High Heat Input Conditions Research Articles

Effect of process parameters on surface formation in laser welding of Al2O3 ceramic

The attainment of formability in ceramic welding presents an imposing quandary within the realm of the manufacturing industry. In this article, the laser welding of Al2O3 ceramics was carried out to compare and analyze the influence of laser power, welding speed, laser duty cycle, and other process parameters on the macroscopic morphology of the weld, weld cracking rate, and welded joint properties. The results show that Al2O3 ceramic welds have a greater tendency to cracking and that the laser power should be matched to the appropriate welding speed. When heat input increases, the weld cracking rate decreases and then increases. Ceramic welded joints with a weld cracking rate of less than 30 % and a bending strength of more than 4 MPa can be obtained when the heat input range is 17–20.5 J/mm for continuous laser welding or 20.5–24 J/mm for pulsed laser welding. In addition, under high heat input conditions, pulsed laser welding reduces the tendency for weld cracking compared to continuous laser.

Grain Structure Evolution in 6013 Aluminum Alloy during High Heat-Input Friction-Stir Welding.

This work was undertaken to evaluate the influence of friction-stir welding (FSW) under a high-heat input condition on microstructural evolution. Given the extreme combination of deformation conditions associated with such an FSW regime (including the highest strain, temperature, and strain rate), it was expected to result in an unusual structural response. For this investigation, a commercial 6013 aluminum alloy was used as a program material, and FSW was conducted at a relatively high spindle rate of 1100 rpm and an extremely low feed rate of 13 mm/min; moreover, a Ti-6Al-4V backing plate was employed to reduce heat loss during welding. It was found that the high-heat-input FSW resulted in the formation of a pronounced fine-grained layer at the upper weld surface. This observation was attributed to the stirring action exerted by the shoulder of the FSW tool. Another important issue was the retardation of continuous recrystallization. This interesting phenomenon was explained in terms of a competition between recrystallization and recovery at high temperatures. Specifically, the activation of recovery should reduce dislocation density and thus retard the development of deformation-induced boundaries.

Development of an Arc Image Classification Algorithm in Tip-Rotating Arc Welding using Camera Image Monitoring and Deep Learning

In this study, we developed a welding system and welding monitoring system for GMA (Gas Metal Arc) aluminum welding using a tip-rotation arc welding torch. Welding was performed under various conditions, including suitable, low-heat, and high-heat input conditions. For welding monitoring, current and voltage were measured, and arc images were obtained. After the experiments, arc images were analyzed and classified based on the bead quality and cross-sectional analysis data. To develop a welding quality prediction model using arc images, a CNN-based model was developed. A total of 5,203 images were trained, and the quality was predicted for 631 images. The prediction accuracy was 99.88% for training data, and the possibility of assessing the quality of welded joints based on arc images during welding was confirmed.

The influence of shoulder-workpiece clearance on channel formation during friction stir channeling at low and high heat inputs

Friction stir channeling (FSC) is a newly developed manufacturing process that can replace the traditional fabrication processes of cooling channels for heat exchangers. Regardless of its application, the size and shape of a cooling channel are fundamental to its efficiency. In FSC, clearance between the shoulder of the tool and the workpiece top surface is a prime factor that significantly influences channel size and shape. This study examined the effect of clearance on channel characteristics using two different clearance values, 0.8 mm and 1.2 mm, respectively. The process parameters are chosen in such a way that the effect of clearance can be understood under low and high heat input conditions on several characteristics. These include channel geometry, dimensions, roof thickness, the roughness of the internal surface of the channel walls, and their topography. A rectangular channel geometry with a larger height and width was found to form at 1.2 mm clearance with high heat input parameters. Lower clearance at low heat input resulted in a successful channel, but a higher clearance value produced a defective channel for the same parameters. In conclusion, the results demonstrate how clearance and the amount of heat input are co-dependent to produce a channel with enhanced characteristics that may directly influence the performance of a cooling channel in various heat exchanger applications.

