Cerium-based conversion films developed on LiAl-layered double hydroxide coatings for corrosion protection of AA7075 aluminum alloys

Abstract

The paper presents several experimental results regarding the influence of various procedures applied to incorporate Ce species in hydrotalcite–type chemical conver­sion coatings on the overall corrosion performance for AA 7075 aluminum alloy as a metallic substrate. Two routes were envisaged: (i) chemical incorporation of Ce by immersion in cerium nitrate solutions and (ii) electrochemical deposition of hydro­phobic Ce - based layer involving ethanolic solutions of stearic acid and cerium nitrate. The chemical route involving immersion in cerium nitrate solutions led to the incorpo­ration of 2.46 – 6.84 wt.% Ce in the composition of the porous conversion layer. The electrochemical process facilitated the formation of a hydrophobic cerium stearate layer on porous hydrotalcite conversion coating showing water contact angles of about 132o and a higher Ce content incorporated of 6.55 – 9.73 wt.%. The corrosion performance of the Ce-based conversion coatings is also discussed.

Advances in processing and characterization of conversion coatings

“…The sacrificial ZnFe alloy coating electrodeposited on steel was further modified by a hybrid sol-gel silane coating [7], while electrodeposited Zn coating on steel was modified by electroless cerium oxide layer deposition and additional sealing in boiling water [8]. Ce was also used in [9] as a dopant in hydrotalcite-type protective chemical conversion coatings on aluminium alloy AA 7075. Finally, the effect of tannic acid embedded in polystyrene coatings either directly or within mesoporous silica-nano-containers on the corrosion protection of steel and zinc substrates was discussed in [10].…”