Cold Metal Transfer Technology Research Articles

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.

A comparative study on Al-Mg-Sc-Zr alloy fabricated by wire arc additive manufacturing with controlling interlayer temperature and continuous printing: Porosity, microstructure, and mechanical properties

Wire arc additive manufacturing (WAAM) technique is a promising approach to producing large-scale metal components due to high deposition efficiency and low production cost. However, fundamental research about WAAM-processed Al-Mg-Sc-Zr alloy was still fewer. In this study, Al-6.54Mg-0.36Sc-0.11Zr (wt%) components were successfully manufactured by WAAM with an interlayer temperature at 100 °C (named IW) and continuous printing (named CP), and the corresponding porosity, microstructure, and mechanical properties of components were studied in detail. The porosity of components as-deposited was relatively low, about 0.385% and 0.116%, respectively. The microstructures of the two components exhibited the same distribution characteristics in XZ and YZ planes: fine equiaxed grains (FEG) at remelted zone + FEG and coarse equiaxed grain (CEG) alternative distribution at middle zone + FEG at the top zone of the molten pool. The average grain size of component IW was about 10.51 ± 6.01 μm, and that of component CP significantly increased, to about 11.85 ± 5.86 μm. The short-circuit transition mode of cold metal transfer technology and the heterogeneous nucleation effect of primary Al3(Sc, Zr) and Al3(Sc, Zr, Ti) phases together promoted the formation of equiaxed grains and refined the microstructures. After heat treatment at 325 °C and 6 h, nano-Al3Sc precipitated with a size of about 15–50 nm. The yield strength (YS) of components IW and CP increased from 171 ± 3 to 261 ± 1 MPa and 168 ± 7 to 240 ± 17 MPa, respectively. Component IW had the highest ultimate tensile strength, about 400 ± 1 MPa. For WAAM-processed Al-Mg-Sc-Zr alloys, the contribution of the strengthening mechanism to YS was solid solution strengthening > precipitation strengthening > fine grain strengthening > dislocation strengthening.

Effect of energy input on fatigue crack growth behavior of titanium alloy Ti6Al4V made by WAAM‐CMT

AbstractThis work deals with the investigation and characterization of Ti6Al4V parts produced with an intriguing manufacturing process belonging to the Wire Arc Additive Manufacturing (WAAM) family: the Cold Metal Transfer technology (CMT). Wall‐shaped parts were produced according to different process parameters, namely the wire feed speed and voltage–current combinations, leading to different energy inputs. The parts were characterized in terms of surface morphology, microhardness, microstructure, tensile properties, and fatigue crack growth. The results suggested that the investigated deposition parameters led to similar results. Moreover, the mechanical and fatigue crack growth behavior was in line with parts of the same alloy produced through other manufacturing routes, whereas the microstructure type was the result of the fast cooling of the molten material. Finally, considering the simple system adopted to avoid oxidation during the deposition stage, the results suggested that CMT is a promising manufacturing technique for titanium alloy semifinished parts.

Mechanical behavior of austenitic stainless steels produced by wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is an innovative technology with the potential to drive the transformation and upgrading of metallic manufacturing industry and construction sector. The advantages of WAAM technology in rapid manufacturing, design freedom, and energy saving have attracted attentions in the construction field. This research study focuses on investigating the microstructural and mechanical behavior of austenitic stainless steels produced by wire arc additive manufacturing through test programs. The stainless steel plates were first additively manufactured using cold metal transfer technology with three types of feedstock wires (ER304, ER308L, ER316L). Tensile coupon specimens and microstructural observation samples were extracted from the WAAM plates. The electron backscatter diffraction (EBSD) experiments were conducted to identify and analyze the microstructures of the WAAM austenitic stainless steels. Five test orientations, namely θ = 0˚, 30˚, 45˚, 60˚, 90˚ relative to the printing layer direction, were designed to investigate the mechanical properties anisotropy. Two types of specimen surface condition (milled type and as-built type) were considered to assess the impact of geometric undulation. The geometric features of the as-built specimens were obtained using 3D laser scanning. A total of 60 tensile tests with the aid of digital image correlation (DIC) system were conducted to obtain the stress–strain responses of the WAAM austenitic stainless steels. The mechanical properties anisotropy of the WAAM austenitic stainless steels was analyzed in detail.

