Experimental Investigation of Similar & Dissimilar Joints on Stainless Steel with TIG & MIG Welded

Now days, most of the structural fabrications possess welded joints that are produced using suitable welding technique. However, the joining of thick plates in a single pass welding is a cumbersome task to many fabricators. Likewise, the selection of welding technique, filler wire and welding condition for the similar and dissimilar welding of several metals is at the development stage. The similar and dissimilar metal joints of have been emerged as a structural material for various industrial applications which provides good combination of mechanical properties like strength, corrosion resistance with lower cost. Selections of joining process for such a material are difficult because of their physical and chemical properties. The stainless steel of similar and dissimilar material joints are very common structural applications joining of stainless steel is very critical because of carbon precipitation and loss of chromium leads to increase in porosity affects the quality of joint leads deteriorate strength. In the present study, stainless steel of grades 310 and 316 were welded by Tungsten Inert Gas (TIG) and Metal Inert Gas (MIG) welding with compound flux of 50 % SiO2 + 50 % TiO2 processes. The mechanical behavior like hardness, tensile strength and bending properties of similar and dissimilar metal joints were investigated. Keywords: Mechanical Properties, ATIG, MIG, SS310, SS316, Micro Structure.

Continuous drive friction welding of AISI 8630 low-alloy steel: experimental investigations on microstructure evolution and mechanical properties

Continuous drive friction welding (CDW) is a state-of-the-art solid-state welding technology for joining metallic components used in aerospace, oil and gas and power generation industries. This study summarises the results of mechanical and microstructural investigations on a modified AISI-8630 steel subjected to CDW. The effects of welding process parameters, including rotational speed, friction and forge forces, during CDW were explored to determine an optimum welding condition. The mechanical properties of the weld, and microstructural characteristics across different regions of the weld were measured and examined. The microstructure characterisation results suggest that the weld zone (WZ) experiences temperatures above Ac3 and the thermo-mechanically affected zone (TMAZ) experiences temperatures between Ac1 and Ac3 of the material. Investigations with electron backscatter diffraction (EBSD) demonstrated the occurrence of strain-induced dynamic recrystallisation in the weld. The weld demonstrated higher yield and ultimate tensile strengths at the expense of ductility and hardening capacity compared to the base metal (BM). The strain hardening profiles of the welds exhibited a dual-slopes characteristic, an indication of different levels of plastic deformation experienced by the constituent phases (i.e., martensite, bainite and ferrite) present in the microstructure. The maximum strength-to-ductility combination and static toughness values were obtained for the weld produced under the highest rotational speed, maximum friction force and an intermediate forge force of 1200-1400 rpm, 37.5-42.5 kN and 60-65 kN, respectively.

Study on Medium-Thick Al-Alloy T-Joints by Dual P-GMAW Bilateral Synchronous Welding

The T-joints of medium-thick 6082 Al-alloy plates created by dual pulsed gas metal arc welding (P-GMAW) and bilateral synchronous welding were investigated to improve weld quality using the adaptive deposition method, which calculates the minimum amount of deposition according to the welding condition, groove size, and cross-sectional area, effectively reducing the heat input and deformation of the welds on the basis of weld filling. The optimized linear energy with a wire feed speed (WFS) of 9.5 m/min can ensure a well-formed weld with a complete root fusion, and high-quality T-joint welds were obtained both in root openings of 0 mm and 1 mm. The biggest penetration was 4 mm, which was four times more than that of the result from a single torch welding process. When the distance between the two welding torches exceeded 20 mm, the molten pool was completely separated, and process pores were observed in the unfused root zone. Influenced by the thermal cycles in asymmetric welding, the hardness distribution changed: the width of the softer zone at the base plate with the fore arc was smaller than that zone with the rear arc. Furthermore, dual P-GMAW bilateral synchronous welding with an asymmetric heat source can further reduce the deformation of the welded joint by about 20% compared to that of symmetric welding.

