Cold Pressure Welding Research Articles

A Synthetic Approach to Cold Pressure Welding on Cogged Surfaces

Pressure welding on cogged surfaces represents a new technological variant of the cold welding. The components that are made from a material with higher plasticity (aluminium, lead etc.), having flat surfaces, are pressed on or between the harder material components (copper, brass, carbon/stainless steel, titanium, etc.) that have cogged surfaces. The main particularity of this technique is to achieve an appropriate joint by deforming only the component with higher plasticity. Due to the low degree of deformation needed, reduced pressure forces are applied in comparison with the classical cold pressure welding. The welding in isolated catching nodes is achieved by gripping, while the aluminium is gliding on the flanks of the teeth. The tensile strength of the joint is relatively low reaching up to 10% of the aluminium part, but can be improved by applying a heat treatment. Welded joints were made in various combinations, resulting in bimetallic or multilayered workpieces. Due to the negligible contact resistance, these joints can be appropriately used for applications in the electrotechnical field.

Electropolymerization of acrylic acid on steel for enhanced joining by plastic deformation

Resource-efficient electrochemical polymerization of acrylic acid (AA) on steel (DC04), from mildly acid Zn2+/ AA-containing aqueous solutions, is presented as an effective and sustainable thin film technology which allows for a precise control of the polymer thickness and morphology. The steel substrates were potentiostatically polarized to -1.4 V (vs. Ag/AgCl) or cycled between +0.1 to -1.4 V (vs. Ag/AgCl) in a degassed 2.0 M AA and 0.2 M ZnCl2-containing aqueous electrolyte solution at pH 6. FE-SEM, AFM, FT-IRRAS, XPS, and electrochemical measurements shed light on the structural and chemical features exhibited by the as-prepared polyacrylic acid (PAA) thin films. When PAA-modified DC04 plates are joined to Al EN AW-1050A H24 specimens by plastic deformation using cold pressure welding (CPW), tensile strength testing unveiled the macroscopic interfacial adhesion-promoting capabilities exhibited by PAA layers to the opposing aluminum oxide surfaces. Carboxylate moieties present in the PAA are shown to form stable chemical bonds with metal oxide surfaces and with amine-epoxy-based resins. Interestingly, higher maximum shear force values are obtained for the PAA films when Zn metallic deposits are not present in the organic layer, but, when these welded specimens are heated up to 200 °C in a N2 atmosphere, it occurred exactly the opposite: Zn particle-containing PAA films showed the highest maximum shear force values for the same deposition time.

Initial Study on Press Welding With Indium Applied to High-Temperature Superconducting DC Feeder Cables

High-temperature superconducting (HTS) DC feeder cable has been proposed for reducing energy loss in railway systems. The feeder cables are required to be installed during the night using a quickly-fabricable low-resistive joint. A soldering technique has been widely used for connecting HTS round-shaped cables in transmission or feeder cable systems. In this study, we proposed applying press welding with indium at room temperature (cold pressure welding) or with heat treatment at 90–120 °C as an alternative candidate for the cable-to-cable joint. First, we examined the necessity of the pre-joint process, polishing the HTS tape, and pickling indium foil with 10% HCl as well as the joining temperature. The examination was performed using tape-to-tape joints with copper-alloy-laminated Bi-2223 tapes. The joint resistance and mechanical strength for railway application were satisfied even by a joint fabricated at room temperature skipping the above two pre-joint processes. Then, we fabricated straight and spiral joints of the model cable made of copper-alloy-laminated Bi-2223 tapes with various joining processes and spiral pitches. The joint resistivity for the model cable joint was less influenced by the joining process and spiral pitch and it was comparable to that of a single tape-to-tape joint. As a conclusion, press welding with indium with a simplified process, joining at room temperature, and skipping some of pre-joint processes can be applied to quick and simple joint fabrication of HTS DC feeder cable.

