Fusion Zone Area Research Articles

Laser welding of dissimilar TiAl/Ti6-Al-4V materials: Effects of rapid in-situ laser pre-heating on microstructure and mechanical properties of the welding joint

TiAl alloy has broad application prospects in the aerospace field. In practical working environments, connecting with other materials is considered an important means of fully utilizing their excellent properties. This study employed a laser in-situ pre-scanning method to preheat the weld seam, achieving the connection between TiAl alloy and Ti-6Al-4V. On this basis, the microstructural evolution of the fusion zone (FZ), fusion line (FL), and heat-affected zone (HAZ) of the welded joint was analyzed in detail. By comparing with traditional welding processes, the effects of laser in-situ preheating on the microstructure and properties of the welded joints were studied. The results showed that the FZ area consists of α2 and martensitic α-Ti, while the FL on the TiAl side features a transition layer of β/B2 phases, providing plasticity and toughness to the welded joint. The in-situ scanning method reduced the cracks generated during welding, resulting in a more uniform distribution of the transition layer. The obtained FZ exhibited higher microhardness. The room temperature tensile strength of the welded joint reached 650 MPa. As the temperature increased, at 400 °C, the tensile strength and elongation reached 571 MPa and 3 %, respectively, significantly higher than the 450 MPa and 1.5 % achieved by conventional welding at the same temperature. When the temperature further increased to 500 °C and 600 °C, Ti-6Al-4V experienced significant softening, becoming the weak point of the welded joint.

Investigating laser and ultrasonic welding of pouch cell multi-foil current collectors for electric vehicle battery fabrication

The escalating necessity for more efficient and defect-free joining of ‘ultra-thin foil collectors-to-tabs’ in electric vehicle (EV) Li-ion pouch cells motivates this study. The prevalent ultrasonic welding (USW) method for these joint types, faces limitations such as design constraints and access requirements, laser welding (LW) emerges as a promising alternative offering flexibility, one-side access and faster speeds with efficient heat input. This study aims to investigate the feasibility of LW as a viable alternative to USW for joining current collectors-to-tab joints. It compares the mechanical, metallurgical, electrical and thermal analysis of the joints to evaluate both welding techniques for joint defects. The comparison of solid-state material mixing during USW and the intermixing of aluminium (Al) and copper (Cu) during fusion LW using EDX analysis presents interesting observations in the study. The USW generates a thin transition layer with intermetallic compounds (IMCs) attributed to the diffusion of Cu into the Al matrix during joining, which is comparatively lower as in the case of LW with higher material mixing with brittle IMCs like Al2Cu and Al4Cu9. However, the joint strength of LW is comparatively lower than the USW joint attributed to the reduced fusion zone area. Furthermore, from the electrical contact resistance and the joint temperature analysis, it was found that the resistance and temperature vary by as much as 13% and 6%, respectively, for the 50 A and 75 A passing currents when the USW is replaced with the LW process.

Mechanical behavior investigation for quenching and partitioning steel dissimilar resistance spot welds

Resistance spot welding is still the most common joining process for autobody structure assembly. It has many advantages and is simple to use, but the main challenge is controlling the process parameters that affect mechanical properties and weld quality. Advanced high-strength steels were developed to meet the demands of automakers such as lighter and stronger autobody. Quenching and partitioning (Q&P 980) steel is a third-generation advanced high strength steel with a combination of high strength and high ductility. In this study, effect of resistance spot welding parameters on the mechanical performance of dissimilar combination of Q&P980 steel and SPFC780Y high strength steel was investigated. Welding current, welding time, electrode pressure and holding time were chosen as the most important process parameters influencing the weld quality. A comprehensive investigation was conducted on geometrical attributes such as nugget size, fusion zone width, fusion zone area, electrode indentation and heat affected zone area and their correlations with peak load (Pmax), failure energy, fracture energy, and elongation at peak load (Lmax). In contrast the failure modes and fracture behavior were studied using scanning electron microscopy. It was observed that using high levels of welding current and welding time while maintaining low levels of electrode pressure and holding time result in a maximum peak load, energy absorption and maximum (Lmax) with pullout failure mode (PF) and this was demonstrated for large nugget size to a critical limit. The methods and findings of this research can be used as a basis for further research and development in the field of dissimilar resistance spot welding.

