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This research was performed with the objective of clarifying the effect of welding speed on melt flows during melt-run welding of SUS304 stainless steel plates with a 6-kW power laser beam on the basis of three-dimensional X-ray transmission in situ observation. As welding speed increased from 25 to 250 mm/s, three kinds of welds characterized by porosity formation and no defects or underfilling due to spatters were produced. The average and the maximum values of measured melt flow velocity were 3 and 10 times higher than the welding speed, respectively. Two kinds of circulation flows at the inlet or the tip of a keyhole were confirmed to control heat transfer in a molten pool. It was found that the circulation flows were so sensitive to the welding speed that bubbles resulting in porosity or spatters were often formed. According to X-ray observation of the formation of spatters with tungsten carbide (WC) tracers, as the melt flow rose along the keyhole wall, the velocity was accelerated from 0.24...

New welding technologies have been implemented in the polymer processing industry in the past few years. Additionally, the most used polymer in complex products is polypropylene. This material can also be mixed with several additives, namely glass fiber, carbon nanotubes, etc. This compatibility with different additives allows products with characteristics that range from impact absorption to electrical conductivity. When it is necessary to join components in PP, they can be welded by hot plate, ultrasonic or laser welding. The present research aims at studying the influence of variables capable of influencing the final quality of the seam, namely those related to injection molding, such as mold temperature and cooling time, laser welding variables and materials, and how laser welding interacts with PP. The results showed that the most influential variables were mold temperature, laser velocity and laser diameter. The seams were analyzed using optical microscopy. They showed perfect contact between the components, despite the high standard variation present in the mechanical tests., info:eu-repo/semantics/publishedVersion

Aluminum and titanium alloys are among the most important and the most frequently used construction materials due to their physical and mechanical properties. Especially in the automotive and aerospace industry these materials allow to reduce the weight of structure which leads to reducing fuel consumption and environment pollution. These materials are often used together which leads to problems with junction between these materials. In addition to the mechanical joints, there is an effort to produce quality welded joints. Series of works focused to welding of Al/Ti joints by conventional and nonconventional welding methods were published [1, 4, 5, 6, 7]. By reduction of dimensions of molten material is possible to reduce the amount of emerging intermetallic phases and welding defects. Electron beam welding appears as suitable method for welding Al/Ti joints because it allows production of very narrow welds. The benefit is also necessity to perform electron beam welding in vacuum which is required for decrease energy losses of incident beam and simultaneously prevents reaction of molten metal with ambient atmosphere. This paper is focused to determine of appropriate parameters for electron beam welding of heterogeneous welds of titanium alloy Ti-6Al-4V and aluminum alloy 6061. Metallographic evaluation, analysis of chemical and phase composition were performed on the test welds for purpose to describing present phases. On the selected welds was evaluated the influence of intermetallic phases on the mechanical properties. The obtained results will be used for further experiments focused to optimize the process of electron beam welding of Al/Ti alloys.

The scope of this paper is to examine the improvement from laser welding by an innovative beam wobbling head towards the welding of tailored blanks parts, widely used in automotive to develop different stiffness aluminum components. For this purpose, butt joints and overlapping joints were produced from sheets made out of two industrial grades, i.e. AA-6082 T6 and AA-5754 H111 of different thickness. The technique was evaluated both with and without the use of a filler wire (AA-5556). The qualification of the welding process encompassed Non Destructive Testing (NDT) and mechanical testing. The results indicate that butt joints tend to fail within the base material (BM) of sheet with smaller thickness. On the contrary, the shear tests on lap joints highlighted a rupture mode occurring in the heat affected zone (HAZ) of the thin sheet. Remarkably, the wobbling process generally allows avoiding porosity when combined with an optimized set of welding parameters. Yet, a residual porosity was always detected in lap joints, varying with the size of the fused zone. © 2017 Trans Tech Publications, Switzerland.

Fe-based alloy modified layers were prepared on 304 stainless steels by high-energy pulse laser-like cold welding cladding technique. The microstructure, composition and phase constituents of the cladding layers were analyzed using SEM, EDS and XRD, respectively. The microhardness, friction-wear and cavitation erosion resistance were also investigated using microhardness tester, pin-on-disk wear-testing machine and ultrasonic vibrator. Experimental results showed that Fe-based alloy modified layer was mainly composed of α-Fe matrix phase and skeleton-like Cr23C6, Cr7C3 carbide reinforced phase, which was dispersively distributed into α-Fe matrix. The microhardness and friction coefficients of Fe-based alloy modified layer were 600HV and 0.4, respectively, indicating an improved wear resistance. The weight loss rate and average erosion depth of the modified layer was 1/5 and 1/10 that of 304 stainless steel in 3.5% NaCl solution after 5-h cavitation erosion test, respectively. The erosion crater depth of the modified layer was uniform, indicating that the cavitation erosion resistance of the modified layer was much better than that of the 304 stainless steel.

