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Wire and arc additive manufacturing (WAAM) produces thin-walled parts superior to other additive manufacturing methods, because of its high efficiency, good compactability, and low cost. However, the WAAM accuracy is limited by its large heat input. Here, 0.8 mm 316L stainless steel welding wire is deposited via speed cold welding to form 30-layered thin-walled samples, with 2 mm thickness, and up to 65 mm height. The effects of three process parameters (the bottom current mode, scanning speed, and cooling time) on the deposition process stability, macro morphology, structure, and mechanical properties are studied. In the experiment, the probability density curves of electrical parameters of sample #GRBC-30 cm/min-10 s on the third and tenth layers were narrower than other samples, which implied a more stable process. The three process parameters mainly affect the deposition morphology and have a minor performance effect. The hardness and tensile properties mainly depend on the deposition direction. Gradual, layer-by-layer current reduction improves the bottom molding and performance, and the deposition efficiency, and stabilizes the process. Scanning speed enhancement or cooling time reduction destabilizes the end formation, reduces the effective deposition rate, and slightly degrades the performance. All deposited samples are distinctly anisotropic, but satisfy the industrial standard. Overall, deposition in speed cold welding mode, with 10 s cooling time, 30 cm/min scanning speed, and gradually reduced bottom current exhibits good stability, and the molding efficiency and mechanical properties are optimal.

High-density polyethylene (HDPE) pipes are widely used in urban natural gas pipeline systems due to their excellent mechanical and chemical properties. However, welding joints are critical weak points in these pipelines, and defects, such as cold welding—caused by reduced temperature or/and insufficient pressure—pose significant safety risks. Traditional non-destructive testing (NDT) methods face challenges in detecting cold welding defects due to the polymer’s complex structure and characteristics. This study presents a microwave-based NDT system for detecting cold welding defects in thermal fusion welds of HDPE pipes. The system uses a focusing antenna with a resonant cavity, connected to a vector network analyzer (VNA), to measure changes in microwave parameters caused by cold welding defects in thermal fusion welds. Experiments conducted on HDPE pipes welded at different temperatures demonstrated the system’s effectiveness in identifying areas with a lack of fusion. Mechanical and microstructural analyses, including tensile tests and scanning electron microscopy (SEM), confirmed that cold welding defects lead to reduced mechanical properties and lower material density. The proposed microwave NDT method offers a sensitive, efficient approach for detecting cold welds in HDPE pipelines, enhancing pipeline integrity and safety.

Joining high-strength, cold-drawn Cu-Mg alloy conductors is a critical challenge for ensuring the reliability of high-speed railway catenary systems. This study investigates the evolution of mechanical properties and microstructure in Cu-0.43 wt% Mg alloy wires joined by multi-pass butt-upset cold welding without special surface preparation. High-integrity joints were achieved, exhibiting a peak tensile strength of 624 MPa (~96% of the base material’s strength). After four upsetting processes, the tensile strength of the weld can reach 90% of the original strength, and the gains from subsequent upsetting processes are negligible. Microstructural analysis revealed the joining process is governed by localized severe shear deformation, which forges a distinct gradient microstructure. This includes a transition zone of fine, equiaxed-like grains formed by dynamic recrystallization/recovery, and a central zone featuring a nano-laminar structure, high dislocation density, and deformation twins. A multi-stage dynamic bonding mechanism is proposed. It progresses from initial contact via thin film theory to bond consolidation through a “mechanical self-cleaning” process, where extensive radial plastic flow effectively expels surface contaminants. This work clarifies the fundamental bonding principles for pre-strained, high-strength alloys under multi-pass cold welding, providing a scientific basis to optimize this heat-free joining technology for industrial applications.

Interest in composite thick coatings with an intermetallic matrix stimulates the development of new deposition techniques like the co-milling of pre-alloyed NiAl powder with platelet-shaped substrates. Obtained coatings were up to several micrometers thick as cold-welding of intermetallic particles was effective only at the start of this process, while later, chipping prevailed over added material. The present experiment covered the co-milling in the planetary ball mill of Ni and Al elemental powders (1:1 molar ratio) with AISI 304 steel platelets for 32 h at 300 rpm. Next, this process was repeated with an admixture of 15 wt.% of CrB2 powder. In both cases, their milling succeeded in producing up to a 200 μm coating after 4 h. The use of light, scanning and transmission electron microscopy (LM/SEM/TEM) helped to establish that the coatings had gradient microstructures with more refined crystallites of NiAl, Al3Ni2 and CrB2 closer to the surface. With the addition of a ceramic phase, the coatings presented higher hardness and lower friction during dry wear tests both at RT and at 500 °C.