Influence of normalized enthalpy on inconel 718 morphology in direct metal deposition

Morphology of each layer contributes to the final shape of a component fabricated by direct metal deposition process, because of the layer-on-layer fabrication technique. Hence, it's a requisite to understand the layer morphology evolution and factors affecting it. The present work deposited single tracks of Inconel 718 at systematically varied process conditions, and investigated their effect on the track/deposit geometry. The various parameters considered for the study are laser power ( P), scan speed ( v), and powder feed rate ( ṁ). The measurements carried on the deposits cross-section using optical microscope are width ( w), height ( h), and depth of penetration ( b). Additionally, dilution ( D %), deposit area, fusion zone shape and area are measured. The change in layer morphology with input parameters either individually or coupled, is also investigated. The coupled parameters are derived from the simultaneous variation of two are more individual parameters, such as linear heat input, line mass, and normalized enthalpy. The results have shown a proper relationship between input parameters and output morphology. Coupled parameters are observed to be a more valid measure in predicting the deposition geometry, than individual parameters. The relations obtained are linear between width and normalized enthalpy, height and line mass respectively. The fusion zone shape is evolving from semicircular to a wavy (double parabolic) nature with increasing energy input. The microstructure observations resulted a scenario of rapid cooling, and dendritic grain morphology.

Hierarchical bead materials multi-property design for wire-feed laser additive manufacturing

Wire-feed laser additive manufacturing has gained attention for years with its promises of high-level automation, reducing materials waste, overall costs, and large-scale volume production. However, printing material with multiple desired bead properties is a great challenge due to the high cost of experimental data and trial and error methods and the interdependent correlations among the properties. This study proposes a comprehensive multi-property integrated design framework based on learning from experiments data to enable quality control of part (bead) surface finish, geometry and microstructural properties. The printed bead process – microstructure – geometry relationships and process features' importance scores are investigated. The overall bead quality (smooth, ripple, and failed), geometry (e.g. bead height, width, fusion zone depth, fusion zone area), and microstructures characteristics are simultaneously optimized to obtain the optimal processing window. Specifically, the desirable property thresholds are defined experimentally, and the microstructures and geometries of printed beads under various process combinations have been predicted by machine learning models and visualized in a 3D contour space. With these predictions, the process parameters are optimized by passing through a set of filters to filter out undesired process candidates from a process searching space. The validation results highlight that the process parameterizations optimized by this framework can speed up the manufacturing of materials with the desired bead multi-performance.

Influence of heat input on bead profile and microstructure characteristics in laser and laser-hybrid welding of Inconel 617 alloy

Bead profile and microstructure analysis are greatly influenced by heat input in any welding process. The present work provides a comprehensive comparative investigation on these aspects during Autogenous Laser welding (ALW) and Laser-MIG Hybrid welding (LHW) processes in Inconel 617 superalloy. In case of LHW, weld bead profile formed was a typical wine-cup shaped one, whereas, in case of ALW, bead profile observed was Y-type shape on account of differences in number of heat sources and intensity profiles. Weld bead width and penetration depth were found to increase with heat input in both ALW and LHW processes. The fusion zone (FZ) area of LHW was found to increase by 3 times as compared to ALW as a result of high heat input in LHW than ALW. Indeed, the addition of MIG source to laser in LHW produced wide upper bead width (trebled) as compared to ALW. Radius of curvature (ROC) at neck zone, an important bead profile characteristic for assessing liquation cracking susceptibility, was found to increase with heat input and was significantly higher in LHW than ALW due to heat stagnation at neck zone. In comparison with ALW, LHW showed a coarser columnar/cellular dendritic microstructure in FZ with segregation of inter-dendritic carbides relatively richer in Mo and Cr. Secondary dendritic arm spacing (SDAS), cooling rates and microhardness will also be discussed.

Using the RSM method of improving process parameters of welding AISI 316 and nickel 201 using CO2 laser

The dissimilar butt welding of nickel 201 and AISI 316 was studied by utilising a 4 kW CO2 laser with the help of Response Surface Methodology (RSM). The effects of laser power are 2580–3420 W; welding speed 450–1150 mm/s; focal position –1 to 0 mm; beam angle 84–96 degrees; and beam offset 0–0.2 mm on weld geometry, i.e., depth of penetration, bead width, and the Fusion Zone Area (FZ). The required weld profile responses for dissimilar butt welding were modeled mathematically. The constructed models were tested using the sequential F-test, lack of fit test, and analysis of variance (ANOVA). Mathematical models are reflected in the output answers within the parameters of the input process. This laser welding process with an optimal condition zone was discovered using a numeric optimization technique. It aids in the optimization of this process’s regulated responses by allowing for more effective parameter combinations. It is clear from the tensile test results that the expected weld strength has been achieved. There is some delta ferrite found in the interdendritic zone in the microstructure and the solidification process reveals columnar grains.

