Transfer Welding Research Articles

Cold metal transfer welding of AlSi7Mg alloy sheets prepared by selective laser melting

Cold metal transfer (CMT) welding of AlSi7Mg alloy sheets prepared by selective laser melting (SLM) was employed using ER4047 and ER5356 filler wire. Effect of the filler wires on hydrogen pores, microstructures and mechanical properties of welded joints was studied. As a result, CMT welding of AlSi7Mg alloy sheets using ER5356 wire reduces the porosity, refines the grains, increases the fraction of high angle grain boundaries (HAGBs), modifies the eutectic Si-rich morphology, and improves the solid solution strengthening of Si elements in the α-Al matrix of the microstructures in the weld metal (WM). Additionally, the morphology of eutectic Si-rich phases in heat affected zone (HAZ) of the welded joint is noticeably changed from the continuous cellular networks in base metal (BM) to totally globularized particles, as a result of the increased welding heat effect with decreasing distance to the WM. Compared with the ER4047 wire, the welded joint with ER5356 wire achieves higher WM hardness and higher ultimate tensile strength (UTS), which have been increased by 13.9 % and 18.6 %, respectively. The enhanced mechanical properties of the welded joints with ER5356 wire are mainly attributed to the reduced porosity and the improved microstructures in the WM.

Sliding wear behavior of cold metal transfer cladded Stellite 12 hardfacings on martensitic stainless steel

Cold metal transfer (CMT) welding technique was used in the manufacturing of hypoeutectic carbide-type Co-based Stellite 12 hardfacings on martensitic stainless steel. It was discovered that the CMT process is capable of producing relatively thick (> 2.5 mm) low diluted single-layer coatings with cored Stellite 12 wire without cracks and pores. These coatings were investigated using microscopy (optical and scanning electron microscopy), X-ray diffraction, and hardness measurements. The high melting point chromium and tungsten particles inside the cored wire were relatively large and therefore remained unmelted in the clad layers. Self-mated sliding wear tests were performed using a pin-on-disc tribometer at room temperature and at 300 °C to determine the wear resistance and friction of the coatings. The coefficients of friction were relatively similar (~ 0.35) at both temperatures. Differences were exhibited in the ~ 40% greater loss of material at high temperature. The wear performance of the CMT clad Stellite 12 coatings did not, however, reach the wear performance of self-mated laser clad Stellite 6 reference material. CMT hardfacing was finally successfully demonstrated on a ring-shaped component.

Comparative wear behaviour of Ni-Cr-B-Si hardface coatings made by cold metal transfer and plasma transfer Arc welding processes

Ni-Cr-B-Si hardface coating plays an important role in the mating components of nuclear power plants. Obtaining a crack-free coating with low dilution and optimum hardness is essential for reactor applications. In general, it is difficult to achieve this through conventional high heat input processes. In this work, Ni-Cr-B-Si hardface coating was successfully developed on 316LN stainless steel substrate by Cold Metal Transfer (CMT) welding process using metal-cored filler wire. Moreover, for comparative analysis, Ni-Cr-B-Si hardface coating was deposited using Plasma Transferred Arc (PTA) process. The obtained coatings were characterised for their microstructure, hardness, and wear behaviour. Results revealed higher hardness and lower specific wear rate of hardface coating made by the CMT process compared to the coating made by the PTA process. The superior behaviour of the CMT coating obtained may be due to its low dilution compared to the coating made using the PTA process. Confocal microscopy on the worn pins revealed abrasive and adhesive wear as a dominant mechanism in the CMT and PTA coatings, respectively. This study concluded that CMT could be used as an alternate potential process for depositing a crack-free hardface coating with superior wear behaviour.

Influence of deposition strategy and heat treatment on mechanical properties and microstructure of 2319 aluminium WAAM components

There is an increasing interest in additive manufacturing of high strength aluminium alloys built with wire and arc additive manufacturing (WAAM) technologies. Al-Cu alloys are susceptible to hot cracking, however, pulse advanced cold metal transfer (CMT-PADV) welding process ensures a low heat input that avoids this defect while reducing the part porosity. This study has demonstrated that porosity below 1 % does not affect mechanical properties of 2319 WAAM walls, whereas the as-built microstructure and applied heat treatment highly influence the properties obtained. Without interlayer dwell time, a fine uniformly distributed equiaxed microstructure is obtained, however, if an interlayer arc stop period is applied, columnar dendritic grains in the interlayer zone is obtained. Heat treatment with low aging temperature and time demonstrated not to be suitable to ensure high mechanical properties and low anisotropy. Instead, if 190 °C and 26-hour aging heat treatment is used, properties up to 324 MPa for yield stress, 452 MPa tensile strength and 8 % elongation can be achieved perpendicularly to the building direction with anisotropy of 1 %, 2 % and 46 %, respectively, for the manufacturing conditions that avoided columnar grains. This fact was critical to ensure highest strength and ductility values and low anisotropy.

