Papers by Keyword: Gas Tungsten Arc Welding

Abstract: The welding between two different grades of aluminum alloy, specifically AA5083 and AA6061-T6, is very difficult to obtain optimal results when using conventional welding methods such as TIG/MIG welding. Therefore, a solid-state joining technique is highly recommended to overcome these problems, one of which is friction stir welding (FSW). The effect of rotation speed on microstructure, microhardness, and tensile properties of dissimilar Friction Stir welded AA5083 and AA6061-T6 aluminum alloys were investigated. Three different rotation speeds (910, 1500, and 2280 rpm) were used to weld the dissimilar alloys. The metallographic analysis of joints showed the presence of various zones such as BM (base material), HAZ (heat affected zone), TMAZ (thermo-mechanically affected zone), and NZ (nugget zone) were observed and analyzed by mean of optical and scanning electron microscope. The results showed that increasing the rotation speed from 900 to 2280 rpm made grain coarsening in NZ and the mass distribution of the material is more evenly distributed, as well as increased hardness and tensile strength of the joint. The highest values in microhardness in NZ and tensile strength at the join were founded at the speed of 2280 rpm and 1500 rpm which was similar to 2280 rpm, respectively.

Abstract: Dissimilar weld-metal joints in aluminum alloys 5083 and 6061-T6 are often found in aircraft, railroad structures, ships, bridges, oil platforms, and building structures. However, welding of dissimilar metals is relatively more difficult due to the different metallurgy and thermophysical properties of the two alloys. The purpose of this study is to evaluate the physical-mechanical properties of the Tungsten Arc Welding (GTAW) process through numerical simulations of different welded joints between the 5083 and 6061-T6 aluminum alloys. The GTAW welding simulation process is carried out by 300 x 100 x 3 mm plate butt joints along 300 mm. GTAW weld metal is prepared for tensile test samples and metal alloy composition, the test is observed in the base metal and welded area. The results of the chemical composition test of the weld metal obtained that the composition is close to Al 5083 base metal so that the mechanical properties of the weld metal tend to be identical with Al 5083 alloy. The results of numerical simulation on the mechanical properties of GTAW weld metal at temperature conditions of 25 to 700 °C obtained several things, including 1) the range of thermal conductivity decreased from 174.393 to 86.424 W/mK. 2) The density increased from 2,348 to 2,663 gr/cm³. 3), the young modulus appears to decrease from 68,667 to 0 GPa. 4) the shear modulus decreases from 25,724 to 0 GPa. 5) the type of heat increases from 0.904 to 17,306 J/gK, and 6) the Poisson ratio increased from 0.335 to 0.5.

Abstract: The aim of the study to investigate the effect of welding current on the microstructure and mechanical properties of gas tungsten arc welding (GTAW) for dissimilar austenite Stainless steel (AISI 309 and 201). Three models of welding currents have been used and their effect on microstructure and mechanical properties investigated. The results reveal that increase of welding currents improved the ultimate tensile strength (UTS) however, the hardness of the weld zone and Heat Affected Zone (HAZ) are similar. On the other hand, the microstructure of base metal AISI 309 and 201of austenite, ferrite structure, and ẟ ferrite of AISI 309 stainless steel were observed.

Abstract: The 0.6 mm tantalum sheet was welded under argon atmosphere by Tungsten Inert Gas Welding (TIG) in order to obtain a welded joint with high-quality and high-reliability. Metalloscope, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were applied to analyze the joint. The results showed that the grain size of the base metal which affected by the welding heat remained the original size or enlarged slightly to 40-70 μm. What’s more, the weld zone was found to be composed of two components with different oxidation degree. And the distribution of these two components was related to the protection atmosphere of the location. The fusion line of the two tantalum sheets was clear which means high welding quality.

Abstract: Because of the general problem of the welding workpiece such as fatigue fracture caused by tensile residual stress lead to initial and propagation crack in the fusion zone. Thus, the mechanical surface treatment of deep rolling on Gas Tungsten Arc Welded (GTAW) surfaces of AISI 316L was studied. Deep rolling (DR) is a cold working process to induce compressive residual stress in the surface layer of the workpiece resulting in hardening deformation which increased surface hardness, and smooth surface that inhibit crack growth and improve fracture strength of materials. The present study focuses on compressive residual stress at the surface of stainless steel AISI 316L butt welded joint of GTAW. The three parameters of DR process were used; pressure 150 bar, rolling speed 400 mm/min, and step over 1.0 mm. The residual stresses analysis by X-ray diffraction with sin²Ψ method at 0, 5, 10, and 20 mm from the center of the welded bead. The results showed that the DR process on the welded of GTAW induce the minimum compressive residual stress-408.6 MPa and maximum-498.1 MPa in longitudinal direction. The results of transverse residual stress in minimum and maximum are 43.7 MPa and-34.8 MPa respectively. The FWHM of DR both longitudinal and transverse direction were increased in the same trend. Furthermore, the microhardness after DR treatment on workpiece surface layer higher than GTAW average 0.4 times.

