Research On Solidification Microstructures,Properties And Mechanism Of Brass Alloy Under Electric Pulse Treatment

It was studied experimentally that the effects of Electric Pulse Treatment (EPT) and modification on casting microstructure, property and cutting performance of lead brass ingots. It is determined that the microstructure of leaded brass is remarkably refined, and the cutting performance is improved by EPT. On the basis of the investigation, a kind of (β+γ) of duplex silicon brass alloy with cutting, wear-resisting and corrosion resistance was fabricated explored by mean of applying EPT in the molten, with silicon instead of lead and utilizing the alloying theory and proper heat treatment. The mechanism model of EP-modified cluster in the (β+γ) of duplex silicon brass alloy molten was established by means of the investigations of the alloy characteristics of liquid-solid transformation and the solid-state phase transformation, which was validated by experiments.The investigation results show that appropriate parameters of EPT can refine casting microstructure of (β+γ) of duplex silicon brass alloy, and increase the solid solubility of Si in the β phase matrix, and decrease the size and quantity of the y phase. Thus, the segregation of y phases, the cutting, wear resistant and corrosion resistant properties of the alloy are improved. Furthermore, when pulse voltage is1000V, the pulse time is30s, the pulse frequency is8Hz, y phase with dot shape distributes uniform in β phase matrix, and y phase size decreases from44μm to22μm. Meanwhile, the volume fraction of y phase reduces from66.23%to49.94%, and the microhardness of matrix increases from336.03HV to399.62HV, and the tensile strength increases from250MPa to380MPa.The mechanism model of EPT in the (P+y) of duplex silicon brass alloy molten indicates that the role of free zinc atoms and Cu-Zn clusters of rich Cu were enhanced, and the numbers of Cu-Zn clusters of rich Cu increased, and the Cu-Zn clusters of rich Cu become smaller by EPT. Moreover, the model is validated indirectly by means of DSC, thermal expansion analysis, the change of the size and volume fraction of the y phase, the microhardness of matrix, and electron microscopic analysis. Meanwhile, on the base of the model, the mechanism of EPT on refining casting structure, improving alloy segregation and increasing wear-resisting and corrosion resistant is analyzed. Based on EPT investigation of the (β+γ) of duplex silicon brass alloy, the heat treatment technology is studied, which can offer steady experimental basis on EPT application. The results show that the microhardness of alloy matrix is75%of the untreated one, which is treated under the optimal EPT parameters (pulse voltage is1000V, the pulse time is30s, pulse frequency of8Hz), then the treating temperature, the (β+γ) of duplex silicon brass alloy ingots are heated at600℃for4h, quenched in water, and then aged at250℃for6h. The heat treatment process not only can drop the high matrix hardness induced from EPT refined crystal and solution strengthening of β phase, but also the modification of y phase can be realized, and the cutting performance is improved. This research provides a theoretical basis for the development of new technology of unleaded free-cutting brass.