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

The purpose of the study is to develop a new sort of lead-free and easy-cutting brass,which is to substitute for the toxic leaded brass. In the study, Phosphorus, magnesium andcalcium are substituted for lead. The lead-free brass is fabricated by melting, casting andextruding processes, we improve the melting process of brass depending on the characteristicof P-Mg-Ca brass. Hot extrusion is used to explore the hot-workability. The effect of addingalloying element on the microstructure of the metal is studied by X-ray diffraction, opticalmicroscope, optical three-dimensional microscope system, scanning electron microscope andEPMA. The machinability and mechanical properties were tested by electron universal testmachine and metal cutting lathe. We have studied the mechanism of the second phaseimproving the machinability of brass. The following results were obtained:(1) Microstructure of the Cu-Zn-P-Mg-Ca is consisting of phased, phased β and secondphase. Maybe the second phase is the composite phase which is composed of Mg3P2、Cu3Pand Ca3P2. The second phase which is brittle will break the continuity of the brass, and thenapprove the machinability of the brass.(2) Increasing the content of phosphorus and calcium will decrease the plasticity of brass,while adding a small amount of magnesium will improve the plasticity of brass. When adding0.9%P,0.6%Mg,0.2%Ca, brass will have excellent mechanical property and machinabilityproperty. Mechanical property Cu-Zn-P-Mg-Ca: Tensile strength σbwas higher than320MPa,yield strength σswas larger220MPa, elongation was higher than10%。(3) Effect of alloying element on the mechanical property of brass: increasing the contentof phosphorus will improve the fluidity of the brass. The fluidity of the brass deteriorated withthe increasing magnesium content, the magnesium will restrain the emerging of second phasewhich is sheet, and the second phase in the P-Mg-Ca brass are rounded or clavate, but whenthe magnesium content is above0.6%, the elongation and tensile strength will decrease.Increasing the Calcium content, the mechanical property will decrease obviously.(4) Mechinability of P-Mg-Ca brass: in the same cutting condition, the cutting force ofP-Mg-Ca brass is a little larger than the cutting force of leaded brass. The alternation ofcutting condition will change the morphology of cuttings. When the cutting speed is low, the cuttings are granules. When the cutting speed is high, the cuttings are spiral. When the cuttingdepth increased, the granules cuttings will transform into spiral cuttings. When the cuttingspeed is low, there is no obvious difference between the chips of extruded brass and the brassof as-cast. While the cutting speed is high, the cuttings of extruded brass are harder to break.The second phase particle will promote cutting to fracture; the critical size of the secondphase particle which can promote shear fracture of chips is3.1μm, so the second phaseparticles in the microstructure can improve the machinability of the brass.(5) P-Mg-Ca brass has good mechanical properties and machinability. It can substitutefor the widely used leaded brass.