Optimization of processing parameters of cold metal transfer joined 316L and weld bead profile influenced by temperature distribution based on genetic algorithm

Austenitic stainless steel alloys find the wide range of application in modern industries like pipework, containers, food production and in medical industries for its excellent processing properties and corrosion resistance. There is enormous literature report on the mechanical properties, appropriate joining of materials using different fusion welding processes. Consequently, the cold metal transfer technique appears to weld materials with low heat input which is a noticeable feature of this welding process. In this paper, cold metal transfer welding is performed on austenitic stainless steel material 316L and its bead geometries such as reinforcement height, depth of weld penetration and bead width profile are examined. The temperature distribution at the welding line is observed by means of the data acquisition unit. Genetic algorithm based optimization technique is used to achieve the desired combination of input variables and weld bead geometry. This developed genetic algorithm optimizes the welding process parameters and geometry of the weld bead, by minimizing the least square error based objective function. The investigation outcome of this paper provides an insight into the characterization of the weldment, the effects of weld current and weld travel speed on temperature profile and mechanical properties include hardness, tensile and residual profiles.

Enhancement of Microstructural and Mechanical Properties of Ultrasonic Vibration-Assisted Cold Metal Transfer Welding of 304 Stainless Steel

Enhancement of Microstructural and Mechanical Properties of Ultrasonic Vibration-Assisted Cold Metal Transfer Welding of 304 Stainless Steel

Formation of long-range ordered intermetallic η''' phase and the involvement of silicon during welding of aluminum-steel sheets

EN AW-6016-T4 aluminum alloy sheets were joined with zinc-coated DC04 steel sheets using the Cold Metal Transfer (CMT) welding process. Si-rich and virtually Si-free commercial filler alloys Al-3Si-1Mn (AA-4020) and Al-4.5Mg-Mn-Zr (AA-5087) were used. The influence of silicon on the formation and morphology of intermetallic phases in the joints was studied. The intermetallic seam was investigated by scanning electron microscopy (SEM), electron microprobe microanalyzer (EPMA) using wavelength dispersive spectroscopy (WDS), and transmission electron microscopy (TEM) using selected area electron diffraction (SAED), energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS). Short-range ordered (SRO) η-Al 5 Fe 2 , long-range ordered (LRO) η'''-Al 5 Fe 2 , and θ-Al 13 Fe 4 phases formed in the Si-poor and Si-rich welds. The presence of Si in the filler metal leads to the additional formation of the α c -Al(Fe , Mn)Si phase. Grains containing η and η''' were identified. The continuous η seam was generally thinner for higher Si contents. It was found that Si contents higher than 3-3.5 at% in the η seam suppressed the formation of LRO η''' and favored the formation of η. • Impact of Si in the filler alloy on the intermetallic seam of Al-steel sheet joints. • Observation of the low-temperature stable, long-range ordered η”'-Al x Fe y phase in industrial welds. • Correlation between Si content and the formation of the η-type phase. • Domain formation of short-range and long-range ordered regions.

Analysis of droplet growth of positive and negative electrode on cold metal transfer welding of aluminum wire

A method was proposed to identify the boundary between droplet and welding wire by processing the image from high-speed photography in the process of Variable Polarity Cold Metal Transfer (VP CMT). The droplet volume and its variation trend in electrode positive (EP) phase and electrode negative (EN) phase of aluminum wire with different parameters were obtained. The results indicated that the melting volume of aluminum wire exhibited a positive linear relationship with the input work of plasma phase, and the droplet increasing volume of aluminum wire in EN phase was approximately 2.2 times that of EP phase under same input work. The droplet transfer process was divided into droplet rapid growth and slow growth stage according to the droplet growth rate. The welding parameters and droplet growth property in the first cycle after the polarity switching (EN to EP, EP to EN) were different from that in the following cycle.

