Efeito do potencial de oxidação na molhabilidade de cordões de solda

Abstract

Weld bead wettability is a governing factor for structural integrity and geometric finish in welded joints, being heavily influenced by the thermal and chemical properties of the shielding gas atmosphere. This work aimed to quantitatively evaluate the impact of different shielding gas compositions on the geometry and spreading of weld beads deposited by the automated GMAW process. The experimental methodology consisted of executing weld beads while maintaining constant input operational parameters. Six experimental groups were tested under distinct atmospheres, including pure reference gases (100% Ar and 100% CO₂), binary mixtures with increasing carbon dioxide contents (8%, 15%, and 20%), and a mixture containing oxygen (Ar + 2%O₂). The filler metal used was an AWS ER70S-6 electrode with a 1 mm diameter. After welding, the samples were cross-sectioned using a metallographic cutter, generating a total of 54 specimens. The resulting images were processed and analyzed using ImageJ software, in which the contact angle at the bead toes was measured. The data were tabulated to calculate the arithmetic mean and the sample standard deviation. The results demonstrated that the controlled introduction of CO₂ acted as a surfactant in the weld pool, progressively reducing the contact angle by 12% and increasing wettability, whereas the presence of O₂ did not indicate any change in wettability, likely due to its low percentage in the mixture. It is concluded that the presence of CO₂ in welded joints acts to increase weld bead wettability, and neither the variation of the carbon dioxide percentage in the mixture with argon nor the presence of oxygen in the atmosphere indicated significant changes.