Until very recently it was my understanding that all aluminum aircraft structures are of 2024. I have sence learned that 6061 is used here and there, and not just in areas where there are welds. Given that 6061 is 2/3 the strength of 2024, where is 6061 most often used? Could I get away with using 6061 for all my skins without increasing the thickness by 1/2 to match the strength of the 2024? FYI, I will be bonding my skins to the airframe using a two-step process of applying Proseal to the substrate using a very fine tooth (80 tpi) trowel (hack saw blade). Let that set up for a day. Then prior to mating, apply a coat of Hysol epoxy over both Proseal surfaces, then mate. This hybrid joint has proven to to be superior to a Hysol joint in peel strength, and superior to Proseal in lap shear strength, but not superior to Hysol in lap shear; but that's okay, because if the Hysol joint fails in peel (unzip), all the lap shear in the world won't help you. The only places where I will be riveting the skins to the airframe will be at certain edges where the bond line would most likely start to peel. A typical location would be where the bondline is plainar, as opposed to around a curved rib or former where a bondline is virtually unable to "unzip". Some would call these "cheater rivets", I just call it good design. So given that in the bonded areas where there are no stress concentrations associated with rivet joints, can I afford to go with 6061 in place of 2024?