PSI - Issue 37

Liting Shi et al. / Procedia Structural Integrity 37 (2022) 351–358 L Shi et al/ Structural Integrity Procedia 00 (2022) 000 – 000

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measured to be 5.9 mm. From Fig. 2a and Fig. 2b, it can be observed that asymmetric notch root angles were repeatedly produced in these welds in both the positive or negative polarity Al-steel RSWs. This is different from the earlier results on AA6022 to HSLA RSWs in Shi et al. (2020b) where uniform notch root angles were consistently observed. The thickness of the intermetallic compounds formed at the interface is less than 3 microns at the periphery of the weld while thicker intermetallic compound layer is found in the center of the weld (Fig. 2c). This is mainly due to the lower heat and increased lateral solidification at the edges of the weld driving solidification to occur last in the center. It is noticed that there is no change in microhardness between the positive and negative Al-steel RSWs (Fig. 2d).

4.2. Tensile testing

The maximum tensile loads of both AA5754-HSLA RSW stack-ups and the AA5754-AA5754 stack-up are plotted in Fig. 3. From Fig. 3, it can be observed that both AA5754-HSLA RSW stack-ups have greater maximum loads than that of RSWs of AA5754 to itself indicating acceptable tensile strength was achieved.

Fig.3. Maximum tensile loads of resistance spot welds of 1.1mm AA5754 to 2.0mm HSLA from (a) tensile-shear specimens; (b) coach-peel specimens. Tensile test results from resistance spot welds of 1.1mm AA5754 to itself are included as baselines. Error bars represent 1 standard deviation.

4.3. Fatigue testing

Fig. 4. Fatigue test result of resistance spot welds of 1.1mm AA5754 to 2.0mm HSLA from (a) tensile-shear specimens; (b) coach-peel specimens. Fatigue test results from resistance spot welds of 1.1mm AA5754 to itself are included as baselines. Data points within the red ellipse are to highlight the fatigue life scatters at a given load range.