| Due to the great harm of toxic Pb elements in lead brass to human body and environment,the standard of GB18145-2014 strictly restricts the maximum lead release from faucets,which results in that it is difficult for the lead brass HPb59-1 to meet the aforementioned standard.In order to solve this problem,granted and supported by the Guangdong Application-oriented Special Funds for Science and Technology R&D——Development and Application of Key technology for New-generation environmentally-friendly brass faucet,and the Guangdong Special Funds for Public Welfare Research and Capacity Building——Development of A New Lead-free and Free-cutting Silicon Brass Faucet Material,our research groups have developed a environmentally-friendly free-cutting high-strength corrosion-resistance silicon brass alloy,which could be used as faucet materials.Undoubtedly,compared with current lead-brass used as faucet,this lead-free silicon brass has unique physical parameters such as density,melting point and solid-liquid phase line.Therefore,it is particularly important to explore the forming process of its complex and thin-walled faucet parts.In view of this,this lead-free silicon brass was adopted as the research object and the low pressure die casting(LPDC)technology was utilized as the forming method,in order to explore the suitable LPDC process for industrialization faucet.It is expected that research results would break the research situation of staying only in materials research and non-entering industrialization development for environmentally-friendly brass alloy.According to technological process of industrially manufacturing faucet parts,homogeneous alloy melts were obtained by melting elementary substance and intermediate alloys,and this homogeneity was verified by the homogeneity in microstructure and properties of sequentially numbered alloy rods,thus optimizing melting process of alloy melts and providing homogeneous alloy rods for subsequent LPDC process.Afterwards,various physical parameters measured were used to simulate the LPDC process of the lead-free silicon brass faucet parts,in order to reveal the influence of process parameters on the flow field and temperature field during filling and solidification.Finally,the LPDC process of faucet parts was performed based on simulation results and thus the relationship between process parameters and microstructures-properties was explored,consequently determining optimization LPDC process parameters.The main conclusions are as follows:(1)Through the analysis of five alloy rods selected from a series of sequentially numbered alloy rods,it is found that alloy melts from the same melting furnace are of homogeneity in microstructure and properties.The microstructure is predominantly composed of bcc ? phases,together with acicular and granular fcc ? phases acted as second phase and distributed in the ?-matrix.Compared with the lead-brass HPb59-1(tensile strength 420 MPa,elongation 12%),the average tensile strength of the alloy rods is 550.0MPa,30.9% higher than that of HPb59-1;the average elongation is 16.9%,40.7% higher than that of HPb59-1.Meanwhile,its brinell hardness is 157.9HB;the average dezincification layer thickness is 140.49?m,far less than that of HPb59-1(369.1?m).The precipitation values of metal contaminants are lower than the corresponding values according to GB 18145-2014.Its corresponding comprehensive cutting performance is 115.23%,similar to that of HPb59-1(115%).These results indicate that the silicon brass can meet the requirements of the faucet products.(2)The filling process and solidification process of LPDC of this silicon brass were simulated based on Anycasting software by different pressure-adding speeds or casting temperatures.The results indicate that the appropriate pressure-adding speed is 9000Pa/s and the appropriate casting temperature is 1000?-1015?.(3)The microstructural evolution and mechanical behavior of this silicon brass was revealed via a variable-controlling approach by LPDC.The results show that: a)with increased casting temperature,a longer time for phase transformation allows the granular ? grain to transform into the acicular type,negatively affecting the elongation;b)with increased filling time,a longer time for phase transformation facilitates the coarsening of ? grain and the formation of acicular and lath-shaped ? phase,negatively affecting the elongation;c)with increased holding pressure,? grain has a finer size and the granular ? precipitation is increased,resulting in improved mechanical properties;d)with increased pressure holding time,? grain exhibits a finer size and ? precipitation exhibits a short rod-like morphology,leading to increased UTS and elongation.(4)As for the faucet mould and silicon brass material selected in this paper,the optimal LPDC processing parameters are a casting temperature of 1000 °C,a filling time of 4s,a holding pressure of 0.0395 MPa,and a pressure holding time of 13 s,respectively.Correspondingly,the optimal mechanical properties are an elongation of 15.0%,a yield strength of 359.8 MPa,and a UTS of 598.9 MPa,respectively.These optimal values are far superior to those of a typical lead-brass HPb59-1(GB/T 4423-2007). |
PDF Full Text Request