The microstructures and mechanical properties of laser welding joints with/without Al5Si foil interlay in an overlap steel-on-aluminum configuration have been investigated. The joints with Al5Si foil interlayer are superior to that without the interlayer at the same welding condition. The Al-Fe intermetallic compound (IMC) layers at the fusion interface are FeAl layer adjacent to the steel matrix, FeAl 3 layer close to the aluminum, and the intermediate Fe 2 Al 5 between the FeAl and FeAl 3 . Si addition can restrict growth of the IMC layer, and change the proportion of the Al-Fe IMCs. The overall thickness of the IMCs can be reduced to 2.0 μm under the welding conditions: laser power: 2.8 kW, defocus distance: 10 mm, and welding speed: 1.5 m/min. The tensile strength of the joints can be improved significantly by the Al5Si foil interlayer. The fracture of the joint with Al5Si interface occurs in the heat-affected zone of the carbon steel at the maximum tensile strength.

A novel laser shock synchronous welding and forming method is introduced, which utilizes laser-induced shock waves to accelerate the flyer plate towards the base plate to achieve the joining of dissimilar metals and forming in a specific shape of mold. The samples were obtained with different laser energies and standoff distances. The surface morphology and roughness of the samples were greatly affected by the laser energy and standoff distances. Fittability was investigated to examine the forming accuracy. The results showed that the samples replicate the mold features well. Straight and wavy interfaces with un-bonded regions in the center were observed through metallographic analysis. Moreover, Energy Disperse Spectroscopy analysis was conducted on the welding interface, and the results indicated that a short-distance elemental diffusion emerged in the welding interface. The nanoindentation hardness of the welding regions was measured to evaluate the welding interface. In addition, the Smoothed Particle Hydrodynamics method was employed to simulate the welding and forming process. It was shown that different standoff distances significantly affected the size of the welding regions and interface waveform characteristics. The numerical analysis results indicated that the opposite shear stress direction and effective plastic strain above a certain threshold are essential to successfully obtain welding and forming workpiece.

The paper presents manual narrow groove welding of marine high-strength titanium alloys of large thickness using special flat devices (nozzle burners), double-sided electron beam welding, and welding technology producing combined high-strength titanium alloys of large thickness (over 200 mm). Electron beam welding technology with filler wire in the vertical and horizontal position of the seam has been developed to fill the gap. The technology for repair of welded joints of titanium alloys of large thicknesses by electron-beam melting has also been developed. The mentioned technologies have been implemented at shipbuilding sites and have passed interdepartmental tests.

In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed microstructural analysis.

Laser beam welding of copper, especially for comparatively high plate thicknesses and low welding speeds, is very challenging critical welding defects are very likely to occur. By reducing the ambient pressure, it becomes possible to increase the process capability in a huge amount. The so called laser beam welding in vacuum (LaVa) process variant allows high quality welding of copper at welding speeds below 2 m/min and thereby a high penetration depth with a comparatively low laser power.

In this study, a new welding technology of dissimilar materials, Cr-based P92 steels and Ni-based Alloy 617 is introduced and demonstrated to investigate its reliability. Firstly, multi-pass dissimilar metal welding between P92 steel and Alloy 617 was performed using DCEN TIG welding technology, buttering welding technique and a narrow gap groove. After welding, in order to understand characteristics of the dissimilar metal welds, metallurgical micro-structures analysis by optical observation and static tensile strength assessment of the dissimilar welded joints were conducted at 700°C.

The characteristics of microstructure, mechanical property and corrosion behavior of Cr26Mo3.5 super stainless steel joints by pulse tungsten inert gas(P-TIG)welding and laser welding were investigated. The results indicate that the widths of the center equiaxed grain zone(EGZ)and the columnar grain zone(CGZ)increase with the increase of heat input in both welding processes. The precipitates of Nb and Ti carbides and nitrides are formed in the weld metal(WM)and the heat affected zone(HAZ). The joints by laser welding show better tensile and corrosion resistance properties than those by P-TIG welding due to the heat concentration and lower heat input. The tensile strength and elongation increase with the decrease of heat input, and the fracture mode of the joints turns into ductile-brittle mixed fracture from ductile fracture when the welding method turns into P-TIG welding from laser welding. Moreover, the corrosion resistance of all joints declines slightly with the increase of heat input. Hence, laser welding is more suitable for welding Cr26Mo3.5 super stainless steel in engineering applications.

