Towards Cr(VI)-free anodization of aluminum alloys for aerospace adhesive bonding applications: A review

Shoshan T. Abrahami, John M.M. de Kok, Herman Terryn, J.M.C. Mol*

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    34 Citations (Scopus)
    34 Downloads (Pure)

    Abstract

    For more than six decades, chromic acid anodizing (CAA) has been the central process in the surface pre-treatment of aluminum for adhesively bonded aircraft structures. Unfortunately, this electrolyte contains hexavalent chromium (Cr(VI)), a compound known for its toxicity and carcinogenic properties. To comply with the new strict international regulations, the Cr(VI)-era will soon have to come to an end. Anodizing aluminum in acid electrolytes produces a self-ordered porous oxide layer. Although different acids can be used to create this type of structure, the excellent adhesion and corrosion resistance that is currently achieved by the complete Cr(VI)-based process is not easily matched. This paper provides a critical overview and appraisal of proposed alternatives to CAA, including combinations of multiple anodizing steps, pre- and post anodizing treatments. The work is presented in terms of the modifications to the oxide properties, such as morphological features (e.g., pore size, barrier layer thickness) and surface chemistry, in order to evaluate the link between fundamental principles of adhesion and bond performance.[Figure not available: see fulltext.]

    Original languageEnglish
    Pages (from-to)465-482
    JournalFrontiers of Chemical Science and Engineering
    Volume11
    Issue number3
    DOIs
    Publication statusPublished - 2017

    Bibliographical note

    Accepted Author Manuscript

    Keywords

    • adhesive bonding
    • aluminum
    • anodizing
    • Cr(VI)-free
    • surface pre-treatments

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