Electrografting of BTSE: Zn films for advanced steel-aluminum joining by plastic deformation

This article presents the application of an adhesion promoting highly crosslinked ultrathin organic-inorganic hybrid layer applied to steel which promotes the subsequent joining process based on plastic deformation. The tensile shear results show that a significant increase of the bond strength between low-alloy steel (DC04) and aluminum (AW1050A H111), upon cold-pressure welding (CPW), could be achieved. Electrografting of an ultra-thin film of 1,2-bis(triethoxysilyl)ethane (BTSE) films on the steel surface was done from ethanolic solutions containing zinc ions. Based on surface spectroscopic analysis it is shown that silanol moieties present in the organosilane deposits can form stable chemical bonds with both the iron oxide covered steel and the aluminum oxide covered aluminum alloy. The successful modification of metal oxide surfaces with BTSE has been demonstrated via SEM-EDX, AFM, PM-IRRAS, and XPS measurements. In addition, electrochemical analysis of the BTSE:Zn films showed that the films lead to very good corrosion properties even at low thicknesses.

Preliminary in-situ study of FIB-assisted method for aluminium solid-state welding at the microscale

In situ studies allow real time monitoring and deep comprehension of phenomena. This approach has been applied to the current research for the development of a novel solid-state welding technique at the microscale. The downscaling of the process has been inspired by Cold Pressure Welding (CPW) working principles and it has been carried out by a tailored setup of a high-resolution Focused Ion Beam – Scanning Electron Microscope (FIB-SEM).This work is primarily aimed at showing how FIB functionalities can be expanded and discussing the challenges that may be encountered by doing that. Therefore, a preliminary FIB-assisted methodology for cold bonding of AA1070 and AA6082 aluminium alloys at the microscale is presented. In situ cross-sectioning of the weld and proper scanning-electron imaging have revealed that, under certain pressure conditions, oxide-free aluminium interfaces are able to be joined at room temperature even at the microscale. Experimental technique improvement and testing of the obtained joints are the next steps needed in this research.

FEM simulation of fabrication of Al-steel layered composites with mechanical bonding through the interfacial concavo-convex lock effect

Development of advanced cold pressure welding technique is needed for fabrication of Al-Steel layered composites with improved bonding strength between the stacked layers. Obtaining of elevated strain at the interface of the composite in combination with mechanical bonding through the interfacial concavo-convex lock effect can provide superior bonding strength. This paper presents the results of the finite element simulation of a special cold roll bonding technique. This technique consisted of two rolling passes. During the first pass the cold roll bonding was performed by work rolls with microscopic sine profile of the surface. During the second pass the cold roll bonding was performed by smooth work rolls. As a result, the Al-Steel layered composite with wavy interface was developed. Simulations of the process of fabrication of composites, consisted of aluminium alloy 6082 and DC04 steel were carried out using the commercial FEM code QForm. Effect of the sine profile of work roll on the composite layers behavior was analyzed. It was numerically shown that special cold roll bonding technique is able to introduce an additional mechanical clinching and elevated plastic strain to the interface of the composite in comparison with conventional roll bonding process. The FEM results of investigation of interface bond behavior can be useful for the development of the improved cold pressure welding technique for manufacturing of Al/Steel composites with high bond strength.

Ab initio prediction of strong interfacial bonding in the Fe|Al bimetallic composite system

Atomic-scale calculations were used to investigate the formation of interfacial bonds in the Fe|Al bimetallic composite system. The results indicate that chemical bonds at pristine Fe|Al interface display more covalent character than constituent materials resulting in enhanced interface strength. Such an interface exhibits large cohesive energy exceeding significantly the value of bulk aluminum. The effect of two technologically relevant solute elements, i.e. carbon and magnesium on the interface strength was analyzed. Our robust yet simple computational model can be used to predict the most efficient combination of steels and aluminum alloys for cold pressure welding, leading to strong interfacial bonding.

