Shielding gas composition is an important parameter for successful gas metal arc welding (GMAW) and has been shown to affect the fume emission rate (FER). The present paper compares thirteen shielding gases and their impact on fume emission rate in the spray transfer regime. Comparisons were initially made at fixed wire feed speed and voltage but the voltage was subsequently optimised for each gas and the tests were repeated.

The variation of FER and particulate size range with shielding gas composition are reported. Results indicate that an increase in the oxygen content of the shielding gas promotes higher nucleation rates and subsequent particle growth, and consequently, increased FER. In Ar-based mixtures, increasing CO₂ had a greater impact than raising O₂ additions and variations in Ar-He-CO₂ mixtures had the least influence on FER’s. Results indicate that CO₂ additions in Ar-based shielding gases are the controlling factor in determining FER due to the effect of CO₂ on welding arc characteristics. Fume generation was significantly higher for 100% CO₂ than Ar-based shielding gases due to the change in weld transfer mode to globular and increased spatter.

XRD analysis of the (bulk) fume identified the Fe₃O₄ -spinel type phase (Magnetite-index card 011-0614 ICDD data base). There was no evidence that shielding gas composition affected the composition of the bulk fume. There was a slight peak shift that indicated that small levels of Mn, as detected by TEM-EDS, substituted for Fe in the Fe₃O₄ phase.

More detailed TEM morphology study indicated a mixture of spherical and faceted particles, including the tendency of the particles to agglomerate in groups and chain-like structures. In some cases rhombohedral particle morphology was observed. Lattice fringes are clearly visible indicating the crystalline structure of the fume particle.