In recent years, the welding of dissimilar metals such as steels and aluminum alloys has attracted much more attentions due to weight reduction, especially in automobile and railway vehicle manufacturing industry. However, many challenges and problems need to be addressed in order to obtain high quality welding joints between steels and aluminum alloys resulting from their differences of thermal-physical properties. The formation of intermetallic compounds (IMCs) in the course of welding will lower the mechanical properties of the joints. Up to now, a few techniques have been tried to weld aluminum alloys and steels, including solid welding and fusion welding. In this work, dissimilar metals of 5182-O and HC260YD+Z were welded by cold metal transfer (CMT) arc-brazing using AlSi₅ as filler metal. The macro and micro morphologies of the overlap joint were investigated using OM, XRD, SEM and EDS analyses. The hardness and shear strength of the joints were tested. Results show that welding line energy can affect the thickness of IMCs existing on the brazing interface and thus depress the combination properties because of the different fracture modes. When the welding speed and wire feed speed are 9 mm/s and 5 m/min respectively, the IMCs thickness is about 6 μm, and the shear strength of the jonts can reach to 160 MPa. Two typical fracture modes of fusion interface fracture and brazing interface fracture were observed. The fracture mode of the position near arc striking is "fusion interface". With the increasing of welding energy, the thickness of IMCs is increased and the fracture mode near arc extinguishing is changed from "fusion interface" to "brazing interface". When the output power of CMT equipment is 150~210 J/mm at welding beam length, the IMCs thickness is less than 9 μm, which benefits the shear strength performance of the joints, and the fracture mode of "fusion interface" can be easily obtained.