PSI - Issue 42

V.K. Yadav et al. / Procedia Structural Integrity 42 (2022) 594–601 V.K. Yadav et al., 2022/ Structural Integrity Procedia 00 (2019) 000 – 000

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three-electrode cell consisting of a reference electrode (Saturated Calomel Electrode), a counter electrode (Graphite rod), and working electrode (1 cm 2 of exposed area). Prior to corrosion test, each specimen was polished mechanically using sand papers of grade #320-1200. Fatigue crack growth (FCG) tests were performed using standard compact-tension (CT) specimen. After completing the FSW, three CT-specimens were extracted using wire electric discharge machining (wire-EDM) method. All the specimens were designed in accordance with the ASTM E647 having width (w) = 32 mm, thickness (B) = 5 mm, and initial crack size (a 0 ) = 6.4 mm. The specimens were extracted such that loading axis was perpendicular to weld direction and notch lies within the weld nugget zone. Before the test, CT-specimens were dipped in the saltwater (i.e., 3.5% NaCl solution) for 100 hours. For FCG test, a sinusoidal waveform having loading frequency of 10 Hz was applied under the load-controlled at two different load-ratios (R) of 0.1 and 0.5. Both load shedding and constant load test were considered for the analysis. The load shedding method was performed until the crack growth rate reached 10 -6 – 10 -7 mm/cycle. Afterward, a constant load test was performed on the specimen till the final fracture. The crack size was monitored using a crack opening displacement (COD) gage (Model: 632.02C 20 MTS, USA). The obtained results were cleaned using the 7-point data reduction technique as mentioned in the ASTM E647. The crack growth results were compared with non-corroded results at both the load-ratios. 3. Results and Discussion 3.1. Microstructure and Mechanical Properties The figure (see Fig.1) presents high-resolution electron backscattered diffraction image of the transition zone of the friction stir welded AA2024-T3 alloy. It clearly indicates that due to the stirring action between tool and metal underneath, metal undergoes dynamic recrystallization process, which results in the uniform, stable, equi-axed, and recrystallized grains of size 3.5 – 4.0 μm within the weld nugget zone while twisted and elongated grains within the thermo-mechanically affected zone.

Fig. 1. Microstructural feature (EBSD plot) of the welded AA2024-T3.