Cold Metal Transfer Pulse Research Articles

An investigation on tensile shear strength of CMT spot weld-brazing of 5052 aluminium alloy and SS 400 galvanized steel

The main purpose of the research is to investigate the effects of spot weld-brazing variables, such as cold metal transfer (CMT) modes and current, on the tensile shear strength of 5052 aluminium alloy for dissimilar joining to SS400 galvanized steel.The method employed in the study was a 3k full factorial design with three replications. Analysis of variance (ANOVA) techniques were employed to identify the variables that influenced the responses of interest. The response optimiser method displayed which factors affected the variables and their impact on strength. In addition, the response optimiser method was employed to find which factors produced the best value for the response variable. A mathematical model was developed to predict the strength of the joints. An optical microscope (OM) and scanning electron microscope (SEM) were also employed to confirm the microstructure. Energy dispersive spectroscopy (EDS) was used to determine the chemical composition of the microstructure.The strength of the weld-brazing joints was affected by the modes and currents used in the joining process. The weld-brazing mode selection was found to have an impact on strength. The synergic mode was shown to have a strength greater than the CMT pulse and pulse synergic modes. The excess or little weld-brazing current was shown to be unsuitable for the joint. The maximum tensile shear strength value was obtained in the synergic mode with a current of 110 A. The resulting prediction model was evaluated with the newly collected experimental data, and the average per cent error was estimated to be 2.07%. In addition, the reaction layer at the aluminium alloy and steel interface was composed of a Fe(Al, Si)3 phase. The optimal conditions for the spot weld-brazing activities resulted in a larger fracture area, a small contact angle, and excellent weld bead geometry.The prediction accuracy of the model appeared satisfactory. However, the altered chemical composition of the filler metals and substrate materials could impact the findings. It is recommended that the electrical signal waveform be studied during spot weld-brazing, as well as the characteristics of other material joints with various other parameters.The weld-brazing mode and current had no significant effect on the type of interface layer of the joints.It is highly possible that the CMT spot weld-brazing technique could be applied to join other dissimilar materials in order to reduce the joining time, but the filler metal chosen must be appropriate.

Investigating the Forming Characteristics of 316 Stainless Steel Fabricated through Cold Metal Transfer (CMT) Wire and Arc Additive Manufacturing.

Wire and arc additive manufacturing (WAAM), recognized for its capability to fabricate large-scale, complex parts, stands out due to its significant deposition rates and cost-effectiveness, positioning it as a forward-looking manufacturing method. In this research, we employed two welding currents to produce samples of 316 austenitic stainless steel utilizing the Cold Metal Transfer wire arc additive manufacturing process (CMT-WAAM). This study initially evaluated the maximum allowable arc travel speed (MAWFS) and the formation characteristics of the deposition bead, considering deposition currents that vary between 100 A and175 A in both CMT and CMT pulse(CMT+P) modes. Thereafter, the effect of the CMT+P mode arc on the microstructure evolution was analyzed using the EBSD technique. The findings indicate that the arc travel speed and deposition current significantly affect the deposition bead's dimensions. Specifically, an increase in travel speed or a reduction in current results in reduced bead width and height. Moreover, the employment of the CMT+P arc mode led to a reduction in the average grain size in the mid-section of the sample fabricated by CMT arc and wire additive manufacturing, from 13.426 μm to 9.429 μm. Therefore, the components of 316 stainless steel produced through the CMT+P-WAAM method are considered fit for industrial applications.

A comparative study on microstructure and mechanical properties of wire-arc directed energy deposited Al–Zn–Mg–Cu alloy based on the cold metal transfer technology

Wire-arc directed energy deposition (DED) of Al–Zn–Mg–Cu alloy faced a tough challenge because of the occurrence of crack and pore defects caused by the high content of alloying elements. Three cold metal transfer (CMT) arc modes were studied to fabricate Al–Zn–Mg–Cu alloy components via the wire-arc DED process, with the aim of optimizing the deposition process and revealing the action mechanism of arc mode on the microstructure and mechanical properties. The effect of the CMT arc mode on the forming accuracy and arc/droplet behaviors was investigated with the assistance of the microscope and high-speed camera. The characteristics of grain morphology, crystallographic texture, and precipitated phase were quantitatively analyzed. The results show that the forming accuracies of deposited samples degenerate when using CMT and CMT pulse modes due to abnormal electrical waveforms and overflow/curve phenomenon. The finest grain size is realized under CMT advance mode because of its induced stirring effect on the molten pool, expanded constitutional supercooling zones, and extremely low heat input. The continuous and coarse precipitated phases in CMT and CMT pulse modes are transferred into dispersive ones in CMT advance mode. Moreover, the quantity and size of pores are also reduced in CMT advance mode. The combined action of microstructure optimization and defect reduction is conducive to improving the mechanical properties. Finally, the preferable ultimate tensile strength (∼278.15 MPa) and top elongation (∼6.50 %) of as-deposited Al–Zn–Mg–Cu alloy are achieved.

