PSI - Issue 14

K. Vijayan et al. / Procedia Structural Integrity 14 (2019) 642–648 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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The variation in the temperature across the weld is shown in Fig.4. It can be seen from the figure that as expected the thermocouple closest to the weld zone is having maximum temperature. Fig.5 shows the variation in the temperature for three different specimens. The temperature profile for the sample which produced good tensile strength indicated higher temperature and gradual rise to the higher temperature. This gradual rise would cause uniform heating which could have resulted in producing better strength.

Fig. 4. Temperature distribution across the weld on the retreating side. Thermocouple 1 is closer to the weld zone and the other sensors values are progressively increasing with distance from weld zone.

Fig. 5. Temperature distribution of the thermocouple near the weld zone for three different samples. The good, intermediate and bad cases are classified based on the tensile strength.

3. Microscopic analysis

The first attempt at classifying FSW was made by Threadgill et al. (2009). Typically, the microstructure can be classified as stated by Nandan et al. (2008):  Unaffected material or parent metal: This includes material remote from the weld. In this region microstructure is least affected due to FSW even though the region could be subjected to thermal cycle.  Heat affected zone (HAZ): The region is zone close enough to the weld that the thermal cycle changes the microstructure. However significant plastic deformation is absent.  Nugget zone: This is the region wherein significant dynamic recrystallization occurs.