Showing papers on "Heat-affected zone published in 2003"
TL;DR: In this paper, the grain structure, dislocation density and second phase particles in various regions including the dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ), and heat-affected zone (HAZ) of a friction stir weld aluminum alloy 7050-T651 were investigated and compared with the unaffected base metal.
934 citations
TL;DR: In this article, the results of microstructural, mechanical property and residual stress investigations of four aluminium AA5083 friction stir welds produced under varying conditions were reported, and it was found that the weld properties were dominated by the thermal input rather than the mechanical deformation by the tool.
666 citations
TL;DR: In this article, the relationship between welding parameters and tensile properties of the joints has been investigated and it was shown that the tensile property and fracture locations of the joint are significantly affected by the welding process parameters.
460 citations
15 Oct 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a low heat input process viz., EBW and another commonly employed process, gas tungsten-arc welding have been employed for welding of duplex stainless steels with and without nickel enhancement.
Abstract: The excellent combination of strength and corrosion resistance in duplex stainless steels (DSS) is due to their strict composition control and microstructural balance. The ferrite–austenite ratio is often upset in DSS weld metals owing to the rapid cooling rates associated with welding. To achieve the desired ferrite–austenite balance and hence properties, either the weld metal composition and/or the heat input is controlled. In the current work, a low heat input process viz., EBW and another commonly employed process, gas tungsten-arc welding have been employed for welding of DSS with and without nickel enhancement. Results show that (i) chemical composition has got a greater influence on the ferrite–austenite ratio than the cooling rate, (ii) and even EBW which is considered an immature process in welding of DSS, can be employed provided means of filler addition could be devised.
404 citations
TL;DR: In this article, the effects of weld residual stress and heat affected zone on the fatigue propagation of cracks parallel and orthogonal to the weld direction in friction stir welded (FSW) 2024-T351 joints were investigated.
385 citations
TL;DR: In this paper, the evolution of temperature and velocity fields during laser spot welding of 304 stainless steel was studied using a transient, heat transfer and fluid flow model based on the solution of the equations of conservation of mass, momentum and energy in the weld pool.
Abstract: The evolution of temperature and velocity fields during laser spot welding of 304 stainless steel was studied using a transient, heat transfer and fluid flow model based on the solution of the equations of conservation of mass, momentum and energy in the weld pool. The weld pool geometry, weld thermal cycles and various solidification parameters were calculated. The fusion zone geometry, calculated from the transient heat transfer and fluid flow model, was in good agreement with the corresponding experimentally measured values for various welding conditions. Dimensional analysis was used to understand the importance of heat transfer by conduction and convection and the roles of various driving forces for convection in the weld pool. During solidification, the mushy zone grew at a rapid rate and the maximum size of the mushy zone was reached when the pure liquid region vanished. The solidification rate of the mushy zone/liquid interface was shown to increase while the temperature gradient in the liquid zone at this interface decreased as solidification of the weld pool progressed. The heating and cooling rates, temperature gradient and the solidification rate at the mushy zone/liquid interface for laser spot welding were much higher than those for the moving and spot gas tungsten arc welding.
268 citations
TL;DR: In this article, a study on near-threshold fatigue crack growth in friction stir welded aluminum alloy 7050-T7451 and a titanium alloy Ti-6Al-4V is presented.
250 citations
TL;DR: In this article, the evolution of temperature and velocity fields during gas tungsten arc spot welding of AISI 1005 steel was studied using a transient numerical model and the calculated geometry of the weld fusion zone and heat affected zone and the weld thermal cycles were in good agreement with the corresponding experimental results.
Abstract: The evolution of temperature and velocity fields during gas tungsten arc spot welding of AISI 1005 steel was studied using a transient numerical model. The calculated geometry of the weld fusion zone and heat affected zone and the weld thermal cycles were in good agreement with the corresponding experimental results. Dimensional analysis was used to understand the importance of heat transfer by conduction and convection at various stages of the evolution of the weld pool and the role of various driving forces for convection in the liquid pool. The calculated cooling rates are found to be almost independent of position between the 1073 and 773 K (800 and 500 °C) temperature range, but vary significantly at the onset of solidification at different portions of the weld pool. During solidification, the mushy zone grew significantly with time until the pure liquid region vanished. The solidification rate of the mushy zone/solid interface was shown to increase while the temperature gradient in the mushy zone at...
