Gas Metal Arc Welded (GMAW) Joint Strength Comparison of Aluminum Sheet (5754) and Exturded (6063) Alloys

The development of lightweight vehicles, in particular aluminum intensive vehicles, require significant manufacturing process development for joining and assembling aluminum structures. Currently, 5xxx and 6xxx aluminum alloys are being used in various structural applications in a number of lightweight vehicles worldwide. Various joining methods, such as GMAW (it is also referred as Metal Inert Gas Welding), Laser and adhesive bonding have been investigated as technology enablers for high volume joining of 5xxx, and 6xxx series alloys. In this study, GMA welding was used to join 5754 non-heat-treatable alloy sheet and 6063-T6 heat treatable extrusion products. The objective of this study was to develop optimum weld process parameters for non-heat-treatable 5754 aluminum and heat treatble 6063-T6 alloys. For both the alloys, the lap joint configuration was used. The GMA welding equipment used in this study was an OTC/Daihen CPD-350 welding systems and DR-4000 pulse power supply. In the first phase of the experiments for 5754 aluminum alloy, the factors selected for the experiment were power input (torch speed, voltage, current, wire feed), pulse frequency, gas flow rate and surface condition. A full factorial design of experiment (DOE) was conducted (DOE #1) to understand the main and interaction effects on lap joint failure and weld penetration. Based on the results from phase 1 results, surface condition was eliminated in the phase 2 experiments. In phase 2 experiments for heat treatable alloys 6063 T6, the factors selected were power input (torch speed, voltage, current, wire feed), pulse frequency, gas flow rate, torch angle, and arc intensity. A partial factorial DOE was conducted (DOE # 2) primarily to understand the main effects and some two level interaction effects. For both phase 1 (non-heat treatable alloy 5754) and phase 2 (heat treatable alloy 6063-T6) experiments, the factors influence on the mechanical properties of the lap joint, metallurgy (weld penetration) and micro hardness were evaluated. Post weld analysis indicates for non heat treatable alloy 5754, power input and gas flow rate are the two signficant factors (statistically) based on lap shear load to failure and weld penentration data. For heat treatable alloy 6063, power input was the significant factor on joint load to failure, however, for weld penetration, power input, pulse frequency and gas flow rate were the significant factors. Based on the joint strength and weld penetration, optimum weld process factors were determined for both non-heat treatable alloy 5754 and heat treatble alloy 6063 T6.