Abstract: In this study the effect of the Titanium and aluminum powder addition on microstructure and mechanical properties of AISI 430 ferritic stainless steel welds produced by gas tungsten arc welding was investigated. It’s observed that the addition of aluminium (Al) or titanium (Ti) reducing the grains size, increase the equiaxed grains fraction and improve the mechanical properties with varying degrees. While the addition of mixture (Al+Ti) leads to better improving in mechanical properties and reducing of grains size up to 85 %. The details of tensile tests, optical microscopic observations, microhardness, tensile test and Scanning electron microscopy (SEM) fractography, are discussed.

Abstract: Gas tungsten arc welding (GTAW) is a widely used method of joining aluminium and its alloys. Despite the fact that a lot of research has been done in this area for several decades, there are many unresolved issues on the welding process control. Optimization of square wave alternating current profiles is one of them. This paper presents the results of studies on control of spatial position of an arc by an improved heat input algorithm taking into account the necessary relationship between direct current of straight and reverse polarity. It is shown that an increase in direct current reverse polarity to over 10 A contributes to expansion of a cathode spots space and, consequently, a greater deviation of the arc from the axis of a tungsten electrode. The spatial position of the arc is almost coaxial to the tungsten electrode when direct current reverse polarity is short-term reduced to 5 A at the final stage. These results are correct for a wide range of the square wave alternating current profiles.

Abstract: In the present study, TC4 titanium alloy was gas tungsten arc welded to evaluate the mechanical and metallurgical properties of the welds. The welds were carried out at different welding conditions such as welding speed and current to identify their effect on microstructural changes and strength of the welds. The results of bead geometry measurements suggests that the fusion zone width and depth was greatly varying with the welding speed and current. It is also observed that the fusion zone microstructure and heat affected zones are greatly controlled by welding conditions. Therefore the mechanical properties of the welds were improved with the changes in welding conditions and are correlated with the metallurgical features of the welds. The optimal welding conditions were analysed using Box-Behnken design and analysis of variance technique for identifying strength of the welds and better bead geometry parameters.

Abstract: The microstructure and corrosion properties of weld fusion zone and the heat affected zones of gas tungsten arc (GTA) welded AA2014 alloy, welded at varying speeds of 1.5mm/s, 2.5 mm/s and 3.5 mm/s were examined for gaining knowledge on the effect of welding speed on corrosion behavior at localized regions of the weldment. The macrostructure and microstructure of the welds were evaluated with optical microscope. The corrosion properties were examined with potentiodynamic polarization in aqueous 3.5% NaCl solution. The GTA welding has resulted in grain refinement fusion zone and dispersion of coarse Al₂Cu phases within the grains and along the grain boundaries of heat affected zones. With increase in welding speed the grain size of AA2014 at the fusion zone reduces significantly and also the corrosion resistance of the fusion zone and heat affected zone could decrease as it shows higher negative corrosion potential.

Abstract: AA2014 is a heat treatable aluminium alloy found its application in light weight structures owing to its superior strength to weight ratio. The alloy was welded with automatic gas tungsten arc welding. The microstructure and mechanical properties of each zone such as parent metal (PM), heat affected zone (HAZ) and fusion zone (FZ) of the weldment were studied using optical microscopy, microhardness survey and micro-tensile testing. The PM with elongated grains with evenly distributed Al₂Cu phases showed a tensile strength of 456 MPa and 24% elongation; the HAZ and FZ offered a reduction in strength and ductility. The grain coarsening with segregation of continuous string of Al₂Cu along grain boundaries in HAZ and the formation of coarse dendritic grains with continuous network of brittle Al₂Cu and a minor fraction of porosity at interdendrite in FZ were attribured to the observed strength reduction in these regions. Keywords: AA2014 alloy; gas tungsten arc welding; optical microscopy; microhardness; micro-tensile testing.