Title: Novel Chrome-Free Bonding Primer for Structural Bonding and Corrosion Protection in Aerospace Applications

Authors: Alexander Peetsch, Claudia Blaffert, Christian Ramm, Martin Renkel, Ruairí O’Kane, Bryce Floryancic, Michael Frank, Omar Abu-Shanab

DOI: 10.33599/nasampe/s.21.0514

Abstract: Aluminum parts in the aerospace industry require specific surface coatings that provide long-term corrosion protection and facilitate bonding performance towards adhesives. These coatings are known as bonding primers. For decades, strontium chromate was used as a corrosion inhibitor in bonding primers to effectively protect aluminum alloys. Despite its outstanding anticorrosive properties, its acute toxicity, carcinogenicity, and mutagenicity made it subject to regulatory restrictions and usage bans (e.g. REACH). Therefore, the aerospace industry seeks for sustainable and less toxic alternatives. This technical paper discusses the development of a waterborne, chrome-free bonding primer based on epoxy chemistry. The paper discloses the application characteristics, cure behavior and film formation on aluminum surfaces. Surface characterization techniques such as SEM and GDOES were used to reveal the interaction with aluminum surfaces and film adhesives. Chemical resistance and corrosion protection performance are discussed by means of fluid immersion, wipe resistance and corrosion testing techniques. Bonding properties were tested in conjunction with Henkel film adhesives. The findings revealed that this novel chrome-free bonding primer can effectively protect aluminum surfaces from corrosion and promote adhesion towards aerospace structural adhesives to replace strontium chromate bonding primers.

References: [1] J. Bishopp, “Aerospace: A Pioneer in Structural Adhesive Bonding”, Handbook of Adhesives and Sealants, 1st Ed., Amsterdam: Elsevier, 2005. [2] N. Eswara Prasad and R. J. H. Wanhill., Aerospace Materials and Material Technologies, Vol. 1, Singapore: Springer, 2017. [3] X. Zhang et al., “Recent advances in the development of aerospace materials”, Progress in Aerospace Sciences, Vol. 97, 22-34, Amsterdam: Elsevier, 2018. [4] S.T. Abrahami et al., “Towards Cr(VI)-free anodization of aluminum alloys for aerospace adhesive bonding applications: A review.”, Front. Chem. Sci. Eng., 11 (2017): 465–482. [5] Official Journal of the European Union, Summary of European Commission Decisions on authorisations for the placing on the market for the use and/or for use of substances listed in Annex XIV to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), 2020/C 132/05, ISSN 1977-091X. [6] S. Ebnesajjad and A. H. Landrock, Adhesives Technology Handbook, 3rd Ed., Amsterdam: Elsevier, 2015. [7] I. Hamerton and J. Kratz, “The use of thermosets in modern aerospace applications”, Thermosets, 2nd Ed., Amsterdam: Elsevier, 2018. [8] F.-L. Jin, X. Li, and S.-J. Park, “Synthesis and application of epoxy resins: A review”, J. Ind. Eng. Chem., 29 (2015): 1-11. [9] P. Visser, H. Terryn, J.M.C. Mol, “Aerospace Coatings”, Active Protective Coatings, Springer Series in Materials Science, Vol. 233, Dordrecht: Springer, 2016. [10] A. S. H. Makhlouf, “Protective coatings for automotive, aerospace and military applications: current prospects and future trends”, Handbook of Smart Coatings for Materials Protection, Cambridge: Woodhead Publishing, 2014. [11] G. Wypych, Handbook of Solvents, Volume 2 - Use, Health, and Environment, 2nd Ed., Toronto: ChemTec Publishing, 2014 [12] ISO 2409:2020 – Paints and varnishes - Cross-cut test, https://www.iso.org/ [13] ISO 9227 – Corrosion tests in artificial atmospheres - Salt spray tests, https://www.iso.org/ [14] DIN EN 2243-1 – Aerospace series - Non-metallic materials - Structural adhesives - Test method - Part 1: Single lap shear, DOI: 10.31030/9836169, https://www.beuth.de/ [15] DIN EN 2243-2 – Aerospace series - Non-metallic materials - Structural adhesives - Test method - Part 2: Peel metal-metal, DOI: 10.31030/9663288, https://www.beuth.de [16] ASTM D3762 – Standard Test Method for Adhesive-Bonded Surface Durability of Aluminum (Wedge Test), DOI: 10.1520/D3762-03, https://www.astm.org

Conference: SAMPE NEXUS 2021

Publication Date: 2021/06/29

SKU: TP21-0000000514

Pages: 14

Price: FREE