Joining of dissimilar 2060-T8 and 2099-T83 Al-Li alloys by pulsed gas tungsten arc welding method: Parametric investigation on the metallurgical, mechanical and residual stress properties

Joining dissimilar aluminum-lithium (Al-Li) materials is crucial in the aerospace sector due to their reduced weight, enhanced strength, and improved corrosion resistance. However, conventional fusion welding often results in defects such as voids, thermal cracks, high residual stresses, and coarse-grain structures, leading to degraded joint properties. To address these issues, this study employed pulsed current gas tungsten arc welding (PGTAW) and investigated the effects of pulse frequency (PFR), pulse duration ratio (PDR), and gas flow rate (GFR) on tensile strength, flexural strength, Vickers hardness, and residual stress using the response surface method. Variance analysis revealed that PFR had the most significant impact on the responses, followed by PDR, while GFR had the least effect. Electron backscatter diffraction results showed that the pulsed current joint (PGTAW-10) had a fine-grained fusion zone structure with a mean grain diameter (MGD) of 14.35 ± 0.16 µm and a high-angle grain boundary (HAGB) fraction of 72.01%. In contrast, the continuous current GTAW joint exhibited a coarse-grained fusion zone structure with an MGD of 37.78 ± 0.10 µm and an HAGB fraction of 57.21%. The phase analysis showed that the fusion zone of both continuous and pulsed current joints consisted of α-Al, θ΄(Al 2 Cu), δ΄(Al 3 Li), T1(Al 2 CuLi), and T₂(Al 6 CuLi 3 ) intermetallic precipitates, while their intensity is decreased for the pulsed current mode. The desirability function revealed an optimum parameter (PFR- 9.59 Hz, PDR- 1:1, GFR- 9.70 L/min) for obtaining maximum tensile strength of 197.09 MPa, flexural strength of 319.64 MPa, Vickers hardness of 95.28 HV, and residual stress of -144.35 MPa. The pulsed current welding mode yielded enhanced metallurgical and mechanical performance compared to the continuous current mode, which may be due to adequate grain refinement, less segregation, uniform dispersion of precipitates, and increased grain boundary transformations associated with the pulse current mode, showing the effectiveness of joining dissimilar Al-Li alloys for aerospace applications.