# Joint Properties of Aluminum Alloy and Galvanized Steel by AC Pulse MIG Braze Welding
## 1 Introduction  
Recently, an environmental problem, global warming, has recently been in the spotlight. Thus, the automotive industry has been under strict emission gas regulations. Lightweight materials (LM), such as aluminum (Al) alloys, magnesium (Mg) alloys, ultra-high-strength steels (UHSS), and carbon fiber-reinforced plastics (CFRP), are extensively used as a way to improve fuel economy, so the joining technology of aluminum (Al) alloy and steel can play an important role. Al alloy and steel have different physical properties, so they are difficult to join. In addition, intermetallic compounds (IMCs) are easily generated at the joint interface, which is significantly brittle. Due to the formation of brittle intermetallic compounds, the weld is weakened and the strength decreases. Therefore, it is necessary to reduce the generation of intermetallic compounds, and a low-heat input process is required as a solution. One of the processes is AC Pulse MIG brazing. The higher the EN ratio, the faster the wire feed rate. Therefore, a low heat generation process that can reduce the occurrence of IMCs becomes possible. [PERSON] et al. studied the dissimilar joining of an Al alloy to galvanized steel (GI), galvanized steel (GA), and uncoated steel using double pulse MIG welding. They reported that the spreadability and wettability of the fillerwire were significantly improved due to the zinc (Zn) layer, when the hot-dip GI steel sheet was used to join the dissimilar materials. The highest tensile shear strength was obtained using the GI steel sheet [1]. The lap joining of a 1 mm-thick Al alloy and stainless steel (STS) was performed to examine the effect of an aluminizing coating and galvanized zinc coating on spreadability via MIG braze-welding using 4043 Al-Si filler wire [2]. They reported that micro-cracks were observed in the aluminized coating zone, whereas the appearance of an excellent formation was observed in the galvanized coating. The highest tensile strength was approximately 193 MPa when the galvanized steel coating was selected. [PERSON] et al. performed dissimilar braze-welding of a 1.2 mm-thick AA5052 alloy to GA, GI, and a SPCC steel sheet using cold metal transfer (CMT) welding. They reported that their joining properties significantly depended on the type of coating. Especially, in the case of GA steel, the coating layer did not sufficiently melt, due to its higher melting point when compared with GI steel. In addition, when the thickness of the coating layer increased, the metal deposition amount decreased by up to 5% and the tensile shear load decreased by 25% [3]. [PERSON] et al. reported the growth mechanism of the IMC layer using DC pulsed MIG arc brazing with flux-cored Al-Si filler wire. The maximum tensile strength was approximately 80 MPa with an IMC layer thickness of less than 2.5 um [4]. In this sense, the formation of an excessive IMC layer in dissimilar braze-welded joints caused the decrease in weld strength, and, therefore, dissimilar joining technology is required to suppress the excessive growth of the IMC layer. Among the low-heat-input processes, AC pulse MIG welding, which is one of promising processes based on gas metal arc welding (GMAW) for dissimilar metal joining, can effectively suppress the growth of IMC layers. AC pulse MIG welding generates a direct current electrode positive (DCEP) and direct current electrode negative (DCEN), it cyclically alternates between these sections, and its heat input can be controlled [5; 6; 7]. [PERSON] et al. conducted the lap joining of a 1.6 mm-thick AA6K21 alloy to 1.4 mm-thick SPRC440 steel using AC Pulse MIG welding with 4043 filler wire. They reported that the IMC layer thickness decreased with EN ratio. The tensile strength obtained at a gap of 0 mm and a EN ratio of 10% was 173 MPa, which is equal to 70% of Al alloy [6]. [PERSON] et al. studied the joining characteristics with the variation in EN ratio using AC pulse MIG braze-welding for joining the Al alloy to the GI steel sheet.