Surface characterization of cerium based conversion coatings

Cerium-based conversion coatings on aluminium alloys: a process review

“…80 The group at the University of Missouri-Rolla (UMR) have reported the formation of satisfactory Ce coatings on AA 7075 by electrolytic deposition, 144 spray 109,110,148 and immersion, using alkaline cleaning as the only pretreatment. 144,147,148 This did not work with AA 2024, 132 although alkaline cleaning has been noted to have relatively little effect on the surface of AA 2024. 51 The UMR claimed that including a deoxidation step overetched the surface and affected the rate of deposition and performance of the coating, [145][146][147] and as acceptable coatings could be deposited without the use of any additional process steps, 144 it appears that efforts to incorporate them were abandoned, at least temporarily (see the section on 'Base etching').…”

“…20,81,172,[201][202][203]217,218 The CSIRO/DSTO group also utilised chromate deoxidation (Parker-Amchem/Henkel Deoxidizer 4/6/7/17) during the 1990s 59,119,127,128 and later, 77,126,129 but it was concluded that, particularly on aerospace aluminium, chromate deoxidation gave poorer protective and coating results than other deoxidisers. 120,123,127,128 More recently, the group at UMR also used chromate deoxidation (Parker-Amchem/Henkel Deoxidizer 7/11) before electrodeposition or immersion coating, 12,13,31,32,131,141,[219][220][221] although, again, chromate did not appear to be a good choice. For instance, they tested Henkel no.…”

“…1 It works extremely well as a soluble inhibitor in cooling water systems, 2 as an inhibiting pigment in paints 2-5 and as a component in deoxidisers 2,4,6 and anodised coatings. 2,4,7 Most importantly, in the context of this review, chromate is a near ideal conversion coating, 1,2,6 as it provides outstanding corrosion resistance 4,[8][9][10][11][12][13][14] and paint adhesion, 10,[14][15][16][17] ease of application, 8,9,[11][12][13][18][19][20][21] self-healing 6,8,9,11,14,18,19,21 and electrical conductivity. 18,19,[21][22][23] It works rapidly 14 at room temperature 14 on a wide variety of metals and alloys 24 while requiring a minimum of maintenance.…”

“…1,25,26 However, chromate is carcinogenic 1,11,18,19,[27][28][29] and has been listed in the USA as one of the Environmental Protection Agency's most toxic substances, 5,18,19,28 with a view to it being progressively phased out. 1,5,[12][13][14][30][31][32] An enormous amount of work has been carried out on chromate, and there are a number of excellent reviews that cover chromate chemistry and practice. 6,14,[33][34][35] An enormous amount of data on potential chromate replacements for aluminium has also been published.…”

Spray Deposition of Cerium Oxide‐Based Conversion Coatings on Al 2024‐T3

“…Cerium‐based conversion coatings have been deposited using electrolytic (current driven) and spontaneous (immersion) deposition methods 17,18 . Processes that deposit cerium‐based conversion coatings that meet the U.S. Department of Defense standard by providing corrosion protection for 336 h (2 weeks) in ASTM B117 salt spray testing have been developed for both aluminum alloys 7075‐T6 and 2024–T3 19–21 .…”