作者: Li Ping Wu, Zhong Dong Yang
摘要: An environmentally friendly molybdate conversion coating based surface treatment was developed for AZ91D magnesium alloy. The EIS technique was employed to study the effects of the conversion bath composition and temperature on the corrosion protection performance of molybdate conversion coatings on AZ91D magnesium alloys. The optimum conditions under which obtained conversion coatings showed the best corrosion resistance were determined. The Nyquist results showed that the value of charge transfer resistance increased by 22.5 times for the sample treated in the optimized molybdate conversion bath.
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摘要: The Ni-P coatings were deposited on AM60 magnesium alloy by electroless plating process without or with accelerators. Without accelerators, the deposition rate is slow and required high bath temperature to obtain compact coating. There have many defects on the surface of the Ni-P coatings which deposited at high bath temperature. The composite accelerators were introduced into the bath for improving the growth rate and the quality of the Ni-P coating. Uniform, with no pores or cracks, “cauliflower-like” structure and complete Ni-P coatings were deposited only taken 20 min with additives at low bath temperature. The XRD result indicates that the structure of the Ni-P coating is amorphous nickel. The corrosion test results indicated that the corrosion resistance of this coated AM60 magnesium alloys increases distinctly as compared to bare alloys.
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作者: Li Yuan Niu, Yi Chang Su, Da Ren Sun, Guang Yu Li
摘要: The new process electroless Sn deposition on cast AZ61 was revealed, which employed to AZ61 magnesium alloy automobile parts and could provide high wear-resistant and high hardness. The pretreatment processes before electroless Sn deposition could ensure better adhesion between Sn coating and magnesium alloy. The speed of the Sn deposition increases quickly with increasing the content of composite catalysts in the plating bath. The technology is environment friendly and cannot cause hazard to environment because of absence of nickel and chromate in the whole process. Wastewater treatment technology of electroless Sn bath was investigated as well.
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作者: Khalid Abdalla, Rahmat Azmi, Aziz Azizan
摘要: The influence of phosphating temperature on the surface morphology and corrosion resistance of zinc phosphate coatings on mild steel was investigated. The phosphate layers were deposited on steel from phosphating bath at different temperatures (45 ~ 75 C). The surface morphology and composition of phosphate coatings were investigated via scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The corrosion resistance of the coatings was evaluated by polarization curves (anodic and cathodic) in an aerated 3.5% NaCl solution. The results showed that the increase in temperature of the phosphating bath up to 55 C caused an increase in surface coverage and in turn resulted in better corrosion resistance. At high temperature (65 °C and 75 °C) the deposition coverage decreased indicating that the best coverage for the phosphate layer on the metal surface was achieved at 55 °C
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作者: T.R. Tamilarasan, R. Sathish Kumar, R. Rajendran, G. Rajagopal
摘要: This article considers an experimental study of Taguchi’s parameters design to maximize the corrosion resistance of electroless Ni-P-nano-TiO2 on low carbon steel substrate. The experiments were carried out based on Taguchi’s L9 orthogonal array considering four coating parameters of three levels each namely, Bath Temperature, pH of bath, Bath Loading, and concentration of TiO2. Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) facilitated the study of the surface morphology and the chemical composition of the coatings. Corrosion performance of the deposits was evaluated by Tafel polarization technique in 3.5 wt. % of NaCl solution. The observation shows that pH level has more significant influence on the corrosion behavior of the composite deposit. The experimental study revealed that the optimum conditions are A3B3C2D1 (Temperature of 88° C, pH of 6, bath loading of 0.5 dm2/l, and TiO2 concentration of 2 g/l).
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