| In aluminum electrolysis industry, for traditional conductive steel rod used as inert anode connector, the existence of low performance of high-temperature resistance, peeling of surface oxidation film formed in electrolysis process, and interface crack with anode is inevitable. In this paper, in order to improve the performances of conductive connecting rod, it is studied that process of preparation for obtaining stable and high corrosion resistance metal conductive connecting rod, powder metallurgy (PM) method used to fabricate samples of the rod, the effects of sintering process on densification of the rod, and the effects of alloy elements (Co, Al, Cr, etc) on oxidation resistance performance of Cu-Ni based alloy. Optimal alloying component can be determined by selecting an alloying constituent with high oxidation resistance performance, and casting method was utilized for optimizing performance of the rod alloy. Above all conclusion can be drawn as follows:1) Study of alloy densification process was conducted. At a lower sintering temperature, the sintering mechanism of Cu-Ni alloy is solid-phase-sintering, and it is hard to for densification, only obtaining a low density of 78%. Liquid-phase-sintering can evidently improve densification, but an excessive high sintering temperature can lead to over-heating. At last an optimal sintering temperature of 1250℃was determined, by which a high density of 95.6% and grain size of 20-30μm are obtained.2) Oxidation experiment of Cu-40Ni-10Fe-5Co alloy at 960℃was performed. It can found that the oxidation film is mainly consisted of Ni element. Addition of Fe and Co element shows marginal improvement of structure and property of oxide film. Moreover, the oxidation film is porous which can not prevent oxygen diffusion, leading to serious oxidation phenomenon inside of matrix.3) Effects of Al and Cr (5-12.5% by weight) on oxidation performance of PM Cu-Ni-Fe-Al and Cu-Ni-Fe-Cr at 850-900℃were investigated and conclusion can listed as follow. Formation of layers is very obvious for oxidation film of Cu-Ni-Fe-5Al. The layers structure from outermost layer to innermost layer is Cu oxide, Cu and Ni mixture oxide, Ni-Fe-Al mixture oxide, Al2O3, respectively. The innermost two layers, especially the Al2O3 layer can prevent oxygen diffusion effectively; As to Cu-Ni-Fe-Cr alloy, a low Cr content could not form a useful oxidation film, while a high Cr content of 10% shows a better oxidation resistance performance which is similar to Cu-Ni-Fe-5A1 alloy. However the difference between the two alloys is that A12O3 tends to be formed in inlayer of Cu-Ni-Fe-5Al oxidation film, while in Cu-Ni-Fe-10Cr oxidation film Cr2O3 tends to form in inlayer of oxidation film firstly, and then with the increase of temperature and oxidation time, it shows protective action in outer layer of oxidation film.4) Compared with alloy fabricated by PM, casting alloy shows better densification and uniform microstructure, facilitating diffusion of selective oxidation elements (Fe, Al and Cr) into oxidation interface and inducing rapid formation of protective layer, which can be represented in a thin, uniform and smooth structure oxidation film and better oxidation resistance property. Oxidised for 24 h at 850℃, the weight of casting Cu-40Ni-10Fe-5Al alloy increases 1.2mg/cm3 and that of casting Cu-40Ni-10Fe-5Cr alloy increases 0.78mg/cm, the oxide film thickness of casting Cu-40Ni-10Fe-5Al alloy is approximately 30-35μm and that of casting Cu-40Ni-10Fe-5Cr alloy is approximately 30μm.5) Oxidation experiments of Cu-40Ni-10Fe-5Al and Cu-40Ni-7.5Fe-10Cr were performed under electrolyte environment with temperature of 960℃. For experiment of Cu-Ni-Fe-5A1 alloy, under the combined actions of electrolyte and oxygen, oxidation films are more easily to come off, due to low adhesive force between Al2O3 and substrate. While in the experiment of Cu-Ni-Fe-10Cr alloy, a very dense Cu-rich oxidation layer was formed in the initial stage of oxidation, moreover, this layer exhibits significantly high chemical stability, and prevents lectrolyte from penetrating into substrate. |
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