# Joint Properties of Aluminum Alloy and Galvanized Steel by AC Pulse MIG Braze Welding
## 2 Materials and Methods  
In the present study, the base metals were a 2 mm-thick AA6061-T6 and a 2 mm-thick GI steel sheet whose dimensions were 200 mm (L) \(\times\) 100 mm (B), as shown in Figure 1a. The AA6061-T6 and GI steel sheets were placed at the top and bottom in a lap joint configuration without a gap between the faying surfaces. Table 1 lists the chemical compositions of AA6061-T6, GI steel, and 4047 Al-Si alloy wire used for the experiment. The mechanical properties of the two base metals are given in Table 2.  
An AC Pulse MIG welding machine was used to join dissimilar materials using 4047 aluminum alloy wire, and filler wire was fed with an angle of 80\({}^{\circ}\) and a drag angle of 10\({}^{\circ}\). The outer diameter of filler wire was 1.2 mm. Before the experiment, two base metals were polished by steel brush to remove the oxide layer and were then cleaned with acetone on the surface. Argon (Ar) shielding gas was supplied with a flow rate of 18 L/min to prevent oxidation during welding. The contact-tip-to-workpiece distance (CTWD) was fixed at 15 mm. The wetting length and wetting angle of Al/Fe dissimilar metal joints were examined in terms of wettability, as defined in Figure 1b [9]. Three samples from each welded joint were prepared to measure the wetting length and wetting angle in the macrostructure image with an imaging calculator. The welding parameters used for the experiment are listed in Table 3.  
In order to evaluate the joint properties of dissimilar welded joints, a tensile shear test using the rectangular specimen with an overlapping length of 30 mm and a total length of 170 mm was carried out at a crosshead speed of 1 mm/min. Three specimens from each welded joint were prepared to evaluate the average tensile shear load. For macrostructure observation using an optical microscope (OM), all samples were polished using SiC paper from 400 to 4000 grit and diamond suspensions of 9, 3, and 1 \(\upmu\)m, and they were then etched in Tucker's reagent (45 mL HCI + 15 mL HNO3 + 15 mL HF + 25 mL distilled water) for 10 s. Elemental analysis of the IMC layer at the interface in scanning electron microscopy (SEM) was performed using energy-dispersive spectrometry (EDS). The fracture surface of the tensile shear specimen was observed to reveal the fracture behavior using SEM.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Materials**} & \multicolumn{8}{c}{**Chemical Composition**} \\ \hline AA6061-T6 & Al & Fe & Si & Mn & Mg & Cu & Zn & Ti & Cr \\  & Bal. & 0.7 & 0.4–0.8 & 0.15 & 0.8–1.2 & 0.15–0.4 & 0.25 & 0.15 & 0.04–0.35 \\ \hline \multirow{2}{*}{GI steel} & Fe & Mn & C & Si & Ti & P & S & \\  & Bal. & 0.18 & 0.032 & 0.02 & 0.001 & 0.014 & 0.005 & & \\ \hline \multirow{2}{*}{4047 aluminum wire} & Al & Si & Fe & Cu & Mn & Mg & Zn & Be & \\  & Bal. & 11–13 & 0.8 & 0.3 & 0.15 & 0.1 & 0.2 & 0.0003 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of AA6061-T6, GI steel, and 4047 Al-Si alloy filler wire.  
Figure 1: Schematic of AA6061-T6 and GI steel welded joints specimen: (**a**) AA6061-T6 and GI steel welded joint; (**b**) definition of torch aiming position, wetting length, and wetting angle.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Metals**} & \multicolumn{1}{c}{**Tensile Strength (MPa)**} & \multicolumn{1}{c}{**Yield Strength (MPa)**} & \multicolumn{1}{c}{**Elongation (\%)**} \\ \hline AA6061-T6 & 331 & 301 & 10 \\ GI steel & 371 & 282 & 39 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mechanical properties of AA6061-T6 and GI steel.