Combined effects of MIG and TIG arcs on weld appearance and interface properties in Al/steel double-sided butt welding-brazing

Abstract

AA5052 aluminum alloy and Q235 low-carbon steel of 3.0mm thickness were butt joined without groove. The combined effects of the MIG-TIG double-sided arc on the weld appearance and interface properties were investigated in three aspects: weld appearance, interfacial properties and joint tensile strength. Form efficiency was defined to evaluate the quality of the weld appearance. The strength of the whole joint and the brazed interface were examined in the tensile tests of joints with and without excess weld metal, respectively. The weld appearance can be well characterized by the form efficiency. The form efficiency is found to be most sensitive to TIG current. Sensibility of the form efficiency to MIG voltage and welding speed is relatively low, indicating that the TIG arc at the back of the weld is the key factor for the double-sided weld appearance. Double-sided weld appearance can be achieved at a maximum welding speed of 2.2cm/s because a part of welding energy is input by TIG arc directly to the back weld. The interfacial properties of the joints are closely tied to the heat input ratio of MIG and TIG. Proper input ratio (1.35–1.64) leads to uniform deformation of the base metals and suppresses the initiation of the cracks in interfacial IMC layer. The differences between the interfacial strength and the whole joint strength indicate that the optimum weld appearance with desirable excess weld metal provides extra 20MPa strength for the whole joint. Benefitting from combined effects of the best weld appearance and toughest interfacial IMC layer, the highest tensile strength of the joint exceeds 70% the tensile strength of 5052 alloy.