Selective Laser Melting Technology Of High-strength Silicon Brass Alloy And Its Microstructure And Mechanical Properties

Silicon brass alloy has excellent comprehensive performances,such as mechanical properties,corrosion resistance,and processing property so on,and thus are regarded as an engineering material widely used in manufacturing industry.Traditional casting process is difficult to form complex shape and thin wall individualized parts,and has the problems of long production cycle and high mold cost,etc.Due to its unique technical advantages,selective laser melting(SLM)technology is expected to solve the above problem during casting of silicon brass alloys and their parts.However,metallic alloys adaptive to SLM should meet the following three basic requirements with regard to physical properties of relatively high laser absorptivity,relatively low thermal conductivity,and especially without volatile elements with low boiling point.Undoubtedly,silicon brass alloy does not meet the aforementioned three basic requirements.On this account,this dissertation studied selective laser melting technology of high-strength silicon brass alloy and its microstructure and properties.By doing so,it is expected to solve the problems of forming complex shape silicon brass alloys and selective laser melting technology.Firstly,silicon brass alloy powder was prepared by gas atomization technology,and sieving and air classification were used to obtain spherical brass alloy powder with the particle size distribution of 15-53 μm and an average particle size of 27.87 μm.XRD and SEM analysis shows that the atomized powder consists of face-centered cubic(fcc)α-Cu(Zn,Si)phase and close-packed hexagonal(hcp)Cu7Si phase,and has a microstructure of columnar and cellular crystals.Due to the volatile zinc element contained in the silicon brass alloy,gas volatilization and powder spattering are apparent during the SLM process.The volatile gas contains 71.2 vol.%ZnO and 28.8 vol.%α-Cu phases.Laser power and scanning speed have important influences on the density and surface roughness of the SLMed silicon brass alloys.The optimized process parameters are the laser power of 190 W,the scan speed of 200 mm/s,the powder coating thickness of 30 μm,and the scan spacing of 80 μm,respectively.The SLMed sample manufactured by the optimized process parameters has high density of 98.8%and a surface roughness of 11.5 μm.Subsequently,high-strength silicon brass alloy were manufactured by the optimized process parameters.The manufactured sample consists of fcc α-Cu(Zn,Si)phase and hcp Cu7Si phase,together with obvious(100)texture,and has a microstructure of cellular and columnar crystals.TEM examination shows that its microstructure is composed of equiaxed Cu7Si phase with grain sizes of 80-210 nm,which is dispersed along phase boundary of equiaxed a-Cu phase of 350-700 nm.Meanwhile,profuse nano-sized twins are embedded into inside the equiaxed a-Cu grains.EBSD test indicates that a typical Gaussian texture{110}<001>is present in the manufactured sample.Tensile test presents that the manufactured sample exhibits a yield strength of 275 MPa,a tensile strength of 371.5 MPa,a fracture plasticity of 7.5%,and a microhardness of 156 HV.Noted that,the yield strength and microhardness are far higher than those of the cast counterpart.Electrochemical corrosion results show that the corrosion resistance of the SLMed brass alloy is better than that of the cast counterpart.Finally,the effects of annealing temperature and holding time on phase component,microstructure,mechanical properties,and electrochemical corrosion properties of the SLMed silicon brass alloy were studied.After annealing treatment,the Cu7Si phase is completely dissolved into the a-Cu(Zn,Si)matrix,and the corresponding microstructure changes from the pre-annealing cellular and columnar crystal structures to the equiaxed structure and annealing twins.Meanwhile,the original texture is weakened in the SLMed sample,and the low-angle grain boundary transforms into high-angle grain boundary during annealing treatment.With the increased annealing temperature and holding time,the ratio of high-angle grain boundary increases gradually;at the annealing temperature of 850 ℃ with the holding time of 1h and the holding time of 4h with the annealing temperature of 600 ℃,the corresponding maximum values are 98.36%and 93.36%,respectively.Concomitantly,the proportion of the E3 boundary increases and the microhardness decreases gradually,accompanied by the increased fractured strain and the increased electrochemical corrosion resistance.In conclusion,in terms of the silicon brass alloy failing to meet the aforementioned three basic requirements,SLM technology of high-strength alloy can be optimized.Furthermore,heat treatment can be utilized to tailor microstructure and properties of the SLMed silicon brass alloy.Therefore,this dissertation can expand the alloy composition range adaptive to SLM technology and the application fields of the silicon brass alloy,which has important scientific and engineering significance.