Optimization of the weld characteristics of plasma-arc welded titanium alloy joints: an experimental study

ABSTRACT Titanium alloys especially Ti6Al4V have wide commercial applications in various sectors of aerospace manufacturing industries owing to their excellent physical, mechanical, and thermal characteristics. Titanium alloys are mostly welded by conventional gas tungsten arc welding process which gives compromisingly higher productivity. There are welding technologies like plasma arc welding that provide high arc energy density results in good-quality welds with higher productivity. In this present investigation, the efforts were put to study and optimize the important welding variables, such as weld current, speed, plasma gas flow rate, and constricted arc length. These parameters govern the most desired characteristics of weld bead such as weld bead width, complete penetration, fusion zone area, and prior β grain size. Optimum solutions were found through desirability-based multi-response optimization by response surface methodology. Microstructural features and mechanical properties were evaluated for the joints welded using the optimum process parameters and found that characteristics are well within the desired criteria.

The effect of Zr addition on the laser welding of SiCp/2A14Al composite

Zr foil was applied in the laser welding of SiCp/2A14Al composites. The Al4C3 phase and pores was decreased in the fusion zone with Zr addition. The area of fusion zone decreased with the amount of Zr addition. Two new phases (Al3Zr and ZrC) were formed in the fusion zone with Zr addition. Al3Zr was strip-like. ZrC was polygonal particle. ZrC particles were formed around the SiC. The size of Al3Zr and ZrC was smaller than that of Al4C3. Only a thin layer of Al4C3 was formed on surface the SiC particles with Zr addition. The pores and pits left by Al4C3 hydration significantly decreased the hardness of fusion zone without Zr addition. The hardness of fusion zone increased with Zr addition. The tensile strength of welded joint increased from 105.6 MPa (without Zr addition) to 234.7 MPa (with 0.1 mm Zr foil). The mechanical strength of welded joints was significantly improved by Zr addition.

Exploration of Parametric Effect on Fiber Laser Weldments of SS-316L by Response Surface Method

Fiber laser welding experiments are conducted on SS316L austenitic stainless steel plates based on the statistical design of experiments technique. A special kind of fixture is designed and fabricated with a facility to provide argon gas and is made up for bead protection. The influence of beam power, welding speed, and defocused position on fusion zone width, fusion zone area, and tensile strength of weldments is studied and discussed briefly. The most influencing factors and their percentage contribution on output responses are identified by analysis of variance technique. Beam power directly influences the bead features, whereas welding speed inversely affects it. However, the defocused position shows an insignificant effect on the fusion zone area within the selected range. The tensile strength increases with an increase in both beam power and welding speed up to a particular optimum value, and beyond that, it starts reducing. The highest hardness value is observed in the fusion zone at ‘1’ mm defocused position below the workpiece surface due to a decrease in grain size and interdendritic spacing. Ductile mode of fracture failure is found in both base material and weldment. The optimum welding condition obtained in this study yields full penetration, narrower weld width, lesser fusion zone area, minimal weld defects, and acceptable tensile strength of weldments.

Effect of angle, distance between electrodes and TIG current on the weld bead geometry in TIG-MIG/MAG welding process

Appropriate control of the weld pool is essential to obtain weld beads in accordance with project specifications. In this context, the TIG-MIG/MAG welding process has appeared as a viable alternative, mainly due to the greater independence between the deposited material and the heat transferred to the plate. Therefore, this study aims to evaluate the influence of input variables in TIG-MIG/MAG welding process on the weld bead geometry. Welds were made varying the TIG current, the TIG torch angle, the MIG/MAG torch angle, and the distance between the electrodes. It was found that it is possible to act upon the geometry of the weld bead varying the parameters evaluated. A larger fusion zone area and penetration are achieved by TIG current TIG torch angle and MIG/MAG torch angle in maximum and the distance between the electrodes in minimum values. Greater bead width is obtained by using the TIG current and MIG/MAG torch angle in the minimum value and distance between electrodes and the TIG torch angle in the maximum values. The highest reinforcement is obtained when using the TIG current, TIG torch angle, and MIG/MAG torch angle in maximum values and the distance between electrodes at the minimum value.

Advanced high-strength AA5083 welds by high-speed hybrid laser-arc welding

High-speed hybrid laser-arc welding (HS-HLAW) at welding speed 6.5 and 7 m/min was used to ensure the strength of the AA5083 alloy weld. The structure and tensile properties of the welds were investigated depending on the heat input during the welding process. It has been shown that the unsteady process of HS-HLAW succeeds the reduced porosity of the weld down to 0.1% of the fusion zone area and insignificant magnesium evaporation in the laser melting zones (0.1%). The strength of the weld metal reaches 98.9% of the initial material strength.