Joining of blanks by cold pressure welding: Incremental rolling and strategies for surface activation and heat treatment

AbstractThe cold pressure welding of metals is a joining by forming technique capable of joining both similar and dissimilar metals in their solid state. In this article collective research on the cold pressure welding of metals with the aim of increasing both the overall weld strength and the weld‐ability is presented. The application of innovative strategies based on electrochemical methods for an optimized conditioning of metal surfaces is investigated. The results account for a noticeable increase in the weld strength of steel‐aluminum joints after a surface activation consisting of either an electrochemical roughening or electrodeposition of a bifunctional organosilane thin film. In addition to the surface activation process regimes for the pre‐ and post‐welding heat treatment is investigated. Both weld strength and weld ability are improved due to heat treatments of steel sheets with various coatings and uncoated aluminium. The cold pressure welding is hereby done by incremental rolling, a new design process that allows for the manufacture of linear and curved joints between sheet metal blanks.

Atomic level bonding mechanism in steel/aluminum joints produced by cold pressure welding

Cold pressure welding of aluminum alloys and steels offers an attractive, cost-effective opportunity of joining the two most important structural materials. Aim of this work is to investigate the bonding mechanism between aluminum alloy EN AW6082 and carbon steel C15, joint by cold extrusion welding after targeted heat treatment. Mechanical testing under tensile loads revealed site specific interface strengths between 30 and 60% of the constituent materials. However, investigation of fracture surfaces indicates that interface strengths can exceed the AW6082 strength in areas where the bonding process substantially enlarged the Fe-Al interface region, due to the welding geometry. Near atomic scale investigations of the interface using aberration-corrected scanning transmission electron microscopy combined with electron energy loss spectroscopy disclose two different regions along the cold pressure welded interface. The majority of the interfacial area is oxygen free with Fe-based and Al-based crystals joining. No intermetallic phase was identified. Adhesion is attributed to a more covalent bond characteristic at the Fe-Al interface evidenced in the Al-L2,3 edge. A small fraction of the steel/aluminum interface was covered with oxidic regions of about 10 nm thickness. This oxide is predominantly an amorphous aluminum oxide, with only few Fe-O bonds. The observed metallurgical bond formation is explained by an extended Bay model through (i) cracking of the brittle, nanoscopic native oxide layer on the materials during forming, (ii) formation of metallic contact between Al and Fe, under reduction of iron oxides by aluminum, and (iii) formation of covalent-like Al-Fe bonds across the interface.

The Interfacial Characterization and Performance of Cu/Al-Conductive Heads Processed by Explosion Welding, Cold Pressure Welding, and Solid-Liquid Casting

The Cu/Al composites conductive head is widely used in hydrometallurgy as the core component of cathode plate. Its conductive properties directly affect the power consumption, and the bonding strength and corrosion resistance determine the conductive head service life. The Cu/Al conductive head prepared by explosion welding, cold pressure welding, and solid-liquid casting methods were investigated in this paper. The interface microstructure and compositions were examined by scanning electron microscope and X-ray energy dispersive spectrometry. The bonding strength, interface conductivity, and the corrosion resistance of three types of joints were characterized. The Cu/Al bonding interface produced by explosive welding presented a wavy-like morphology with typical defects and many of brittle compounds. A micro-interlocking effect was caused by the sawtooth structures on the cold pressure welding interface, and there was no typical metallurgical reaction on the interface. The Cu/Al bonding interface prepared by solid-liquid casting consisted mainly of an Al-Cu eutectic microstructure (Al2Cu+Al) and partial white slag inclusion. The thickness of the interface transition layer was about 200–250 µm, with defects such as holes, cracks, and unwelded areas. The conductivity, interfacial bonding strength, and corrosion resistance of the conductive head prepared by explosive welding were superior to the other two.

