# Prediction of Transient Temperature Distributions for Laser Welding of Dissimilar Metals
## 4 Results
### Temperature Probes  
The nonlinear physical properties such as density, thermal conductivity, diffusivity, and the change in total enthalpy were simulated as functions of transient temperature distribution. Among those properties and by utilizing the model, an estimation of time-dependent temperature distribution using different probe points was highly likely. Hence, influence of temperature on the changes in microstructure and consequent changes in thermomechanical properties were highly predictable by using an iron-iron carbide diagram, time temperature transformation diagrams, etc. The entire geometry is considered as two different temperature probe domains for two different materials. The maximum and minimum temperatures for the domains are predicted. The maximum temperature is achieved along the weld line, where the path of the laser beam is acting, as shown in Figure 7a. It reaches around 3300 K for both domains in a zero offset condition. The average temperature of the two domains is different as AISI 316 is less thermally conductive than Ti6 Al4V (Figure 7b) [52]. Furthermore, the average temperature increases as the process progresses and reaches a range of 1200-1250 K after 17 s. It is a computational procedure. The temperature achieved at any point at a certain instant can be represented by a point probe on the domain, and thus the heat propagation procedure can be understood properly. There is a difference of almost 50 K in average temperature even in that short span. [PERSON] et al. [53] observed a 40-50 K difference in two-domain temperatures for a dissimilar study with austenitic stainless steel and copper, due to same type of differences in thermal properties. Boundary temperature probes are taken along the weld line (see Figure 8a), perpendicular to the weld line, along with the thickness (see Figure 8b), and both sides at the same distance from the weld line. The center of the plate reaches the maximum temperature at t = 9 s, when the heat source is just at the top of the center, and started decreasing as the source moves forward due to cooling(see Figure 9b).The nature of the distribution is obvious and resembles that of a study done by placing four thermocouples 2 and 3 mm from the weld line on both sides [54]. Figure 9a shows the temperature gradient of a point together with the thickness. At a thickness of 2 mm, the temperature reaches near 2600 K. It was also observed that the peak temperature was not reached at a same time for the top and bottom surface, but there was little delay at the bottom and not the top region. This is due to the late response of absorption in the bottom surface. The bottom surface took a fraction of second more time than the top. However, both surfaces maintained maximum temperature more than the melting point. It shows that almost full penetration can be achieved as it is more than the liquidus temperature of either material. Temperature changes along the domain probes were recorded  
Figure 8: Boundary temperature probe points (**a**) along weld line (y axis) and (**b**) along the thickness (z axis). Figure 7: (**a**) Maximum and minimum temperature computational plot for domain 1 (AISI 316L side) and (**b**) comparative average temperature with time for domain 1 (green) and domain 2 (blue). Figure 10: Boundary temperature probe points perpendicular to weld line (x-axis). Figure 9: Temperature distribution of three different points (**a**) along the thickness perpendicular to the weld line and (**b**) along the weld line. There is a temperature difference of up to 200 Kat points (0, 20, 0) and (20, 20, 0). The maximum temperature reached in the middle of the work pieces at traverse direction lies between 1100 K and 1200 K, while the edges along the traverse direction remain below 1000 K. This also satisfies the experimental observation of a k-type thermocouple in a welding study of two dissimilar materials [25]. Edge temperature probes along the top and bottom edge of the weld line (Figure 12) are used for temperature distribution (Figure 13).