I know Ford has experiment in recent models with bonding aluminum to steel for a lot of their panels and I think they were just using multi-part epoxy. Several manufacturers do use special epoxy adhesives instead of spot welds to attach stiffening ribs to sheet metal in non structural parts (hood, door, fender, trunk, etc). These days the technology behind gluing is amazing. At work we often use special UV glues and two part adhesives to bond stainless to aluminum, glass to stainless, stainless to zinc coated or galvanized steel. Loctite actually has a massive selection of some very nice adhesives. One of the applications we have is gluing an electrical box to the side of a stainless steel housing (can't weld it or bolt it in that location). When the adhesive cures, I can pretty much stand on the small 4x4 box, and that's not even the extreme heavy duty adhesive.
