EVOLUTION OF MICROSTRUCTURE AND MECHANICAL PERFORMANCE OF TIG-WELDED AA6061–AA6063 JOINTS: INFLUENCE OF JOINT CONFIGURATION AND HEAT INPUT

Abstract

Dissimilar aluminium alloys are widely used in automotive and aerospace structures because they are lightweight and strong. However, joining these alloys by fusion welding remains challenging because their different chemical compositions and thermal behaviour strongly affect weld quality. This study investigates how joint configuration and heat input influence the microstructure, phase stability, and mechanical performance of TIG-welded AA6061-AA6063 joints. Plates of AA6061 and AA6063 were welded using 4043 filler metal in single-V, half-V, double-V, lap, and no-joint configurations, with welding currents ranging from 110 to 130 A. Mechanical testing (tensile strength, hardness, impact), SEM/EDS, XRD, and spectrometric analysis were conducted to evaluate changes induced by welding conditions. The weld metal showed reduced aluminium content and significant increases in silicon, magnesium, and copper due to dilution with the 4043 filler. Heat input and joint configuration substantially influenced hardness and toughness. Quantitative evaluation showed that a half-V configuration at 130 A achieved the highest hardness (150.63 HV), while the double-V configuration at 130 A delivered the highest impact energy (41.34 J). The single-V configuration at 130 A produced the maximum tensile strength (98.7 MPa) with 19.6% elongation. SEM/EDS analysis revealed increased pore density with rising heat input, which was suspected to be due to higher gas entrapment during solidification. XRD showed no major phase transformations across the joint designs, suggesting that mechanical variations were primarily governed by microstructural refinement and elemental redistribution rather than the formation of new phases. These findings provide novel insight into the optimization of TIG welding parameters for dissimilar 6xxx-series aluminium alloys, providing practical guidance for lightweight structural applications.