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    Mechanisms of joint formation throughout semisolid stir welding of AZ91 magnesium alloy

    , Article Transactions of Nonferrous Metals Society of China (English Edition) ; Volume 23, Issue 9 , September , 2013 , Pages 2585-2590 ; 10036326 (ISSN) Hosseini, V. A ; Aashuri, H ; Kokabi, A ; Sharif University of Technology
    Joining in the semisolid state is considered a possible method to join alloys to each other. The mechanisms taking part in semisolid stir welding of AZ91 alloys were investigated. Two 7.5 mm-thick AZ91 pieces and a 2 mm-thick Mg-25%Zn interlayer piece were placed in a heating plate. After holding for 3 min at a desired temperature, the weld seam was stirred by a rotational tool. The heating plate was travelled on a trolley at a constant speed of 4.6 cm/min. In addition, one sample was welded without interlayer. Evolution of welding as a function of stirring rate, tool shape and temperature was studied throughout this welding process with scanning electron and optical microscopes. Interlayer... 

    Gas metal arc welding process control based on arc length and arc voltage

    , Article ICCAS 2010 - International Conference on Control, Automation and Systems, 27 October 2010 through 30 October 2010, Gyeonggi-do ; 2010 , Pages 280-285 ; 9781424474530 (ISBN) Mousavi Anzehaee, M ; Haeri, M ; Doodman Tipi, A. R ; Sharif University of Technology
    In this paper, we present a method to dynamically observe two important variables of a Gas Metal Arc Welding (GMAW) process, i.e. arc voltage and arc length. To do this, we use Kalman filter to estimate these two variables in a high level noisy environment of GMAW process both in open and closed loop modes  

    The effect of gas tungsten arc welding and pulsed-gas tungsten arc welding processes' parameters on the heat affected zone-softening behavior of strain-hardened Al-6.7Mg alloy

    , Article Materials and Design ; Volume 55 , March , 2014 , Pages 335-342 ; ISSN: 02641275 Hadadzadeh, A ; Ghaznavi, M. M ; Kokabi, A. H ; Sharif University of Technology
    The heat affected zone (HAZ) softening behavior of strain-hardened Al-6.7Mg alloy welded by gas tungsten arc welding (GTAW) process was investigated. Increasing the heat input during welding led to formation of a wider HAZ. Moreover, the size of the precipitates was increased at higher heat inputs. Consequently, by increasing the heat input, lower strength was obtained for the welding joints. At the second stage of the study, pulsed-GTAW (PGTAW) process was employed to improve the strength of the joints. It was observed that the overall strength of the welding joints was improved and the fracture during tensile test was moved from the HAZ to the fusion zone. Moreover, the effect of duration... 

    On the failure behavior of highly cold worked low carbon steel resistance spot welds

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Vol. 45, issue. 3 , Oct , 2014 , p. 1376-1389 ; 10735623 Khodabakhshi, F ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Highly cold worked (HCW) low carbon steel sheets with cellular structure in the range of 200 to 300 nm are fabricated via constrained groove pressing process. Joining of the sheets is carried out by resistance spot welding process at different welding currents and times. Thereafter, failure behavior of these welded samples during tensile-shear test is investigated. Considered concepts include; failure load, fusion zone size, failure mode, ultimate shear stress, failure absorbed energy, and fracture surface. The results show that HCW low carbon steel spot welds have higher failure peak load with respect to the as-received one at different welding currents and times. Also, current limits for... 

    Welding current and arc voltage control in a GMAW process using ARMarkov based MPC

    , Article Control Engineering Practice ; Volume 19, Issue 12 , December , 2011 , Pages 1408-1422 ; 09670661 (ISSN) Mousavi Anzehaee, M ; Haeri, M ; Sharif University of Technology
    A predictive functional controller based on ARMarkov model structure has been designed to control welding current and arc voltage in a GMAW process. The closed loop system performance is investigated through computer simulations and is compared by those achieved from implementing two commonly used controllers i.e. PI and feedback linearization based PID. The local stability of the closed loop system is analyzed in the presence of uncertainties in the linearized model of the process as well as the control parameters. Finally it is shown that the proposed controller performs like a PI controller along with a pre-filter compensator  

    Upset resistance welding of carbon steel to austenitic stainless steel narrow rods

