Benefits from H2 and CO2 additions in argon gas mixtures in GMAW

The effects of shielding gas composition on wire melting rate, deposition efficiency, and geometry of the welds were studied. Commercial shielding gases were evaluated, among them pure Ar, pure CO2, Ar + CO2 mixtures and Ar + 5% H2. The Ar + 8% CO2 mixture exhibited superior deposition efficiency and weld bead wettability. In contrast, the wire melting rate obtained with Ar + 5% H2 mixture was significantly higher than all other tested gases. In order to simultaneously obtain the advantageous characteristics produced by the CO2 and H2 additions, further tests were performed with ternary mixtures consisting of Ar + 5% H2 with various CO2 contents. The best results were obtained with Ar + 5% H2 + 7% CO2 mixture, which yielded an increase in wire melting rate with deposition efficiency and weld bead wettability similar to those of the Ar + 8% CO2.