Research On The Preparation And Machinability Of Lead-Free Free-Cutting As-Hydrogenated Titanium Brass

Lead brass is widely used in plumbing equipment and other industries due to its excellent electrical and thermal conductivity,antibacterial property and machinability.Nevertheless,lead brass can damage the environment and human health.In this paper,the titanium hydride particles are used to replace the lead of lead brass.The titanium brass prepared by smelting is heat-treated under a hydrogen atmosphere to form titanium hydride,thereby a lead-free free-cutting as-hydrogenated titanium brass is prepared.The microstructure,machinability and corrosion performance of titanium hydride brass are analyzed.The conclusions are as follows:(1)A titanium brass is prepared by alloy smelting method,and the as-cast titanium brass includes an α-phase(Cu0.64Zn0.36),β-phase(Cu-Zn),and Cu-Ti phase that is only distributed in the β-phase.A lead-free free-cutting as-hydrogenated titanium brass is prepared by a hydrogenation treatment of titanium brass.During the hydrogenation,the β-phase nucleate and growth,and the Cu-Ti phase gradually precipitates and reacts with hydrogen atoms to form titanium hydride particles.These titanium hydride particles are oval in shape,and their size about 3 μm.(2)The hardness of as-hydrogenated titanium brass is higher than that of the common brass(Cu-40Zn)and lead brass(HPb59-1).Its hardness increases gradually with the increases of titanium content.A plurality of titanium hydride particles aggregate in titanium hydride brass,and the size reaches the chip breaking requirement,which is beneficial to improve the cutting performance of the as-hydrogenated titanium brass.The chip shape of as-hydrogenated titanium brass is mainly characterized by short spiral shape or short C type,and the cutting surface quality is good.As the titanium content increases,the size of the chips is shorter and the chip breaking effect is more obvious.However,when the amount of titanium added exceeds 5 wt.%,the chips are converted into a spiral shape and the surface finish is lowered.The high strength and hardness result in the worse machinability of the as-hydrogenated titanium brass.The corrosion resistance of as-hydrogenated titanium brass improved with the increase of titanium content.In the course of corrosion,the titanium element of β-phase region forms a(Cu-Ti)galvanic cell with copper element,which inhibits the corrosion of zinc atoms.With the formation of a dense titanium oxide layer,the dezincification corrosion rate of brass is greatly reduced,and the corrosion resistance of ashydrogenated titanium brass is significantly improved.(3)Among the as-hydrogenated titanium brass with a titanium content of 2 wt.%,3 wt.%,4 wt.%,and 5 wt.% respectively,the best machinability is exhibited with 4 wt.% titanium.Whose chip shows a short C shape,and does not produce continuous chip during continuous cutting.The chip breaking effect of hydrogenated titanium brass is inferior to that of the lead brass(HPb59-1),but it is much superior to the common brass(Cu-40Zn).This chip can meet the application requirements of automated processing.Moreover,the surface finish and corrosion resistance of hydrogenated titanium brass are better than common brass and lead brass.Based on these results,it is feasible to substitute lead-free titanium brass for lead brass.