4. Conclusions
The fatigue behavior of Al-Al and Al-steel RFSSW joints are systemically studied, and several conclusions are listed as below:
1. Al-Al RFSSW joint has homogeneous hardness distribution across the welding seam, but Al-steel RFSSW joint has discrete hardness distribution.
2. With stress amplitude or Δσ/σb increasing, the stress concentration within the joint of Al-Al joint grows, resulting in the fatigue striations with thickness direction gets more obvious in the crack initiation region.
3. Regardless of stress amplitude or Δσ/σb varying, Al-steel RFSSW has discrete hardness distribution, leading to fatigue crack initiation from edge of Al-steel joint.