# Investigating the Welding Parameters in Friction Stir Welding of Yellow Brass 405-20
## 2 Materials and Methods
### Empirical FSW
Since researchers use k-type thermocouples for measuring the temperature at one point of the weld zone, which is not only time-consuming but also does not provide an opportunity to measure the joint strength and hardness due to the embedment of tiny thermocouple wires at HAZ, a thermal imager seems competent in resolving the time and effort issues during welding. Testo's IRSoft software version 4.7 was used for image processing, allowing us to measure the temperatures at multiple locations of HAZ, as shown in Figure 12 for DOE 4. In this image, there were four interfaces; the top left interface shows the multiple locations of the hot spot (HS) and cold spot (CS), which are the maximum and minimum temperatures respectively during welding. The top right shows the temperature scale or maximum and minimum values of the scale in which temperature can be measured. The bottom left interface shows the values of CS and HS. The bottom right shows the actual welding scenario schematic. Various HS can be measured along with CS using a thermal imager simply through gentle mouse clicks at different locations of the top left window. The recorded HS was the maximum possible value of HS at the HAZ obtained from FSW. Supporting strips were used to support the joint location for effective welding. In other words, the tool entered the supporting strips on one side, transversed while rotating along the weld line of specimens, and exited again from the supporting side on the other side, as shown in Figure 10.  
Figure 10: A friction stir weld. After the specimens were welded in the processing phase of empirical FSW, specimens were tested for their joint strength and hardness to accomplish the postprocessing research activities. Side strips welded with the specimens were cut using an electric saw, as shown in Figure S2. A sample cut by the electric saw is shown in Figure S3. Joint strength was tested using a tensometer with a crosshead speed of 1 mm/min, as shown in Figure S7, under the guidelines of ASTM standard (E8/E8M-13a) Three samples were tested for each welding experiment, as per the DOE Table 5, and weld strengths were averaged accordingly. A broken FSW sample is also shown in Figure 8.0 Hardness was tested on the Rockwell hardness testing machine at various points of samples, shown in Figure S8. A diamond cone was used as an indenter with a pre-load of 29.42 N and a total applied load of 147.1 N by placing the welded specimen on the Rockwell hardness tester platform, as shown in Figure S8. The weld zone was especially exposed to the indenter to measure the weld hardness. The average value of hardness value was then computed and hardness values were recorded as the average of two values at the two joint hardness locations of HAZ, as shown in Figure 8.1 Welded brass burrs can be seen in Figure 10, which were removed from welded specimens before tensile testing of specimens. A simulation in Figure 6 showing the burr, as achieved from its experimental counterpart, is shown in Figure 8.2 The burrs in simulated Figure 6 are coming out of the top or bottom sides of the weld zone due to the reason that the whole specimen was fixed in all three axes as necessary boundary conditions for the current FSW problem theme. However, experimental burrs were forcefully moved at the outer edges of the specimen due to the combined (traverse and rotational) movements of both the pin and shoulder of the FSW tool, as shown in Figure 8.3  
pitch of 24.17 revolutions per mm, as shown in Figure 8.4 This value of the revolutionary pitch is evaluated to be smaller in Figure 8.5  
Revolutionary pitch can be defined as a ratio of rotational speed (rpm) and traverse speed (mm/min). It seems that the smaller the value of the revolutionary pitch, the greater will be the weld quality in terms of both temperature and strength. In Figure 12, temperature distribution indicates that the maximum temperature achieved experimentally and numerically during FSW of brass was 598 \({}^{\circ}\)C again for DOE4.