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Adherence of electrodeposited Zn-Ni coatings on EN AW2024 T3 aluminium alloy

Alexis, Joël and Adrian, Denise and Masri, Talal and Petit, Jacques-Alain Adherence of electrodeposited Zn-Ni coatings on EN AW2024 T3 aluminium alloy. (2004) Surface Engineering, 20 (2). 121-127. ISSN 0267-0844

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Official URL: http://dx.doi.org/10.1179/026708404225010748

Abstract

The use of hexavalent chromium in surface treatments will be reduced in the future, as it is suspected to be carcinogenic. Electrodeposition of Zn-Ni, which is currently used on steel, represents a non-chromate alternative surface treatment for the corrosion protection of aluminium alloys. Zn-Ni coatings were electrodeposited onto an EN AW2024 T3 aluminium alloy sheet in a laboratory flow cell. To obtain several percentages of Ni in the coatings, solutions with different Ni2+ concentrations were used. The influence of a specific pretreatment to promote adherence, such as zincate immersion (109 g L-1 ZnO, 525 g L-1 NaOH) or phosphoric anodisation (36 wt-%H3PO4, 20°C) prior to electrodeposition was also investigated. The smoothness of the coating, measured on a three-dimensional roughness tester, increased when the percentage of Ni increased. This can be explained by a microstructural refinement observed using SEM and AFM. These microstructural changes are due to the evolution of the crystal structure of the coatings and can be observed by X-ray diffraction. The mechanical properties of the coatings (hardness and Young's modulus) were measured by microindentation and nanoindentation. The adherence of the coatings was tested by a scratch test and a three point bending test dedicated to coatings. The scratch behaviour of the coatings was a function of the percentage of Ni. The scratches observed indicate a ductile fracture for coatings with a low percentage of Ni and a brittle fracture for a high percentage of Ni. Bending tests demonstrated the favourable effect of pretreatments such as zincate immersion or phosphoric anodisation as well as adhesion enhancement as a function of increasing percentage of Ni.

Item Type:Article
Additional Information:Thanks to Maney Publishing editor. The definitive version is available at http://www.maneyonline.com/doi/abs/10.1179/026708404225010748
Audience (journal):International peer-reviewed journal
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Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
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Deposited On:07 Jan 2014 14:43

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