I have done some extensive testing with different adhesives and 6061. The best by far is Locktite E-30-CL. Used to be known as Locktite glass bonder.
Its clear and has a 30 working life. Found this as a tip from a Locktite engineer years ago. He said that it outperformed all of there other products for alum.
I have put this stuff through shear tests you wouldn't believe..That said it might just eat plastic for lunch! But for $8.00 you get a 50ml twin syringe set...so a pretty cheap test. Part #29329