The characterisation of Ce-Mo-based conversion coatings on Al-alloys: Part I

Microstructural and electrochemical characterization of environmentally friendly conversion layers on aluminium alloys

“…1,3,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Amongst the alternative pre-treatments one of the most promising involves rare earth metals, particularly Ce. conversion layers (CeCL) on Al alloys started to be investigated in the mid 80's by Hinton and co-workers.…”

“…For this reason, in the reviewed literature a wide variation on the conversion bath composition has been detected, with different Ce ions sources and acidifying agents. 1,3,[16][17][18][19][20][21][22][23][24][25] Also different surface pre-treatments have been applied to the Al alloys prior to the conversion treatment. Nevertheless, some of them are very complex and laborious to be used industrially, [17][18][19]21,23 or either are proprietary of the aircraft industry.…”

“…Mansfeld and co-workers [17][18][19] have also used EIS to investigate the corrosion behaviour of Al alloys covered with Ce conversion coatings, however, it seems that the results obtained by these authors are more linked to the thickening of the Al oxide layer than to the presence of a CeCL itself. 20 In this work the electrochemical behaviour of Al Alloy 2024-T3 (AA2024) covered with a CeCL was investigated in 0.5 mol L -1 NaCl solution using polarisation curves and EIS. The influence of some pre-treatments in the surface Cu content, prior to the immersion in the conversion bath, and its influence on the formation of the CeCL are discussed on the basis of SEM and EDX analysis.…”

Development of Cerium-Rich Layers on Anodic Films Formed on Pure Aluminium and AA7075 T6 Alloy

“…7,8,9 The protective properties of the anodic oxide films formed in sulfuric acid, with or without tartaric addition, may be enhanced by addition of rare earth compounds (e.g cerium-based compounds) before, during or after anodizing. [10][11][12][13] The main benefits of cerium-based layers are high corrosion resistance, non-toxicity, and a relatively fast deposition process.14,15 Hughes et al, 16 Hinton et al 17 and Mansfeld et al 18 achieved enhanced corrosion resistance for AA2024 and 7075 aluminum alloys after spontaneous deposition of conversion coatings in Ce(III) solutions at ambient temperature. Their results have been taken as a starting point for this research.…”

“…14, 15 Hughes et al, 16 Hinton et al 17 and Mansfeld et al 18 achieved enhanced corrosion resistance for AA2024 and 7075 aluminum alloys after spontaneous deposition of conversion coatings in Ce(III) solutions at ambient temperature. Their results have been taken as a starting point for this research.…”