Recent Developments in Cladding and Coating Using Cold Metal Transfer Technology

Recent Developments in Cladding and Coating Using Cold Metal Transfer Technology

Characterization of cold metal transfer and conventional short-circuit gas metal arc welding processes for depositing tungsten carbide-reinforced metal matrix composite overlays

This paper compares the processing characteristics of advanced CMT (cold metal transfer) and conventional GMAW-S (gas metal arc welding with short-circuit metal transfer) processes for depositing Ni-WC MMC (nickel-based metal matrix composites reinforced with WC) overlays. In contrast to common expectations, advanced CMT technology with mechanically assisted droplet transfer could not demonstrate significant advantages over the GMAW-S process; on the contrary, CMT exhibits marginal disadvantages in terms of carbide transfer efficiency, volume fraction of retained WC, and deposition rate. Some carbides originally contained in the core of the feed wire are blown away and expelled out of the processing zone leading to physical losses of WC particles during the deposition processes, which is more significant for the CMT process owing to much higher waveform cycle frequency and cyclic feed wire retractions. CMT exhibits superior waveform stability, better control over penetration depth, marginally lower dilution level, and exceptional arc stability. The main parameters affecting carbide transfer efficiency and volume fraction of retained WC are wire feed speed and travel speed for both processes; increased wire feed speed and travel speed generally lead to decreased carbide transfer efficiency and reduced volume fraction of retained WC. Shielding gas may have different effects on the outcomes for the CMT and GMAW-S processes. CMT overlays show comparatively higher W and lower Fe concentration in the matrix, while GMAW-S overlays show a higher concentration of Fe in the matrix (due to elevated dilution level) with marginally higher matrix microhardness and more herringbone-like secondary carbide precipitates.

Formation optimization of downward overlaid Inconel 625 on curved surface of X65 pipeline basing on dynamic behavior of molten pool

In practical engineering, overlaying on curved surfaces with constantly changing gravity components usually leads to various defects. In this study, Inconel 625 was downward overlaid on curved surface by cold metal transfer (CMT) process with varied heat input, and the dynamic behavior of the molten pool was observed by high speed camera. At high heat input (0.422 kJ/mm and 0.372 kJ/mm), the volume of the molten pool continued to expand due to the downward flow of the liquid, ultimately leading to overflow or instability defects. In contrast, low heat input (0.230 kJ/mm) will make the molten pool shrink during overlaying, which was attributed to the continuously weakened gravity, the relative position between the heat source and the molten pool was then changed. A well-formed and defect-free weld overlay was obtained at optimized heat input 0.230–0.280 kJ/mm. Compared with gas tungsten arc welding (GTAW) process, the weld overlay obtained employing CMT process has the largest thickness and the most uniform fusion line, while the content of Fe element was less than 0.5%. It was confirmed that CMT technology has great potential for overlaying on curved surface.

INVESTIGATION OF THE EFFECT OF HEAT TREATMENT ON Cu – Al ALLOYS OBTAINED BY WIRE-ARC ADDITIVE MANUFACTURING

By methods of optical, scanning and transmission electron microscopy, studies have been carried out to establish the influence of Al, Si andMg on the formation and change of the structure, phase composition and distribution of elements of Cu–Al alloys obtained by wire-arc additive manufacturing with cold metal transfer, and after their heat treatment. The main factors determining the mechanical behavior of Cu-Al alloys after the addition of Si and Mg and their heat treat- ment are determined and analyzed. It is shown that the increased strength and hardness of the Cu-Al alloy is explained by grain grinding and the formation of particles of the second phases between the layers of the deposited metal. The features of the distribution of the main elements (Cu, Al) and secondary elements (Si, Mg) in the process of wire-arc additive manufacturing are revealed. Recently, studies of the Cu-Al alloy have been carried out, which have shown that Al as a solid solution element in the Cu-Al alloy can increase the formation of deformation twins and the density of dislocations. In addition, it was found that the addition of micro-alloying elements to the Cu–Al alloy significantly improves its me- chanical properties. The kinetics of the growth of intermetallic compounds such as CuAl2, Cu9Al4, Cu3Al in Cu–Al casting alloys has been studied. As a result of the complex of technological measures, the modes of obtaining additive billets of Si–Al, Cu–Al–Si and Cu–Al–Si–Mg alloys were selected. Technological equipment has been improved to obtain blanks as part of the work. The microstructure, phase composition and mechanical properties of Si–Al, Cu–Al–Si and Cu–Al–Si–Mg alloys obtained bywire-arc additivemanufacturing using coldmetal transfer technology are investigated.

