TWI Industrial Member Report Summary 808/2004
S D Rostami
For over 50 years adhesive bonding of aluminium alloys has been commonplace. The chromic/sulphuric acid etch followed by an anodisation process to produce a controlled oxide layer is a favoured and common surface pre-treatment that is used in the industry. Chromic/sulphuric acid etching involves the use of hexavalent chromium, Cr6+, compounds.
However, these compounds are highly hazardous, cancer-causing substances. Recent European Union Directives will restrict the use of chromic/sulphuric acids etching in the metals pre-treatment industry thus alternative methods to the chromic/sulphuric acid surface pre-treatment will be needed in the near future.
A number of alternative processes are being investigated as possible alternatives. One process is based on in-situ creation of aluminium hydroxide (pseudo-boehmite) and the subsequent use of its hydroxyl groups in a condensation reaction with epoxy organosilanes. After this treatment, epoxy functional groups at the aluminium surface become available for incorporation in organic reactions such as adhesive bonding, corrosion protection and/or decorative coatings. In this project, the process for surface pre-treatment of aluminium alloys for adhesive bonding is described. Its effects on the durability performance of bonded joints are evaluated.
To quantify the effect of boiling water and organosilane functionalisation on the durability performance of two aluminium alloys adhesive-bonded with two epoxy adhesives.