Effect of post-weld heat-treatment and solid-state thermomechanical treatment on the properties of the AA6082 MIG welded joints

Post-weld heat treatment (PWHT) and solid-state thermomechanical treatment (TMT) via friction stir processing (FSP) have been shown to enhance the mechanical properties of aluminum alloys. The current work investigates the effects of PWHT and TMT on the microstructure and mechanical performance of AA6082-T6 welded butt joints welded using the MIG process. The 5 mm thick AA 6082-T6 plates were joined in butt configuration using MIG welding with ER 5356 filler wire, 120 A current, 0.3 mm/s weld speed, and argon shielding gas at 15 L/min flow rate. PWHT was performed on the MIG welds per the T6 temper procedure. TMT was implemented via FSP using a pinless tool rotating at 800 rpm and traversing speed at 200 mm/min with a 3° tilt angle. Microstructural analysis, hardness mapping, tensile testing, and fracture surface evaluation were utilized to characterize the as-welded, PWHT, and TMT samples. The results demonstrate that both PWHT and TMT significantly refine and homogenize the microstructures of the welded joints. However, the TMT samples displayed superior hardness and tensile strength compared to the as-welded and PWHT conditions. The TMT-processed welds achieved approximately 99% joint efficiency versus only 69% and 85% for the as-welded and PWHT samples. In summary, PWHT and especially TMT via FSP are effective at enhancing the mechanical properties of MIG welded AA6082-T6.