In this paper, the weld nugget zone nearby the Friction Stir Welding (FSW) joint between dissimilar materials has been modeled using a Functionally Graded Material (FGM) concept. In the real FSW process the weld nugget zone increases in size with time as the tool head travels along the specimens. Similarly this phenomenon is simulated numerically by increasing the size of FGM area with the welding tool moving forward, as illustrated in Figure 1. The rate of growth of the FGM region is estimated from the rotational and forward speed velocities of the tool. For a three dimensional FSW model, time-varying material field simulations and corresponding thermal analysis are performed using ABAQUS^®. User defined subroutines USDFLD and DFLUX, are used to build the material field and the load of heat flux, respectively.

To verify the proposed modeling approach numerical investigations are compared with FSW experimental data gathered by C.M. Chen and R. Kovacevic (2004). The experiment conducted by them was a FSW process between two dissimilar metals, Al6061 alloy and AISI-1018. The temperature history at two specific locations has been recorded by two embedded thermocouples.  Preliminary result shows that numerical simulation and experiment data compare well, and same trends for the temperature histories are obtained.  Figure 2 shows the comparison of the temperature history at two specific locations where the thermocouples have been embedded. the Discrepancies at higher time, that is away from the measuring points, are attributed to the way the experiment has been performed; perfect bonding was not achieved after a certain time, the tool was broken, and heat was dissipating at higher rate in the experiment as compared to the numerical simulations which assumed ideal conditions. In the final version of the paper, additional simulations will be performed and comparison with other available experimental investigations will be provided. Furthermore, thermo-mechanical analysis will be performed and conclusions will be outlined.