Cold Metal Transfer Method Research Articles

Effects of zinc coating on magnesium alloy–steel joints produced by cold metal transfer method

Magnesium alloys are lap-joined to galvanised and bare steel sheets by a cold metal transfer method. The weld appearance, cross-section, tensile strength and fracture behaviour of these joints are characterised by scanning electron microscopy, tensile tests and energy-dispersive spectroscopy. The joints were found to have good weld appearance and satisfactory tensile strength. The spreadability and wettability of the Mg alloy–galvanised steel joint are superior to those of the Mg alloy–bare steel joint, but the tensile strength is lower. In particular, the presence of Zn on the galvanised steel sheet improves wettability but decreases tensile strength. Aluminium has a high affinity for Fe, and the thinner layer of Fe–Al improves the mechanical properties of the Mg alloy–bare steel joint.

Weldability and Distortion of Mg AZ31-to-Galvanized Steel SPOT Plug Welding Joint by Cold Metal Transfer Method

In this study, cold metal transfer (CMT) plug welding of 1 mm thick Mg AZ31 to 1 mm thick hot-dipped galvanized mild steel (i.e., Q235) was studied. Welding tests were performed and the process variables optimized with Mg AZ61 wire and 100% argon shielding gas for a plug weld located in the center of the 25 mm overlap region. It was found that it is feasible to join 1 mm thick Mg AZ31 workpiece to 1 mm thick galvanized mild steel using CMT plug welding. The optimized process variables for CMT plug welding Mg AZ31-to-galvanized mild steel were a wire feed speed of 10.5 m/min, a predrilled hole with a diameter of 8 mm in Mg AZ31 workpiece and a welding time of 0.8 s. CMT plug welded Mg AZ31-to-galvanized mild steel joints were composed of the fusion zone between Mg AZ31 base metal and Mg weld metal, Mg weld metal (i.e., combined base metal, filler wire and Zn coating), and the brazing interface between magnesium weld metal and galvanized mild steel. The brazing interface mainly consisted of Al, Zn, Mg, Si intermetallic compounds and oxides (i.e., Fe3Al, Mg2Si, MgZn, and MgZn2), and magnesium solid solution. The static strength of CMT welded-brazed Mg AZ31-galvanized steel was determined primarily by the strength and area of the brazed interface and thickness of the intermetallic reaction layer.

Microstructure and mechanical properties of cold metal transfer welded aluminium/dual phase steel

In this work, an attempt was made to join A6061-T6 aluminium alloy to Dual Phase 800 steel using AlSiMn filler by cold metal transfer (CMT) processes. The effect of process parameters on the microstructures and tensile strength of the joints are analysed. Microstructural analysis revealed the formation of the Fe–Al intermetallic (IM) layer. The IM layer thickness was found to be very small. Electron microscopy analysis revealed the presence of long plate shape (Al5FeSi) and fragmented particles in the IM layer. At the interface, ⊖-FeAl3 and η-Fe2Al5 phases were formed. Pulsed process resulted in better joint strength when compared to conventional CMT method. X-ray diffraction study revealed the formation of the Fe3Al and η-Fe2Al5 phases in the weld. The welding currents and arc length correction factor had significant effects on the joint strength. Tensile failure occurred at the heat affected zone.

The Microstructure of Weld Overlay Ni-Base Alloy Deposited on Carbon Steel by CMT Method

Ni-base alloys, like Inconel 625, exhibit a high temperature corrosion and oxidation resistance. For this reason, these alloys are typically used as a one of the most important coating material and can be applied in a different environments and elements of devices having various applications. In this work, Inconel 625 was deposited onto a carbon steel P235GH by Cold Metal Transfer method. Due to the segregation of Ni, Cr, Nb and Mo elements the Inconel 625 weld overlays cladded on boiler pipes P235GH obtained the dendritic structure, with the formation of a second phases at the end of solidification. The presence of γ (with high dislocation density), the Laves and (Nb,Ti)C phases was revealed by means of TEM examinations. The multipoint EDS analysis confirmed the presence of low Fe concentration in the Inconel 625 alloy coatings. The concentration profiles of Ni, Cr, Mo and Nb performed across the dendritic structure showed segregation of these elements.

Degradation Processes of Al-Zn Welded Joints

Welding of metal materials belongs to non-demountable joints. Current trend especially in an automotive industry is to join materials with a different melting temperature. Most of all, there are dural profiles with ferrite or austenite steel. The reason for this is the effort to lower the weight of the whole construction and at the same time preserve sufficient mechanical characteristics. However, there is a big risk of different electrical potentials of both of these metals in this type of non-demountable joints. The experimental part of this paper brings evaluation of mechanical-corrosion processes of overlapped joints produced by the CMT (cold metal transfer) method. The base material for weld bead is dural sheet AlMg3 and dural sheet with a surface treatment aluzinc DX51D+AZ 150. Material AlSi5 in the form of a wire was used as an additional material for a welding bath. Method CMT was used in order to create a weld bead. Initial analysis of weld bead was done visually using a binocular microscope. Further, a metallographic analysis of weld bead and base material was processed. The aim was to identify the heat affected area around the welded joint. Microhardness of intermetallic aluminium phases was measured, after the identification of intermetallic phases a chemical analysis EDS was processed. Prepared samples underwent corrosion degradation in a salt spray environment in compliance with the norm ČSN EN ISO 9227. Visual and metallographic evaluation of the individual samples was processed after every week of exposition to the salt spray environment. The goal of this experiment was to record the initial impulse of galvanic corrosion which consists in corrosion degradation in the area of welded joint.

