Study On Control Of Inclusions In CuCr Alloy Prepared By Aluminothermic Reducion-Electronmagnetic Casting

CuCr alloy can be destined to have a wide application in the field which requires high conductivity and high stringent, such as the lead frame of integrated circuit, electrodes, electric contact and high strength conductor. It is a kind of highpower and high voltage contact material with extensive prospect. However, the traditional methods, such as metallurgy process, infiltrating way and vacuum arc melting, have lots of shortcomings, such as the high production cost, complicated techniques, bad consistency and low rate of finished products, especially the difficulties in preparing large size of ingots. Aiming at the problems, our team proposes a new preparation method based on aluminothermy reduction process-electroslag remelting and has obtained related patents twice. In our previous work, it shows that the CuCr alloy directly prepared by aluminothermic reduction-electromagnetic casting has the defect of stomata and oxide inclusions. In this paper, the existing state and distribution of inclusions and stomata in CuCr alloy prepared by aluminothermic reduction-electromagnetic casting are systematically analyzed, which provides theoretical foundation for electroslag refining.First, the values of△Gθ、△G and△H of different temperature were obtained through thermodynamics calculation. The results show that the adiabatic temperatures is2848K, and the△G of the reducing reactions are much lower than zero, so Al is feasible to be used as reductant. The kinetics of the CuO-Cr2O3-Al system was studied by DTA technique, and the kinetic constants were calculated by Freeman-Carroll differential method. To the CuO-Cr2CO3-Al system, the apparent activation energy Ea is151.272kJ/mol, the reaction order n is2.48, and the kinetic equation isdt/dα=0.2464×105e-151272/Rr(1-α)2.48.Second, the alloy prepared in different process conditions was characterized via SEM, EDS and metallographic microscope, in which the existing state and micro-structural defects of inclusions are analyzed. The results show that:there are three distinct regions:copper-rich regions, chromium-rich regions and the inclusion regions. Inclusions are mainly in the form of stomata and Al2O3phase, mainly locating in the copper-rich phase and the interface area of chromium-rich phase and the copper-rich phase.Then, the composition of phases of the smelting slags and alloy were characterized via XRD. The results show that:the slag consists of Al2O3and a little of Cr, the alloy consists of Cr, Cu and a little of A12O3.Last not the least, the distribution of stomata and inclusions were systematically studied via metallographic microscope and Image-Pro Plus. The results show that:to apply EMS and increase water flow can also reduce the porosity, among which the doubled water flow can reduce18%of the stomata. And Cr particles can be refined by using copper mold. Also adding Na3AlF6, CaF2, CaO, heating agent can effectively reduce the inclusion content in the alloy.