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. The similar Al-Al RFSSW joint is significantly influenced by stress
amplitude, while the fatigue behavior of dissimilar Al-steel joint is
insensitive to stress amplitude.
4. 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.
The current observation of the fatigue properties and behavior of
similar Al-Al and dissimilar Al-steel RFSSW joints shall accelerate the
lightweight design for vehicle industry.