Composition Design,microstructure And Properties Of Lead-free Silicon Brass With Free-cutting Property

Lead-brass has been widely applied in sanitary,electrical,equipment manufacturing and many other industries because of its excellent mechanical,cutting-free,corrosion resistance and formability properties.However,element lead is toxic.So the development of lead-free and free-cutting alloys to replace lead-brass is the world’s topic in manufacturing industry.New lead-free and free-cutting brass used for the faucets products must meet some standards,such as the element exudation,the mechanical property,the cutting property,and the corrosion resistance,etc.The development of faucets products of lead-free and free-cutting brass covers two procedures,i.e.,introduction of new brass and advanced manufacture of products.This dissertation focuses on the former procedure.By adding elements Si and Al,the lead in the binary Cu-Zn alloy was replaced along with some compound modifier elements Re,Ti,and B.Alloy composition and microstructure were designed and adjusted by the zinc equivalent rule.Subsequently,lead-free silicon brass ingots were prepared in the medium-frequency induction furnace,and the optimum casting process was determined.The effects of Si and Al contents on the microstructure evolution,the amount of metal contaminants,the mechanical properties,the machinability and the dezincification corrosion resistance were systematically studied.The conclusions are as followings:(1)In the designed silicon brass,the zinc equivalent increases with the increase of Si and Al content,and thus its matrix structure is transformed from(α+β)→ β →(β+γ).When the zinc equivalent is in the range of 0.437 to 0.462,the resultant structure is of(α + β)brass;When the zinc equivalent is in the range of 0.470 to 0.472,the resultant structure is single β phase;When the zinc equivalent is in the range of 0.480 to 0.499,the resultant structure is of(β + γ)brass.the value of element pollutant exudation is less than the standard requirements.(2)The hardness and tensile strength of the silicon brass increase and the ductility decreases with increasing the contents of Si and Al.The tensile strength,elongation and hardness were 635 MPa,20%,130.5 HB respectively,when the mass fraction of Si,Al and zinc were 0.69%,0.5% and 0.437,respectively.These values are larger by 30-50% than those of the HPb59-1.(3)The cutting experiments show that the two silicon brasses with the zinc equivalent of 0.437 and 0.487 have the chip shape of "C" with respective roughness of 1.32 μm and 1.59 μm.When the zinc equivalent is 0.462 and 0.456,the chip of of the resultant silicon brasses is short and respective roughness is 1.90μm and 2.01 μm.When the zinc equivalent is 0.472,the chip of the resultant silicon brass is spiral and its roughness is 1.09μm.When the zinc equivalent is 0.437,0.472 and 0.487,the cutting performance the resultant silicon brasses is equivalent to the HPb59-1.(4)The thickness of dezincification layer of 9 kinds of the resultant silicon brasses is less than 200 μm.Especially,the dezincification layer of the resultant alloy with 0.442 zinc equivalent is 92.38μm and corresponding corrosion resistance is the best.The dezincification layer thickness decreases by 30% to 40% compared with the used lead brass faucet HPb59-1.