Effects of shielding gas control: welded joint properties in GMAW process optimization

Abstract

One function of shielding gases used in welding processes, such as hydrogen (H 2 ), oxygen (O 2 ), carbon dioxide (CO 2 ), nitrogen (N 2 ), helium (He), argon (Ar) and their mixtures, is protection of the weld pool against harmful contamination that could generate defects. In addition to this primary function, shielding gases significantly affect the shape of the weld, weld geometry, seam appearance, metallurgical and mechanical properties, welding speed, metal transfer, arc stability or beam and fume emissions. The shielding gas is thus a key factor in determining weld joint properties and welding process efficiency. As welding processes have become enhanced and welding research has advanced, different combinations of shielding gas mixtures have become available under a wide variety of trademarks, each claiming to offer the best efficiency. The shielding gas flow rate in GMAW welding is usually set according to empirical experiment. The flow generally remains unchanged throughout the entire welding process and is set at maximum values of the welding parameters so that there is sufficient gas cover. This setting means, however, that unnecessarily large quantities of shielding gas may be consumed in other phases of the welding process. In view of constantly increasing prices and shortfalls in helium supply, there is a need to optimize the use of shielding gas. Consequently, an ability to closely monitor the shielding gas blend and reduce waste can provide valuable cost savings. This paper examines the effects of shielding gas mixtures and their components, presents a cross-comparison of shielding effects in fusion welding and suggests guidelines for adaptive controllability of shielding gas in advanced adaptive fusion welding. The study reviews scientific case studies and experiments from the point of view of the effect of the shielding gas on the process efficiency and process outcome. The study considers shielding gases for welding of both ferrous metals (i.e. carbon steels, stainless steels, high-strength steels) and non-ferrous metals (i.e. aluminium and its alloys, nickel and its alloys and copper and its alloys). Appropriate choice of shielding gas and use of an optimum flow rate results in better quality in terms of increased productivity, reduced gas consumption and improved weld geometry properties, microstructure and mechanical properties. Although some blends can be used effectively in many different processes, other blends appear process-dependent; they produce far poorer results when utilized in non-appropriate processes. Particle image velocimetry (PIV) and Schlieren techniques can be used for visual sensing of gas flow during fusing welding. Moreover, an adaptive alternative gas supply can improve welding performance and weld quality and reduce harmful fume emission.

Investigation on TIG welding parameters of 2205 duplex stainless steel

“…The shielding gas is used not only to protect the molten drop and bead but also to modify metal transfer, penetration and bead width of the weld, for spatter control and post-weld cleaning, to control welding fume generation and to influence the metallurgical and mechanical properties of the weld. Shielding gas selection is therefore a determinant for welding process efficiency [37]. The maximum hardness was observed when the gas flow rate was 12 L/min, welding current was 190 A and the welding speed was 170 mm/min.…”

Influence of rotation frequency and rotation diameter on mechanical properties and microstructure of weld metal produced by MCAW-RE

“…Mukhopadhyay et al [49] stated that proper weld joints can be achieved by a suitable matching of the consumable electrode and the shielding gas mixture. In this respect, Mvola et al [50] state that the use of a mixture containing 5 to 25% CO 2 is suitable for low alloy steels, because the addition of CO 2 stabilizes the arc, changes the arc characteristic, and results in an increase of the metal transfer frequency. However, there is a relationship between the microstructure of welds and the shielding gas, because an increase in CO 2 contributes to a coarser microstructure with a higher volume fraction of nonmetallic inclusions, besides the growth in the burn rate of alloy elements of the base metal, such as silicon and manganese.…”

Influence of shielding gas on the mechanical and metallurgical properties of DP-GMA-welded 5083-H321 aluminum alloy

“…For example, Mvola and Kah [5] investigated the effect of shielding gas control on the metallurgical and mechanical properties in GMA welding. They found that the shielding gas was a major factor in determining weld joint properties.…”