Mechanical Properties of Pulsed Current Multipass GMA Weld of Al-Zn-Mg Alloy

The growing interest of using thick section of high strength aluminum alloy like Al- Zn-Mg in the fabrication of lightweight large transport container and pressure vessels necessitates the gas metal arc welding (GMAW) of this alloy. Due to its high strength, the weld joint of AI-Zn-hAg alloy is highly sensitive to fatigue failure, thus in any engineering application, an assurance about its desired tensile, fatigue and fracture toughness properties are of utmost importance. In the light of the recent observations on the superiority of using pulsed current GMAW over the conventional continuous current one to improve the mechanical properties of single pass weld of A/-Zn-Mg alloy, the present investigation has been planned to study the characteristics of multipass weld of thick section of this alloy prepared by employing pulsed current GI^AW process. The multipass welding of 25mm thick extruded section of an Al-Zn-Mg alloy has been carried out using pulsed current and continuous current gas metal arc welding (GMAW) processes. The welding has been carried out by employing 1.6mm diameter AI-!\/lg ('/41VS ASME: SFA-5.10 ER 5183) filler wire and commercial argon as shielding gas. The pulsed current welding has been performed by varying the pulse parameters such as the pulse frequency and duration and their effects on dilution, zinc pick-up, precipitation behavior, porosity content and tensile properties of the weld are studied. It is observed that the variation in pulse parameters affects the microstructure and dilution of weld deposit. The change in weld dilution has been found to control its chemistry (especially zinc level) and precipitate content dictating tensile properties of the weld. The characteristics of the pulsed current weld has been compared to those of the weld prepared by continuous current GMAW. The properties of the pulsed current weld are found superior to those of the conventional continuous current weld.