197 citations
TL;DR: The relationship between welding parameters and weld properties is discussed in this article, where the authors show that the maximum hardness is observed in the weld nugget, and the hardness decreases gradually from the weld needle through the heat affected zone, to the base metal.
Abstract: Hot rolled DH36 carbon steel, 6.4 mm in thickness, was friction stir welded at speeds of 3.4 mm s-1 (8 in min-1), 5.1 mm s-1 (12 in min-1), and 7.6 mm s-1 (18 in min-1). Single pass welds free of volumetric defects were produced at each speed. The relationships between welding parameters and weld properties are discussed. Optical microscopy, microhardness testing, and transverse and longitudinal tensile tests have been performed. Bainite and martensite are found in the nugget region of the friction stir welds whereas the base material is comprised of ferrite and pearlite. The maximum hardness is observed in the weld nugget, and the hardness decreases gradually from the weld nugget, through the heat affected zone, to the base metal. Tensile testing also indicates overmatching of the weld metal relative to the base metal. Maximum hardness and longitudinal (all weld metal) tensile strengths increase with increasing welding speeds. Weld transverse tensile strengths are governed by the base metal prope...
151 citations
25 May 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, tool wear and the rate of wear for hardened, steel, right-hand screws rotating at 1000 rpm in the friction-stir welding of Al 6061+20 vol.%Al2O3 particles were observed to decrease for increasing weld or traverse speeds.
Abstract: Tool wear and the rate of wear for hardened, steel, right-hand screws rotating at 1000 rpm in the friction-stir welding of Al 6061+20 vol.%Al2O3 particles were observed to decrease for increasing weld or traverse speeds. When sufficiently long traverse distances were reached, tool wear became small or negligible, and an optimized tool shape emerged. This shape was slightly different at 6 and 9 mm s−1 weld speeds but in each case a self-optimized tool shape emerged. This self-optimizing wear phenomena and tool shape result by counter motions of solid-state flow regimes which depend upon both tool rotation speed and actual weld traverse speed. Although sound, porosity-free welds are obtained with both the unworn, threaded pin tool and the worn, unthreaded pin tool, microstructures vary and the worn pin tool produced a narrower heat affected zone with less drop in hardness than the threaded pin tool.
150 citations
TL;DR: In this paper, the authors used a three-dimensional numerical heat transfer model to calculate the weld pool surface profile by minimizing the total surface energy, and calculated the shape and size of the fusion zone, finger penetration characteristic, and the solidified free surface profile were in fair agreement with the experimental results for various welding conditions.
Abstract: The temperature profiles, weld pool shape and size, and the nature of the solidified weld pool reinforcement surface during gas–metal arc (GMA) welding of fillet joints were studied using a three-dimensional numerical heat transfer model. The model solves the energy conservation equation using a boundary fitted coordinate system. The weld pool surface profile was calculated by minimizing the total surface energy. Apart from the direct transport of heat from the welding arc, additional heat from the metal droplets was modeled considering a volumetric heat source. The calculated shape and size of the fusion zone, finger penetration characteristic of the GMA welds, and the solidified free surface profile were in fair agreement with the experimental results for various welding conditions. In particular, the computed values of important geometric parameters of fillet welds, i.e., the leg length, the penetration depth, and the actual throat, agreed well with those measured experimentally for various heat inputs...
TL;DR: In this paper, the weldability of friction stir welded hot rolled AZ31B-H24 magnesium alloy sheet, 4 mm in thickness, was evaluated, varying welding parameters such as tool rotation speed and travel welding speed.
