Electrodepositon Zn-fe Alloy In Zincate Solution

The zinc-iron alloy elcctroplating was popular for its cheapness and high corrosion resistance. The corrosion resistance will be even better after passivated. The zinc-iron alloy elletroplating bath was obtained by adding ferrous ion and chelate agent in zincate solution. The cathode and anode polarize curve was measured when changed the concentration of the element in electroplating bath. The apprearance of the layer was observed by microscope. The influencing factor of the layer appearance such as the concentration of ZnO, chelate agent, ferrous ion and additive was investigated by Hull trough test. The zinc-iron alloy elletroplating technics with shining appearance layer was obtained. The corrosion resistance of the layer was investigated by using immersion-test, polarize curve and the electrochemistry impedence. The microcosmic photograph of zinc-iron alloy was investigated by XRD.The influencing factor of the iron content of the alloy such as the element of the electroplating bath was investigated, as well as the electroplating time and the current density. The result is the iron content in the layer decreased when increasing ZnO, NaOH or chelate agent concentration in the solution. When increasing the concentration of the ferrous ion in the solution, the iron content in the layer increased. When the current densiry increased or the electroplating time lengthed, the iron content in the layer decreased. The zinc-iron alloy elletroplating technics, which can electrodeposition zinc-iron alloy with the iron content between 0.3%-0.7% was zinc oxide 10-14g/L, sodium hydroxide 100- 140g/L, ferrous ion25-50mg/L, chelate agent15-25g/L, additive4ml/L and the current density was 1A/dm². The polarize curve of the passivated zinc-iron alloy layer with different iron content and the passivated pure zinc layer was measured in the 5%NaCl solution. The corrosion resisitance was better when the iron content was 0.5%. There was no rust on the surface of the passivated 5 micron thick layer with 0.5% iron, after 2000h immersed in 5%NaCl solution.The influencing factor of the iron content in zinc-iron alloy such as pulse frequence, working proportion and pulse average current density was investigated by using SMD-30 pulse power. The iron content was lowest at 200Hz, when using the same working proportion. The iron content decreased when the working proportion increased, when using the same pulse frequence. The corrosion resistance of the layer that elelctrodeposited by different pulse parameters was investigated by immersion test, polarize curve and the electrochemistry impedence. The corrosion resistance of the layer obtained by pulse current was better than obtained by DC, and the pulse current efficiency was higher than that of DC. The zinc-iron alloy with the best corrosion resistance was obtained by using pulse frequence 1000Hz, working proportion was 30% and the average current density was 1A/dm²How the pulse parameters influencing the iron content in the layer when adding rare earth in the electroplaintg bath was investigated, as well as the concentration of Ce³⁺ or La³⁺. When adding more Ce³⁺ or La³⁺ in the electroplating bath, the iron content in the layer decreased. The iron content of the alloy which was between 0.2%-0.5% became stably when changing the pulse Working proportion, after adding Ce³⁺ or La³⁺ in electroplating bath. When the pulse frequence was 50Hz, the iron content was 0.2%. The corrosion resistance was tested by polarize curve and electrochemistry impedence in the 5%NaCl solution, after adding Ce³⁺ in the solution, the layer with the best corrosion resistance was obtained when the pulse frequence was 125Hz and the proportion was 30%. When adding La³⁺ in the solution, the layer with better corrosion resistance only obtained when the pulse frequence was 125Hz or higher.