The Study For Transition Electroplate Of Cr-Fe Alloy

The electrodepositing Cr-Fe alloy coating was studied in the chloride system of trivalent chromium and bivalent iron. The satisfaction Cr-Fe alloy coating was obtained. An atomic absorption spectrometry was used to determine iron content in the coating. The effect of various craft conditions on chrome and iron alloy surface polarization curve by zeta potential scanning method of electrochemistry system was considered. Pure chromium coating was substituted by iron and chromium alloy coating in trivalent chromium and bivalent iron bath, not only eliminated the serious contamination, economized the energy, saved the chromium resources, but also obtained hard chromium alloy which was easy to form the amorphous state. The coating had a more superior capability than the crystalline state. The factors of effect on the coating surface appearance were considered by SEM to observe the coating microstructure.The electrolysis system, which was the CrCl₃·6H₂O + FeCl₂·4H₂O + NH₄Cl + H₃BO₃ + NH₂CH₂COOH + vitamin C+ NaCl, was considered .The optioned experiment condition ,which could attain coating of luminously, smooth, uniformity and compact, was obtained by observing the coating quality ,content of the chromium and iron as well as the current efficiency. The optioned conditions were that glycine containing was 0.6 mol/L, current density D_k=10 A/dm², pH=1.8～2. 2, the temperature 15～25℃, the plating time 10～20 min, the electrical conductivity was NaCl. The experimental results indicated that the current efficiency and the ratio of chrome and iron reached maximum when the current density is 10 A/dm² in the range of 5～15 A/dm².Along with coating from the substrate to the surface, the iron content gradually reduced, and the chromium content gradually increased, and the ratio of iron and chrome also increased. When pH was in the range of 1. 25～2. 0, the current efficiency of iron and chrome deposits gradually elevated. When pH was 2.0, the current efficiency was the highest. When pH continue increased, the current efficiency also declined. When KBr,NaCl were added, the current efficiency of taking NaCl as the electrical conductivity was the bigger, and the chromium content was also the bigger. The ratio of chrome and iron was obviously increased with joining of lauryl dimethyl benzyl ammonia chloride (1227) to the bath .Using the different complexant, the current efficiency was the biggest with glycine, and HBF₄ was the second one, and sulfamic acid was the smallest. The coating was smoother, luminous and compact with glycine. When reagent was changed into the thionamic acid, but there was nearly no coating with sulfamic acid. Using HBF₄ as complexant, the coating was thick, but the coating nearly peeled off, and became dark in the surface.It could be seen from polarization curve that the polarization curve was moved to negative orientation, potential difference increased and the cathode polarization increased by agitating under the same condition. Agitating was disadvantageous to separate out H₂, but was advantageous to electroplate Cr-Fe alloy. With the temperature elevated, the polarization changed slightly which was disadvantageous to electroplate Cr-Fe alloy. The polarization curve was migrated to plus orientation with the increasing of pH. The influence of polarization curve was not appearance in the pH range of 1.8～2.2. The polarized ability was bigger to use glycine as the complexing agent, and the coating of luminously and reliable might be electroplated. When the glycine density was 0.6mol/L, the polarization was the biggest, and it was advantageous to separate out Cr-Fe alloy.The coating surface had the Small crack and a tiny spherical body pellet, which is crystalloid by observation of the microstructure picture of the coating.The satisfaction Cr-Fe alloy coating was obtained in the chloride system of trivalent chromium and bivalent iron by the direct-current power. The transition plate of Cr-Fe was realized, that was the chromium content gradually increased from the substrate to superficial of coating. When direct-current power and alternating and direct anisomerous power were used to plate steel pipe, there were no coating. But the uniformity, smoother, luminous and thicker coating was obtained when the pulse power galvanization was used. The galvanization of steel pipe wall was realized which was very difficult. The ratio of Cr and Fe and the coating quality as well as the current efficiency might be changed by changing the galvanization craft condition as well as the complexing reagent, the additive and so on.