Environmentally-friendly surface treatments

The presentation will focus upon both existing and novel developmental processes for the replacement of the hexavalent chromium containing 40/50V Bengough-Stuart anodise (CAA), with particular emphasis on their resultant performance in structurally bonded systems. Two systems of particular interest are based upon a phosphoric acid based electrolytic deoxidiser (EPAD) studied in combination with a standard sulphuric acid anodise and an alternating current-direct current phosphoric-sulphuric (ACDCPSAA) anodise in a benign electrolyte. It has been shown that the EPAD provides an open porous structure in order to enhance adhesion to the modified sulphuric acid anodised (SAA) surface. Additionally, a post anodising (PAD) treatment has been used to further aid structural adhesion in combination with the aforementioned processes. As a control, the standard 40/50V Bengough-Stuart chromic acid anodising (CAA) has been used as a baseline performance indicator in adhesion tests. Adhesion levels have been established using single lap shear and modified wedge test configurations. Overall, excellent initial joint strengths and durability have been found with both EPAD and ACDCPSAA, suggesting that these environmentally benign treatments may be used as possible drop-in replacements for the currently used CAA process.