Refill Friction Stir Spot Welding Al Alloy to Copper via Pure Metallurgical Joining Mechanism

The current investigation of refill friction stir spot welding (refill FSSW) Al alloy to copper primarily involved plunging the tool into bottom copper sheet to achieve both metallurgical and mechanical interfacial bonding. Compared to conventional FSSW and pinless FSSW, weld strength can be significantly improved by using this method. Nevertheless, tool wear is a critical issue during refill FSSW. In this study, defect-free Al/copper dissimilar welds were successfully fabricated using refill FSSW by only plunging the tool into top Al alloy sheet. Overall, two types of continuous and ultra-thin intermetallic compounds (IMCs) layers were identified at the whole Al/copper interface. Also, strong evidence of melting and resolidification was observed in the localized region. The peak temperature obtained at the center of Al/copper interface was 591 °C, and the heating rate reached up to 916 °C/s during the sleeve penetration phase. A softened weld region was produced via refill FSSW process, the hardness profile exhibited a W-shaped appearance along middle thickness of top Al alloy. The weld lap shear load was insensitive to the welding condition, whose scatter was rather small. The fracture path exclusively propagated along the IMCs layer of Cu9Al4 under the external lap shear loadings, both CuAl2 and Cu9Al4 were detected on the fractured surface on the copper side. This research indicated that acceptable weld strength can be achieved via pure metallurgical joining mechanism, which has significant potential for the industrial applications.

Radio Frequency Induction Welding of Silver Nanowire Networks for Transparent Heat Films

Transparent heat films (THFs) are attracting increasing attention for their usefulness in various applications, such as vehicle windows, outdoor displays, and biosensors. In this study, the effects of induction power and radio frequency on the welding characteristics of silver nanowires (Ag NWs) and Ag NW-based THFs were investigated. The results showed that higher induction frequency and higher power increased the welding of the Ag NWs through the nano-welding at the junctions of the Ag NWs, which produced lower sheet resistance, and improved the adhesion of the Ag NWs. Using the inductive welding condition of 800 kHz and 6 kW for 60 s, 100 ohm/sq of Ag NW thin film with 95% transmittance at 550 nm after induction heating could be decreased to 56.13 ohm/sq, without decreasing the optical transmittance. In addition, induction welding of the Ag NW-based THFs improved haziness, increased bending resistance, enabled higher operating temperature at a given voltage, and improved stability.

CFD-based modelling of phase transformation in laser welded low-carbon steel

This paper presents a numerical model of the laser welding of steel, taking into account the heat and mass flows, as well as thermal effects associated with phase transformations. It was assumed that the heat source is a laser with a symmetrical power distribution of the TEM10 beam in two welding condition variants: a stationary heat source and a source moving at a constant speed along the sample. After reaching the melting temperature, the movement of the liquid phase was forced by the Marangoni effect acting on the surface of the welding pool. For the laser power applied, the surface of the welding pool was assumed to be flat. It was proposed an algorithm for the forecasting of the phase changes during heating and cooling. Diffusive phase transformations during cooling were modelled using Johnson-Mehl-Avrami-Kolmogorov (JMAK) equations. Diffusionless transformations occurring when cooling rates exceed the critical ones were modelled using Koistinen-Marburger (KM) equations. Calculations were made for a rectangular sample welded in air and cooled spontaneously in the atmosphere. The boundary conditions were simulated assuming a constant coefficient of heat exchange and radiation to the environment. The start and end time of the changes occurring in the cooling phase were calculated based on the average cooling rate in the temperature range 800–500°C (v8/5). The model was tested for the test material: S355J2 steel.

Effect of ultrasonic impact time on Microstructure and properties of 7A52 aluminum alloy tandem MIG welded joint

7A52 (Al-Zn-Mg-Cu) alloy is a high-strength aluminum alloy, its welded joints are often accompanied by defects such as poor wear resistance and low fatigue strength. Herein, we try to optimize the welded joint of 7A52 aluminum alloy by using ultrasonic impact treatment (UIT). Generally, the mechanical properties such as microhardness and fatigue strength of the welded joint after UIT will be improved. 7A52 aluminum alloy tandem metal inert gas (MIG) welded joints with UIT time per unit area of 2.5 min, 5 min, 10 min, 15 min, 30 min, and 75 min were studied. Through the surface topography, microstructure observation, and mechanical properties test, the time parameters of excessive treatment, lack of treatment, and proper treatment were selected, and the effects of UIT, excessive treatment, lack of treatment, and proper treatment on fatigue strength were analyzed. Test results show that, the mechanical properties of welded joints after UIT are improved. The proper treatment time is 15min and its fatigue strength is 37.86MPa, respectively under the stress ratio of 0.1. Compared to the original welding condition with a fatigue strength of 28.61MPa, the fatigue strength of the welded joints of 7A52 aluminum alloy increased by 32.33%. The largest percentage of grain size reduction occurs when the UIT is 15 min. Moreover, excessive treatment and lack of treatment will not further refine the grains and optimize the mechanical properties.