Sensing and characterization of backside weld geometry in surface tension transfer welding of X65 pipeline

With the exploitation of marine oil and gas resources, steel catenary risers (SCR) have been widely used worldwide, which has promoted the development of automatic pipeline welding technology. Root-pass welding is critical in the pipeline welding process, since the resulting backside weld geometry largely affects the corrosion resistance and fatigue properties of the pipeline. STT (surface tension transfer) welding has been one of the main methods of root-pass welding for pipeline, in which the short-circuiting period, peak current period and base current period can be identified clearly. A signal sensing method based on the change in arc voltage during the peak current period (ΔU¯) was proposed to characterize the backside weld pool geometry with the help of heat amount inputted to the pipe in 1 s (J). Unlike pulsed gas metal arc welding (GMAW-P), the peak arc force of the short-circuiting transfer was not large enough or was not with sufficient time to excite the weld pool oscillation with a large amplitude, further to affect the backside weld height and width to a great extent. Thus, J, which has a great influence on the weld pool volume (that will determine the backside weld pool geometry to some extent when full penetration occurs) in the low current range, was introduced and was included to corresponding models to characterize the backside weld pool geometry jointly with ΔU¯. The results showed that the models were accurate under the welding parameters and conditions in the present work, which could be applied in the subsequent prediction and control of backside weld geometry in the STT welding.

Dynamic growth model of Fe2Al5 during dissimilar joining of Al to steel using the variable polarity cold metal transfer (VP-CMT)

Further development of the car lightweight in automotive industry significantly depends on the reliability of the Al/steel dissimilar joint, since more and more Al alloy parts are used in the car manufacturing. It has been proved that the Al/steel dissimilar joint strength can be effectively increased when the intermetallic compound (IMC) growth, especially the Fe2Al5 layer thickness, is controlled at certain level. Because the Fe2Al5 is the dominant phase of the entire IMC layer in the Al/steel dissimilar joint, and cracks usually initiate at this location when damage is conducted. Therefore, for the automotive industry assembly line, the prediction model monitoring the Fe2Al5 layer thickness of each Al/steel weld seam is desired to ensure the dissimilar joint quality and reliability. In the present research, a numerical dynamic growth model based on element diffusion laws is established to calculate the IMC layer thickness of Fe2Al5 phase during the variable polarity cold metal transfer (VP-CMT) welding of aluminum to steel in the function of welding heat input and location. To build up effective connection between the welding heat input and the actual temperature history of Al/steel interface, a finite element analysis (FEA) model is customized for the present VP-CMT process. The Fe2Al5 layer thickness calculation results are further validated using electron back-scattered diffraction (EBSD) characterization under scanning electron microscopy (SEM), confirming a 2.3 % deviation between the model prediction and actual layer thickness.

Corrosion resistance and metallurgical behaviour of CMT welded Al-LCS dissimilar butt joint exposed in simulated industrial environment

Cold Metal Transfer welding is a predominant process for joining the Aluminium and Low Carbon Steel (LCS) dissimilar joints with enhanced properties. In addition, these joints have vast application in various simulated industrial environmental conditions. However, the formation of thick intermetallic layers during welding over these joints leads to invoking the corrosion attack and causing a catastrophic failure that is the primary concern in life prediction of the joint. Hence, the corrosion behaviour of AL-LCS dissimilar butt joint exposed in the simulated industrial environment has been studied experimentally and it has been compared with the Cold Metal Transfer (CMT) welded aluminium and LCS similar joints. The potentiodynamic polarization and the electrochemical impedance spectroscopy were carried out in 3.5% aggressive sodium chloride medium with varying benzotriazole corrosion inhibitor with varying the concentrations like 10 ppm, 15 ppm and 20 ppm. The results showed that the corrosion resistance behaviour of CMT welded dissimilar joints are increased with increasing inhibitor concentration. The inhibitor showed effective performance, and the efficiency is also found to be 78–80% at 20ppm, which revealed the enhanced corrosion resistance of dissimilar metal joints in simulated industrial conditions. Finally, the dissimilar joints are characterized by sophisticated analytical techniques.

CMT welding-brazing of al/steel dissimilar materials using cycle-step mode

Cycle step (CS) process is an advanced mode in cold metal transfer (CMT) welding technology, in which allows to set both the numbers of individual droplets and the pause time between cycles. This novel mode enables a reduced weld heat input and exhibits clear-rippled beads with high degree of reproducibility and high tolerance for workpiece gaps. In the present study, the CMT-CS process was used for welding-brazing of AA5052 aluminum alloy to galvanized low carbon steel with Al-5Si filler wire. A visually acceptable weld with clear fish-scale ripples was successfully obtained in a lap joint configuration. The influence of CMT cycle and interval time on the weld heat input, weld morphology, microstructure and mechanical properties of aluminum/steel dissimilar joints was explored. The results showed that the increase of CMT cycles led to the increase of weld heat input and it in turn increased the braze width and deceased the contact angle; while, the increase of interval time resulted in the decrease of weld heat input and it increased the weld spot spacing and decreased the density of the fish-scale ripples. The change of CMT cycle and interval time had very limited impact on the phase composition of the interfacial reaction layer. The joint strength basically increased with the increased CMT cycle; while, it increased first then deceased with the increased interval time. Two kinds of fracture modes were observed, namely interfacial shear failure and fusion zone failure. The bending angle decreased with the increase of weld heat input.