The repair of magnesium alloy castings is of great importance in terms of engineering and economic benefits. This study employs the cold welding technique to repair the ZM5 alloy, and the effects of current and preheating treatment on the microstructure and mechanical properties were investigated. The increase in current exacerbates the cracks, while the preheating treatment can effectively control them. However, the liquefaction cracks occur near the heat-affected zone after preheating at 300 °C. The microstructure of the repaired zone shows finer dendritic structure consisting of α-Mg and β-Mg 17 Al 12 phases. After preheating treatment, the repaired zone shows the microhardness of 72 HV 0.1 , higher than the non-preheating samples (65 HV 0.1 ), and the substrate (63 HV 0.1 ). The average tensile strength of the preheated samples is 110 MPa higher than the non-preheating samples, and reaching 88.7% of the substrate. The fracture mechanism for both the substrate and repaired samples was brittle failure.

The lignite-derived carbon from self-protection pyrolysis was employed to balance the fracturing and cold-welding of magnesium during ball milling. Particle size analysis indicates that the introduction of lignite-derived carbon can effectively reduce the particle size of Mg while the introduction of graphite does no help. Besides, the effect of lignite-derived carbon on crystallite size reduction of Mg is also better than graphite. A moderate cold-welding phenomenon was observed after ball-milling Mg with the lignite-derived carbon, suggesting less Mg is wasted on the milling vials and balls. Molecular dynamic simulations reveal that the balanced fracturing and cold-welding of magnesium during ball milling is mainly attributed to the special structure of the lignite-derived carbon: graphitized short-range ordered stacking function as dry lubricant and irregular shape/sharp edge function as milling aid. The preliminary findings in current study are expected to offer implications for designing efficient Mg-based hydrogen storage materials.

The ongoing requirement for the lightweight design of automotive resulted in the wide application of ultra-high-strength steel (UHSS), such as the 1500 MPa made by hot stamping (TS1500) and 1180 MPa manufactured by cold rolling (SPC1180). In the present research, cold metal transfer (CMT) lap welding was employed to join TS1500 and SPC1180 dissimilar metals. A thermal–mechanical coupled model was developed, and the associated behaviors that occurred in CMT process were reproduced efficiently by the in-house FE code JWRIAN-Hybrid. The high-temperature material properties of TS1500 were clarified. The predicted temperature field, residual stress distribution and welding deformation were verified experimentally. The analyzed and measured results showed good agreement with each other. The critical phase transformation temperatures of TS1500, including Ac1, Ac3 and Ms, were gauged as 740, 810 and 390 °C, respectively. On the UHSS welded joint, the largest tensile stress was located on the outside of heat affected zone on TS1500 sheet, which can reach about 650 MPa, while the peak on SPC1180 sheet was only 120 MPa. It presented the significant influence of both material strength and constraint conditions. There was a compressive stress about − 130 MPa at the weld zone due to the martensite transformation. The out-of-plane deformation modes were the convex shape in both the longitudinal and transverse directions. The maximum out-of-plane displacement-Z in the center of welded joint was about 1.38 mm. For the UHSS CMT welded lap joint, the strength grade of steel couple had a significant effect on welding deformation rather than the residual stress.

- Galati ABSTRACT 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 fiat surfaces, are pressed on or between the harder material components (capper, 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

Cold metal transfer (CMT) welding and metal inert gas (MIG) arc welding of a novel Al-Zn-Mg-Cu-Er-Zr alloy are systematically analyzed. The effect of the two welding processes on the morphology, microstructure, and mechanical properties of welded joints was investigated. The evolution of the microstructures and grain structures in the welded joints is studied using an optical microscope (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results show that both welding methods obtain well-formed full-penetration welds, and the width of the heat-affected zone (HAZ) of CMT welding is smaller than that of MIG welding. The two welded joints reveal coarse cellular grain structures with precipitates of η (MgZn2), Al3Er, and S (Al6CuMg4) secondary phases. The average grain size of the weld metal in the cold metal transfer welding (12.96 μm) joint is much finer than that of the metal inert gas arc welding joint (22.63 μm), with a higher proportion of high-angle grain boundaries (HAGBs). The hardness of cold metal transfer welding and metal inert gas arc welding weld zones is 103.9 HV and 92.6 HV, respectively, and the tensile strength of the joint is 334.0 MPa and 270.3 MPa, respectively.

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.