    , Article Journal of Materials Engineering and Performance ; Volume 25, Issue 11 , 2016 , Pages 4902-4910 ; 10599495 (ISSN) Ozlati, A ; Movahedi, M ; Mohammadkamal, H ; Sharif University of Technology
    Springer New York LLC 
    Effects of welding current (at the range of 2-4 kA) on the microstructure and mechanical properties of upset resistance welds of AISI-1035 carbon steel to AISI-304L austenitic stainless steel rods were investigated. The results showed that the joint strength first increased by raising the welding current up to 3 kA and then decreased beyond it. Increasing trend was related to more plastic deformation, accelerated diffusion, reduction of defects and formation of mechanical locks at the joint interface. For currents more than 3 kA, decrease in the joint strength was mainly caused by formation of hot spots. Using the optimum welding current of 3 kA, tensile strength of the joint reached to ~76%... 

    A new refill friction spot welding process for aluminum/polymer composite hybrid structures

    , Article Composite Structures ; Volume 174 , 2017 , Pages 59-69 ; 02638223 (ISSN) Karami Pabandi, H ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology
    A new refill friction spot welding process called Threaded Hole Friction Spot Welding (THFSW) was introduced to join AA5052 aluminum to short-carbon-fiber-reinforced polypropylene (PP-SCF) composite sheets. The process was based on filling of the pre-threaded hole by melted and re-solidified polymer. The results showed that THFSW was successful to join aluminum to polymer sheets and the hole was completely filled with melted polymer. Formation of a reaction layer composed mostly of Al, C and O as well as interlocking between the threaded hole and the re-solidified polymer were recognized as main bonding mechanisms. Maximum shear-tensile strength of the joints reached to ∼80 percent of the... 

    Effect of liquation on the tensile properties of cast Mg–9Al–1Zn Alloy fusion welds

    , Article Science and Technology of Welding and Joining ; Volume 25, Issue 8 , 2020 , Pages 698-705 Pouranvari, M ; Jiryaei Sharahi, H ; Movahedi, M ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    This paper aims at understanding the role of liquation and solidification phenomena on the tensile properties of arc welded cast AZ91 magnesium alloy. Owing to its refined microstructure, the fusion zone exhibited improved ductility/strength compared to the base metal. It is demonstrated that the partially melted zone (PMZ) which is characterised by constitutional liquation of eutectic β-Mg17Al12 phase is the weakest link in the weldment. The reduced strength and ductility associated with the liquation phenomena are due to the increased volume fraction and thickness of the eutectic β-Mg17Al12 in the PMZ as well as the formation of liquation micro-cracks in a network of brittle intermetallic... 

    Corrosion behavior of aluminum 6061 alloy joined by friction stir welding and gas tungsten arc welding methods

    , Article Materials and Design ; Volume 39 , 2012 , Pages 329-333 ; 02641275 (ISSN) Fahimpour, V ; Sadrnezhaad, S. K ; Karimzadeh, F ; Sharif University of Technology
    Wrought aluminum sheets with thickness of 13. mm were square butt-welded by friction stir welding (FSW) and gas tungsten arc welding (GTAW) methods. Corrosion behavior of the welding zone was probed by Tafel polarization curve. Optical metallography (OM) and scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS) were used to determine morphology and semi-quantitative analysis of the welded zone. FSW resulted in equiaxed grains of about 1-2 μm, while GTAW caused dendritic structure of the welded region. Resistance to corrosion was greater for the FSW grains than the GTAW structure. In both cases, susceptibility to corrosion attack was greater in the welded region... 

    Resistance spot welding of ultra-fine grained steel sheets produced by constrained groove pressing: Optimization and characterization

    , Article Materials Characterization ; Volume 69 , 2012 , Pages 71-83 ; 10445803 (ISSN) Khodabakhshi, F ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Constrained groove pressing as a severe plastic deformation method is utilized to produce ultra-fine grained low carbon steel sheets. The ultra-fine grained sheets are joined via resistance spot welding process and the characteristics of spot welds are investigated. Resistance spot welding process is optimized for welding of the sheets with different severe deformations and their results are compared with those of as-received samples. The effects of failure mode and expulsion on the performance of ultra-fine grained sheet spot welds have been investigated in the present paper and the welding current and time of resistance spot welding process according to these subjects are optimized.... 