Metallurgical and Mechanical Characteristics of an AA5183 Alloy Plate Performed by a Cold Metal Low-Power Additive Manufacturing Technology

In this work, an AA5183 alloy plate was successfully deposited by low-power cold metal transfer technology. The forming defects, microstructural characteristics, and mechanical properties were investigated. The results show that the number of defects increases gradually along the building direction of the deposited plate. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, electron probe microanalysis, electron backscatter diffraction, and transmission electron microscopy were employed to study the distribution of alloying elements, deposited microstructural characteristics, and the crystal structure of intermetallic compounds in the Al alloy plate. The tensile samples perpendicular to the building direction presented greater tensile strength and superior plasticity compared to those parallel to the deposition direction. The average UTS was 327 ± 0.65 MPa and the average EL was 30.6 ± 2.0%. The UTS of conventionally forged 5083-H32 (Al-Mg4.5) alloy is 324 MPa; the UTS of extruded 5083-H116 (Al-Mg4.5) alloy is 305 MPa. Further, the strength of our prepared plate reaches the value needed for industrial applications of the 5083 Al alloy. The differences in the strength and plasticity of the samples assessed under multiple sampling methods were analyzed based on a synergistic strength–ductility mechanism.

Microstructures and Properties of Al-Mg Alloys Manufactured by WAAM-CMT.

A wire arc additive manufacturing system, based on cold metal transfer technology, was utilized to manufacture the Al-Mg alloy walls. ER5556 wire was used as the filler metal to deposit Al-Mg alloys layer by layer. Based on the orthogonal experiments, the process parameters of the welding current, welding speed and gas flow, as well as interlayer residence time, were adjusted to investigate the microstructure, phase composition and crystal orientation as well as material properties of Al-Mg alloyed additive. The results show that the grain size of Al-Mg alloyed additive becomes smaller with the decrease of welding current or increased welding speed. It is easier to obtain the additive parts with better grain uniformity with the increase of gas flow or interlayer residence time. The phase composition of Al-Mg alloyed additive consists of α-Al matrix and γ (Al12Mg17) phase. The eutectic reaction occurs during the additive manufacturing process, and the liquefying film is formed on the α-Al matrix and coated on the γ phase surface. The crystal grows preferentially along the <111> and <101> orientations. When the welding current is 90 A, the welding speed is 700 mm/min, the gas flow is 22.5 L/min and the interlayer residence time is 5 min, the Al-Mg alloy additive obtains the highest tensile strength. Under the optimal process parameters, the average grain size of Al-Mg alloyed additive is 25 μm, the transverse tensile strength reaches 382 MPa, the impact absorption energy is 26 J, and the corrosion current density is 3.485 × 10−6 A·cm−2. Both tensile and impact fracture modes of Al-Mg alloyed additive are ductile fractures. From the current view, the Al-Mg alloys manufactured by WAAM-CMT have a better performance than those produced by the traditional casting process.

Investigation on the fracture behaviour of wire arc additive manufactured rotor steel weldments after heat treatment

This paper discusses the additive welding of Cr-Mo steel weldment carried out with Cold Metal Transfer Technology (CMT). The mechanical characterization including fracture behaviour and metallography of the Wire Arc Additive Manufacture (WAAM) weldments in the As Welded (AW) and Post Weld Heat Treated (PWHT) conditions were investigated. The longitudinal and transverse orientations parallel to building and deposition directions respectively were found to influence the fracture behavior of weldments. The specimens of longitudinal direction showed lower toughness and tensile strength when compared to the specimens of transverse direction both in the case of AW and PWHT weldments. Orientation was also observed to influence the elastic–plastic fracture toughness (J integral) values both in the as welded and heat-treated specimens. Fracture topographical analysis of specimens carried out by Scanning Electron Microscope (SEM) in association with Energy Dispersive Spectroscopy (EDS) showed the presence of soft ductile features and Mn deposition respectively in the specimens of transverse direction and justified the findings.

Effect of interlayer temperature on microstructure evolution and mechanical performance of wire arc additive manufactured 300M steel

The 300M steel straight wall parts (SWPs) are fabricated by wire arc additive manufacturing based on cold metal transfer technology. The effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the SWPs are investigated. The results show that the surface waviness of the SWP first decreases and then increases with the increase of interlayer temperature, and the lowest surface waviness is controlled in 0.47 mm at the interlayer temperature of 200 °C. In the top region, the microstructure mainly consists of untempered martensite and slightly changes with the increase of interlayer temperature. In the middle and bottom regions, the microstructure is mainly composed of tempered martensite as the interlayer temperature is 100 or 200 °C. However, when the interlayer temperature is increased above 400 °C, the needle-like bainite and feather-like bainite are gradually formed due to the slow cooling rate and long dwell time in the bainite transformation zone. The microhardness and ultimate tensile strength in the top region are significantly higher than those in the middle and bottom regions, which are attributed to the enhanced solid solution strengthening effect of untempered martensite. The tensile fracture morphology is transformed from the quasi-cleavage fracture mode to the ductile mode with the increase of interlayer temperature or the decrease of distance from the substrate.

