Effect Of Heat Treatment Process On Mechanical Properties And Corrosion Resistance Of Environmentally Friendly Lead-free Silicon Brass

Due to its good mechanical properties,formability,free-cutting performance and corrosion resistance,lead brass has been widely used in sanitary,electrical and electrical,equipment manufacturing and other industries.However,lead?Pb?has great harm to the environment and human health.In recent years,countries around the world have introduced specific systems that restrict the use of Pb.The development of lead-free environmentally friendly brass that has no toxic effect on the human body has become an inevitable trend.In this dissertation,by adjusting the Al and Sicontents,the zinc equivalents of the brasses are gradually increased,environmentally friendly lead-free silicon brass ingots with three typical structures,i.e.,?+?phase,?phase and?+?phase were prepared,and then were made into faucet products using low-pressure casting.After that,the castings were treated with different heat treatment process parameters.Combined with metallographic microscopy,scanning electron microscope,X-ray diffraction,X-ray photoelectron spectroscopy,electrochemical workstation and transmission electron microscope,etc.,the effects of heat treatment process on the microstructure,mechanical properties and corrosion resistance of three typical types of lead-free silicon brasses were systematically studied.The main conclusions are as follows:?1?When the as-cast lead-free silicon brass alloys were tempered at the temperature no less than 250?,the?phase inside the?+?phase alloy would obviously grow,the microstructures of the?phase and?+?phase alloys do not change significantly,while the grain boundary phase grows locally.If the alloys were solid solution at 600?and tempered at above200?,thin strip phase precipitated along the grain boundaries,while a little phase precipitated inside the grain.As the tempering temperature increases,the above-mentioned grain boundaries and intragranular precipitated?phase or?phase would grow slightly.?2?As the zinc equivalent of the alloy increases,the strength of the lead-free silicon brass alloy gradually increases.When the zinc equivalent is greater than 45%,the tensile strength of the lead-free silicon brass exceeds 535 MPa,which is 100 MPa higher than that of lead brass alloy.The elongation of the lead-free silicon brass alloy is up to 14.3%,lower than that of lead brass alloy.After 600?-solid solution and 200?-tempering,the strength and plasticity of the lead-free silicon brass alloy are improved largely.Especially,the?+?phase alloy has the best comprehensive mechanical properties after 600?-solid solution and 250?-tempering,while the?phase and?+?phase alloys have the best comprehensive mechanical properties after600?-solid solution and 200?-tempering.?3?Among the as-cast lead-free silicon brasses,the?+?phase alloy with zinc equivalent of 43.3%and the?+?phase alloy with zinc equivalent of 49.3%,have the best dezincification corrosion resistance,and the corresponding average thicknesses of the dezincification layer are96.7 and 45.6?m,which are smaller than those of lead brass alloys.After 600?-solid solution and 250?-tempering,the dezincification corrosion resistances of the lead-free silicon brass alloys have been greatly improved.During the dezincification and corrosion process,Al and Sielements gather on the surface of the alloys and combine with oxygen to form Al₂O₃ and SiO₂films,which fill the defects of Cu₂O films and thus improves the resistance to dezincification corrosion.In the dezincification corrosion process of the?+?and?+?phase brass alloys,the different potentials of constituted phases would cause anodic corrosion of?phase or?phase,thereby changing the resistance to dezincification corrosion of the alloys.?4?The salt spray corrosion resistance of the lead-free silicon brass alloys is higher than that of HPb59-1 alloy,and yet lower than that of dezincification resistant brass.After 600?-solid solution and 250?-tempering treatment,the resistance to salt spray corrosion of the lead-free silicon brass alloys have improved.The salt spray corrosion products of lead-free silicon brass alloys are mainly Zn O,CuCl,Al₂O₃ and SiO₂,and the formation of SiO₂ oxide film improves the resistance to salt spray corrosion.?5?After heat treatment,the?+?phase alloy with zinc equivalent of 43.3%has the best combination of microstructure,mechanical properties and corrosion resistance.The optimal heat treatment process is 600?-solid solution and 250?-tempering treatment.Correspondingly,the tensile strength of the alloy is 454.2 MPa,the elongation is 17.6%,and the average thickness of the dezincification layer is 118.7?m.