Dissimilar materials joining by TIG-MIG hybrid welding

Abstract

Tungsten inert gas welding (TIG) and Metal inert gas welding (MIG) are well-established welding techniques for joining of similar materials. However, the individual technique had several limitations in order to join dissimilar materials like aluminium and steel. These limitations for joining dissimilar materials can be overcome by combining two of these welding techniques, that is combining TIG welding with MIG welding. In these TIG-MIG hybrid welding, TIG torch was used for preheating purpose, and MIG torch was used for welding purpose. In this case, both torches will be moved simultaneously. By combining TIG welding with MIG welding, the major limitation was the instability of MIG welding arc in the argon gas atmosphere was resolved. In these study Al6061 aluminium alloy and Q235 galvanized steel were joined using three different welding techniques in lap joint configuration, which were TIG welding, MIG welding and TIG-MIG hybrid welding. Effect of welding parameters like welding voltage, welding current, gas flow rate and cooling rate on joints properties like weld bead appearance, microstructure features and tensile properties were investigated. Effect of supercooling on weld properties was also studied using a water-cooled copper backing plate. Microstructural characterization was done with the help of an optical microscope and FESEM. Various intermetallic phases were detected using XRD. Comparison of all three welding techniques shows that weld bead appearance and tensile strength of joint made by TIG-MIG hybrid welding was better compared to the other two welding techniques. The optimized weld parameters were identified for the maximumimprovement in the tensile strength of the joint. Maximum strength achieved was 160 MPa at a heat input of 662.4 J/mm at welding parameters TIG current 80A, voltage 18V and MIG current 120A, voltage 15.6V with a welding speed of 4 mm/secand a gas delivery pressure of 2 kg/sq.cm. Supercooling using water-cooled copper backing plate showed significant improvement in welded joint tensile properties. The results were discussed based on the microstructure features observed, especially based on the thickness of inter interlayer formed.