Analysis of the influence of filler metal and shielding gas on galvanized steel welded joints

ABSTRACT

The wide adoption of galvanized steel in the industrial segment, such as the automotive industry, is based on excellent properties in providing durability and weight reduction to manufactured products, in addition to reducing environmental impacts and costs in the production chain, avoiding corrosion, and providing longer lifecycle useful due to the protective zinc layer. However, this layer when submitted to the welding process implies potential defects due to evaporation of zinc vapor and fragility of the liquid metal during welding, with potential generation of porosity, lack of penetration or melting. Ultimately, these defects can significantly impact the reduction of mechanical properties, cracks, and fractures in welded joints. In this work these implications are analyzed through the microstructural characteristics of joints welded with ZAR230 galvanized steel by the GMAW and FCAW welding processes, evaluating the mostly common factors that are modified on an industrial scale in this welding technique: the type of filler metal, whether solid wire or tubular – self-protected with gas protection and without gas protection, and the type of protection gas (with mixtures of 92% Ar + 8% CO², 80% Ar + 20% CO² and 95% Ar + 5% O²). Using scanning optical microscopy techniques, metallography, tensile tests and microhardness, the results indicate that all tested conditions have acceptable mechanical properties of hardness and traction, with variation in the presence of defects, inclusions and welding bead, with the best combination being the use of solid wire with mixture 92% Ar + 8% CO².

Keywords
Galvanized steel; Metal cored wire; Shielding gas