Progress in Solid State Joining of Metals and Alloys

In this overview, a new solid-state joining method for metals and alloys is presented, where the best features of gas metal arc welding, friction stir welding and cold pressure welding are combined. The invention, which is known as the Hybrid Metal Extrusion & Bonding (HYB) process, utilizes continuous extrusion as a technique to squeeze the aluminum filler material into the groove between the two plates to be joined under high pressure to achieve metallic bonding. Originally, the idea was to use the HYB process for simple butt joining of aluminum plates and profiles. However, over the years it has evolved into a multi-functional joining process handling a wide range of different joint configurations (butt, fillet and slot welds) and base metal combinations (Al, Fe, Ti and Cu). At present, up to four different metals can be joined together in one pass using the HYB PinPoint extruder and AA6082 as filler wire.

Brushing for High Performance Cold Pressure Welded Bonds

Joining of steel and aluminum is a commonly applied manufacturing process to obtain lightweight components. Cold pressure welding by means of direct extrusion allows gaining high bond strengths between these two materials. The contacting surfaces are usually prepared by using scratch brushing to enhance the bond strength. Most studies have shown the benefit of the brushing whereas the resulting bond strength scatters. Variations in the parameters of the brush treatment are presumed to be a major cause for the variations in strength. Within the presented work, scratch brushing parameters are adjusted to further improve the resulting bond strength. Cracking of the surfaces at low strains is a beneficial effect to enhance the bond strength. Therefore, the crack formation of the surfaces brushed under different conditions is analyzed in tensile tests. Roughness, residual stresses and microstructural changes of the aluminum surfaces resulting from brushing processes are evaluated to enhance the understanding of the cracking mechanism. Concluding, the brushing parameters are adjusted to improve bond strengths up to the material strength of the used aluminum.

Fabrication and characterization of a bimetallic Al/Cu tube using the tube sinking process

In this work, two types of bimetallic tubes were fabricated from aluminum alloy and pure copper using the tube sinking process. The joint quality of the bimetallic tubes was evaluated using the so-called push experiment to determine the bonding shear strength. In addition, different microstructural studies were conducted in order to study the interface character of the layers. It was found that the bonding shear strength of the aluminum-clad copper was slightly higher than that of the copper-clad aluminum. Also, the former exhibited lower bonding shear strength variation than the latter. The discontinuous intermetallic components were detected at the latter interface for both types of bimetallic tubes. Also, it was interesting to note that a relatively thick aluminum oxide layer was found to be formed partially at the copper-clad aluminum tube layer interface. Signs of the cold pressure welding mechanism based on the film theory were indicated in aluminum-clad copper, whereas localized oxidation and wear phenomenon between the aluminum and copper layers deteriorated the bonding strength in copper-clad aluminum.

Investigation of Cold Pressure Welding: Cohesion Coefficient of Copper

Joining materials by forming is an interesting approach to the manufacture of hybrid (multi material) parts. By establishing a cold pressure weld between metallic surfaces, high quality joints with superior properties can be achieved. Reliable cold welding conditions are difficult to set up, however, since the weld initiation requires extraordinary clean, virtually sheer surfaces. Until today such conditions could only be achieved under a high vacuum conditions. Various studies on cold pressure welding reported that under vacuum welds can be established at significantly lower deformation than in a normal atmosphere. Since adverse deformation is currently needed in industrial cold pressure welding processes like the cold roll cladding of metal bands, a new process with in-line electrochemical surface treatment, is investigated. The ECUF process is intended to supply clean and thereby highly activated surfaces to the cold pressure welding process.This paper presents first results on the weld-ability of copper specimens with regard to the influence of the welding environment: air, argon and KCl solution. Butt welds were made by pressure welding of previously fractured specimens.

Shear Resistance of Joints Spot Cold Pressure Welding

The statement from the specialty literature that with the increasing diameter of spot welded by cold pressure decreases the amount of resistance to shear force is due to reporting of the breaking by shear at the circular section of the point. Our experimental research shows that a welded cold joint in spots, correctly done, will be torn off near the weld spot by drawing the point from one of the tins. By reporting the force to the real section of breaking it resulted a constant shear resistance, no matter which the size of the welded point was. Therefore, the approximate theoretical calculation of the breaking force of a cold welded point, correctly executed, can be achieved by knowing the mechanical properties of the metal base and taking into account the real section of the breaking point given by points periphery and the thickness of the panel after deformation. The calculation is encompassing, because due to cold hardening, the real mechanical characteristics are higher.