    Experimental investigation into the effects of weld sequence and fixture on residual stresses in Arc welding process

    , Article Journal of Materials Engineering and Performance ; Volume 21, Issue 6 , June , 2012 , Pages 892-899 ; 10599495 (ISSN) Kohandehghan, A. R ; Serajzadeh, S ; Sharif University of Technology
    This study concentrates on the effects of weld sequence and welding fixtures on distribution and magnitude of induced arc welding residual stresses built up in butt-joint of Gas Tungsten Arc Welding (GTAW) AA5251 plates. Aluminum plates have been welded under different welding conditions and then, longitudinal and transverse residual stresses were measured in different points of the welded plates employing hole-drilling technique. The results indicate that welding sequence significantly alters the distributions of both longitudinal and transverse residual stresses while the changing in the weld sequence leads to 44% decrease in longitudinal residual stress. Besides, both the geometry of weld... 

    Effect of welding sequence on residual stress distributions in GTA welding of AA5251 plate

    , Article International Journal of Materials Research ; Volume 103, Issue 3 , 2012 , Pages 371-377 ; 18625282 (ISSN) Kohandehghan, A. R ; Serajzadeh, S ; Sharif University of Technology
    In this paper, a thermo-mechanical model has been used to predict the temperature history and residual stress distribution in gas tungsten arc welding of AA5251 plates. This model has also been utilized to estimate the residual stresses under different welding sequences, while in the model the effect of temperature on material properties were taken into account. In order to verify the predictions, residual stresses within the welded samples and weld pool geometry were experimentally measured employing hole drilling and macro-examination of weld cross-section, respectively. The comparison between numerical and experimental data shows a reasonable agreement. The predictions show that the... 

    Mechanical properties and microstructure of resistance spot welded severely deformed low carbon steel

    , Article Materials Science and Engineering A ; Volume 529, Issue 1 , 2011 , Pages 237-245 ; 09215093 (ISSN) Khodabakhshi, F ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    The welding of nanostructured low carbon steel sheets produced by severe plastic deformation (SPD) has been considered in the present paper. Constrained groove pressing (CGP) method is used for imposing the severe plastic deformation to the steel sheets as a large pre-strain. The SPDed sheets are joined using resistance spot welding (RSW) process. The results show that severe plastic deformation can effectively increase the electrical resistivity of steel sheets; therefore it can affect the microstructure and mechanical properties of spot welds. Microstructure and mechanical properties of fusion zone, heat affected zone (HAZ), recrystallized zone and base metal of SPDed sheets are... 

    Arc welding induced residual stress in butt-joints of thin plates under constraints

    , Article Journal of Manufacturing Processes ; Volume 13, Issue 2 , 2011 , Pages 96-103 ; 15266125 (ISSN) Kohandehghan, A. R ; Serajzadeh, S ; Sharif University of Technology
    The purpose of this work is to assess the effect of welding fixtures on distributions and values of residual stresses during Gas Tungsten Arc Welding (GTAW). The butt-joint GTAW of AA5251 plate is investigated using a transient thermo-mechanical analysis performed by the finite element program, ABAQUS. The model considers two different welding conditions including unconstrained and perfectly constrained conditions while macro examination and residual stress measurements by implementing hole drilling techniques are utilized to evaluate the predictions. The results show that the utilizing of a welding fixture alters the temperature field within the plate being welded and the depth of the weld... 

    Analysis and characterization of the role of NI interlayer in the friction welding of titanium and 304 austenitic stainless steel

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; 2015 ; 10735623 (ISSN) Muralimohan, C. H ; Ashfaq, M ; Ashiri, R ; Muthupandi, V ; Sivaprasad, K ; Sharif University of Technology
    Springer Boston  2015
    Joining of commercially pure Ti to 304 stainless steel by fusion welding processes possesses problems due to the formation of brittle intermetallic compounds in the weld metal, which degrade the mechanical properties of the joints. Solid-state welding processes are contemplated to overcome these problems. However, intermetallic compounds are likely to form even in Ti-SS joints produced with solid-state welding processes such as friction welding process. Therefore, interlayers are employed to prevent the direct contact between two base metals and thereby mainly to suppress the formation of brittle Ti-Fe intermetallic compounds. In the present study, friction-welded joints between commercially... 