Investigation of the tensile strength of the CMT and PCMT joints of AA8011 aluminum alloy

The advanced variant of gas metal arc welding (GMAW) known as cold metal transfer (CMT) developed by Fronius in Austria is used to overcome heat-input- and fusion-related issues such as porosity and cracking in welding of AA8011-H18 alloy sheets. AA8011-H18 alloy sheets 3 mm thick were welded using normal CMT-GMAW and pulsed CMT (PCMT)-GMAW processes. The microstructure of the weld metal and heat-affected zone was analyzed using an optical microscope. The tensile properties and hardness of joints were evaluated and compared. The results revealed that the PCMT-GMAW joints showed 26.45, 48.97 and 40.42% improvements in tensile strength, yield strength and elongation, respectively, compared with CMT-GMAW joints. The superior tensile performance of PCMT-GMAW joints compared with that of CMT-GMAW joints is due to the current pulsing effects along with the wire retraction mechanism, which aids in reducing the heat input and controlled droplet transfer.

Effect of the Deposition Process on High-Temperature Microstructure and Properties of the Direct Energy Deposition Al-Cu Alloy

The excellent microstructure and mechanical properties of Al-Cu alloy deposited using the Direct Energy Deposition (DED) process has been shown in previous studies, which is the most likely aluminum alloy material to meet the load-bearing requirements of hypersonic aircraft. However, its high-temperature performance and the law of microstructure transformation during the high-temperature process still need to be determined. In this paper, DED Al-Cu alloy samples were prepared using the Cold Metal Transfer (CMT) process, CMT Pulse process, and CMT Pulse Advanced process. The effect of different deposition processes on the microstructure and mechanical properties of the deposits was investigated at 200 °C for 30 min. The results show that the Al-Cu alloy’s main strengthening phase θ′ is excessively transformed into the equilibrium θ phase after the high-temperature process, which is the main reason for the degradation in the DED Al-Cu alloy’s properties at high temperatures. Different deposition processes have almost no effect on the high-temperature performance of the DED Al-Cu alloy, and the deposition process can be selected according to the product’s structure.

Potentiodynamic Corrosion Behavior and Microstructural Characteristics of Pulsed CMT-Welded AA2014-T6 Aluminium Alloy Joints: Effect of PWHT

AA2014-T6 is an Al-Cu-Mg-based precipitation-hardened aluminium alloy widely used in aerospace due to its high strength to weight ratio. This alloy is joined by a pulsed cold metal transfer (PCMT) arc welding process to overcome the high heat input related problems in gas metal arc welding (GMAW) such as a coarser dendritic structure in the fusion zone (FZ), wider heat affected zone (HAZ), solidification and HAZ liquation cracking, softening in HAZ, and poor corrosion resistance of welded joints in salt environment. The joints were subjected to PWHT of artificial aging (AA), solution treatment (ST), and solution treatment + aging (STA) conditions. The corrosion rate was determined using a potentiodynamic corrosion test in a solution of 3.56 wt.% NaCl with pH values of 4, 7, and 11. Results disclosed that the PCMT joints subjected to the potentiodynamic corrosion test in NaCl solution of pH-4, pH-7, and pH-11 disclosed very low, moderate, and extremely high pitting corrosion, respectively. The corrosion resistance of ST joints was improved by 53.34%, 15%, and 15.12% in pH-4, pH-7, and pH-11 NaCl solution compared to as-welded joints. The pitting potential of ST joints is comparable to BM. The BM showed the pitting potential of −175, −450, and −550 mV in pH-4, pH-7, and pH-11 NaCl solution. The ST joints showed 75.29%, 29.16%, and 27.85% lower corrosion potential compared to STA joints in pH-4, pH-7, and pH-11 NaCl solution, respectively. The ST joints disclosed the lower pitting potential of −105, −425, and −505 mV in pH-4, pH-7, and pH-11 NaCl solution, respectively, whereas the STA joints revealed greater pitting potential of −425, −600, and −700 mV in pH-4, pH-7, and pH-11 NaCl solution, respectively. The superior corrosion resistance of ST joints compared to AA and STA joints is attributed to the dissolution of precipitates in Al solid solution resulting in a lower potential difference in FZ. This minimizes the preferential sites for pitting corrosion to occur.

