Heat-affected zone

About: Heat-affected zone is a research topic. Over the lifetime, 18787 publications have been published within this topic receiving 231744 citations.

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 (H2), oxygen (O2), carbon dioxide (CO2), nitrogen (N2), 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.

Continuous wave-Nd: yttrium–aluminum–garnet laser welding of AM60B magnesium alloy

Abstract: This study shows that the formation of macroporosity and overfill in the weld pool were the most pronounced problems during continuous wave Nd:yttrium–aluminum–garnet laser welding of AM60B die cast magnesium alloy. The influences of various welding parameters on the formation of porosity and overfill were investigated with particular emphasis on the mechanism and prevention of porosity formation. It was found that the macro pores in the weld pool were mainly formed by the expansion and coalescence of the preexisting pores in the base metal. The amount of macro- porosity in the weld pool could be reduced to approximately that in the base metal by reducing heat input, i.e., by increasing welding speed and decreasing laser power. Increasing the beam defocusing did not reduce porosity in the weld metal until the beam was highly defocused and a shallow weld pool, characteristic of conduction mode welding was obtained. Overfill was observed for deep penetration autogenous welds and its formation could be attributed to porosity formation and the resulting displacement of the liquid metal over the top surface of the workpiece.

Resistance Element Welding of 6061 Aluminum Alloy to Uncoated 22MnMoB Boron Steel

Abstract: A novel resistance element welding technology was applied to join 6061 Al alloy and uncoated 22MnMoB boron steel. To conduct the resistance element welding process, a technological hole was drilled in the Al sheet into which a Q235 steel rivet was inserted. Resistance spot welding was carried out at the rivet. The mechanical properties, fracture morphology, nugget formation process, dynamic resistance, microstructure, and hardness distribution of the resistance element welding were investigated. Traditional resistance spot weld joints were also prepared for comparison. Resistance spot welding could barely join Al 6061 and boron steel, and had a maximum tensile shear force of less than 1000 N. Novel resistance element welding could join the metals reliably with a maximum tensile shear force of over 7000 N and a relatively high toughness. Nugget formed at the interface of rivet and steel acted as loading position, and IMC interlayer connected rivet and aluminum.