brasses,and resultant relative machinability was analyzed.The conclusions in this paper can be drawn as following:(1)With the increased of the zinc equivalent in the silicon brasses,the content of ? phase decreases and ? phase increases.Meanwhile,the shape of ? phase gradually changes from large block to small granule and needle.With the further increase of zinc equivalent,the content of ? phase decreases and the content of ? phase increase,and the shape of ? phase gradually changes from small starflower to big granulate.The silicon brasses with ?+? phases have better chip breaking performance than that with ?+?.Especially,the silicon brass with zinc equivalent of 46.9% has the best chip-breaking performance,which can reach the 80%~90% of HPb59-1.The chip with respect to this brass is the tiny C-shape.With the increase of zinc equivalent,the chip thickness decreases,and the serration degree in free face increases.With the further increase of zinc equivalent,the fibrous structure in the cutting face and the fibrationed degree in back face of the chip decreases.The shearing-sliding area presents periodically within chip,and the locus of the fracture of the chip is the adiabatic shear zone.(2)For the ?+? silicon brass with 46% zinc equivalent,the degree and frequency of chip serration gradually increases with the increase of cutting speed;with the increase of the feed,the serration degree and chip thickness increases,but the serration frequency decrease;with the increase of cutting depth,the degree and frequency of the chip serration,chip thickness increases.(3)Under the same cutting parameters,the roughness and work-hardening degree of processed surface of prepared silicon brasses increase with the increase of zinc equivalent,and the roughness of processed surface is smaller than that of lead brass.For the ?+? silicon brasses with the increase of zinc equivalent,the roughness and work-hardening degree of processed surface decreases,and residual compressive stress along the axial direction surface increases gradually.Correspondingly,the roughness,work-hardening degree and residual compressive stress of processed surfaces increase with the increase of zinc equivalent.(4)The main tool wear type of the cutting tool with respect to the silicon brasses is adhesive wear.Under the same cutting parameters,with the increase of zinc equivalent,the tool wear and the length of tool-chip interface decrease,and the degree of adhesion increases gradually.Compared with the cutting tool with smooth rake face,the micro-texture cutting tool is beneficial to improve the chip breaking performance and anti-adhesion performance in machining of silicon brasses.Under the same processing conditions,the curling ratio of chip with respect to different textured tools can be drawn as followings: transverse texture>Z texture>longitudinal texture>circular texture;the bond degree of tool as the following: Z texture > circular texture > longitudinal texture > transverse texture.The test result of engineering application for textured cutting tool shows that the cutting tool with longitudinal texture can bring about the smaller roughness of processed surfaces and tool wears.Therefore,it can bring about the desired effect in improving the machinability of the silicon brasses.