Abstract: A method for treating the surface or surfaces of an aluminium or aluminium alloy containing substrate to confer corrosion resistance in which a porous layer is created on the surface or surfaces and then the surface or surfaces are treated with a solution or gel comprising a metavanadate ion, and further treated with a solution comprising a metal ion selected to coprecipitate with the metavanadate ion to form a sparingly soluble compound within the pores of the porous layer. A corrosion resistant coating for aluminium or aluminium alloy comprising a porous surface layer containing within the pores a deposit of a sparingly soluble metal metavanadate. The porous layer may be an oxide layer produced for example by acid anodising.