Abstract: The weldability of friction stir welded hot rolled AZ31B-H24 magnesium alloy sheet, 4 mm in thickness, was evaluated, varying welding parameters such as tool rotation speed and travel welding speed. Sound welding conditions depended mainly on sufficient heat input during the welding process. Insufficient heat input, which was generated in the case of higher travel speed and lower rotation speed, caused an inner void or lack of bonding in the stir zone. The microstructure of the weld zone was composed of five regions: base metal, heat affected zone, thermomechanically affected zone, stir zone I and stir zone II. Unlike the general feature of friction stir welded aluminium alloys, the grain size of the weld zone was larger than that of the base metal. Stir zones I and II were characterised by partial dynamic recrystallisation and full dynamic recrystallisation, respectively. The hardness of the weld zone was lower than that of the base metal owing to grain growth. A wider range of defect free weldin...
TL;DR: In this paper, a numerical model combining the methods of enthalpy, effective-viscosity and volume-of-fluid is developed to simulate the metal transfer process in gas metal arc welding.
Abstract: A numerical model combining the methods of enthalpy, effective-viscosity and volume-of-fluid is developed to simulate the metal transfer process in gas metal arc welding. The model describes not only the influence on droplet profile and transfer frequency of electromagnetic force, surface tension, and gravity, but it can also model the nonisothermal phenomena such as heat transfer and phase change. The model has been used to study the shape of the melting interface on the welding wire, the droplet oscillation at wire tip, the characteristics of relevant physical variables and their roles in metal transfer. We find that the taper formation in spray transfer is closely related to the heat input on the unmelted portion of the welding wire, and the taper formation affects the globular–spray transition by decelerating the transfer process. The formation of satellite drops during the metal transfer process is also considered. High-speed photography, laser-shadow imaging, and metallographic analysis validate the numerical model, and recommendations are made on the topics that require further consideration for a more accurate metal transfer model.
TL;DR: In situ Spatially resolved X-Ray Diffraction (SRXRD) experiments were performed in the heat-affected zone (HAZ) of gas tungsten arc (GTA) welds of AISI 1005 C-Mn steel to directly observe welding induced phase transformations as mentioned in this paper.
TL;DR: In this paper, a transport phenomena-based numerical model is developed to predict the keyhole geometry and temperature profiles in the weldment during laser welding of aluminum alloys, which can be used to prevent macroporosity formation.
Abstract: A transport phenomena-based numerical model is developed to predict the keyhole geometry and temperature profiles in the weldment during laser welding. The model can be used to prevent macroporosity formation during laser welding of aluminum alloys. The experimental results show that the weld metal contains large pores when the welding mode changes from conduction to keyhole mode or vice versa due to changes in welding variables. Based on this observation, the mathematical model predicts macroporosity formation when welding is conducted under conditions where small changes in welding parameters lead to a change in the welding mode. The model has been used to predict the geometry of the keyhole and the fusion zone, and the weldment temperature field for laser beam welding of aluminum alloys 5182 and 5754. The calculated weld pool depth, width, and shape for different welding speeds agreed well with the experimental results. The calculations showed that the keyhole profiles for high-speed welding were asymmetric. Negative beam defocusing resulted in a deeper keyhole than that obtained with positive beam defocusing. The transition from keyhole to conduction mode was more abrupt for negative beam defocusing. The model could predict the formation of macroporosity during laser welding of aluminum alloys 5182 and 5754. The results provide hope that transport phenomena-based models can be useful to prevent the formation of macroporosity during keyhole mode laser welding of aluminum alloys.
TL;DR: In this paper, the authors presented predictions for a stationary welding process by the free-burning argon arc and treated the whole region of the welding process, namely, tungsten cathode, arc plasma, and stainless steel anode, in a unified numerical model to take into account the close interaction between the arc plasma and the molten anode.
Abstract: Numerical modeling of free burning arcs and their electrodes is useful for clarifying the heat transfer phenomena in the welding process and to elucidate those effects which determine the weld penetration. This paper presents predictions for a stationary welding process by the free-burning argon arc. The whole region of the welding process, namely, tungsten cathode, arc plasma and stainless steel anode is treated in a unified numerical model to take into account the close interaction between the arc plasma and the molten anode. The time dependent development of two-dimensional distributions of temperature and velocity, in the whole region of the welding process, are predicted at a current of 150 A. The weld penetration geometry as a function of time is thus predicted. It is shown also that different surface tension properties can change the direction of re-circulatory flow in the molten anode and dramatically vary the weld penetration geometry.
