Solder or weld will have problems. Solder will not have a high enough tensile strength to hold the joint in place and you can solder or braze aluminum but its normally not that structural. See Dura fix on the Internet it might be a product you could try. The weld has the problem of shrinkage that might well cause the original part to warp or become effectively smaller, again increasing the force on the hinge. The finished clamp may have to be resized. A used one or have a new part machined from billet could be a solution.
Bill McCune
Parker, Co