State of the art hexavalent chromium free surface pretreatments for aluminium alloys

2012-04-05T14:09:44Z (GMT) by Gary Critchlow Keith Yendall R.H. Dahm
At the present time, the phosphoric acid anodising (PAA) process [1] is widely used in America for the pretreatment of aluminium alloys used in adhesively bonded structures. With the replacement of the Forest Products Laboratory (FPL) etch in the anodising line with a hexavalent chromium free alternative [2], this has solved many of the environmental problems associated with the ever increasing regulations enforced by both national and local authorities. However, this route has never been favoured in the European aircraft industry due to the superior bond durability offered by chromic acid anodising (CAA) relative to PAA in corrosive environments. Furthermore, CAA has been shown to have twice the anodising throwing power and generally higher peel strengths to that of PAA [3].