2. Experimental procedure
The studied materials include Aluminum (Al 1060) and steel (DIN 1623)
sheets, cleaned and grinded, with thickness of 2.0 mm and area of 50 x
150 mm.
The
welding was conducted using RFSSW machine provided by Aerospace
Engineering Equipment (Suzhou) Co., Ltd. The critical processing
parameters are: (1) rotation speed: 2000 RPM; (2) penetration depths
2.40 and 1.85 mm for Al-Al and Al-steel joints; (3) penetration speed: 1
mm/s.
After welding, the cross-section of Al-Al and Al-steel joints were
electron spark cut and
polished
for optical microscope observation. The hardness test was measured along
the welding seam, upper and lower sheets (1 mm distance from the welding
seam). The loading is 0.245 N and a dwell time of 10 s. The Al-Al and
Al-steel specimens were tensile tested by
Zwick/Roell
Z250 with a strain rate of 1mm/min. The tension-tension fatigue tests
were conducted using sinusoidal wave in load control mode with R=0, and
the testing frequency is 30 Hz by Instron 8801. The stress amplitude
(Δσ=(σmax-σmin)/2) was set as 0.2, 0.3
and 0.4 of the joint shear strengths (σb) to
quantitative analysis and comparison. After the fatigue test, all the
specimens were stretched to fracture for observing fatigue damages.