Underwater laser welding for 304 stainless steel with filler wire

Underwater laser welding for 304 stainless steel with filler wire was successfully performed with a self-designed double-side gas-shielding nozzle. The effects of the back gas flow rate, travel speed and wire feed speed on the welding appearance, geometry characteristics of cross section, defects and mechanical property of butt joints were investigated. While the bottom surface of joint touched the water directly, the surface appearance was uneven and some small pores formed. With increasing the back gas flow rate to 50 L/min, the stable local dry cavity around welding zone was generated and an underwater laser welded joint without defects was obtained. After the optimization of process parameters, the tensile strength and impact toughness of the underwater laser welded joint approached those of in-air joint basically, and the using of filler wire improved the tensile strength of butt joint significantly. Compared to the in-air joint, the water cooling effect decreased both the area and width of fusion zone of underwater joint. This accelerated cellular dendrites grew up from fusion line to the bead center, which reduced the number of equiaxial grain and thus decreased the tensile strength slightly. In addition, the high cooling rate decreased the grain size, but increased the lathy ferrite content in fusion zone of underwater joint, decreasing the toughness of weld metal.

Prediction modelling and process optimization for forming multi-layer cladding structures with laser directed energy deposition

In the laser Directed Energy Deposition (DED) manufacturing of parts, severe deformation caused by the uneven geometric characteristics of a multi-layer deposition fusion area occurs extremely easily due to the complexity and insufficient understanding of the process. The above results in a significant decline in the overall geometric quality of the parts. To study the influence of the laser DED process parameters on the geometric characteristics of multi-layer cladding, a response surface method was used to carry out an experimental study of the multi-layer cladding structures. Statistical prediction models of multi-layer cladding manufacturing were established among the laser power, scanning speed, powder feeding rate, lap ratio and cladding width, cladding zone area, fusion zone area, and flatness ratio. The accuracy, adaptability and relevance of the models were verified. The influence of each process parameter on the geometric characteristics of the multi-layer cladding structure was analysed, and the laser DED process parameters were optimized. Experimental results show that the surface forming quality of specimens processed with optimized process parameters is good. Relative errors between the experimental and predicted values of the geometric characteristics of specimens are less than 9%; thus, the prediction models can suitably predict and control the geometric characteristics of a multi-layer cladding structure. The proposed optimization of process parameters can significantly improve the geometric quality of parts and has substantial value in engineering applications.

Analysis of weld characteristics of micro plasma arc welded thin stainless steel 306 L sheet

Abstract This work demonstrates joining of thin steel sheet using micro plasma arc welding (MPAW) process. A series of welding experiments are carried out by applying full factorial design of experiment. The process parameters considered are welding current, welding speed and stand-off distance. A sufficient number of trial experiments are conducted to find suitable process window for MPAW of 500 μm thick SS-316 L sheets. Seven weld bead geometry characteristics (viz., area of fusion zone, top bead width, bottom bead width, bead height or penetration, reinforcement, width of left side of heat affected zone (HAZ) and width of right side HAZ), three tensile properties (ultimate tensile strength, yield strength and percentage elongation), micro-hardness and grain size of HAZ are considered as weld quality parameters. Various outlier tests are applied first time in welding for detection of extreme data from the tensile data set. The effects of heat input and process parameters on the measured weld quality parameters are studied. Analysis of variance (ANOVA) is also applied to estimate the relative importance of individual parameter and their interaction on the total variability. Finally, regression models are developed for representing the input and output relationship of the MPAW process.

Investigation of Welding Speed Parameters on Ni-Base Superalloy by Laser Welding Process

Nickel-base superalloys are used as a land-base turbine engine due to its excellent properties at elevated temperatures. Nickel base superalloy, grade IN-738. Laser welding is commonly chosen for the refurbishment of the turbine blade. This paper aims to focus on understanding welding speed parameters in laser welding method. With constant power at 400 watts, welding speeds were varied from 1, 3, 5, and 8 mm/s. All of these alloys have no cracks found in fusion zone, HAZ, and bulk area. Increasing welding speed results in less heat energy input, reduces the penetration depth and weld pool area. The 1mm/s, which were subjected to the highest heat energy input, results in very small size of the γ’ precipitates in the fusion zone due to re-precipitation of the γ’ precipitates during the solidification process. The fusion zone also exhibits the highest hardness. The size of the γ’ precipitates in HAZ area are much larger, compared to the fusion zone The bulk areas have no effect from the heat and showed much larger size of the γ’ precipitates, which was caused by microstructural degradation during service, leads to the lowest hardness value among the three zones.

