Shielding gas

About: Shielding gas is a research topic. Over the lifetime, 6697 publications have been published within this topic receiving 58668 citations.

Study on porosity formation in laser welds in aluminium alloys (Report 1) : Effects of hydrogen and alloying elements

Abstract: Summary The CO2 laser welding of aluminium alloys, A3003, A6061, A6N01, A5052, A5083 and A5182, was carried out at different welding speeds and the behaviour of porosity formed in the laser welds was investigated to make clear the mechanism of porosity formation. Three types of porosity were observed. The observed number of voids (Type A) of less than 50μm diameter decreased with an increase in welding speed and solidification rate because of lack of time for nucleation and growth of gas bubbles during laser welding. According to the analysis of porosity gas in the laser welds of A3003, A6061, A6N01 and A5052, hydrogen was about 90 vol% of total porosity gases and the rest was nitrogen. And for A5083 and A5182 alloy welds with deeper penetration, a small amount of helium, used as a shielding gas, was also detected. Besides, for the laser welds in Al-Mg alloys, the majority of porosity was formed along the solute band with Mg enrichment. The Mg induced polygonal porosity (Type C) and larger porosity (Type ...

CO/sub 2/ laser beam weldability of Zircaloy 2

Abstract: BWR (boiling water reactor) fuel rods are manufactured by stacking pellets into a zirconium alloy, cladding tube-zircaloy 2(Zr2). A fuel rod is designed as a pressure vessel in order to prevent failure of the cladding and release of radioactive fission products. As a result, there are very strict requirements from the welding methods employed. The usual welding methods for Zr2 are based on the tungsten inert gas (GTAW) resistance welding (RW) and electron beam welding (EBW) processes. There is very little information about laser beam welding (LBW) of Zr2. The recent development of multikilowatt laser systems has led to dramatic improvements in their welding performance. In the present work, laser beam welding of Zr2 was investigated. A comparison with GTA welding was carried out. The use of a high-power laser beam to weld nuclear fuel containers made of zircaloy has many advantages: (1) The high-power density of the focused laser beam enables very high welding speeds in comparison with arc welding. As a result, a narrow heat-affected zone is produced and the distortion of the parts is reduced to a minimum. (2) The beam can be transmitted to different stations alternatively, even to ones located far from one another. Itmore » also transmits to hot cells, glove boxes or any inert gas pressure chamber through suitable windows. (3) The process can easily be automated to enhance mass production. It is very simple, does not require skilled welders, and does not need the use of different electrodes, collets, etc. (4) The laser beam does not contaminate the weld metal with tungsten or other elements.« less

Study on hybrid heat source overlap welding of magnesium alloy AZ31B

Abstract: The magnesium alloy AZ31B was overlap welded by hybrid welding (laser-tungsten inert gas arc). According to the hybrid welding interaction principle, a new heat source model, hybrid welding heat source model, was developed with finite element analysis. At the same time, using a high-temperature metallographical microscope, the macro-appearance and microstructure characteristics of the joint after hybrid overlap welding were studied. The results indicate that the hybrid welding was superior to the single tungsten inert gas welding or laser welding on the aspects of improving the utilized efficiency of the arc and enhancing the absorptivity of materials to laser energy. Due to the energy characteristics of hybrid overlap welding the macro-appearance of the joint was cup-shaped, the top weld showed the hybrid welding microstructure, while, the lower weld showed the typical laser welding microstructure.

Gas nozzle for laser welding

Abstract: A laser system includes a nozzle assembly for use in directing a shielding gas around a laser beam and thereby protecting the point of focus from contamination by the atmosphere as is useful in welding and cutting applications. The nozzle includes a manifold section for admitting a shielding gas such as inert gas through a diffuser formed therein which exits from an outlet aperture through a nozzle tip section. The geometry of the nozzle is such that a certain amount of the shielding gas is flowed backward through an inlet aperture in the manifold section and thence into a housing container reflecting mirrors for directing and focusing the laser beam through the nozzle assembly. The remaining shielding gas, which is the bulk of the gas admitted, passes out through the outlet aperture in column fashion around the laser beam. By producing a back flow of shielding gas, aspiration of air through the housing and onto the workpiece is avoided. In addition, the necessity of having alternative means for preventing such aspiration in the form of windows or lenses closing off access to the housing is also prevented. The nozzle assembly is in two parts to facilitate interchanging of nozzle tips with the manifold, thereby providing a range of outlet opening sizes.