# Joint Properties of Aluminum Alloy and Galvanized Steel by AC Pulse MIG Braze Welding
## 3 Results and Discussion  
### Effect of Process Parameters on Wettability  
#### 3.1.1 Torch Aiming Position  
The effects of the different torch aiming positions on the bead appearance, cross-sectional bead morphology, and wettability are shown in Table 4. Dissimilar braze welds were produced under the following welding parameters: welding current of 70 A with an EN ratio of 0%, welding voltage of 19 V, and welding speed of 500 mm/min. The result indicated that the torch aiming position, the distance from the edge of the Al alloy sheet, had a considerable effect on wettability and joint strength. When the torch aiming position was \(-1\) mm, the sound joints did not form, due to unstable arc formation. In contrast, for other conditions, a uniform bead appearance was formed when the aiming position was set, ranging from 0 to +2 mm. From the observation of the formation of cross-sectional bead morphology, the total amount of metal deposition significantly increased by changing the torch, aiming from 0 to 2 mm, but the wetting length decreased with wetting angle. This result tends to be related to the wettability, spreadability, and coating layer of the steel surface when overlaying the filler metal on the steel. In the case of the torch aiming position being on 0 and 1 mm, the molten filler metal under MIG arc heat was easier to wet with the steel due to the zinc (Zn) coating layer on the steel surface, and therefore, dissimilar joints exhibited a low wetting angle and long wetting length [9; 10]. This similar result was also confirmed by [PERSON] et al. [11]. They compared with the spreadability and the wettability using Zn-coated steel and uncoated steel. The wetting angle of braze-welded joints without the Zn coating exhibited a much shorter wetting length and greater wetting angle than those of Zn-coated steel. This wettability resulted in a decrease in weld strength. When the torch aiming position was set to 2 mm, the arc covered more of the Al alloy surface with faying. As a result, compared with the torch aiming positions of 0 and 1 mm, the wetting angle increased and the wetting length decreased. From a study in the literature reported by [PERSON] et al., moving the torch aiming position from steel to the Al alloy side had a positive influence, reducing significantly on the growth of the IMC layer [4]. Therefore, the torch aiming position can play an important role among the process parameters. In the present study, the +2 mm torch aiming position considered under the following results was set as the fixed parameter, and then the effect of the variations in welding current and EN ratio on the wettability and joint strength was examined. \begin{table}
\begin{tabular}{c c} \hline \hline
**Process Parameter (Unit)** & **Value** \\ \hline Electrode diameter (mm) & 1.2 \\ Welding speed (mm/min) & 500 \\ Work angle/drag angle (degree) & 80/10 \\ Shielding gas & Ar 99.9\% \\ Shielding gas flow rate (l/min) & 18 \\ CTWD (mm) & 15 \\ Welding current (A) & \(50,60,70\) \\ Welding voltage (V) & 19 \\ EN ratio (\%) & \(0,10,20\) \\ Torch aiming position (mm) & \(-1,0,+1,+2\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Welding parameters used for experiments. The results obtained for torch aiming positions are summarized as follows:  
* When the torch aiming position was \(-1\) mm, dissimilar joining did not occur. * When the torch aiming position was 0 mm, dissimilar joints were formed with a bead morphology of a right-angle triangle, but there was concavity on the bead surface, where stress concentration resulting in failure occurred during tensile loading. The maximum tensile shear load of dissimilar joints was 6.8 kN. * In the case of the +1 mm torch aiming position, the bead morphology was similar to that for 0 mm. The maximum tensile shear load was 8.4 kN. Failure occurred at the stress concentration along the fusion line. * For an aiming position of +2 mm, the amount of the metal deposition significantly increased compared with 0 and 1 mm.