PSI - Issue 13

Yanning Guo et al. / Procedia Structural Integrity 13 (2018) 806–812 Yanning Guo/ Structural Integrity Procedia 00 (2018) 000 – 000

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In Fig. 1(b), five tensile test specimens were numbered Sample 1 to Sample 5, which respectively represent the heat affected zone, the advanced thermo-mechanically affected zone, the stirred zone, the retreating thermo mechanically affected zone, and the heat affected zone. The specimens were cut along the welding direction according to the size shown in Fig. 1(b).

a

b

Welding direction

Advancing side Retreating side

Fig.1 (a) Position of tensile test specimens, (b) Sample

3. Results and discussion 3.1. 2024 alloy tensile properties

The dynamic tensile tests at room temperature were performed by the TSHB system under strain rates of 1300 and 2600 per second (s -1 ). Fig.2 is the true stress-strain curves of 2024, which the welding speed is 150mm/min, the rotation speed is 400rmp and the strain rate is 1300s -1 . As can be seen in Fig.2, yield strength of the heat-affected zone (513MPa) is much higher than the stirred zone (370MPa) and the thermo-mechanically zone (336MPa). And the flow stresses of dynamic impact have a little instability near the yield point, it is the beginning of plastic deformation. Then they become steady, which indicates that the force equilibrium is obtained only after plastic deformation. All five curves present a peak stress at a particular strain and then have a sharp drop. It is because when the flow stress reaches the peak, the 2024 aluminum alloy enters the strain softening stage, and then the failure occurs. Therefore, the sharp drop is attributed to the fracture of material. This is the result of the internal damage accumulation with the increase of strain. For all specimens, the value of peak flow stress is higher than the yield strength. Thus, the strain rate strengthening effect of 2024 aluminum is obvious. As the non-uniform heat and plastic flow during welding, the peak flow stress of the heat-affected zone (544MPa) is higher than that of the stirred zone (478MPa) and the thermo-mechanically affected zone (471MPa). The fracture strain of heat-affected zone (0.21) and thermo-mechanically affected zone (0.18 and 0.20) are lower than that of stirred zone (0.23).

600

500

400

300

1 2 3 4 5

200

True Stress (MPa)

100

0.00

0.04

0.08

0.12

0.16

0.20

0.24

True Strain

Fig.2 The stress-strain curves of 2024 (400rmp-150mm/min 1300s -1 )