| Abstract | The biggest challenge faced by transportation industries in structural assembly is the joints’ integrity upon exposure to environmental conditions while maintaining excellent mechanical properties. Combination of mechanical and adhesive joining can provide high joint strengths, increased energy absorption and high fatigue lives. A weld-thru method has been previously employed where the parts to be assembled are friction stir welded (FSW) in the presence of a structural adhesive/sealant between the parts. However, this technology suffers adhesive damage due to weld-induced heat generated locally affecting the joints’ durability and mechanical properties. Also, most adhesive/sealants have Tg below the temperature attained during welding (450 to 500 oC), unable to withstand the weld-induced heat. In this paper, an inverse technology, called flow-in or weld-bond was used to bond Al-Al and Al-steel using a low viscosity epoxy adhesive in combination with FSW and arc welding processes. In this method, the welding step in overlap mode is performed first. The adhesive is applied later through the welded gap via capillary forces. Since welding and adhesive application are independently performed, the adhesive safely fills the gap while maintaining the joints’ integrity. The performance of the weld-bonded joints of pretreated Al and steel alloys as-assembled and after various environmental degradation (international standards) including combinations of heat, humidity, sub-zero temperatures, salt-spray and UV exposure, has been evaluated. The results show tremendous increase (1.7 times) in joint strengths on weld-bonded specimens in comparison to the weld-alone and adhesive-alone specimens with no change even after degradation. A simple surface treatment prior to adhesive application is found to help the joints sustain the salt-spray conditions. The fatigue life of the weld-bonded joints is found to be higher than those prepared using individual techniques. |
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