Many years ago, some of the tankers and trailers had unpainted aluminum skins. Direct application of pressure-sensitive vinyl graphics to these surfaces often resulted in adhesion failures.
The cause of adhesion problems on aluminum is usually oxidation on the surface of the metal. Whether you are applying an emblem to a vehicle surface or a label to an aluminum part or bonding aluminum extrusions together using very high bond (VHB) tape, you must remove this contaminant.
Unpainted aluminum begins to oxidize almost immediately. A telltale sign of oxidation is to rub the surface with a clean cotton rag. Any black residue on the rag indicates that oxidation has begun.
Exposed to the elements, aluminum begins to oxidize immediately. Unless you remove this oxidation, pressure-sensitive films and tapes will not adhere properly.
The first step in cleaning oxidized aluminum surfaces is to degrease the aluminum, wiping it down with a wax and grease remover. Saturate the surface with the solvent. Before the solvent has a chance to evaporate, dry the surface with a clean rag. Then clean the surface again with isopropyl alcohol (IPA).
While you can remove oxidation with a commercial acid brightener, the more common procedure is to abrade the surface with either a red or grey Scotch-Brite™ pad or steel wool. After scouring the aluminum with the Scotch-Brite™ pad, wipe the surface clean with IPA. After cleaning, rub the aluminum with a clean rag to check for any remaining oxidation. The surface should now be clean for application of vinyl graphics or high bonding tape.