The invention provides an intermetallic and composite metallic gap filler. A structural assembly of an aircraft which includes a structural element constructed of a composite material which includes a matrix material and plurality of fibers positioned to extend through the matrix material, wherein at least a portion of the plurality of fibers are accessible from a surface of the structural element. A fastener secures the structural element to a structural component. A metal structure comprising gallium is positioned in contact with a surface of the fastener. The metal structure extends from the surface of the fastener and contacts at least a portion of the at least a portion of the plurality of fibers. Also included is a method for assembling a structure.