I agree with Mint Julep. Read the discussion at that link. Then realise that if you test using shear strength or even peel strength tests you are going to get a false impression that your process gives you good strength. It may do in the short term but long term there will probably be a rash of disbonds. I suggest you try the wedge test ASTM D3762, but read DOT/FAA/AR – TN06/57, May 2007 for acceptance criteria. Adhesive bonds to aluminium involve the formation of ionic and covalent bonds with the oxides produced during surface preparation at the surface of the metal. These oxides have an affinity for the formation of hydrated oxides when exposed to humidity. For the oxides to hydrate, the chemical bonds formed at the time of bonding must dissociate, thus leading to disbonding. This is why strength tests do not prove the adequacy of surface preparation processes. The secret to success is to treat the surface at the time of preparation to prevent that hydration. Please note that hydration related failures can be totally independent of loads, so don't think that just because loads are low that surface preparation is not needed. Doubling the overlap to account for bad processing will simply result in twice the size of disbond.
Regards
Blakmax