Investigations of Microstructure and Mechanical Properties in Wire + Arc Additively Manufactured Niobium–Zirconium Alloy

Herein, the feasibility of the gas tungsten arc welding‐based wire + arc additive manufacturing process for fabricating thin wall structures of niobium‐1 wt% zirconium (NbZr1) alloy is investigated. Three different heat input conditions (low, medium, and high) have been selected for fabricating it. The microstructure is characterized by using optical microscopy, scanning electron microscopy, X‐ray diffraction, energy‐dispersive spectroscopy, and electron backscattered diffraction (EBSD). The microstructure shows the columnar dendritic structure elongated in the build direction. No cracks or porosity are observed in the structure. Average Vickers hardness for low, medium, and high heat input conditions are 146.6, 162.1, and 163.5 HV, respectively. There is an increasing trend of microhardness value along the deposition height, which can be attributed to the difference in secondary dendritic arm spacing and the formation of precipitates. The tensile strength of the specimen is comparable to the conventional and additively manufactured structures. EBSD analysis confirms that possible subgrains are responsible for good mechanical properties at room temperature. In the majority of the tensile samples, the failure mechanism has been identified as a ductile fracture. The mechanical characteristics fluctuate with locations in each of the thin walls, suggesting anisotropy in the deposits.

Understanding the effect of particle reinforcement on friction stir weldment: A review

Friction stir welding is a solid-state environment-friendly joining process with many advantages over all fusion welding processes. Many variants in friction stir welding are used for uplifting the process to its maximum possible extent. One such variant is particle reinforcement in the weldment, which is used for improving the mechanical properties by enhancing the metallurgical aspects in the weld region. Generally, micro- and nano-sized ceramic particles are used for reinforcing, which have a much higher melting point than the materials to be joined. From the literature studies, particle size plays a prominent role in attaining better mechanical properties in reinforcing techniques. In addition, an increase in particle size decreases the corresponding mechanical property. Higher heat input conditions like higher tool rotational speed and low welding speed are preferred as they better mix reinforced particles with the matrix material in the weld zone. However, the higher input conditions in the regular friction stir welding process coarsen the grains, thereby deteriorating the mechanical properties of the joint. Increasing the number of passes and switching the direction between the passes leads to uniform distribution of particles and enhance the mechanical properties. This review article's main aim is to understand better reinforcement particles in the weld line of a friction stir welding process. Also, the author emphasizes reinforcing the combination of nano and microparticles to reduce the cost of reinforcement without compromising the mechanical properties. The work mentioned above is missing in the open literature.

Tailoring of Dissimilar Friction Stir Lap Welding of Aluminum and Titanium

An approach was proposed to optimize dissimilar friction stir lap welding of aluminum and titanium alloys. The basic concept of the new technique included (i) the plunging of the welding tool solely into the aluminum part (i.e., no direct contact with the titanium side) and (ii) the welding at a relatively high-heat input condition. It was shown that sound welds could be readily produced using an ordinary cost-effective tool, with no tool abrasion and no dispersion of harmful titanium fragments within the aluminum side. Moreover, the intermetallic layer was found to be as narrow as ~0.1 µm, thus giving rise to excellent bond strength between aluminum and titanium. On the other hand, several important shortcomings were also revealed. First of all, the high-heat input condition provided significant microstructural changes in the aluminum part, thereby resulting in essential material softening. Furthermore, the new approach was not feasible in the case of highly alloyed aluminum alloys due to the relatively low rate of self-diffusion in these materials. An essential issue was also a comparatively narrow processing window.

