Effect of heat input on microstructure and mechanical properties of A7020-T6 alloy joined by TIG welding

In this study butt joining of 7020-T6 alloy was performed using tungsten inert gas (TIG) welding with continuous (constant) and pulsed current. Effect of heat input on microstructure and mechanical properties of the joints was investigated. Microstructural examinations were conducted using optical and scanning electron microscopy. Differential scanning calorimetry (DSC) was used to identify the precipitates phase evolution. Temperature at the welding region was recorded by inserting thermocouples. Hardness and tensile strength of the joints was evaluated. Results showed that current pulsing leads to relatively finer grain size in weld metal compare to the one welded by constant current. In either cases of constant and pulsed current, the grain size and the width of heat affected zone increased with increasing heat input. Unlike earlier studies in precipitation hardening aluminum alloys, strength of the weld metal were increased as compare to base metal in T6 condition. The enhancement in mechanical properties of weld metal was attributed to the solution annealing and re-formation of strengthening precipitates on cooling from welding temperature.