Multi-response mathematical modelling, optimization and prediction of weld bead geometry in gas tungsten constricted arc welding (GTCAW) of Inconel 718 alloy sheets for aero-engine components

The gas tungsten constricted arc welding (GTCAW) parameters namely Main Current, Delta Current, Delta Current Frequency and Welding Speed were optimized to obtain full penetration and optimum weld bead geometry using Response Surface Methodology (RSM) to join thin Inconel 718 alloy sheets (2 mm thick). Empirical relationships were formulated to predict the weld bead characteristics such as width of bead, depth of penetration, width of heat affected zone (HAZ) and area of fusion zone (FZ). The weld bead characteristics were predicted with good accuracy using developed empirical relationships. The direct and interaction effect of GTCAW parameters on weld bead geometry is discussed in this paper.

Investigation of the Correlation between Hydrogen Cathodic Charging Conditions and Toughness Properties of Longitudinal Submerged Arc Welded X65 Pipeline Steels

This research work focuses on the investigation of the correlation between hydrogen cathodic charging conditions and toughness properties of a welded X65 pipeline steels. The experimental technique which was applied to determine the characteristic parameters associated with toughness was the crack tip open displacement after hydrogen cathodic charging process. The hydrogen cathodic charging process was carried out in an electrolytic cell with applied current densities of 10, 20, 30 mA/cm2 and hydrogen cathodic charging duration 48 h. Through this study, interesting results were provided concerning the diffusion depth and the diffusion coefficient of atomic hydrogen as far as toughness properties. The maximum diffusion depth value is assigned for each current density field in the region of heat-affected zone and the minimum in the area of fusion zone. In addition, the highest diffusion coefficients are attributed to heat-affected zone and the lowest to fusion zone, for all applied current densities. Finally, the fusion zone is considered to be more prone to the occurrence of embrittlement phenomena compared to base metal. The rate of toughness parameters drop is higher for current densities between 0-10 and 20-30 mA/cm2, where the cathodic current promotes the electrochemical reduction in hydrogen cations to atomic hydrogen.

Effect of laser welding process parameters on dissimilar joints of AISI 316 and nickel 201

Abstract The dissimilar butt welding of nickel 201 and AISI 316 was investigated using 4 kW CO2 laser welding machine. The effects of welding power (2580 - 3420 W), welding speed (450 - 1150 mm/min), focal position (-1 to 0 mm), beam angle (84 - 96 degrees) and Beam offset (0 - 0.2 mm) on the welded bead geometry like depth of penetration (DP), bead width (BW), area of penetration (AP) and heat input (HI) were analyzed with Response Surface Methodology (RSM). The central composite design was used for this experimental plan. Mathematical equations were formed to find the required heat input and weld profile responses dissimilar butt welding process. Output responses reflect the results for mathematical models within the range of process parameters used. Numerical optimisation technique was used to identify the optimal condition region of all this laser welding process. It helps to achieve better process parameter combination for the controlled responses of this process. Depth of penetration is the most important output response to achieve the good dissimilar joint. The welding power and welding speed are the two factors which influencing more on the strength of dissimilar joint even though all the other three factors are involving. The beam angle does not show any considerable change on bead width and Fusion Zone Area (FZ) and also there is no significant influence of the beam offset on bead width. An optimization results were confirmed by experiments to validate values of the process parameters values found from RSM. In microstructure studies some delta ferrite is seen in the interdendritic region and also the solidification shows columnar grains. The tensile test results the fracture in the base metal which proves that the weld strength is good as expected

Magnetic-Field-Induced Partial-to-Full Penetration Evolution and Its Mechanism During Laser Welding

The geometry and tensile strength of magnetic-field-assisted laser-welded Ti-6Al-4V joints have been studied. Due to the effects of the magnetic field on the melt flow behavior during welding, the weld penetration depth increased from 4.27 mm (partial penetration) to 5.00 mm (full penetration) and the curvature of the weld cross-section decreased, improving the weld tensile strength. The fusion zone was enlarged, showing a maximum increase of 53.4% in area when the magnetic field intensity was 90 mT. The increased penetration depth and fusion zone area suggest that application of a magnetic field can improve the energy utilization of the laser during laser butt welding. The mechanism of the magnetic-field-induced penetration depth evolution is discussed. This study provides a new energy-saving method to obtain a full-penetration weld using laser welding at lower power.