Concluding Remarks
The combination of FSW and adhesive bonding into friction stir
weld-bonding was studied regarding quasi-static and fatigue performance.
In order to benchmark the process, it was compared against overlap FSW
and adhesive bonding.
The epoxy adhesive used was characterized taking into consideration the
curing temperature, showing that even though it cures at room
temperature, higher temperature curing will increase strength while
reducing ductility. Degradation temperature was also found to be above
reported temperatures incurred during the welding procedure.
In the joints quasi-static testing, overlap FSW showed lower strength
and ductility than FS weld-bonding joints. Downward force during
welding, showed a significant effect in strength and ductility of FSW
joints, with both increasing up to 550 kgf. The same trend was not
observed in the FS weld-bonded joints, with the highest strength and
ductility achieved at 450 kgf, with a joint efficiency of 94.96%. In FS
weld-bonded joints the critical weld edges were kept close by the
adhesive, leading to increase mechanical performance. As such, adhesive
strength and the quality of the surface treatment are more significant
to joint strength than downward force during welding. Adhesive bonded
joints showed the highest strength and ductility given the relatively
large overlap.
In cyclic loading at R=0.1, similar trends to the quasi-static loading
were observed. Adhesive bonding achieved the highest fatigue strength
followed by FS weld-bonding and FSW showed significantly lower fatigue
strength (41.6% strength of adhesive bonded joints at
106 cycles). The hook defect serves as a fatigue crack
initiation location and leads to the failure of FSW joints. Adhesive
joints fail in an adhesive / cohesive manner, while FS weld-bonding fail
through the adhesive immediately followed by cracking through the hook
defect.
Acknowledgements
This work was supported by FCT, through IDMEC, under LAETA, project
UIDB/50022/2020. Funding provided from NORTE-01-0145-FEDER-000022
SciTech – Science and Technology for Competitive and Sustainable
Industries is acknowledged. The authors acknowledge the funding provided
by FCT project PTDC/EME-EME/29340/2017 – DisFri.
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