Research On The Microstructure And Properties Of Unleaded Si-Mg-Ca Brass

Lead brass is widely used in plumbing and sanitary ware,electrical and electrical,instrumentation,equipment manufacturing and many other industries because of its excellent mechanical properties,cutting performance,corrosion resistance and molding performance.But Pb is toxic,destroying the environment and harming the human body.Therefore,the development of lead-free and free-cutting brass is an important issue to be solved urgently.Si,Mg,P and Ca elements are used to replace Pb elements,and a free-cutting lead-free free-cutting brass is prepared on the premise of ensuring the mechanical properties of the material and not reducing the cutting performance.The alloy material is prepared by smelting,and the copper rods obtained by casting are hot extruded,the structure and performance differences of the two brasses under different processes are analyzed,and the Gibbs free energy and copper alloy phase diagram are used to judge the type of second phase in alloy structure.The matrix structure of as-cast Si-Mg-Ca brass is mainly composed ofαandβphases,and most of the intermetallic compounds distributed along the phase boundary.The second phase particles in the alloy are mainly Ca₃P₂,Mg₃P₂ and Cu₃P.The tensile strength of as-cast Si-Mg-Ca brass is between 295～375 MPa,the elongation after break is between 1.5～5.5%,and the hardness is between 110～125 HB.When the main components of lead-free Si-Mg-Ca brass are59 wt.%Cu,0.7 wt.%Si,0.6 wt.%Mg,0.6 wt.%P,0.1 wt.%Ca,0.5 wt.%Sn,0.15 wt.%Al,the alloy shows excellent Comprehensive performance.Its tensile strength is 335.85 MPa and hardness is 116.19 HB and the corrosion resistance of the alloy is relatively excellent.The average thickness of the dezincification layer is 189.1μm.The elements in the alloy that play the role of dezincification resistance are mainly Sn,Si,and Al.After extrusion,theβphase in the matrix structure increases,and theαphase is extruded into a small willow shape.The second phase particles are elongated in the stretching direction after being extruded,and are distributed in the phase boundary or phase in a spherical or rod shape,the type of the second phase has not been changed.The tensile strength of as-extruded Si-Mg-Ca brass is between 500～550 MPa,the elongation after break is between 22～26%,and the Brinell hardness is between 110-124HB.After being extruded,twins and a large number of dislocations appear in the structure,which significantly improves the mechanical properties of alloys.Under different cutting parameters,the surface roughness value of as-cast Si-Mg-Ca brass which the content of Ca is 0.1 wt.%and the surface processing quality is the best.The surface roughness of as-extruded Si-Mg-Ca brass is about 8.4μm.The chips of as-cast Si-Mg-Ca brass and as-extruded Si-Mg-Ca brass are both serrated chips.According to the chip shape,the cutting performance of the as-cast Si-Mg-Ca brass which the content of Ca is 0.1 wt.%and as-extruded Si-Mg-Ca brass which the content of Ca is 0.25 wt.%are best,both chips are ideal C chips.According to the Griffith fracture theory,the critical size of the second-phase particles in the Si-Mg-Ca brass matrix is 1.46μm,and there are a large number of dispersed compound particles in the brass matrix with a size of 4～5μm,which significantly improves the cutting performance of Si-Mg-Ca brass.