TL;DR: In this paper, high-intensity ultrasonic wave is conducted into aluminum alloy 7075-T6 to observe the effect of emission waves on the weldability during inert gas tungsten arc (GTA) welding.
TL;DR: In this article, the velocity of the liquid metal in the weld pool increased with time during heating and convection played an increasingly important role in the heat transfer, and the peak temperature and velocity increased significantly with laser power density and pulse duration.
Abstract: Alloying element loss from the weld pool during laser spot welding of stainless steel was investigated experimentally and theoretically. The experimental work involved determination of work-piece weight loss and metal vapour composition for various welding conditions. The transient temperature and velocity fields in the weld pool were numerically simulated. The vaporization rates of the alloying elements were modelled using the computed temperature profiles. The fusion zone geometry could be predicted from the transient heat transfer and fluid flow model for various welding conditions. The laser power and the pulse duration were the most important variables in determining the transient temperature profiles. The velocity of the liquid metal in the weld pool increased with time during heating and convection played an increasingly important role in the heat transfer. The peak temperature and velocity increased significantly with laser power density and pulse duration. At very high power densities, the computed temperatures were higher than the boiling point of 304 stainless steel. As a result, evaporation of alloying elements was caused by both the total pressure and the concentration gradients. The calculations showed that the vaporization occurred mainly from a small region under the laser beam where the temperatures were very high. The computed vapour loss was found to be lower than the measured mass loss because of the ejection of tiny metal droplets owing to the recoil force exerted by the metal vapours. The ejection of metal droplets has been predicted by computations and verified by experiments.
TL;DR: In this paper, the authors conducted creep tests on P122 steel cross weld specimens at 70 MPa after post weld heat treatment (PWHT) for different durations and found that the duration of PWHT did not influence the rupture time and all the specimens failed in a typical Type IV manner.
TL;DR: In this article, the microstructural change related with the hardness profile has been evaluated for friction stir welded, age hardenable 6005 Al alloy, and sound joints were successfully formed under a wide range of friction stir welding conditions.
Abstract: The microstructural change related with the hardness profile has been evaluated for friction stir welded, age hardenable 6005 Al alloy. Frictional heat and plastic flow during friction stir welding created fine and equiaxed grains in the stir zone (SZ), and elongated and recovered grains in the thermomechanically affected zone (TMAZ). The heat affected zone (HAZ), identified only by the hardness result because there is no difference in grain structure compared to the base metal, was formed beside the weld zone. A softened region was formed near the weld zone during the friction stir welding process. The softened region was characterised by the dissolution and coarsening of the strengthening precipitate during friction stir welding. Sound joints in 6005 Al alloys were successfully formed under a wide range of friction stir welding conditions. The maximum tensile strength, obtained at 507 mm min-1 welding speed and 1600 rev min-1 tool rotation speed, was 220 MPa, which was 85% of the strength of the...
Patent•
30 May 2003TL;DR: In this article, a method of controlling an arc welding system during a welding process is described, which includes dynamically regulating a rate of advancement and instantaneous melt rate of the electrode during each welding cycle in response to predetermined events occurring during the welding process.
Abstract: A method of controlling an arc welding system during a welding process is disclosed. The welding process has a plurality of welding cycles in which a consumable electrode (14) is advanced towards a workpiece (16). The method includes dynamically regulating a rate of advancement and instantaneous melt rate of the electrode during each welding cycle in response to predetermined events occurring during the welding process. The melt rate may be coordinated with the rate of advancement of the electrode to provide a wide range of stable deposition rates with a shielding gas such as CO2. An arc welding system for carrying out the method is also disclosed.
15 Aug 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, microstructural studies and mode I fracture experiments have been performed on both base material and three families of friction stir welds (FSWs) in 7 mm thick, 2024-T3 aluminum plate, designated hot, medium and cold due to the level of nominal heat input during the joining process.
