# Prediction of Transient Temperature Distributions for Laser Welding of Dissimilar Metals
## 5 Conclusions  
A transient (time-dependent) 3D model in COMSOL is used to generate the geometry, mesh, isothermal contour, and temperature distribution along a weld line, and weld thickness is predicted for a fiber laser welding of dissimilar butt joints. Temperature-dependent materials properties, such as heat capacity, thermal conductivity, and density, are considered for both AISI 316L and Ti6 Al4V. Latent heat for phase change is also accounted for in the model. The process parameters (laser power and velocity) are considered suitable for achieving full penetration of a 2.5 mm thickness butt joint of these materials. Some results are compared with offset scanning toward Ti6 Al4V side as well. Major conclusions from this analysis follow:  
1. Temperature distribution along the weld line throughout the process at laser spot irradiation shows that the average maximum temperature generated is near 3300 K. Maximum temperatures along the traverse direction (for fixed y value) on z = 0 plane in the middle (x = 5 and x = 15) and edges (x = 0 and x = 20) of the work pieces are approximately 1200 and 1000 K, respectively.
2. Temperature distribution along the thickness shows that even the bottom-most surface along the z-axis achieves an average temperature near 2400 K. A significant  
Figure 16: Temperature distribution of three different points on interface: (**a**) 0.3 mm offset and (**b**) 0.6 mm offset toward Ti6 Al4V.  
penetration depth can be achieved. The average temperature of the two domains ranges from 1150 K to 1200 K during the process. iii. There are differences in the thermal properties of these two materials. Ti6 Al4V has a higher melting temperature. It would take more time than 316L to reach it, as the model was done in zero offsets. The offset of the laser heat source in the same arrangement can create a better-quality welding by adjusting the variations in thermal properties as predicted from the model. Welding interface temperature can be minimized up to 500-1000 K by offsetting the laser beam toward the Ti-6 Al-4V side. iv. Transient distribution of peak temperature from the weld line along the x-axis is plotted and it decreases as it moves far from the source, for obvious reason. Near the weld line, it decreases sharply and the sharpness decreases as the distance increases from the weld line. The difference of maximum temperature between the edge lines (along x = 0 and x = 20) on the z = 0 plane lies between 20 and 100 K. The maximum temperatures can reach up to 1200 K for both samples along the edges mentioned, which indicates recrystallization for AISI 316 and presence of both \(\alpha\) phase and \(\beta\) phase for Ti6 Al4V that occur within the sample width range. v. Transient isothermal contours help to understand the heating and cooling phenomena during the process. At higher temperature, AISI316L has a lower thermal conductivity compared to Ti6 Al4V; thus, the steel part attains a higher temperature near the weld zone. Temperature history of two nearby points in traverse direction makes it understandable that even within two nearer points; one can be in heating mode and one in cooling mode. This fact demonstrates the complex type of deformation, which is the main source of residual stresses.