The dissimilar materials lap-joint of Ti-6Al-4V titanium (Ti) and 6061 aluminum (Al) alloys was achieved through a metal inert gas (MIG) arc weld-brazing process. The relationships between the major MIG arc weld-brazing parameters such as travel speed of MIG torch, MIG welding current, argon flow rate of MIG torch, wettability of weld bead and mechanical property of Ti/Al lap-joint specimens were investigated. A proposed approach that integrates the Taguchi method, grey relational analysis (GRA) and fuzzy logic was employed to obtain the optimal MIG arc weld-brazing parameters. The proposed approach was adopted to solve the MIG arc weld-brazing process with multiple quality characteristics (QCs). The experimental procedure of this study not only improves the wettability of weld bead, but also increases the tensile strength of Ti/Al lap-joint specimens. Confirmation experiments revealed that this study could efficiently optimize the MIG arc weld-brazing parameters, and the average tensile strength of Ti/Al lap-joint specimens could reaches 178 MPa. During the MIG weld-brazing, higher argon flow rate of the MIG torch that produces turbulence to the weld pool and brings outside air could create a high amount of porosity over the weld bead.

Compared with the low-carbon steel sheet, use of Al alloys as automotive parts has many advantages such as higher weight-strength ratio and recoverability. The reduction of fuel utilization could be accomplished by using light materials such as Al panels and body frame of the vehicles. The vehicle structures adopt Al alloys that could lead to weight reduction and energy saving. Due to the outstanding resist of corrosion, the galvanized steel sheet has been extensively employed by the automotive industry as well. The dissimilar materials joining performance of Al alloy and galvanized steel sheet has been paid growing attention in manufacturing industries (Zhang et al. 2013). The brittle intermetallic compounds (IMCs) are formed between the interface of Al and steel during welding process, it is difficult to achieve a proper joint of Al/steel by means of the traditional arc welding process (Lin et al. 2018). Therefore, Chen et al. ( 2019) utilized the friction stir welding process to produce the lap joints of 6061 Al alloy and steel sheet. When the welding parameters were set at optimal conditions, the maximum failure load of specimen was achieved at 2.26 kN. Dong et al. (2016) employed the refilled friction stir spot welding process to produce the lap joints of Al alloy and steel sheet. When the welding parameters were set at optimal conditions, the maximum tensile-shear fracture load of specimen was achieved at 3.044 kN. All of the tensile-shear testing specimens failed at the interface between Al and steel. Lü et al. (2018) used the laser fusion weld-brazing process to produce the lap joints of Al/steel. When the welding parameters were set at optimal conditions, the maximum tensile fracture load of specimen was achieved at 152.5 MPa. Wider lap interface between Al and steel, and narrow heat affect zone (HAZ) were formed by employing this laser weld-brazing process. However, these novel weld-brazing processes have disadvantage of either lacking versatility or high cost.The MIG weld-brazing process has been recommended to obtain higher quality of joints between Al and steel that using appropriate heat input to melt Al alloy but maintain the steel in solid state. Shao et al. (2015) adopted a pulsed double electrode MIG welding process to generate the joint of Al/steel. The low heat input was used to the specimen that