Study On Microstructures And Properties Of Lead-free Cu-Zn-Sn-Mg-X Alloys

Lead copper alloys have been widely used in the field of automobile industry,machinery,electrommunication,household electrical appliances,drinking water projects,toys,instrument manufacturing,etc.Owing to the excellent mechanical properties and cutting performance of lead copper alloys.However,the use of lead causes great harm to the environment and the human body,so no doubt the study of new environment-friendly copper alloys will bring significant social benefits and potential economic value.Moreover,understanding of the relationship and rules between microstructure and properties has important theoretical significance.In this paper,the alloy composition is based on QSn4-4-4(GB/T 5231-2001),Cu-Sn-Zn-Mg-Si(or Mn)unleaded free cutting copper alloys are developed by adding a small amount of Mg,Si(or Mn).The alloys are casting in the induction furnace and graphite mold.The microstructure is observed by scanning electron microscope,the phase is analyzed by X-ray diffractometer,the mechanical properties and cutting performance are measured.The main contents are as follow:(1)Zn,Sn,and Si,Mn are soluble in a phase which generates first during solidification,while other excess elements distribute among dendrites,as the form of Sn-rich solid solution,small amount of compounds,Cu2Mg,Cu4MgSn,Cu4MnSn are generated.(2)In Cu-Zn-Sn-Mg-Si alloys,the content of Mg barely affects the strength;the addition of a small amount of Si increases the strength and the hardness of the alloy;the intermetallic compound Cu4MgSn can help to improve the hardness as well.(3)In Cu-Zn-Sn-Mg-Mn alloys,when the content of Mg exceeds 1.5%,the tensile strength of the alloys decreases,the elongation decreases,the yield strength and hardness are barely influenced.The addition of Mn not only greatly improves the strength,but also increases the hardness of the alloy.(4)The addition of Mg improves the cutting performance of the alloy,while the change of the content of Si and Mn has no obvious influence on the cutting performance.Increasing the content of Mg increases the amount of Cu2Mg,the particles formed by these intermetallic compounds can replace lead in copper alloys to some extent,so that the alloys have excellent cutting performance.(5)The alloys with Mn addition exhibit better mechanical properties than the alloys with Si addition,including higher strength and hardness,the cutting performance of the alloys depends on the content of Mg only.