Influence of Chemical Pretreatments on Surface Morphology and Bondability of Aluminium

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Abstract
Wettability combined with a strong oxide layer are needed for adhesive bonding and these properties can only be examined by making joints with an adhesive and testing them. The best test for this purpose is the climbing drum peel test. Surfaces must be pickled and anodized. The acids used for pickling influence the anodized structure and chromic-sulphuric acid mixture followed by anodizing in chromic acid gives optimum results. Metal pickled in sulphuric acid shows lower peel strength on bonding. Electron-micrographs show a clear relation between surface morphology and bondability and a fine etchpit structure within coarser etchpits gives the most desirable structure. Low strengths are associated with either weak oxide or a weakened aluminium surface.