PRETREATMENT OF ALUMINUM - TOPOGRAPHY, SURFACE-CHEMISTRY AND ADHESIVE BOND DURABILITY

This paper reports on work in which bonded joints between a clad aluminium alloy (L165, comprising Cu 4.4%, Mg 0.5%, Si 0.8%, Mn 0.8%), with different pretreatments, and an epoxy resin (Ciba-Geigy's Redux 312/5) have been examined. The datum for comparison of the pretreatments is the Boeing phosphoric acid anodization (BAC 5555). Other treatments include sulfuric acid anodizing in combination with a phosphoric acid dip and a sulfuric acid/ferric sulfate etch. The topographical structure of the surface layers formed has been examined using scanning and transmission electron microscopy in conjunction with ultramicrotome sectioning. The chemical composition of pretreated surfaces has been characterized by X-ray photoelectron spectroscopy and depth profiling using argon-ion etch performed. Adhesive bonds have been prepared and their durability assessed using wedge test specimens. The data collected have been used to calculate crack growth and strain energy release rate as functions of time for the bonds produced. Surfaces of failed specimens have been examined to establish the locus of failure.