Analysis of Microstructure and Mechanical Properties for Welding Joints of Dissimilar Metals between Magnesium and Titanium by Cold Metal Transfer Method

Welding-brazing joining of Dissimilar metals between AZ31B Mg alloy and industrial pure titanium TA2 is studied by cold metal transfer(CMT) welding technology. The microstructure、element distribution of the welding joints were analyzed to show joining mechanism. The results show that, cold metal transfer welding technology is a feasible method for dissimilar metals Mg and Ti joining. The gagnesium and titanium sheets can be joined by forming new phases in the transition joining zones. The weld metal zone is constituted by ?-Mg solid solution,skeleton shaped Mg17Al12 intermetallic compound, and granular distributed Mg17Al(Zn)12. The joining of magnesium and titanium mainly depends on the Ti3Al, and Mg17Al12 intermetallic compounds. At the same time, diffusions of Ti atoms and Al atoms also affect the formation of the joints during welding process. Therefore, enough quantity of heat input must be ensured to make the local titanium parent metal to melt and titanium atomic diffuse, so as to improve the joining strength during the welding process.

Possibilities of joining galvanized sheet steel using the CMT method (cold metal transfer)

A new method of joining galvanized sheet steel is the cold metal transfer (CMT) process developed by Fronius1-4. This method involves the use of a short-circuit arc, and its characteristics, which ...

Comparative tests of steel car body sheet welds made using CMT and MIG/MAG methods

Results of tests on the influence of automatic welding process parameters using the cold metal transfer (CMT) method on the quality of lap joints made of 0.8 mm steel car body sheets (DC 04) were described. These joints were compared with joints executed using a traditional short arc in gas shielding (MAG). Research work included visual and metallographic inspections, microhardness measurements, and mechanical properties tests of the welded joints. It was noted that the CMT method allowed for the joining of thin workpieces at much higher velocities than previously used in arc welding in shielding gases (approximately four times faster than using MIG/MAG methods), while maintaining very good quality. Metallographic tests were also used to state the changes taking place in the joint and welded material depending on parameter changes. Additionally, attempts were made to determine a mixing factor for both upper and lower metal sheets. It was observed that increased arc length caused deeper depth of fusion of the material of the lower sheet, resulting in an incremental increase in the mixing factor.

Cold metal transfer joining aluminum alloys-to-galvanized mild steel

The cold metal transfer (CMT) welding–brazing process provides a potential method to join dissimilar metals. In this research, various 1mm thick aluminum alloys were joined to 1mm thick mild steel (Q235) by the CMT welding technology. It was found that it is feasible to join aluminum alloys-to-galvanized mild steel using the cold metal transfer method. The optimum process variables for weldability of aluminum-galvanized steel of dimension 200mm×50mm×1mm could be obtained with a wire of Al4043, 100% argon shielding gas, a welding voltage range of 12–14V, a deviation distance range of 2–3.5mm, a welding speed range of 6–8mm/s and a wire-feed speed range of 4–6m/min. The joint strength depended primarily on the thickness of the intermetallics and softening of the Al heat-affected-zone. By properly controlling the heat input (100–200J/mm), the degradation of the HAZ property and thickness of the intermetallic reaction layer can be minimized, and consequently produced a hybrid aluminum-to-steel joint which had comparable strength to that of CMT weld-brazed Al-to-Al joint.

Effect of a post-weld heat treatment on the mechanical and microstructure properties of AA6061 joints welded by the gas metal arc welding cold metal transfer method

This work studies the effect of a post-weld heat treatment (PWHT) on the mechanical and microstructure properties of an AA6061 sample welded using the gas metal arc welding (GMAW) cold metal transfer (CMT) method. The CMT method was used because the method provides spatter-free welding, outstanding gap bridging properties, low heat input and a high degree of process flexibility. The welded samples were divided into as-welded and PWHT samples. The PWHTs used on the samples were solution heat treatment, water quenching and artificial aging. Both welded samples were cut according to the ASTM E8M-04 standard to obtain the tensile strength and the elongation of the joints. The failure pattern of the tensile tested specimens was analysed using scanning electron microscopy (SEM). A Vickers microhardness testing machine was used to measure the hardness across the joints. From the results, the PWHTs were able to enhance the mechanical properties and microstructure characteristics of the AA6061 joints welded by the GMAW CMT method.

Interfacial phenomena of cold metal transfer (CMT) welding of zinc coated steel and wrought aluminium

The interfacial microstructures and intermetallic compounds produced by cold metal transfer (CMT) welding of wrought aluminium to zinc coated steel have been investigated. The results showed that the reaction layer mainly consists of FeAl3 phase and the thickness of the layer was decreased to 7–8 μm owing to the low heat input of the CMT method. And the thin reaction layer guarantees the tensile property of the joint. At last, according to the interface characteristic of the dissimilar metal joint, the interfacial reaction process was described in detail.