Numerical and Experimental Investigation of Heat Distribution and Residual Stress Variation on Stacked Thin Sheets of CRNO Electrical Steel Post Tungsten Inert Gas and Cold Metal Transfer Welding

Abstract The paper presents a numerical and experimental investigation on the stacking of thin, cold rolled nongrain-oriented (CRNO) electrical steel sheets post-tungsten inert gas (TIG) and cold metal transfer (CMT) welding for predicting the effects of TIG and CMT welding current on weld geometry, temperature field, and residual stress distribution in thin, stacked weld sheets. Numerical simulation of a transient nonlinear thermal three-dimensional (3D) element based on actual weld conditions was carried out using ansys software by employing a moving heat source model based on a 3D Gaussian distribution to predict changes in temperature. As a result of the thermal history provided by the model, a mechanical analysis is performed to determine the residual stress distribution and the surface distortion in the element. A significant increase in weld penetration and weld width of the samples was observed with the increase in welding current, as well as a change in the temperature field in the weld zone. Moreover, both the experimental and numerical data are consistent in their estimation of the generation of residual stresses in the weld samples. A numerical model is presented for predicting the thermomechanical behavior of TIG and CMT welded stacked CRNO structures in the stator core of electric motors.

Microstructure and Pitting Corrosion Resistance of AISI 430 Ferritic Stainless Steel Joints Fabricated by Ultrasonic Vibration Assisted Cold Metal Transfer Technique

The influences of ultrasonic vibration during cold metal transfer welding process on the microstructure, element distribution and pitting resistance of AISI 430 ferritic stainless steel joints with ER 308L as filler metal were investigated. The combined effects of mechanical vibration, acoustic streaming and cavitation of ultrasonic vibration significantly refined the primary ferrite grain in the weld metal and then impacted the subsequent solid-phase transition process, leading to the ~45% reduction of ferrite content in the weld metal. Moreover, these effects also resulted in the homogenization of alloying elements in the weld metal. The pitting corrosion resistance of the welded joints with ultrasonic vibration was increased compared with that of without ultrasonic vibration, but lower than the base metal. The pitting resistance of the weld metal with ultrasonic vibration was higher than that of the weld metal without ultrasonic vibration and base metal, while that of the one without ultrasonic vibration was lower than the base metal.

Analysis of Controlled Driving and Spreading Behavior of Molten Pool in Cold Metal Transfer

The controlled short-circuit transfer is used to control the heat input of the molten pool and the base metal in the cold metal transfer welding process, including droplet formation, droplet transfer and molten pool flow. Based on the influence of arc pressure on the surface of the molten pool, droplet impact and residual energy on the flow behavior of the molten pool, this research proposes the arc pressure driving model, the droplet impact driving model and the residual energy transfer model on the molten pool surface respectively, and on this basis, a theoretical model of controlled driving and spreading of the cold metal transition bath is proposed. The theoretical relationship between the surface shape of the keyhole and the driving force, and the relationship between the surface shape of the molten pool and the welding current are established. The model accurately predicts the formation width and contact angle of the molten pool in a specific interval, which can better control the welding process and geometry.

Interfacial layer regulation and its effect on mechanical properties of Ti6Al4V titanium alloy and T2 copper dissimilar joints by cold metal transfer welding

TC4 titanium alloy and T2 copper sheets were joined by cold metal transfer welding with ERCuMnNiAl filler metal, and the influence of interfacial microstructure on the mechanical properties and fracture behavior of resultant joints was investigated. β-Ti phase and various intermetallic compounds, such as Ti2Cu, TiCu, and AlCu2Ti phases, were orderly formed in Ti/Cu reaction zone. The AlCu2Ti phase has blocky and island-like morphology, and increasing welding heat input accelerated the transformation of AlCu2Ti phase from blocky to island-like, resulting in a significant change in the properties of joints. All the joints fractured along the interface on Ti side due to the inferior performance of AlCu2Ti phase. The fracture behavior was strongly related to the thickness and distribution of AlCu2Ti phases. And the joints with different welding heat input of 2.06 kJ/cm, 3.40 kJ/cm, and 4.28 kJ/cm exhibited cleavage, ductile-brittle-mixing, and quasi-cleavage fracture, respectively. The suitable thickness (10.22 μm) of blocky AlCu2Ti and the dispersive distribution of island-like AlCu2Ti were formed when the welding heat input was 3.40 kJ/cm, and the average tensile strength of the joint reached 186 MPa.