Study on appearance and mechanical behavior of additively manufacturing of Ti–6Al–4V alloy by using cold metal transfer

Compared with the gas metal arc welding (GMAW), the cold metal transfer technology can significantly reduce the welding heat input owing to obtain the output current of almost zero in the droplet detaching, which has a greater advantage in additive manufacturing. In this work, the cold metal transfer was employed to study the law of appearance and mechanical behavior of additively manufacturing of Ti–6Al–4V alloy. The results showed that the continuous and uniform weld appearance could be obtained when the current of 120 A–130 A was used. In the top layer, middle layer and bottom layer of thin-walled components, the same microstructure was obtained with the different parameters, which were mainly consisted of the columnar original β grains and acicular martensite α’. The max-hardness was obtained in the bottom zone (BZ) of thin-walled component. With the increase of welding current, the hardness values in BZ were decreased. With the increases of current, the tensile strength was reduced, which caused by the grain growth.

Lap Joining of Titanium to Galvanized Steel by Cold Metal Transfer Technology

Lap Joining of Titanium to Galvanized Steel by Cold Metal Transfer Technology

Investigation on H13 buildups produced with wire arc additive manufacturing: Deposition strategies-induced microstructural evolution and mechanical performances

In this work, H13 buildups were produced through wire-arc additive manufacturing based on cold metal transfer technology. Four different deposition strategies were employed for the fabrication and the microstructural evolution and mechanical properties of the corresponding buildups were compared. A bimodal microstructure for all buildups produced in the overlap zone (OZ) and body zone (BZ), respectively, despite a mixture of lath-shaped martensites and blocky δ-ferrites in the OZ and a slightly coarser but still fine martensites in the BZ. The as-deposited mechanical properties were evidently superior to the properties of the base metal after annealing, but slightly inferior to that after quenching and tempering. Compared with the components with different deposition patterns between adjacent layers, the relatively enhanced hardness and wear-resistance properties were acquired for the ones with the same scanning strategies, being responsible for the smaller retained δ-ferrite size in the OZ and slightly refined martensites in the BZ. The deposition strategy had a negligible influence on the wear surface hardness, all decreasing gradually from the wear zone to the transient zone and finally keeping stable as a result of the locally martensitic evolution. As the in-situ thermal history was influenced by the deposition strategies, both of the microstructural distribution and mechanical performances were affected by the deposition strategies. Besides, the applied strategies, characterized by the different scanning directions between adjacent tracks, had a negligible influence on microstructures and mechanical properties following comparison with the counterparts with the different directions between adjacent layers.

Fabrication of bulk Al-Co-Cr-Fe-Ni high-entropy alloy using combined cable wire arc additive manufacturing (CCW-AAM): Microstructure and mechanical properties

Additive manufacturing is a very promising manufacturing method widely used in various industries. In this study, for the first time, a new type of combined cable wire (CCW) with multi-element composition has been designed and developed for arc additive manufacturing (AAM) of non-equiatomic Al-Co-Cr-Fe-Ni high-entropy alloy. CCW composed of 7 filaments and 5 elements has the advantages of high deposition efficiency, self-rotation of welding arc and energy saving capability. Thin HEA walls were fabricated under pure argon gas using cold metal transfer technology. Microstructural observations of the developed HEA reveal (i) BCC and FCC phases, (ii) Good bonding between layers and (iii) defect-free microstructure. The developed alloy exhibits high compression strength (∼2.9 GPa) coupled with high elongation (∼42 %) values (possess both strength and ductility). It has been identified that by varying the heat input via torch travel speed, the microstructure and mechanical properties of the HEA can be controlled. From this feasibility study, it has been proved that the innovative CCW method can be used to manufacture HEAs with CCW-AAM. Further, the study highlights the advantage of the rapid cooling involved in the CCW-AAM process which gives rise to superior mechanical properties.

