2.3. Mechanical properties tests
The microhardness arrangement of the entire weld cross section was
detected by a LECO-AMH43 Vickers hardness tester with
a testing load of 300 gf and a dwell
time of 13 s. The spacing between adjacent indentations was 0.5 mm.
Small dog-bone shape tensile
testing specimens were machined by wire cut electrical discharge
machining and tested on AGS-X-50kN testing machine at a strain rate of
1.3×10-3 s-1. The FCG rate tests
were performed on INSTRON-8801 testing machine at room temperature by
using the compact tension (CT) specimens. All fatigue testing specimens
were polished and tested with a load ratio of R=0.1. Sine wave loading
with a frequency of 10 Hz was used. The crack length was measured
continuously by the compliance method with crack mouth clip gauge
(3541-010M-040M-ST). The crack length and cycle number were recorded at
every increment of 0.05 mm in crack length. Fig. 1 shows the dimensions
of CT specimens and the sampling position. Fig. 2 shows the macro
morphology of FSW joint and the fractured CT specimens after FCG test,
illustrating that the welded joint shows good quality with no obvious
weld defects.