Automated laser welding with filler wires for bridging gaps and for connecting complex devices has been established for different metal materials. In spite of that, it is still a challenge to transfer this welding process to the brittle material glass. Therefore, glass welding is often realized through a manual process by heating the glass with a gas flame. In addition, welding of non-rotational components requires filler material for gap bridging between the joining partners, which is applied manually today. This work presents an experimental and numerical study on laser welding of fused silica using glass fiber as a filler material to bridge gaps. The goal was to achieve a defined weld penetration depth and heat affected zone which is important for the production of optical elements. Therefore, a CO2 laser heats up the glass components as well as the glass fiber within a temperature controlled welding process. The numerical investigations were used to identify the general process window for welding fused silica. Within the experimental study, the process parameters, such as the defined welding temperature, laser focal spot size, and feed rate were varied to investigate their impact on the welding outcome. In addition, the impact of the filler wire coating on the material composition of the welded component in the joint zone was investigated. Compared to the manual process, laser welding with glass fiber as a filling material leads to a highly reproducible process enabling a high automation level.

In this article, molecular simulations were adopted to explore the cold welding processes of copper nanowires with both single-crystalline and fivefold twinned structures. It was verified that the twinned nanowires exhibited enhanced strength but lowered elastic limit and ductility. Both nanowires could be successfully welded through rather small loadings, although their stress–strain responses toward compression were different. Meanwhile, more stress was accumulated in the twinned nanowire due to repulsive force of the twin boundaries against the nucleation and motions of dislocations. Moreover, by characterizing the structure evolutions in the welding process, it can be ascertained that perfect atomic order was finally built at the weld region in both nanowires. This comparison study will be of great importance to future mechanical processing of metallic nanowires.

Background Modern hip implants typically feature modular heads, which allow for easy exchange and removal from the femoral stem at the time of revision. However, owing to fretting, corrosion, or cold welding, the modular head may be difficult or impossible to separate from the underlying trunnion, especially if the implant has titanium interfaces between the head and the stem. We have repeatedly encountered difficulty removing the titanium sleeve adapter in the M2a-MagnumTM implant. Although the manufacturer warns about this complication and cases with these difficulties have been reported to the United States FDA, we believed this topic is important to study, because the frequency of difficulties in head removal is unknown and the complications related to this event have not been characterized.

Aiming to reduce the weight of components, thus allowing a profit in terms of energy saving, automotive industry as well as aircraft industry extensively uses aluminum alloys. The most widely used joining technology in aircraft industry is riveting, while welding seems to be used in the car industry in the case of aluminum alloys. However, welding technology is characterized by many defects, such as gas porosity; oxide inclusions; solidification cracking (hot tearing); and reduced strength in both the weld and the heat affected zones which could limit its development. Many techniques are used for aluminum alloys welding, among them is electron beam welding (EBW), which has unique advantages over other traditional fusion welding methods due to high-energy density, deep penetration, large depth-to-width ratio, and small heat affected zone. The welding parameters that yield to optimal weld joint have been previously obtained. These optimal parameters were validated by welding a specimen using these parameters. To evaluate this optimal weld joint, complete, microstructural observations and characterization have been carried out using scanning electron microscopy, optical microscopy, and energy dispersive X-ray analysis. This evaluation leads to description and quantification of the solidification process within this weld joint.

Experiments were carried out to investigate the effect of electron beam welding speed in the range 20–120 m/h on the properties of welded joints in 20-mm-thick plates of D16 alloy. The distribution of magnesium in the cross section of welded joints in dependence on the welding speed was determined. The structure of the welded joints was investigated by optical and electron microscopy. The hardness in different zones of the welded joints after welding and different types of heat treatment was measured. The relationship between the chemical composition, structure and mechanical properties of the welded joints produced at different welding speeds was determined.

The results of investigation into laser, microplasma and hybrid laser–microplasma methods of welding aluminium alloys are presented. The optimum energy values for welding with the radiation of CO2 lasers are determined. Shortcomings of microplasma welding are outlined and the main advantages of hybrid laser–microplasma welding are discussed. Detailed study of the macro- and microstructures of the welded joints and the heat affected zone shows that in all cases the structure is sufficiently equiaxed, dense, without visible defects and is dendritic.

Experimental results confirm that the application of adaptive pulsed-arc welding with regulated heat input to welded material refines the structure of the metal, lowers the degree of softening of the fusion zone of the welded joint and greatly increases the mechanical properties of the welded joints, including structures working at low temperatures.