Multiphase CFD simulation and experimental investigation of friction stir welded high strength shipbuilding steel and aluminum alloy

This study executed the volume of fluid (VOF) based multiphase computational fluid dynamics (CFD) simulation by incorporating a modified analytical model for dissimilar friction stir welding of DH36 shipbuilding steel and 6061-T6 aluminum alloy. The impact of rotational speed on the temperature and plasticized material flow associated with the tool–material interaction was investigated. The simulation results revealed that the variation in rotational speed was significantly affected the temperature and material flow around the FSW tool. The maximum velocity and strain rate were obtained at the outer edge of the shoulder due to the lowest dynamic viscosity on the Al6061 side. The velocity vectors revealed that the material flow pattern was discontinuous in the advancing side at low heat input, whereas it was improved and became uniform at higher heat input conditions. Transmission electron microscopy (TEM) analysis revealed the formation of a dual-phased intermetallic compound (IMC) layer of FeAl 3 and Fe 2 Al 5 at the interface. Its thickness increased with an increase in rotational speed due to the enhanced intermetallic reaction at a higher temperature and strain rate. The rotational speed of 875 rpm produced the maximum joint strength~207.4 MPa at the IMC layer thickness of 4.83 ± 0.65 µm. The grain structure was refined under dynamic recrystallization, and the hardness improved significantly as the heat generation and strain rate increased. The intercalated structures acted as the hardest zone because of extensive IMCs formation, i.e., Fe 3 Al at 450 rpm and 600 rpm, and Fe 3 Al + FeAl at 875 rpm and 1200 rpm.

In-Depth Characterization of Laser-Welded Aluminum-and-Copper Dissimilar Joint for Electric Vehicle Battery Connections.

With advancements in the automotive industry, the demand for electric vehicles (EVs) has remarkably increased in recent years. However, the EV battery, which is a vital part of the EV, poses certain challenges that limit the performance of the EVs. The joining of dissimilar materials for different components affects the electrical and mechanical performances of EV batteries. Laser beam welding is a promising technique for joining Al and Cu for application in secondary battery fabrication because of the precise control over heat input and high process speed. However, the production of Al-Cu joints remains challenging because of the differences between their thermal and metallurgical properties and the resulting formation of brittle and hard intermetallic compounds, which reduce mechanical and electric properties. Thus, it is vital to characterize the weld to improve joint performance and enhance the laser welding process. This study investigates the joining of an Al alloy (AA1050) with Ni-coated Cu using a continuous-wave Yb fiber laser. The evaluation of the weld morphology showed a correlation between the weld characteristics and process parameters (laser power and welding speed). The weld interface width and penetration depth into the lower sheet (Cu) both increased with increasing heat input. Optical microscopy of the weld cross-section revealed many defects, such as voids and cracks. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) was employed to examine the weld microstructure. The composition analysis revealed the presence of mixed morphology of Al-Cu eutectic alloy (α-Al+Θ-Al2Cu) phase in the form of dendrites in the weld fusion zone with traces of the highly brittle Al4Cu9 phase at a high heat input condition. Furthermore, the electrical contact resistance of the weld seam was measured to determine the correlation between heat input and resistance. In addition, Vickers microhardness measurements were performed on the weld cross-section to validate the SEM/EDS results.

Characterization of thermal behavior of a micro pulsating heat pipe by local heat transfer investigation

The thermal behavior of Pulsating Heat Pipes (PHPs), which is inherently time-dependent, could also significantly change from local position to local position. Hence, the evaluation of local heat flux distributions could lead to a better understanding of the fundamental governing mechanisms of PHPs, which are, so far, only partially understood. In fact, most of the studies regarding the working principles of PHPs have focused on analysing the heat transfer rate averaged over the evaporator and condenser areas, or on evaluating the overall thermal resistance of the system. A 7-turn micro-PHP with an inner diameter of 0.32 mm was charged with HFC-134a at filling ratio of 46% and tested in bottom heated mode. The external wall temperature distribution of the condenser was measured by a high-speed and high-resolution infrared camera. The local heat fluxes exchanged between the fluid and the PHP wall were estimated in the whole condenser by solving the inverse heat conduction problem with the temperature maps as input data. In order to study the PHP working regimes, the local heat transfer behavior was furthermore investigated in terms of characteristic frequencies of the oscillatory flow by means of the wavelet method, coupled with a statistical approach. At low heat input the variations over time and along space of axial coordinate in the heat flux were significant and each tube showed multiple peaks in the power spectrum. On the other hand, the variation weakened under the high heat input conditions and the dominant fluid oscillation frequency was found more clearly around 1.2 Hz. All the qualitative and quantitative pieces of data are comprehensively presented to give further information regarding the device behavior at different heat input.