    Effect of alloying elements on weld metal mechanical properties in shielded metal Arc welded API-X 80 steel

    , Article AIST Steel Properties and Applications Conference Proceedings - Combined with MS and T'10, Materials Science and Technology 2010, 17 October 2010 through 21 October 2010 ; October , 2010 , Pages 781-789 ; 9781935117131 (ISBN) Sheykh Jaberi, F ; Hoseini, H. M ; Kokabi, A. H ; Sharif University of Technology
    Microstructure and mechanical properties development of X80 weld metal by addition of different amounts of alloying elements such as Nickel and Manganese to the covering of electrodes were investigated. For this reason samples were welded with electrodes that Ni value changed between 0.8%- 3.5% in tow critical amounts of Mn: 0.7 and 1.6. Tensile test and microhardness results indicated the suitable ranges of Ni and Mn for acceptable mechanical properties. In addition, optical microscopy and scanning electron microscopy were applied to link the microstructure with mechanical properties. The hardness of weld metals were found to increase linearly with Mn and Ni, which was attributed mainly to... 

    Effects of different heat flux schemes in modelling of transport phenomena during gas tungsten arc welding of AA1050

    , Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 224, Issue 10 , 2010 , Pages 1537-1553 ; 09544054 (ISSN) Kohandehghan, A. R ; Serajzadeh, S ; Sharif University of Technology
    A three-dimensional model is utilized to predict temperature distribution and fluid flow during the process of gas tungsten arc welding (GTAW). In order to evaluate the effect of the heat flux model on the accuracy of predictions, two types of heat sources - with different natures based on Gaussian surface heat flux and volumetric Goldak's double-ellipsoid heat flux distributions - are taken into account. These heat flux schemes are input into a model simulation of GTAW of AA1050. In the next stage, the transient temperature distribution within the metal being welded is predicted for each heat flux model using FLUENT computational fluid dynamics software. The fusion and heat-affected zones... 

    Investigation of weld pool in aluminum alloys: geometry and solidification microstructure

    , Article International Journal of Thermal Sciences ; Volume 49, Issue 5 , 2010 , Pages 809-819 ; 12900729 (ISSN) Farzadi, A ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
    In the present research, weld pool geometry, thermal cycle, temperature and velocity fields during gas tungsten arc welding of aluminum alloys were predicted by solving three-dimensional equations of conservation of mass, energy and momentum under steady-state conditions. Welding experiments were then conducted on several samples with different thicknesses and chemical compositions. The geometries of the weld pools as well as the thermal cycles were measured. It is found that the calculated geometry of the weld fusion zone and the weld thermal cycles are in good agreement with the corresponding experimental results. In addition, the magnitude of the maximum velocities under different... 

    Robust estimation of arc length in a GMAW process by an adaptive extended Kalman filter

    , Article Transactions of the Institute of Measurement and Control ; Volume 38, Issue 11 , 2016 , Pages 1334-1344 ; 01423312 (ISSN) Mousavi Anzehaei, M ; Haeri, M ; Sharif University of Technology
    SAGE Publications Ltd  2016
    An adaptive extended Kalman filter is designed to estimate the arc length in a gas metal arc welding system. The simulation results show that the estimated variables track the true variables of the non-linear model with negligible error and are robust against parameters uncertainties. The proposed estimator also operates adequately in a highly noisy welding environment. Because of the low computational requirements and little lag produced in the process dynamic, use of the proposed estimator would be valuable in the design of a controller for the gas metal arc welding system  

    Influence of filler wire and wire feed speed on metallurgical and mechanical properties of MIG welding–brazing of automotive galvanized steel/5754 aluminum alloy in a lap joint configuration

    , Article International Journal of Advanced Manufacturing Technology ; Volume 82, Issue 9-12 , 2016 , Pages 1495-1506 ; 02683768 (ISSN) Mehrani Milani, A ; Paidar, M ; Khodabandeh, A ; Nategh, S ; Sharif University of Technology
    Springer-Verlag London Ltd 
    In this research, the galvanized steel with thickness of 2 mm was joined to the 5754 aluminum alloy with thickness of 3 mm by the cold metal transfer MIG welding–brazing process. The effect of the filler wires (AlSi3Mn, AlSi5, and AlSi12) and wire feed speeds (4.7, 5, and 5.3 m/min) on metallurgical and mechanical properties have been discussed. According to the experimental results, thickness of intermetallic compound (IMC) layer which was formed along the interface during the MIG welding–brazing was varied by changing of parameters. In addition, the results indicated that by increasing of the wire feed speed, the thickness of IMC layer at first decreased and then increased. Results...