Shielding Gas Influence On AA5086 Welded Joints: Residual Stresses Analysis, Microstructural Characterisation and Mechanical Properties

Samples of AA5086 aluminium alloy were welded by gas tungsten arc welding (GTAW) with alternating current using three different shielding gases. The samples were welded with pure argon (Ar), a mixture of argon and helium (Ar + He) and a new mixture composed of argon, nitrous oxide and oxygen (Ar + N2O + O2). The effect of the shielding gas on the residual stresses and on the mechanical and microstructural properties of the welded joints was evaluated and compared with the base metal. The new gas mixture produced compressive residual stresses in the longitudinal and transverse directions in the weld metal. Tensile test of welded joints indicated similar values for yield strength and ultimate tensile strength; however, these values were lower compared to the base metal. The new gas mixture provided a welded joint with hardness values in the weld metal and heat affected zone close to the base metal values and with greater magnitude compared to samples welded using pure argon and mixture of argon and helium. Microstructural characterisation performed by optical and scanning electron microscopy showed that the new mixture produced welded joints with lower porosity.

Effects of Active Gases on Droplet Transfer and Weld Morphology in Pulsed-Current NG-GMAW of Mild Steel

The current research of narrow-gap gas metal arc welding (NG-GMAW) primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect. However, the high cost and operation difficulty of the methods limit the industrial application. In this study, small amount of active gases CO2 and O2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO2, being added into the pure argon shielding gas, changes from 5% to 25%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O2 is added. Both CO2 and O2 are favorable to stabilizing arc and welding process. O2 is even more effective than CO2. However, O2 is more likely to cause slags on the weld surface, while CO2 can improve the weld appearance in some sense. The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant. This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

Lung Decortication With Argon Plasma Energy for the Treatment of Chronic Pleural Empyema

Lung decortication for the treatment of chronic pleural empyema remains a technically challenging procedure that is associated with bleeding and air leak. The recent advent of pure argon plasma has provided thoracic surgeons with an electrically neutral energy source for dissection and coagulation of pulmonary tissue with minimal depth of necrosis. In this article, we describe the technique of lung decortication with argon plasma energy (PlasmaJet, Plasma Surgical, Roswell, GA, USA) for the treatment of chronic pleural empyema. With appropriate application, the PlasmaJet can facilitate the removal of fibrous cortex with satisfactory hemostasis and aerostasis. Argon plasma energy can potentially be a useful adjunct in lung decortication. Controlled trials are needed to determine its role in the surgical management of advanced pleural empyema.

Effects of active gases on droplet transfer and weld morphology in pulsed-current NG-GMAW of mild steel

The current research of narrow-gap gas metal arc welding (NG-GMAW) primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect. However, the high cost and operation difficulty of the methods limit the industrial application. In this study, small amount of active gases CO2 and O2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO2, being added into the pure argon shielding gas, changes from 5% to 25%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O2 is added. Both CO2 and O2 are favorable to stabilizing arc and welding process. O2 is even more effective than CO2. However, O2 is more likely to cause slags on the weld surface, while CO2 can improve the weld appearance in some sense. The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant. This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

Effects of active gases on droplet transfer and weld morphology in pulsed-current NG-GMAW of mild steel

Small amount of active gases CO 2 and O 2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO 2 , being added into the pure argon shielding gas, changes from 5% to 5%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O 2 is added. Both CO 2 and O 2 are favorable to stabilizing arc and welding process. O 2 is even more effective than CO 2 . However, O 2 is more likely to cause the inclusion defects in the weld, while CO 2 can improve the weld appearance in some sense. The weld surface concavity, which is sensitive to the formation of lack-of-fusion defect in NG-GMAW, is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant.

Investigating the dynamics of Lake Kivu with quantum technology

<p>Lake Kivu, located on the border of Rwanda and the Democratic Republic of Congo, is a very peculiar lake in several aspects. The meromictic lake shows a vertical stratification dominated by high salt concentrations of up to 6 ‰ resulting in a very thick monimolimnion of 420 m (max depth ~492 m). This extremely large non mixing part of the lake functions as a reservoir for very high concentrations of volcanogenic gases like methane and carbon dioxide (up to 20 and 100 mmol/l respectively) resulting in a growing hazard for millions of local residents. Our aim of this study is to get insights into the hydrological dynamics, solute transport and the lakes mixing behavior utilizing radiometric dating with <sup>39</sup>Ar.</p><p>The noble gas isotope <sup>39</sup>Ar (t<sub>1/2</sub> = 269 a) covers a unique time span for studying the dynamics of aquatic and glacial systems of the last millennium. Although this tracer has been acknowledged for decades, studies so far are limited by its low abundance, little radioactivity and hence huge required sample sizes (~1000 L water). Until today environmental routine measurements are mainly confined to groundwater reservoirs, where nearly unlimited sampling is possible. The application of techniques from atomic physics using a magneto optical atom trap (MOT) solves the problem by reducing sample volume requirements by several orders of magnitude. The problem of the very low isotopic abundance of 10<sup>-16</sup> is resolved by resonant multi-photon scattering of <sup>39</sup>Ar in the MOT. This technique named Argon Trap Trace Analysis with its very low minimal sample size of 0.5 cm³STP pure argon enables easy sample handling in the field as well as common sampling procedures like Niskin bottles for aquatic systems, drill core sampling for glacial systems or as in the case of Lake Kivu spray chamber gas sampling in remote places. It is thus a door opener for new geophysical research fields that were excluded from radio-argon dating so far.</p><p>Here we present our most recent results of sampling campaigns in 2018 and 2019 using samples of about 25 – 40 L gas-water mixtures corresponding to 0.5 – 10 cm³STP pure argon showing surprisingly high ages for the lake water.</p>