Influence of Heat Input on Cold Metal Transfer Welded Joints

ABSTRACT During welding, the heat input is a critical parameter in determining the quality of the joints welded by any welding process. In the case of dissimilar welding, as dissimilar metals have significant differences in melting point, it is challenging to achieve an adequate joint. The emerging cold metal transfer welding process can resolve it effectively by controlling the heat while joining dissimilar metals. Therefore, in this research work, Aluminum-galvanized steel dissimilar joints were fabricated using varying heat inputs and their mechanical, metallurgical, and corrosion properties were evaluated. Furthermore, the second-phase formation at the weld interface has been investigated, and corrosion behavior is analyzed using electrochemical techniques in a 0.1% sodium chloride environment. The Tafel polarization and electrochemical impedance spectroscopy studies reveal it improved corrosion resistance due to an increase in heat input. The reduced solidification defects and the establishment of an appropriate intermetallic layer thickness with a suitable microstructure at the interface are the reasons for the improved corrosion resistance and strength of the dissimilar joints.

Comparative Studies on Normal and Pulsed Cold Metal Transfer Welding of Aerospace Grade Aluminum Alloy 2024

Abstract Aluminum alloy 2024 (AA2024) sheets are mostly used in the fuselage and wings of the aircraft and structural applications; it is because of better fatigue resistance and high strength. The joining of AA2024 through gas metal arc welding (high heat input) is complicated because of hot cracking (solidification cracking), softening of the heat-affected zone (HAZ), and formation of porosity. However, these problems could be minimized by employing cold metal transfer (CMT) (low heat input) welding. The ultimate aim of the present research is to compare the metallurgical integrity and mechanical properties of the butt-welded AA2024 through normal CMT (N-CMT) and pulsed mode CMT (P-CMT) methods. The fine-grain structure observed in the P-CMT contributed better mechanical properties compared to N-CMT. The segregations of magnesium, silicon, and copper have revealed the intermetallic compounds such as aluminum-copper (2:1), Al2CuMg, magnesium silicide, and tetracopper silicide. This results in an intergranular fracture of both N-CMT and P-CMT joints. Besides, P-CMT exhibited a higher ultimate tensile strength and % elongation than the N-CMT. Also, the joint efficiencies of N-CMT and P-CMT were 64 % and 68 %, respectively. Furthermore, the hardness value in HAZ of N-CMT (93 HV) was inferior to P-CMT (126 HV). Hence, P-CMT is recommended for joining AA2024 compared to N-CMT.

Effect of the current waveform on the droplet transfer in CMT welding high-nitrogen steel

During the welding process of high-nitrogen steel, droplet bursts often occurs, which is caused by the escape of nitrogen. To analyze the influence of the current waveform on the cold metal transfer (CMT) welding process of high-nitrogen steel, a high-speed camera and current and voltage sensors were used to establish a simultaneous acquisition system for droplet transfer visualization and electrical parameter waveform monitoring. In this way, the characteristics of the droplet transfer behavior of the high-nitrogen steel CMT welding process were analyzed. The results showed that the solubility of nitrogen in the droplet decreased as the energy input rose, causing nitrogen to escape in the form of bubbles. When the pressure difference inside and outside of the droplet was greater than the surface tension, droplet cracking occurred. In the CMT welding process of high-nitrogen steel, the peak stage of the current waveform had a relatively high influence on droplet transfer. The condition of stable droplet transfer was that the peak phase current was 100–150 A, the time was 4.55–6 ms, and the maximum energy input in the peak stage was 15.5 J per CMT cycle. The current in the waiting phase, which was under 100 A, did not affect the droplet transfer behavior but did affect the shape of the molten pool. The increase in the peak wire feed speed reduced the CMT cycle time, but had little effect on droplet transfer.

Microstructure and Mechanical Property Improvement of AZ31B Induced by the Combination of Cold Metal Transfer Welding and Friction Stir Processing

Microstructure and Mechanical Property Improvement of AZ31B Induced by the Combination of Cold Metal Transfer Welding and Friction Stir Processing