The Microhardness and Microstructural Changes of Mechanically Affected Zone by Cold Pressure Welding in Aluminum Rod

The Microhardness and Microstructural Changes of Mechanically Affected Zone by Cold Pressure Welding in Aluminum Rod

Joining with Electrochemical Support: Cold Pressure Welding of Copper – Weld Formation and Characterization

Cold pressure welding is a versatile process that can be used to weld most metals. It is, however, difficult to achieve a weld at room temperature through the application of pressure. As in every welding process, several different parameters have to be considered: the metals to be welded and their properties in terms of surface condition, cleanliness, strength of the metal, and so on. The surface condition and surface preparation methods are the most important parameters, since the cold weld is based solely on the contact between the two metal surfaces that are involved. Joining with electrochemical support (ECUF) is a new approach that overcomes most of the current process barriers and limitations through optimized electrochemical surface treatment and an improved process technology based on a pilger roll. This paper provides an overview of the ECUF process and current research results on the pressure welding of pure copper (CW004A). The formation of the weld has been investigated and the welding interface characterized in respect of its microstructure.

Joining with electrochemical support (ECUF): Cold pressure welding of copper

Joining metals using electrochemical support (ECUF) is a new process for cold pressure welding sheets and parts. This new process is based on an electrochemical in-line surface treatment followed by incremental pilger rolling. The ECUF process intends to cold pressure weld materials under optimized conditions. Oxide layers on metal surfaces are known to inhibit the formation of cold pressure welds. The in-line electrochemical treatment will be used to remove these surface oxides for specific engineering metals and alloys. Hence, an improved pressure weld formation at lower forces and smaller reduction ratios is expected for the electrochemically treated surfaces. Using a more flexible pressure welding process, the number of applications could be greatly improved. First tests with copper were performed to analyse the efficiency of the proposed electrochemical surface treatments. Two electrochemical treatments, the cathodic oxide-reduction and cyclovoltammetric oxide-reduction, were compared with conventional treatments (degreasing and scratch brushing) regarding their influence on the cold pressure welding process of copper. The weld strength of lap welds has been investigated as well as the necessary reduction threshold to form a weld. It was found that the electrochemical oxide reduction resulted in higher weld strength. The results of scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDX) indicate that surface oxides were successfully removed by the electrochemical surface treatments.

Study on the Welding Process and Application of Al/Cu Materials

The characteristics of welding process for aluminum-copper dissimilar material such as friction welding, explosive welding, brazing and cold pressure welding are discussed firstly in this paper. Then the welding technology and its application for aluminum-copper dissimilar material are summarized. Finally, the outlook is analyzed for the welding process of aluminum-copper dissimilar material.

Research on Cold-Rolled Bimetal of High-Tin Aluminum Alloy and Steel

Bimetal of high-tin aluminum alloy and steel was fabricated by cold-rolling process; microstructure, bonding strength and bonding mechanism for bonding interface of the bimetal were investigated under cold-rolling and recrystallization annealing state, respectively. Experimental results indicate that tin phase of bimetal in cold-rolling state shows a belt type distribution, however, it, in recrystallization annealing state, is uniformly distributed just like some “isolated islands”. A well bonding interface, between layers of high–tin aluminum alloy and pure aluminum, can be obtained, and it is difficult to distinguish one layer from the other; but the interface, between layers of low-carbon steel back and pure aluminum, is clear and uneven. And meanwhile, bonding mechanism of bimetal interface, in cold-rolling state, is cold pressure welding and mechanical occluding, But it, in recrystallization annealing state, is cold pressure welding, mechanical occluding, and metallurgic bonding. After recrystallization annealing, at 350°C for 2h,the bonding strength of bimetal approaches to 92.4MPa, which is about 26% higher than that of cold-rolling state.