Papers by Keyword: Chemical Conversion Coating

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Authors: Yan Bo Wu, Si Si Zeng, Peng Sun
Abstract: In this paper, we made two different chemical conversion coatings on aluminum alloy by TiOSO4 and Na2WO4. The morphology of the chemical conversion surface layers were observed by scanning electron microscopy (SEM). The microcosmic phase structures were characterized using X-ray diffraction (XRD). Electrochemical method was used to study the coatings corrosion resistance. The results indicated that the two conversion coatings were crystal structure material, the surface of coating were both show pothole structure. TiOSO4 coating have better corrosion resistance than Na2WO4 coating.
Authors: En Hou Han, Wan Qiu Zhou, Da Yong Shan, Wei Ke
Authors: Xiang Jie Yang, Hua Lan Jin
Abstract: The morphology and the mass change of the AZ91D alloys matrix after pretreatment, the morphology and the phase composition of chemical conversion coatings formed by phosphate and stannate were studied using scanning electron microscope, X-ray diffraction and the mass loss method. The corrosion resistance of the coatings were studied by salt spay test and damp heat test. The results show that the phase composition of matrix before and after pretreatment is almost changeless and the mass diminishes a litter, the deep micro flaw appears near between α-Mg and β phase during acidic pickling. The phosphate chemical conversion coating is mainly composed of Mg, MgO and some amorphous phase, and the stannate conversion coating is crystal structure and mainly composed of Mg, Al12Mg17 and MgSnO3•3H2O. Results from salt spay test and damp heat test indicate that the two coatings also can provide good protection for the magnesium alloy matrix, and stannate is better than phosphate.
Authors: Wan Qiu Zhou, Da Yong Shan, En Hou Han, Wei Ke
Abstract: A phosphate conversion coating was deposited on diecast AZ91D magnesium alloys, the film was a complex phosphate containing Mg and Al,which showed amorphous structure. Corrosion resistance of conversion coating in 3.5%NaCl was investigated by polarization curve. It was showed that the anodic branch of polarization curve for the phosphate conversion coating presented typical passivation characteristic. Immersion test results showed that the corrosion rate of phosphate conversion coating was less than that of chromate Dow7 film.
Authors: Shi Guo Du, Jun Yan, Hai Ping Cui, Bin Wang
Abstract: Molybdate conversion coatings were prepared on the anodized surfaces of aluminum alloy substrates, and the corrosion resistance in 3.5% NaCl solution was also investigated. The effects of the main parameters on the quality of the coatings were discussed. The morphology and chemical composition of the conversion coatings was examined by SEM and EDS. SEM observation showed that the coatings were composed of small sheet grains with tiny cracks between them. EDS analysis showed that the main element of the coatings was molybdenum. The results of polarization curve showed that the coatings effectively inhabited the pitting corrosion of aluminum alloy substrates. In the end the possible conversion mechanism was discussed.
Authors: Hiroyuki Umehara, S. Terauchi, M. Takaya
Authors: Yan Bo Wu, Si Si Zeng, Peng Sun
Abstract: Ti-W composite coating was made by chemical conversion method on aluminum alloy. By orthogonal experiment, the optimal coating-forming conditions were the concentration ratio of TiOSO4 and Na2WO4 was 0.3 g/L:0.3 g/L、KMnO4 1.0 g/L、NaF 1.0 g/L、reaction temperature 40°C、reaction time 2min. The morphology of the coating was observed by scanning electron microscopy (SEM). Coating composition and the microcosmic phase structure were characterized using energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) respectively. Electrochemical test was used to study the coatings corrosion resistance. The results indicated that the composite chemical conversion coating is a crystal structure material that composites with Al、Mn、W、Ti et al., its surface appears as a accumulation of fibroid spherical particles, the crystallinity of conversion coating is better than uncoated sample obviously. The corrosion potential of the coating is improved to -0.440V, they were both prove the corrosion resistance has improved.
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