Effects of pH Value of the Electrolyte and Glycine Additive on Formation and Properties of Electrodeposited Zn-Fe Coatings

Environmentally friendly and cyanide-free sulfate bath under continuous current and the corrosion behavior of electrodeposits of zinc-iron alloys were studied by means of electrochemical tests in a solution of 3.5% NaCl in presence and absence of glycine. The effects of pH on the quality of Zn-Fe coatings were investigated in order to improve uniformity and corrosion protection performance of the coating films. The deposit morphology was analyzed using scanning electron microscopy (SEM), and X-ray diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. It was found that the uniformity and corrosion resistance of Zn-Fe coating films were strongly associated with pH of the coating electrolyte. To obtain the effect of pH on the film quality and corrosion performances of the films, the corrosion test was performed with potentiodynamic anodic polarization method. It was also observed that uniformity and corrosion resistivity of the coating films were decreased towards and then improved with increasing pH value of the electrolyte. The presence of glycine in the plating bath decreases the corrosion resistance of Zn-Fe coatings

A Comparative Study on the Effects of Different Thermochemical Coating Techniques on Corrosion Resistance of STKM-13A Steel

The corrosion resistances of three different thermochemical coatings (grown using titanizing, boriding, and borotitanizing treatments) applied to STKM-13A steel surfaces were investigated. The coatings were characterized using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 2D profilometry, and microhardness experiments. The corrosion tests were conducted using both electrochemical and static immersion methods, in 3.5 pct NaCl and 40 pct HF acid solutions, respectively. The corrosion resistance of STKM-13A steel was enhanced after the coating process. The specimens were exposed to more corrosion in the HF solution than in the NaCl solution. The best corrosion resistance was obtained in the borotitanized and borided specimens immersed in the NaCl and HF solutions, respectively. The borided STKM-13A steel sample showed even less cumulative weight loss than Inconel 625 in the static immersion HF acid solution test. This suggests potential use of the borided STKM-13A steel in the uranium production units of nuclear power plants as an alternative to more costly alternatives such as Monel, Inconel, and Hastelloy. (C) The Minerals, Metals \& Materials Society and ASM International 201