AC anodising

For many years, AC anodising of aluminium foil has been a commonplace in the cod coating industry. Since the early 1990s, researchers have evaluated and optimised these techniques to adapt and adopt their use for aluminium foil to be used, for example, in the manufacture of metallic honeycomb (see earlier). Work is now in progress to modify these processes for use with the sheet aluminium... 

The panels were washed in solvent to remove surface dirt and then immersed in 10% phosphoric acid at 50°C and AC anodised for 30 s using a current density of 4 A/dm. Another approach was to wash the panels in solvent to remove surface... 

Figure 14 AC anodising in phosphoric acid ultramicrotomed/TEM micrograph through anodised 6060-T6 alloy substrates [39] (Courtesy Elsevier Limited).

In both cases the anodised substrates were washed in water and dried at 60°C. AC anodising of aluminium produces significantly thinner oxide films than by the more conventional DC processes. Johnsen et al. estimated the thicknesses as 0.2 p.m for sulphuric acid and 0.1 p.m for phosphoric acid. 

Comparison of wedge tests results for CAA and AC DC pretreated aluminium/epoxy joints conditioned at 50°C in deionised water. The legend refers to different parameters used in the AC anodisation step in the AC DC process... 

Johnsen et al. found that the durability of the bonded joints, assessed by the Wedge Test [40] (Fig. 16), almost irrespective of electrolyte used, to be nearly as good as obtained using conventionally pretreated adherends, which had been CSA pickled and then DC anodised in phosphoric acid [38]. Bjprgum et al., however, found that an AC PAA pretreatment yielded joints which failed cohesively whereas the AC SAA joints tended towards adhesion failure [39]. 

Johnsen, B. B., Lapique, F., Bj0rgum, A. (2004). The durability of bonded aluminium joints a comparison of AC and DC anodising pretreatments. International Journal of Adhesion and Adhesives, 24, 2, 153-161. 

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