Influence of an Al-Sc modified filler on the microstructure and mechanical properties of TIG welded dissimilar AA7075-T6/AA2024-T4 aluminium joints

Aluminium alloys such as AA7075-T6 and AA2024-T4 which possess high strength, are highly recommended for aircraft structures due to their superior strength to weight ratio and mechanical properties. However, dissimilar welding often causes porosity, cracking, and HAZ softening, reducing joint integrity and reliability. This work investigates the dissimilar TIG welding of AA7075-T6 and AA2024-T4 using conventional and Sc-modified ER5356 filler materials. Welding parameters were optimized through the Taguchi L9 design to evaluate their effects on tensile strength, microhardness, and weld quality. A filler containing ∼0.2 wt.% Sc was developed to assess the effect of microalloying, with results showing that filler composition significantly influences weld performance. Sc addition promoted fine Al3Sc precipitates, leading to grain refinement and a more homogeneous, defect-resistant microstructure. This improved tensile strength by ∼25% and microhardness by 7–8% compared to conventional filler welds. SEM and EDS analyses confirmed fine equiaxed grains and a uniform distribution of Sc-rich precipitates. The fractography analysis showed the dominance of ductile fracture and improved resistance to crack propagations. This study illustrates that the selective addition of Sc to the conventional filler material can greatly improve the quality, strength and reliable performance of the welds.