Heat input represents a critical process parameter that significantly influences the quality of tungsten inert gas (TIG) welding. In this study, a comprehensive investigation of heat input effects on the welding quality of thin-gauge aluminum alloy was conducted through integrated theoretical analysis and experimental validation. The research established an optimal heat input range of 296–321 J/mm for 3 mm thick 5083 aluminum alloy plates in TIG welding applications, within which welded joints demonstrated minimal defect formation and superior mechanical performance. Both numerical simulations and experimental results revealed a distinct non-monotonic relationship between heat input and joint properties: when operating below the optimal range, progressive increases in heat input resulted in corresponding improvements in fusion characteristics and mechanical properties. Conversely, exceeding the optimal range led to progressive grain coarsening within the weld microstructure, accompanied by measurable degradation in key mechanical properties including tensile strength and hardness.

The wetting behaviors of Al-Si-Cu-Mg-Zn brazing materials on 5083 aluminum alloy substrate were investigated through changing the proportion of Mg from 0 to 2 wt.%. The experimental results showed that the welding process goes through the three following stages: slow spreading, fast spreading, and stabilizing. The wettability of the brazing material was improved effectively, and the porosity of the interfacial layer was reduced, with the addition of Mg. With Mg content at 1 wt.%, the wetting diameter reached a maximum value of 20.46 mm. The reaction mechanism of the wetted interfacial layer between the brazing material and substrate alloy was illustrated with dynamic data, provided through experimentation and simulated thermodynamic calculation, and showed that the wetting behavior of the resultant Al-7.5Si-15Cu-1Mg-5Zn brazing material was dominated primarily by a diffusion reaction from elemental magnesium.