PSI - Issue 17

Liting Shi et al. / Procedia Structural Integrity 17 (2019) 355–362 Jidong Kang/ Structural Integrity Procedia 00 (2019) 000 – 000

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Table 2 Resistance Spot Welding Schedules.

Electrode combination (Al/steel)

Weld Force (N)

Hold Time (ms)

Weld Current (kA)

Aluminum

Aluminum or Steel

Preheat Stage Weld Time (ms)

0.8-mm X626

0.8-mm X626

MRD/MRD

2669

None

60

250

24.8

10ms at 16% VS

1.2-mm AA6022

1.2-mm AA6022

MRD/MRD

3114

151

250

23.3

0.8-mm X626

0.9-mm LCS

MRD/ballnose

3559

None

540

250

13.9

6 kA, 40 ms, 10 ms cool

1.2-mm AA6022

1.2-mm LCS

MRD/Smooth

3781

1550

250

11.8

Metallographic specimens were prepared using the same procedure as presented in previous studies of Kang et al. (2017). The average aluminum weld nugget diameter of the four stack-ups (Fig. 3) were measured on the metallographic specimens as 6.2 mm, 6.2 mm, 7.5 mm, and 7.4 mm, respectively. In the aluminum and aluminum steel RSWs, the MRD electrode broke the oxide layer on the aluminum surface and concentrated defects in the center of the weld nugget occupying about 1/3 of the whole weld nugget diameter. No defects were found at the periphery of the weld nugget where it is easy to form cracks due to a high stress concentration.

Fig. 3 Cross section of RSWs of (a) 0.8-mm X626 to itself (b) 1.2-mm AA6022 to itself (c) 0.8-mm AA6022 to 0.9-mm HDG LCS and (d) 1.2 mm AA6022 to 1.2 mm HDG LCS.

Shear specimens (Fig. 4) were designed following ASTM B831-14 (2015) and Kang et al. (2013), (2008) to directly measure the shear strength of the HAZ and weld nugget of aluminum RSWs. The shear test procedure is referred to the previous studies of Shi et al. (2019). The shear strength of the IMC layer was measured using mini shear specimens designed by Kang et al. (2019 ), as shown in Fig. 5.

Fig. 4 Shear test specimen for weld nugget.

Fig. 5 Mini shear test specimen design. All dimensions in mm.