Understanding radiation effects in friction stir welded MA956 using ion irradiation and a rate theory model

An outstanding challenge in the manufacturing and joining of oxide dispersion strengthened steels is retaining the nanofeatures in the alloy throughout the fabrication and welding process. MA956 was friction stir welded with two different sets of welding parameters, resulting in a medium and high heat input. After welding, 5 MeV Fe++ ion irradiations were performed at doses ranging from 50 to 200 dpa in the temperature range of 400 to 500 °C. Post-irradiation characterization was performed with scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy to investigate the Y-Al-O dispersoids, voids, and dislocations. After welding, the dispersoid microstructure coarsened, resulting in fewer and larger dispersoids regardless of heat input. After irradiation, the dispersoid behavior in the welded material was sensitive to temperature, exhibiting growth behavior attributed to Ostwald coarsening at 500 °C but a mixture of nucleation and more muted growth at 400 and 450 °C, attributed to competing mechanisms of radiation-enhanced diffusion and Ostwald coarsening. Void swelling correlated to heat input; being more prevalent in the welded conditions occurring at lower doses and in higher values relative to the base material. The low values of swelling despite microstructure coarsening caused by welding demonstrate the excellent swelling resistance of MA956, even after welding with the highest swelling values of 0.5% noted in the stir zone high heat input condition at 450 °C, 200 dpa. The dislocation behavior was inconsistent: the strongest trend was that network density was higher for welded versus base material, and an increase in loop diameter with temperature was observed. A rate theory model based on the observed microstructure suggests at high temperature interstitial loss to sinks was more likely to be dominant compared to mutual annihilation via point defect recombination, because of an increase of the radiation diffusion coefficient with temperature regardless of initial welded microstructure.

On the interaction of cooling rate with thermal-microstructural-mechanical characteristics of laser-welded α + β titanium alloy

ABSTRACT The joining of thin sheet Ti-6Al-4V alloy has potential application as an encapsulation of miniature components. However, it is quite challenging to achieve a defect-free joint in a fusion welding process since the complexity increases many folds with reduced thickness of the materials. In the present investigation, thin sheet Ti-6Al-4V alloy is welded under different process parameters (26, 45, and 74 J/mm), using a controlled and regulated pulse laser welding technique. The weld joints are further analysed using an experimental and numerical approach to explore the interplay of thermal-microstructural and mechanical characteristics. The outcome of the present investigation reveals better surface quality, desirable microstructural changes, and enhanced joint strength for the joints fabricated under the least heat input condition (26 J/mm). Such overall improvement in the joint characteristics is associated with the high value of cooling rate (2834 K/s), leading to the formation of fine needle-shaped α’-martensite, which corresponds to maximum joint efficiency of 90%. Surface finish is another crucial factor that is affected by the amount of heat input. Joints fabricated under low heat input conditions (26 J/mm) exhibits a lower roughness value (Ra~5.67 µm) as compared to joints fabricated under high heat input conditions (74 J/mm).