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.

A review on Cold Metal Transfer (CMT) technology of welding

Cold metal transfer (CMT) is a novel technique of joining, which is an improvised version of the gas metal arc welding (GMAW) techniques, in which the wire of the filler metal is deliberately pulled backwards after the short circuit. The retracted wire aids the disengagement of droplets during the short circuit, thereby transferring the metal into the pool of molten without the support of electromagnetic force. Due to this, the input of heat is greatly reduced and spatter is eliminated to greater extent. Lower volume of heat makes the technique of CMT welding a more ideal one for joining thin sheets and plates. Employment of CMT welding technique curtails spatter, distortion of joints and also requires limited clean up. CMT have made it possible to join together Al and steel. In addition to this, in this technique, the length of the arc can be monitored and can be controlled easily through mechanical means. Therefore, the stability of the arc is perfect, irrespective of the surface to be joined and during faster rate of joining, thereby making it possible to employ the technique of CMT welding in all position and for any application. This paper reviews in brief, the history, applications and principle of operation of the CMT welding technique. In addition to these, the several types of recently evolved types of CMT welding techniques namely CMT pulse advanced, CMT advanced, CMT + P, CMT Dynamic and the research findings of several relevant experimental works were discussed in brief.

Development of Pulsed Cold Metal Transfer and Gas Metal Arc Welding Techniques on High-Strength Aerospace-Grade AA7475-T761

High-strength aluminum alloy (AA7475) sheets are widely used in aerospace sectors due to its better performance, global suitability, and multifunctional features. The welding of AA7475 in the fusion welding process like gas metal arc welding (GMAW) is difficult due to cracks generation. However, these problems could be overcome by different variants of GMAW process, like pulsed and normal cold metal transfer (PCMT and NCMT) techniques. The main objective of this research work is to deliver a better insight into mechanical and metallurgical properties of butt joint welded AA7475 through PCMT, NCMT, and GMAW techniques with ER5356 and ER4043. The defects-free butt joints were observed for PCMT, NCMT, and GMAW processes with ER5356, whereas the presence of porosities is found for ER4043. The microsegregation of Fe, Si, Mg, Zn, and Cu leads to the emergence of Mg2Cu, Mg2Si, Al2Cu, Al2CuMg, MgZn2, Mg2Zn11, and Fe2Al6 phases in the AA7475 weldments. The development of binary brittle intermetallic Mg2Si phase affects the tensile strength of all weldments made with ER4043. Better joint efficiency (96.11%), impact toughness (12.1 ± 0.8 J), and microhardness (119 ± 7.4 HV) are found in PCMT with ER5356 compared to other processes. Because of the low heat input utilised, PCMT provides better joint strength and microstructural integrity than NCMT and GMAW.

Effects of Thermal Cycling on Wire and Arc Additive Manufacturing of Al-5356 Components

Wire and arc additive manufacturing (WAAM) provides a promising alternative to conventional machining for the production of large structures with complex geometry, as well as individualized low quantity components, using cost-efficient production resources. Due to the layer-by-layer build-up approach, process conditions, such as energy input, deposition patterns and heat conduction during the additive manufacturing process result in a unique thermal history of the structure, affecting the build-up properties. This experimental study aims to describe the effects of thermal cycling on the geometrical and material properties of wire arc additive manufactured Al-5356 aluminum alloy. Under consideration, that Al-5356 is a non-heat treatable alloy, a significant effect on geometrical formation is expected. Linear wall samples were manufactured using pulsed cold metal transfer (CMT-P) under variation of wire-feed rate, travel speed and interpass temperatures. The samples were analyzed in terms of geometry; microstructural composition; hardness and residual stress. Furthermore, the mechanical properties were determined in different building directions.

Wire Arc Additive Manufacturing (WAAM) of Aluminum Alloy AlMg5Mn with Energy-Reduced Gas Metal Arc Welding (GMAW).

