This work presents a review of the three most efficient non-destructive testing methods. The methods are radiography, eddy current and ultrasonic inspection. These particular techniques were chosen because they are able to cover most of the industrial needs for welding joint inspection. The aim of this work is to present the physical background of operation for the given methods, discuss their benefits, limitations, and typical areas of application, and compare them with each other. In the first part of this work, all three methods and their variations are described in detail with schemes and figures which represent their working principles. It appears that, although all the given methods can detect all types of flaws in welded joints, they have their specific limitations. For example, ultrasonic testing is able to detect defects only in certain directions. The eddy current technique is also sensitive to defect direction, but it can be applied for inspecting conductive materials only. The main flaw of radiography is the resolution: it is not usable for very fine defects. The second part of the work is for comparing the testing methods and for drawing the conclusions. The methods are compared according to the possible materials, defect types and their position, as well as the possible areas of application. This part gives the background for choosing a proper welding joint testing method for certain applications in the welding industry.

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.

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For many years, the manufacturing industry has shown interest in the opportunities offered by welding of dissimilar metals. The need for appropriate and effective techniques has increased in recent decades because of efforts to build light and strong vehicles with reduced fuel consumption. In addition, the thermal conductivity, corrosion resistance, and recyclability are other reasons to weld dissimilar non-ferrous metal. Early gas metal arc welding (GMAW) processes had limited control of the heat input, a prerequisite for effective welding of dissimilar metals, but the advanced GMAW processes of the past decades offer new perspectives. The objective of this paper is to review the main principles of the fusion welding of dissimilar metals. The study briefly investigates the challenges in welding the main possible combination of categories of non-ferrous metal. Some experiments performed on dissimilar metals using GMAW processes are then reviewed, highlighting those made using advanced GMAW processes. The study collates data from the scientific literature on fusion dissimilar metal welding (DMW), advanced GMAW processes, and experiments conducted with conventional GMAW. The study shows that the welding procedure specification is a crucial factor in DMW. Advanced GMAW processes have significant potential in the fusion welding of dissimilar non-ferrous metals of different grades. Accurate control of the heat input allows more effective prediction of the intermetallic properties and better control of post-heat treatments. Increased understanding of advanced GMAW processes will permit the development of more accurate specifications of welding procedures for DMW. Process flexibility and adaptability to robotic mass production will allow a wider range of applications and the avoidance of costly alternative methods.

The effect of heat input on the microstructure and mechanical properties of dissimilar S700MC/S960QC high-strength steels (HSS) using undermatched filler material was evaluated. Experiments were performed using the gas metal arc welding process to weld three samples, which had three different heat input values (i.e., 15 kJ/cm, 7 kJ/cm, and 10 kJ/cm). The cooling continuous temperature (CCT) diagrams, macro-hardness values, microstructure formations, alloy element compositions, and tensile test analyses were performed with the aim of providing valuable information for improving the strength of the heat-affected zone (HAZ) of both materials. Micro-hardness measurement was conducted using the Vickers hardness test and microstructural evaluation by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical properties were characterized by tensile testing. Dissimilar welded samples (S700MC/S960QC) with a cooling rate of 10 • C/s (15 kJ/cm) showed a lower than average hardness (210 HV5) in the HAZ of S700MC than S960QC. This hardness was 18% lower compared to the value of the base material (BM). The best microstructure formation was obtained using a heat input of 10 kJ/cm, which led to the formation of bainite (B, 60% volume fraction), ferrite (F, 25% volume fraction), and retained austenite (RA, 10%) in the final microstructure of S700MC, and B (55%), martensite (M, 45%), and RA (10%), which developed at the end of the transformation of S960QC. The results showed the presence of 1.3 Ni, 0.4 Mo, and 1.6 Mn in the fine-grain heat-affected zone of S700MC. The formation of a higher carbide content at a lower cooling rate reduced both the hardness and strength.