With only a few exceptions, some degree of surface treatment is applied to all metal surfaces prior to
adhesive bonding. The surface treatment applied will depend upon the requirements of the bond and service
conditions that it will see and will generally be chosen on a “fit-for-purpose” basis. The minimum preparation
which is usually carried out might include a simple degrease to remove processing aids, such as oils and
waxes, and contaminants. However, it is recognised that the current state-of-the-art processes for structural
or semi-structural metal bonding are highly complex, multi-stage treatments including conversion coating and
anodic oxidation. Alternatives to the commonly-used degreasing processes are sought for many reasons, for
example: established processes may not be adequate for difficult-to-remove materials; the processes may
use VOCs; they can be carcinogenic or ozone depleting. Regarding the higher treatments, the anodising
processes, in particular, are difficult, time consuming and costly to carry out. There are also legislative
drivers which make utilisation of the more complex processes, especially those which utilise hexavalent
chromium, highly undesirable. Other factors such as energy and chemical disposal costs also deserve
consideration when considering the need for environmental or operator “friendly” processes.
This paper will consider a number of alternative friendly surface treatments which might be considered as
drop-in replacements for the current industrial standards. The friendlier surface treatments include two
simple cleaning methods, namely: seaweed-based cleaners and CO2 laser ablation. In addition, to cover the
spectrum of processes, two novel anodising methods will also be discussed. These are based upon
electrolytic phosphoric acid deoxidising plus sulphuric acid anodising (EPAD+SAA) and alternating currentdirect
current (ACDC) anodising.
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
Department
Materials
Citation
CRITCHLOW, G.W., YENDALL, K.A. and LU, J., 2007. Friendlier surface treatments - for metals. Presented at: Society for Adhesion and Adhesives in conjunction with BASA, One Day Symposium on 'Greener Adhesives and Sealants', 5th December 2007, London.