Abstract: Detailed microstructural studies and mode I fracture experiments have been performed on both base material and three families of friction stir welds (FSWs) in 7 mm thick, 2024-T3 aluminum plate, designated hot, medium and cold due to the level of nominal heat input during the joining process. Microstructural studies indicate that the FSW nugget grain structure is relatively uniform in all welds, with a banded microstructure existing on horizontal cross-sections traversing the weld region; the spatial wavelength of the bands corresponds to the tool advance per revolution. The microstructural bands have elevated particle concentrations, with the particles having the same elemental content as base metal impurities, implying that the FSW process is responsible for the observed particle redistribution and microstructural banding. Furthermore, particle redistribution in all welds resulted in (a-1) particle size and volume fraction reduction on the advancing side of the weld nugget and (a-2) an attendant increase in particle volume fraction on the retreating side of the weld nugget. Finally, results indicate that hardness minima are present in the heat affected zone (HAZ) outside of the weld nugget on both the advancing side and retreating side for all welds, with the hot weld having the lowest overall weld hardness. Results from mode I fracture tests indicate that the measured critical COD at a fixed distance behind the crack tip is a viable fracture parameter for FSW joints that is capable of correlating the observed load-crack extension response for both the base metal and all FSWs. In addition, critical COD measurements indicate that FSW joints have a through-thickness variation in fracture resistance. Finally, the observed ductile crack growth path (which remained in the FSW region for all FSW joints) can be correlated with the locations of hardness minima, with microstructure variations affecting local fracture processes and the corresponding crack path.
TL;DR: In this article, an experimental set up was designed and realized in order to achieve the friction welding of plastically deformed steel bars, where parts having same and different diameters deformed plastically, but same material was welded with different process parameters.
25 Jun 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, an analytical description of the thermal field generated during welding and surface treatment by a CO2 laser source was developed and allowed optimal process parameters to be stated for the experimental investigation.
Abstract: A study on improved laser weldability of a type 22Cr–5Ni–3Mo (UNS S32205) duplex steel is presented. To counterbalance the excess of δ-ferrite formed in the as welded joint, samples were surface treated by using the same laser source adopted during welding. An analytical description of the thermal field generated during welding and surface treatment by a CO2 laser source was developed and allowed optimal process parameters to be stated for the experimental investigation. Experimental results demonstrated that both microstructure and elemental distribution between δ-ferrite and γ-austenite could be restored to values close to those of the solution treated parent metal. The capability of achieving a good structural control of the weld bead microstructure by an optimized selection of laser parameters for the post-weld surface treatment was thus demonstrated.
TL;DR: In this paper, the influence of welding and sticking on the magnetic properties of non-oriented electrical steels was evaluated and the influence was shown to be significant for magnetic core properties.
TL;DR: In this article, the welding procedure selected was a gas shielded metal arc welding, working in pulsed current mode (MIG-P), to obtain an improved control of the metal transfer to the molten pool.
TL;DR: In this paper, non-oriented electrical steels have been cut with two different techniques, the laser cutting and the mechanical cutting, to investigate the effect of the first technique on magnetic properties, different cutting parameters have been tested.
TL;DR: In this paper, a 3D simulation of the non-steady state of a porthole die is performed to predict the welding pressure of product by FE simulations and experiments.
TL;DR: In this paper, the joint properties of dissimilar formed Al alloys, cast Al alloy and wrought Al alloy, were examined with various welding conditions, including friction stir welding, under a wide range of welding conditions.
Abstract: The joint properties of dissimilar formed Al alloys, cast Al alloy and wrought Al alloy, were examined with various welding conditions Friction stir welding method could be applied to join dissimilar formed Al alloys which had different mechanical properties without weld zone defects under wide range of welding condition The weld zone of dissimilar formed Al alloy exhibited the complex structure of the two materials and mainly composed of the retreating side material The mechanical properties also depended on the dominant microstructure of the weld zone with welding conditions The different mechanical properties of the weld zone with welding conditions were related to the behavior of the precipitates of wrought Al alloy and Si particles of cast Al alloy The higher mechanical properties of the weld zone were acquired when a relatively harder material, wrought Al alloy, was fixed at the retreating side
TL;DR: In this paper, a heat affected zone (HAZ) extension lower than 5μm was observed and microstructural analysis showed that this HAZ suffers a heating between 548 and 596°C where α-liquid phases are present.