1. Introduction
Lightweight
is one of the most important directions in the global development of new
energy mobility [1 ]. Several
concepts were developed as: (1) Hybrid sandwich metal-plastic structure
[2 ]; (2) High strength alloys
[3 ,4 ]; (3) Material joining, e.g.
self-piercing riveting (SPR)
[5 ], electric resistance
welding (ERW) [6 ] and friction
stir welding (FSW) [7 ].
FSW has achieved outstanding welding properties, but the key-holes
within the joint will bring in a weak bonding interface
[8 ] and poor mechanical
stability [9 ].
To
overcome the above challenges, refill friction stir spot welding (RFSSW)
was proposed and developed
[10 ], which works on similar
Al-Al and dissimilar Al-steel metallic joints
[7 ], as well as metal-polymer
composites [11 ]. However, the
fatigue behavior of the similar and dissimilar material joints
fabricated by RFSSW are seldom examined. As the physical properties
between Al and steel are different, the joint interface shall have
different effects on the fatigue behavior. The present research shall
accelerate the design of similar and dissimilar materials joining under
RFSSW process.