Kissing Bond Phenomena in Solid-State Welds of Aluminum Alloys

The occurrence and nature of kissing bonds have been studied in three solid-state welding processes: friction stir welding, extrusion charge welding, and extrusion seam welding. A kissing bond is the descriptive term for two surfaces lying extremely close together, but not close enough for the majority of the original surface asperities to have deformed sufficiently in contact for atomic bonds to be created. Depending on their location and extent, they may have detrimental effects on the fatigue life and through-thickness load-bearing capacity of the component. This paper presents analogies between kissing bonds in the above-mentioned joining methods using fractographic evidence and phenomenological hypotheses. The effects of these discontinuities on the mechanical properties of these joints produced in 6xxx-Series aluminum alloys used in automotive and marine structural applications are discussed.