The Development Of The Green Unleaded Free-Cutting Brass

The Lead brass is used in various fields of machinery manufacturing widely because of its superior performance, easy molding cutting and ability corrosion resistance. However the lead is extremely harmful in the environment. The purpose of this research is to produce a kind of unleaded free-cutting brass, which can used to instead of the traditional lead brass.The experiment is based on the theory of lead brass cut ability, considering using Si, Al and Mg to replace Pb, and using common casting to get brass alloy which microstructure is (β+γ). The second phase y becomes small and mass by modification to play the role of lead to broken crumbs. The number of particle to broken crumbs is added by compound composed of Mg, Cu and Si in the alloy.The effect of adding Ti and Mg on the microstructure and corrosive properties of the alloy were study by optical microscope, SEM, energy spectrum analyzer. The mechanical properties, corrosion resistance and cutting performance are reviewed by the tests of mechanical, dezincification and cutting. The corrosion process and mechanism of cutting process are analyzed.The microstructure of the brass consists of matrix P, tiny metamorphic y and particle composition of Mg. The y is changed from the large flower-like into a small dot and distribution diffuse in theβby modification of Ti, and the mechanical properties of the alloy is improved. The number of compound increase as the content of Mg adds. The performance of alloy strengthened as compound particle disperse in matrix distribution when the content of Mg less than 2%.The depth of dezincification and the weightlessness are decreased after modification and heat treatment. However, Mg promotes dezincification. The corrosion resistance performance of this unleaded brass is excellented. The depth of dezincification is 131μm, the order of magnitude of diffusion coefficient of Zn is 1011～1012, and the weightlessness of alloy conforms to index regression.The scraps become smaller, cutting force decreases and cutting performance improved by adding Ti and Mg in the alloy. The factors effecting force are in the order of depth of cut, feed rate and cut speeding. According to the fracture theory of Griffith, the critical dimension of particle was calculated, which is 0.88μm.