This study investigates the effect of micro-sized fluxes (ZnO, Al2O3, TiO2, CuO, SiO2, and CaCO3) on the depth of penetration (DOP) in AISI 304 L stainless steel using Activated Tungsten Inert Gas (A-TIG) welding. While nano-fluxes offer benefits, their high cost and agglomeration limit industrial use. The research finds that SiO2 micro-flux increases DOP by 189% over conventional TIG (C-TIG) and 53% over nano-flux A-TIG, presenting a cost-effective alternative. Micro-fluxes enhance arc constriction, increasing current density at the anode root and improving penetration through strengthened reverse Marangoni convection. A D-optimal design, regression modeling, and response surface methodology were used to analyze process behavior, with Analysis of Variance confirming model accuracy (adjusted R2 of 96%). Optimized conditions (SiO2 micro-flux at 170 Amp) achieved the highest penetration, with less than 2% error between predicted and actual values. This study demonstrates that micro-fluxes offer deeper penetration, lower heat input, and operational cost savings, making them a scalable solution for enhanced weld penetration.

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