Influence of zinc ethyl silicate primer with different fluoride concentrations on FCAW overlayer weld

Structural steels that require coating with pre-construction paints to avoid corrosion are utilized in important industrial segments. These paints, known as primers, act as corrosion inhibitors; however, they can have a detrimental impact on welding performance and compromise the quality of welds. In order to overcome these challenges, new alternatives need to be developed to achieve welds that are, at the very least, equivalent to those obtained on uncoated plates. To this end, this work aims at promoting the production of welds on plates coated with primer and varying concentrations of fluoride added to the base formulation, by means of 1.2-mm-diameter tubular wire classified as E71T1-C1A2-CS2 with CO₂ gas protection. In a comparative analysis, the influence of non-filler primer and primer with 7.5% and 15% by mass of lithium fluoride was examined. It was found that the primer inhibits the adhesion of welding spatter on the plates. The electrical signals recorded during welding indicated globular metallic transfer mode under all conditions. Lithium fluoride filler increases the voltage cycle frequency reducing the droplet molten metal size. The average current tends to decrease in the presence of the primer, and the addition of fluoride exacerbates the trend. Therefore, samples with fluoride filler exhibit lower thermal inputs compared to the other samples. The effects mentioned above may be associated to the lithium lower ionization potential. It was also observed that the primer does not influence the weld microstructure in comparison with welds with no primer. Fluoride filler incorporation apparently increases the volumetric fraction of acicular ferrite and aligned second-phase ferrite, while simultaneously reducing the fractions of primary ferrite at the grain boundary and of intragranular ferrite. Weld morphology was slightly changed by shop primer and fluoride filler nevertheless to verify this behavior, additional measures must be carried out.