Gong Zhu-qing

Electrodeposition of Ni-Cr alloy on aluminum substrate

Ni-Cr alloys with mass fraction of 1.4%–23.9%Cr, 76.1%–98.6%Ni, and hardness of 70.5–80.5HR were electrodeposited on aluminium substrate from the trivalent chromium sulphate-chloride solution using citric acid as complexing agent. The aluminium was pretreated by means of degreasing and eroding, polishing and twice chemical immersion of zinc. The effects of electrodeposition parameters such as current density, temperature, pH value and bath concentration on the composition and hardness of deposits were investigated. The results show that the Cr content increases with the increase of current density and the decrease of temperature, and that it increases with the increase of pH value to a maximum and then decreases. The increase of Cr content leads to the increase of hardness of the Ni-Cr layers. The deposits with high Cr content are of good corrosion resistance. Good adherence of Ni-Cr deposits to aluminium substrate is obtained. The Ni-Cr alloys are the Ni-Cr solid solution with fcc crystalline structure. The Ni-Cr alloy deposits are fine, bright and smooth and compact.

Influence of potential on structure and properties of microarc oxidation coating on Mg alloy

Purpose – To obtain an optimized microarc oxidation (MAO) coating on magnesium alloy from an environmentally‐friendly electrolyte free of Cr6 +  and PO43− and to investigate the influence of oxidation potential on the morphology, composition, structure, and other properties such as micro‐hardness and corrosion resistance.Design/methodology/approach – A constant potential regime was applied to produce the coatings and scanning electron microscopy, energy dispersive spectroscope, X‐ray diffraction, hardness testing and electrochemical methods were used to study coating properties.Findings – The results clearly show that oxidation potential plays an important role in the formation of coating structure and properties. The MAO coating is smooth and white and consists of two layers. The external layer is loose and porous and enriched in Al and Si. Moreover, the content of Al and Si increase with operated potential. The inner layer is compact and the content of Al and Si are lower than are those of the external ...

The electrochemical behaviour of pulse-plated nanocrystalline iron-nickel-chromium alloy

The corrosion behaviour of pulse plating nanocrystalline iron‐nickel‐chromium (Fe‐Ni‐Cr) alloys in acidic, alkaline and salt solutions has been studied. The corrosion resistance of nanocrystalline Fe‐Ni‐Cr alloys in various compositions and other nanocrystalline referred in literatures have been compared. The results reveal that the corrosion of Fe69Ni10Cr20S alloy has dominant superiority over the other nanocrystalline materials.

Corrosion leaking of preheater weldment in alumina factories

Stress corrosion cracking (SCC) and anticorrosion measures of TU42C weld-joint were studied by constant load experiments and pickling experiments. The results show that in 40% (mass fraction) NaOH solution at 110 °C, caustic SCC occurs in TU42C weld-joints at the applied potential of −1 020 mV(vs SCE) for 3 d while at the potential of −950 mV(vs SCE) for 10 d. All the cracks are intergranular. In the 10% sulfuric acid, the cracks have the most negative self-corrosion potential −432.5 mV(vs SCE) and are active to be further corroded by the acid. Because of the same corrosion behaviour as the lab weldment, preheater’s cracking in alumina factories is attributed to the combining actions of previous caustic SCC in Bayer solutions and continuous acid corrosion by pickling with the addition of RD. The following measures are effective to prevent the corrosion failure of preheater, such as post-weld heat treatment at 620 °C to relax the residual weld stress, addition of CC3 and L826 as the corrosion inhibitors to improve the pickling and cleaning by the high pressure water instead of by pickling.