PROGRESSIVE CMT CLADDING FOR RENOVATION OF CASTING MOLD

The paper presents the results of the research focused on the possibility of renewal of molded parts of molds in high-pressure casting of aluminum alloys by cladding welding. Two materials - Thermanit 625 and Thermanit X - were tested. Weld-on layers were produced by CMT - Cold Metal Transfer technology in a protective atmosphere of Ar. The cllad resistance in the molten melt of the aluminum alloy EN AB AlSi8Cu3 for 120 and 300 minutes was evaluated. Furthermore, ball-on-disc wear resistance of welds was assessed. The results were compared with the reference material - AISI / SAE 309 base tool steel.

Comparative analysis of structure and mechanical properties of parts produced by electron-beam additive manufacturing and cold metal transfer

Currently, the most prospective industry development areas are prototyping and additive manufacturing. In contrast to more precise powder technologies, faster wire technologies providing non-porous products are of great interest. This paper contains a comparative analysis of the effect of two wire technologies – electron-beam additive manufacturing and cold metal transfer – on the structure and mechanical properties of Aluminum Alloy 5056. Electron beam power is close to arc power at optimal printing parameters, but cold metal transfer is cheaper due to the impulse nature of the arc. In addition, the arc method is implemented in an argon atmosphere, and this accelerates the applied layer cooling. In general, the grain structure of the material is refined due to the lower heat transfer and accelerated cooling. This results in increased strength and microhardness. The constant heat removal from the substrate and the increase in the product weight change thermal conditions of the following layer. This is controlled by beam/arc powder reduction, but each layer has its own thermal history affecting the structure and properties. In particular, the more heat is transferred to the layer from the previous layers, the less strong it is. When a certain height (about 30 mm) is passed, cooling is intensified by the large mass of the product and the strength is increased again. This is most characteristic for cold metal transfer. However, these fluctuations are rather small. Mechanical properties along the growth direction are highly stable in both technologies. Cold metal transfer also shows less alloying magnesium burn-off. In general, currently the cold metal transfer technology is more cost effective and provides better quality products.

Uticaj strategije izrade na mehaničke osobine niskolegiranih čelika visoke čvrstoće u aditivnoj proizvodnji žicom i električnim lukom

Wire arc additive manufacturing (WAAM) which is literally based on continuously fed material deposition type of welding processes such as metal inert gas (MIG), tungsten inert gas (TIG) and plasma welding, is a variant of additive manufacturing technologies. WAAM steps forward with its high deposition rate and low equipment cost as compared to the powder feed and laser/electron beam heated processes among various additive manufacturing processes. In this work, sample parts made of low allow high strength steel (ER120S-G) was additively manufactured via WAAM method using robotic cold metal transfer technology (CMT). The process parameters and building strategies were investigated and correlated with the geometrical, metallurgical and mechanical properties on the produced wall geometries. The results obtained from the thin wall sample parts have showed that with increasing heat input, mechanical properties decreases, since higher heat accumulation and lower cooling rate increases the grain size. The tensile tests results have showed that casting steel (G24Mn6+QT2) mechanical properties which requires 500 MPa yield strength can be compared to with as build WAAM process having 640 MPa yield strength. Tensile strength were fulfilled for S690Q and yield strength is very close to the reference value.

Microstructural evolution and mechanical properties of deep cryogenic treated Cu–Al–Si alloy fabricated by Cold Metal Transfer (CMT) process

Cryogenic treatment is an effective route to obtain fine grained microstructure in materials. In this work, the effect of deep cryogenic treatment (DCT) on the microstructural evolution and mechanical properties of a copper-aluminum-silicon (Cu–Al–Si) alloy deposited by cold metal transfer (CMT) technology was investigated. Copper-rich Cu–Al–Si alloy with ~8.3% aluminum content was deposited on T2 copper substrate using an innovative dual wire feed system based on CMT technology. The deposited alloy was subjected to DCT for varying time duration (0, 6, 12 and 24 h). Evaluation of microhardness and tensile properties showed that the deep cryogenic treatment enhanced these properties. Microhardness increased about 10% with the increase in the DCT time duration. Under tensile loading conditions, the DCT conducted for 12 h provided the best properties, with an increase in both the tensile yield and ultimate strengths (~20% increase). Microstructural evolution and grain orientation were investigated using Electron Back Scattered Diffraction (EBSD). Microstructural studies revealed the formation of subgrains, fine grains and deformation twins due to DCT. Significant grain refinement was achieved due to the increase in the formation of high angle grain boundaries. It is summarized that the deep cryogenic treatment induces microstructural evolution: (i) grain refinement and (ii) texture randomization, and improves the mechanical properties of Cu–Al–Si alloy.