Large-scale aluminum parts are used in aerospace and automotive industries, due to excellent strength, light weight, and the good corrosion resistance of the material. Additive manufacturing processes enable both cost and time savings in the context of component manufacturing. Thereby, wire arc additive manufacturing (WAAM) is particularly suitable for the production of large volume parts due to deposition rates in the range of kilograms per hour. Challenges during the manufacturing process of aluminum alloys, such as porosity or poor mechanical properties, can be overcome by using arc technologies with adaptable energy input. In this study, WAAM of AlMg5Mn alloy was systematically investigated by using the gas metal arc welding (GMAW) process. Herein, correlations between the energy input and the resulting temperature–time-regimes show the effect on resulting microstructure, weld seam irregularities and the mechanical properties of additively manufactured aluminum parts. Therefore, multilayer walls were built layer wise using the cold metal transfer (CMT) process including conventional CMT, CMT advanced and CMT pulse advanced arc modes. These processing strategies were analyzed by means of energy input, whereby the geometrical features of the layers could be controlled as well as the porosity to area portion to below 1% in the WAAM parts. Furthermore, the investigations show the that mechanical properties like tensile strength and material hardness can be adapted throughout the energy input per unit length significantly.

Effect of variants of gas metal arc welding process on tensile properties of AA6061-T6 aluminium alloy joints

This article describes the influence of gas metal arc welding (GMAW) variants on tensile properties of welded thin sheets of AA6061-T6 aluminium alloy. Single V butt joints were fabricated using the four variants of the GMAW process (constant current, pulsed current, cold metal transfer and pulsed cold metal transfer) under optimized conditions. Transverse tensile properties of the welded joints were evaluated, and a microhardness survey was done along the cross section of the joints. Higher hardness is recorded in the weld metal, i.e., 79 Hv for the pulsed cold metal transfer (PCMT) joint which is 14% higher than the continuous current GMAW joints. It is observed that a PCMT-welded joint exhibited the highest tensile strength of 227 MPa which is 16% higher than the continuous current GMAW joints. The fracture surface of the tensile specimens is highly dominated by the dimples with tearing ridges which suggests that the joints have experienced sufficient plastic deformation before failure irrespective of the welding process. The results demonstrated that the joints fabricated using the PCMT process exhibited superior tensile properties with controlled segregation of phases compared to the other variants of the GMAW process due to the pulsing effect associated with the retraction of the wire.

Influence of post weld heat treatment on tensile properties of cold metal transfer (CMT) arc welded AA6061-T6 aluminium alloy joints

AbstractAluminium alloys of 6xxx series are widely used in the fabrication of light weight structures especially, where high strength to weight ratio and excellent weld-ability characteristics are desirable. Gas metal arc welding (GMAW) is the most predominantly used welding process in many industries due to the ease of automation. In this investigation, an attempt has been made to identify the best variant of GMAW process to overcome the problems like alloy segregation, precipitate dissolution and heat affected zone (HAZ) softening. Thin sheets of AA6061-T6 alloy were welded by cold metal transfer (CMT) and Pulsed CMT (PCMT). Among the two joints, the joint made by PCMT technique exhibited superior tensile properties due to the mechanical stirring action in the weld pool caused by forward and rearward movement of the wire along with the controllable diffusion rate at the interface caused by shorter solidification time. However, softening still exists in the welded joints. Further to increase the joint efficiency and to minimize HAZ softening, the joints were subjected to post weld heat treatment (PWHT). Approximately 10% improvement in the tensile properties had been observed in the PWHT joints due to the nucleation of strengthening precipitates in the weld metal and HAZ.

Process variable optimization in the cold metal transfer weld repair of aerospace ZE41A-T5 alloy using central composite design

The pulsed cold metal transfer (CMT+P) process was evaluated for the repair of aerospace structural components made from ZE41A-T5 magnesium alloy. The choice of welding variables was considered to be unique for the material type, weld design and geometry, and application-specific requirements. A design of experiment (DOE) method based on a rotatable 3D central composite design (CCD) was used to systematically establish relationships between independent welding variables and the resultant output variables of the CMT+P process, including the development of mathematical models based on second-order polynomial. A multiple response desirability function approach was then used for process optimization. The CMT+P process produced high-quality welds in the alloy. Welding process variables were established to produce desired weld penetration and weld reinforcement and complete fusion with minimal weld defects. Optimal domains of the independent variables were achieved; where the welds comply with the application-specific (repair of gearbox housing) requirements and acceptable class A weld quality of the aerospace fusion welding standard AWS D17.1.

Correlations between Microstructure Characteristics and Mechanical Properties in 5183 Aluminium Alloy Fabricated by Wire-Arc Additive Manufacturing with Different Arc Modes.