Experimental investigation on thermosyphon aid phase change material heat exchanger for electronic cooling applications

In this work, cooling of electronic modules is experimentally investigated using a thermosyphon aid phase change material (PCM) heat exchanger with different thermic fluids such as n-hexane, benzene and DI water respectively. The experiments are conducted simultaneously by evaluating the thermal performance of thermic fluids and heat power stored by PCM for various heat inputs ranging from 70 to 110 W. At high heat input conditions, the value of low thermal resistance, maximum convective heat transfer coefficient (CHTC) and percentage of heat extraction of n-hexane are 0.350 K/W, 185.53 W/m2K and 99.2% respectively. Low enthalpy of vapourization and a high degree of superheat is the criteria for the obtained results. Also, temperature variation in PCM during melting is analysed by the influence of vapourized thermic fluids for different heat inputs. The maximum heat power stored by PCM is found as 7.78 W for vapourized n-hexane at 110 W due to high mass flow rate and less time for reaching steady-state temperature (SST) of PCM. The solidification of PCM is noted using cold water at regular time intervals during power-off conditions and observed that n-hexane influenced molten PCM takes 25 min for complete solidification.

Welding Process Improvement of 347H Stainless Steel Boiler Tube for Mitigating Reheat Cracking

Many failures at the welded joint of 347H tubes have recently occurred during the short-term operation of the boiler tubes. To mitigate reheat cracking or strain induced precipitation hardening, the finite element analysis and experiment for optimization of welding procedure were performed. Preheating, high inter-pass temperature, low and high heat input conditions were compared with existing welding procedure. According to mechanical analysis, high inter-pass temperature and high heat input condition showed the lower plastic strain and tensile residual stress at the inner area of heat-affected zone. At high temperature tensile test, the high inter-pass temperature condition had lower yield strength and higher elongation, while the high heat input condition showed higher yield strength and smaller elongation. In the specimen of high heat input condition, the dissolution of most precipitates and coarse grain were observed in the heat-affected zone. Relatively small amount of dissolution and smaller grain got shown in high inter-pass temperature condition. Therefore, high inter-pass temperature condition can be an alternative. Through X-ray diffraction analysis, it was confirmed that nitrogen was added to Super304H and carbon was substituted for the existing crystal structure of Nb(C,N). This will mitigate reheat cracking by increasing the solvus temperature of Nb(C,N) and reduce the grain coarsening. Key words: Strain induced precipitation hardening, Carbide dissolution, Plastic strain, Heat input, Inter-pass temperature

In-situ formation of Zn oxide particles in CuZn matrix during friction stir processing

Cu–30Zn plates were friction stir processed at a rotational speed of 1120 rpm and a traverse speed of 50 mm/min. Two kinds of samples were produced. The first sample was friction stir processed without using a secondary phase. In the case of the second sample, Al2O3 particles were incorporated into the Cu–30Zn plates to produce a surface nanocomposite. In the absence of Al2O3 particles, the produced sample showed the typical microstructures of friction stir processed brass alloys. However, in the presence of Al2O3 particles, the SZ showed a bimodal grain structure, and Zn oxide particles were formed. The high heat input condition of FSP caused the evaporation and scape of Zn from the CuZn matrix. The evaporated Zn reacted with oxygen of the air entrapped between the Al2O3 particles, which formed in-situ and encapsulated Zn oxide particles. This phenomenon has not been yet reported in the literature.

Towards process consistency and in-situ evaluation of porosity during laser powder bed additive manufacturing

There is a synergy between welding and additive manufacturing with reference to spatial and temporal variations of heat transfer. In this research, in-situ measurements of heat transfer conditions are considered as a viable qualification methodology for additive manufacturing (AM). Infrared imaging (IR) was performed within a laser powder bed fusion (L-PBF) AM machine equipped with an IR camera. Infrared thermal signatures as a function of space and time, while processing Ti6Al4V and 316L stainless steel powders, were extracted and analysed. The analyses correlated the defect evolution at low- and high-heat input conditions to thermal decay and integrated intensities. The IR based results were validated by processing a 316L cylinder with engineered porosities and detecting the same with ground truth data from computed tomography.

