AVS 46th International Symposium
    Applied Surface Science Division Monday Sessions
       Session AS-MoM

Paper AS-MoM8
Functionalised Plasma Polymer Coatings for Improved Durability of Aluminium-epoxy Adhesive Joints

Monday, October 25, 1999, 10:40 am, Room 6A

Session: Imaging and Small Area Analysis
Presenter: B.J. Tielsch, Kratos Analytical, UK
Authors: B.J. Tielsch, Kratos Analytical, UK
M.R. Alexander, The Corrosion and Protection Centre, UMIST, UK
G.E. Thompson, The Corrosion and Protection Centre, UMIST, UK
T.M. Duc, BIOPHY Research S A, France
E. McAlpine, Alcan International, UK
Correspondent: Click to Email
There is much interest in the use of plasma polymer (PP) coatings to promote adhesion and/or inhibit corrosion of metals.@footnote 1@ These offer environmental and performance benefits over conventional "wet" processing methods such as chromic acid anodising (CAA). Here, we explore the use of carboxylic acid functionalised PP as an adhesion promotion coating on aluminium. The acid functionality, retained from the monomer structure in the plasma deposition process, is intended to form stable chemical bonds with both the aluminium oxide/hydroxide surface and epoxy based adhesives.@footnote 2@ Plasma polymerised acrylic acid and a plasma co-polymer of acrylic acid and octadiene, have been deposited onto plasma etched AA6016 aluminium alloy using RF deposition apparatus. An amine hardened epoxy-based adhesive formulation has been used to bond single lap shear (SLS) joints of PP-coated and CAA alloy. Combining tensile testing of SLS joints with locus-of-failure determination from imaging-XPS and TEM, the relative success of the pretreatments can be gauged. Joint durability was probed by testing joints after storage in water at 60 °C. A decrease in joint strength upon ageing was accompanied by a visual change from failure in the adhesive to failure at a near interfacial region. Chemical state differences in the XPS C1s core level between the acid containing PP and the epoxy containing resin were imaged over the fracture surface. This allowed the effect of PP deposition conditions upon the locus-of-failure and the relationship between this and the failure load to be investigated. Furthermore, information on the distribution of the amine hardener was obtained by imaging of the nitrogen peak. TEM examination of sections taken from the fracture surfaces was correlated with the information obtained using imaging XPS. @FootnoteText@ @footnote 1@R.H. Turner, I. Segall, F.J. Boerio, G.D. Davis, J. Adhesion 62, p. 1 (1997) @footnote 2@M.R. Alexander, S. Payan and T.M. Duc, SIA 26 p. 961 (1998).