The effect of arc modes on the microstructure and tensile properties of 5183 aluminium alloy fabricated by cold metal transfer (CMT) processes has been thoroughly investigated. Heat inputs of CMT processes with three arc modes, i.e., CMT, CMT advance (CMT+A), and CMT pulse (CMT+P), were quantified, and their influence on the formation of pores were investigated. The highest tensile strength was found from samples built by the CMT+A process. This agrees well with their smallest average pore sizes. Average tensile strengths of CMT+A arc mode-built samples were 296.9 MPa and 291.8 MPa along the horizontal and vertical directions, respectively. The difference of tensile strength along the horizontal and vertical directions of the CMT+P and CMT samples was mainly caused by the pores at the interfaces between each deposited layer. The successfully built large 5183 aluminium parts by the CMT+A arc mode further proves that this arc mode is a suitable mode for manufacturing of 5183 aluminium alloy.

A Comparative Study of Additively Manufactured Thin Wall and Block Structure with Al-6.3%Cu Alloy Using Cold Metal Transfer Process

In order to build a better understanding of the relationship between depositing mode and porosity, microstructure, and properties in wire + arc additive manufacturing (WAAM) 2319-Al components, several Al-6.3%Cu deposits were produced by WAAM technique with cold metal transfer (CMT) variants, pulsed CMT (CMT-P) and advanced CMT (CMT-ADV). Thin walls and blocks were selected as the depositing paths to make WAAM samples. Porosity, microstructure and micro hardness of these WAAM samples were investigated. Compared with CMT-P and thin wall mode, CMT-ADV and block process can effectively reduce the pores in WAAM aluminum alloy. The microstructure varied with different depositing paths and CMT variants. The micro hardness value of thin wall samples was around 75 HV from the bottom to the middle, and gradually decreased toward the top. Meanwhile, the micro hardness value ranged around 72–77 HV, and varied periodically in block samples. The variation in micro hardness is consistent with standard microstructure characteristics.

The Process of weld brazing CMT (Cold Metal Transfer pulse) for assembly of the different thin sheets

This paper describes the experimental program realized for the research of the behavior at the assembly through weld-brazing CMTP (Cold Metal Transfer pulse) of thin sheets of copper with aluminum. Four variants were chosen and studied, settling the best conditions for the assembly. They were made welded samples which were analyzed in volume terms of metallurgical and mechanical structure. It was also analyzed the influence of cooling velocity on the structure.

Cold metal transfer welding of aluminium to magnesium: microstructure and mechanical properties

This paper reports the procedure to join aluminium A6061-T6 to AZ31B magnesium alloy using Al-5%Si filler by cold metal transfer and pulsed-cold metal transfer processes. The effect of process parameters on the microstructure of weld, nugget/magnesium interface and tensile strength of the joints are analysed. Microstructural analysis shows that the diffusion layer thickness increases with increase in the welding current. The diffusion layer thickness was found to vary depending on the process. Pulsed process resulted in high joint strength compared to conventional method. X-ray diffraction study revealed the formation of different phases in the weld. The welding current, welding speed and the wire-feed rate had significant effect on the joint strength. Failure at the weld/Mg interface was observed.

Effect of arc mode in cold metal transfer process on porosity of additively manufactured Al-6.3%Cu alloy

In this study, the effect of arc mode in cold metal transfer (CMT) process on the porosity characteristic of additively manufactured Al-6.3%Cu alloy has been systematically investigated. The variants include conventional CMT, CMT pulse (CMT-P), CMT advanced (CMT-ADV) and CMT pulse advanced (CMT-PADV) and experiments were performed on both single layer deposits and multilayer deposits. The mechanism of porosity generation using the CMT arc mode variants is discussed. It was found that deposit porosity is significantly influenced by the arc mode type of CMT process. Conventional CMT is not suitable for the additive manufacturing process because it produces a large amount of gas pores, even in single layer deposit. CMT-PADV proved to be the most suitable process for depositing aluminium alloy due to its excellent performance in controlling porosity. With correct parameter, setting the gas pores can be eliminated. It was found that the key factors that enable the CMT-PADV process to control the porosity efficiently are the low heat input, a fine equiaxed grain structure and effective oxide cleaning of the wire.

Vibration Tests at Thin Stainless Steel Sheets Joined by CMT Pulse with CuSi3 Filler Material for Determination of the Elasticity Modulus

t is presented a method for determining the mechanical characteristics based on the vibration response of the CMT (Cold Metal Transfer) joints from thin sheets of stainless steel joined with CuSi3 filler wire. The experimental results obtained by vibration testing will be compared with the theoretical results, and with those obtained by classical methods from stress-strain diagram. Technical details are given also for obtaining these joints (parameters, equipment specifications) indicating also their applicability.