Processing of copper by keyhole gas tungsten arc welding for uniformity of weld bead geometry

ABSTRACT Keyhole gas tungsten arc welding (K-GTAW) was applied to characterize the weld bead geometry in case of the 6 mm thick electrolytic tough pitch copper. Various conditions of welding speeds and preheating on the bead geometry were studied for its uniformity. Visual examination, macro bead dimensional analysis, microhardness profile across the transverse section, microstructural analyses were performed to investigate the K-GTAW on electrolytic tough pitch copper. The results revealed that full penetration of 6 mm can be obtained in a single pass using keyhole mode in GTAW. Keyhole length and width were majorly affected by the welding speed and preheating temperature. Significant variations in weld bead geometry were observed even when high heat input conditions were applied without preheating. Uniform weld bead geometry of 5 mm bead width and depth to width ratio of 0.42 was obtained for a length of 80 mm using appropriate preheating of 300°C and heat input condition of 1.37 kJ/mm (resulted from 300 amperes welding current, 120 mm/min welding speed, and 15.3 volts voltage). In the uniform weld bead geometry, the weld and heat affected zones were consisted of coarse grains relative to base material, wherein the micro hardness variations were observed.

Relationship between FSW parameters and hardness of the ferritic steel joints: Modeling and optimization

The response surface method was used to study the influence of friction stir welding on the hardness of the ferritic carbon steel joints. The input parameters were tool rotational speed, tool traverse speed, and tool axial force. In addition, FSW parameters were optimized to obtain the highest value of the hardness. Microstructure and hardness of the joints were characterized using optical microscopy, orientation imaging microscopy, transmission electron microscopy, Vickers hardness, and tensile test. The results showed that among the parameters, axial force had the most effect on the hardness of the joints. The best situation for FSW was obtained at rotational speed, traverse speed, and the axial force of 980.4 rpm, 66.6 mm/min, and 2.95 kN, correspondingly. The optimum condition during FSW caused a maximum hardness of 197 Hv. The most important result of this study was the fact that the hardness of the joints does not follow the Hall-Petch relationship, which was due to the change of ferrite morphology and formation of the pearlite phase in the joints at higher heat input conditions. The lower heat input condition caused higher dislocation densities. Moreover, the influence of residual gas contamination is disclosed for the joints welded with and without Ar shielding gas.

Superior mechanical properties in high-Ni transformation induced plasticity steels after friction stir welding

The high-Ni TRIP steel plates were butt joined by friction stir welded. For this aim, the rotational and traverse speeds were set at 600rpm-100 mm-min−1 and 950rpm-50 mm-min−1. The optical microscopy, X-Ray diffraction (XRD, orientation image microscopy, and tensile test were employed for the characterization of the joints. The results showed that friction stir welding replaced the large grains of the base metal with fine and equiaxed grains by continuous dynamic recrystallization (CDRX). In addition, friction stir welding lead to the stabilization of the austenite. The lower heat input condition caused finer grain sizes. Using lower heat inputs resulted in more retained austenite by means of both work hardening and finer grain size mechanisms. The friction stir welded joints showed superior UTS and elongation of 1130 MPa-115 % and 1050 MPa-76 % respectively for the low and high heat input conditions compared to that of the base metal i.e., 880 MPa-60 % due to stabilization of austenite and formation of more transformation induced plasticity (TRIP) effect. The low heat input joint showed superior tensile properties thanks to more austenite stabilization.

Experimental investigation of microstructure and mechanical properties of IS2602-EN31 MIG welded joint

In this paper, Experimental investigation is carried out on IS2062-EN31 dissimilar MIG weldments and influence of different heat inputs on the properties different zones of welded structures. Low heat input (5.7238 kJ/mm), high heat input (6.714 kJ/mm) conditions are selected and with help of these heats input conditions made of 8 mm thickness defect free weldments are prepared. It is found that the joint fabricated at a low heat input condition showing excellent metallurgical and mechanical properties. Both Mechanical and metallurgical properties of the joint improved with low heat input condition, fine grain size was measured with at welded zone and it decreased. Tensile and hardness is improved due to grain size was observed to be Eight with high and Nine low heat input condition.