Study On Compositional Design And Preparation Process Of Unleaded Free-Cutting Brass

In order to solve the problems of lead hazards in smelting processes of HPb59-1 brass on human body and easy precipitation of lead in long-term storage process, new types of unleaded free-cutting brass were presented in this paper, using Mg and Al instead of Pb element. Designing compositiones of the alloys, selecting modification treatment and drafting heat treatment process were conducted.With the aids of electronic universal testing machine, optical metallographic microscopy, scanning electron microscopy (SEM) and metal cutting lathe, the mechanical properties and flow properties of the prepared alloys were tested. Microstructure was also observed.Corrosion resistances and cutting properties were analyzed.60Cu-Zn-0.5Si-1.5Mg-2.0Al alloy with different contents of A1 and Mg was prepared withβphase for matrix andγphase for the second phase using the conventional casting process.The grains became smaller andγphase particles size distribution was more uniform after 0.05wt.%Ti modification.The ultimate tensile strength of 60Cu-Zn-0.5Si-1.5Mg-2.0Al alloy was increased from 315 to 452MPa while the corrosion depth was decreased from 864 to 265um. Moreover, the corrosion rate was decreased and the corrosion resistances were improved. The flow property of 60Cu-Zn-0.5Si-1.5Mg-2.0Al alloy was increased by 35% after 0.05wt.% Ti modification.After modification and heat treatment, inner stress of 60Cu-Zn-0.5Si-1.5Mg-2.0Al alloy was reduced, thereby zinc loss was reduced and the dezincification corrosion depth decreased. After 24 hours in CuCl2 solution corrosion, the dezincification layer thickness was only 118μm, which indicated 60Cu-Zn-0.5Si-1.5Mg-2.0Al alloy had good corrosion resistances.The results of electrochemical corrosion experiment found 60Cu-Zn-0.5Si-1.5Mg-2.0Al-0.05Ti alloy after heat treatment, the corrosion potential of 381 mV up to 561 mV, corrosion resistant performance. After modification treatment and heat treatment, the chip geometry of 60Cu-Zn-0.5Si-1.5Mg-2.0Al alloy became smaller and the cutting force was reduced. So cutting property was improved. The critical size of second phase particles was only 0.92um. Through the investigation of the relationship between the cutting force and cutting condition, suggesting that the influence of cutting depth on cutting performance of 60Cu-Zn-0.5Si-1.5Mg-2.0Al-0.05Ti alloy was obvious.