Research On Microstructure And Performance Of Environmental Friendly And Free-cutting Silicon Brass

Research and development of lead-free brass is a significant project in the brassindustry nearly20years in domestic, a number of studies in exchange for many goodachievement, but because of the limitation of cost and preparation process, smost ofthem were rejected by industrialization, industry and universities have to review theresearch direction of lead-free brass. After the C69300alloy came out in Japan,silicon brass become the most potential study object, but economic factors driving thereseachers research on silicon brass with lower copper content. Due to a lack ofprofound theory, the progress to research silicon brass is slow, and there is still noalternative which can instead leaded brass primely at present.In this paper, the phase diagram calculation, microstructure, DTA, XRD, SEMand hardness, dezincification corrosion resistance test and milling force test were usedto compare the cutting performance and corrosion resistanc of silicon brass withdifferent phase composition, meanwhile the effect of B and RE elements on siliconbrass were also studied, the main conclusions were drew as follows:1. In the process of grain refiner screening, both of the elements of Ti and Fewould be form hard point ally with P element, which were visible to the naked eye,affected on the performance of the brass polishing and electroplating, and increasedthe cutting tool wear and tear. Therefore, Ti and Fe elements were unsuitable refiningagent for phosphorus silicon brass.2. In this experiment, the matrix of2-3-RE and2-3-B alloy was single β phase,with much phosphorus silicon phase distributed on it, which acted as chip breakingparticles, the chip morphology and surface roughness were the smallest, thecomprehensive cutting performance of2-3-RE alloy was better than that of HPb60-2brass.3. The electrochemical extraction technology was used to separat the particlephase from silicon brass, and more accurate composition of the particle phase wasmeasured, results showed that the prticles included P,Si,Cu,zinc,Sn and La elements,of which Sn and La elements were contribute to the production of phosphorus siliconphase; the black phase in3-3-RE alloy should be κ phase, but still need furtherconfirmation. 4. Both B and RE elements could improved the dezincification corrosionresistance performance. Silicon brass with lower copper content, had a betterdezincification corrosion resistance if adding RE element, of which2-3-RE alloy hadthe thicknest dezincification layer, namely262.94μm; while sillicon brass withhigher copper content and adding B element, the dezincification corrosion resistancewas better, of which the dezincification corrosion resistance of3-2-B alloy is best, thedezincification layer thickness was only238.97μm.5. For alloy with single β phase matrix, the morphology of corrosion isuniformity dezincification corrosion, while alloy matrix with (α+β) phases, β phasewas corroded preferentially, but both of their corrosion mechanisms were zincpreferentially dissolved; the corrosion morphology of leaded brass was penetrationcorrosion, which only β phase was corroded, the mechanism was zinc preferentiallydissolved, and then for the uniform corrosion and the corrosion mechanism isdissolve-redeposition.