Electron beam welding, despite a long history and widespread arc and laser technology, is still widely used in industry. The main applications for this high efficiency welding process are: automotive, electronics, electrical engineering, aerospace and mechanical engineering industry. The technology ensures high-quality welded joints in structural metals in a wide range of thickness from 0.025 mm to 300 mm. It is also used for the production of films and coatings by deposition and surface modification. In the paper approximated examples of the use of the electron beam are given by the welding, rapid prototyping, texturing surface, cladding with wire and powder as well as alloying. It also provides information about the possible techniques that can be used during these processes and the trends in electron beam welding.

The miniaturization of electronics devices into nanometer scale is indispensable for next-generation semiconductor technology. Ag nanowires (Ag NWs) are considered to be the promising candidates for future electronic circuit owing to the excellent electrical and thermal properties. The nanojoining of axially positioned Ag NWs was performed by molecular dynamics simulation. Through the detailed atomic evolution during the nanojoining, the results indicate that the temperature and the distance between Ag NWs in axial direction have a great impact on nanojoining effect. When the nanojoining temperature is relatively high, the atoms are disordered and the atomic queues become to distort with strong thermodynamic properties and weak effect of metal bonds. At the relatively low temperature, the Ag NWs can be well connected with good junction quality and their own morphology, which is similar to the cold welding without fusion, while the distance between Ag NWs should be controlled for interaction and diffusion of interfacial atoms at nanowires head. When the Ag NWs are placed on Si and SiO2 substrate, because the atomic species and lattice structure of substrate material can differently affect the motions of Ag atoms through the interactive force between the atoms, the nanojoining quality of Ag NWs on Si substrate is better than that on the SiO2 substrate. So, for getting effective and reliable nanojoining without nanosolders and other materials, the temperature, distance and substrate surface should be reasonably controlled and selected, providing helpful theoretical guidance for experiment and application of nanojoining.

The Mg/MoS2 composites were prepared by ball milling under argon atmosphere, and the effect of MoS2 on the crystal structure and hydrogen storage properties of Mg was investigated. It is found that 10 wt% of MoS2 is sufficient to prevent particle aggregation and cold welding during the milling process. The crystallite size of Mg will remain constant at slightly less than 38.8 nm with the milling process due to the size confinement effect of MoS2. The dehydrogenation temperature of MgH2 is reduced to 390.4-429.4 °C due to the crystallite size reduction. Through fitting by Johnson-Mehl-Avrami model, it is found that Mg crystal grows by three dimension controlled by interface transformation during the process of MgH2 decomposition. MoS2 has a weak catalyst effect on the decomposition of MgH2 and activation energy of 148.9 kJ/mol is needed for the dehydrogenation process calculated by the Arrhenius equation.

Three methods of completing closed (circular and annular) welded joints in welding the 1570C alloy of an Al–Mg–Sc system with a thickness of 11 and 35 mm (using the output wedge, a tool with a moving tip, friction welding) are discussed. The range of double stirring (the beginning to end of the welded joint) has a heterogeneous microstructure and mechanical properties. The distributions of the hardness of the weld metal after the first and second stirring cycle are similar if the working length of the tip is the same, and greatly differ if the working length of the tool used for the second pass is variable (as in welding with a moving tip). The ratio of the tensile strength of the welded joint and the parent metal is not lower than 0.9, which is higher than in arc welding. It is shown that the three methods of completing the closed joints can be used in practice.

Thin ultra-high strength steel shaped as 700 mm long U-beams have been laser welded in overlap configuration to study the influence of welding sequence on distortions. Three different welding direc ...

Electron beam welding facilitates a very high energy density, which is a significant advantage when welding materials with a high thermal conductivity like copper. Nevertheless, in EBW of copper, u...

Nano-size aluminum nitride (AlN) powders have been successfully synthesized with a high efficiency method through annealing from milling assisted by discharge plasma (p-milling) alumina (Al2O3) precursors. The characterization of the p-milling Al2O3 powders and the synthesized AlN are investigated. Compared to conventional ball milling (c-milling), it can be found that the precursors by p-milling have a finer grain size with a higher specific surface area, which lead to a faster reaction efficiency and higher conversion to AlN at lower temperatures. The activation energy of p-milling Al2O3 is found to be 371.5 kJ/mol, a value that is much less than the reported value of the unmilled and the conventional milled Al2O3. Meanwhile, the synthesized AlN powders have unique features, such as an irregular lamp-like morphology with uniform particle distribution and fine average particle size. The results are attributed to the unique synergistic effect of p-milling, which is the effect of deformation, fracture, and cold welding of Al2O3 powders resulting from ball milling, that will be enhanced due to the introduction of discharge plasma.

In order to obtain a better understanding of the welding mechanism in contact separation, electrical endurance tests were conducted with AgSnO2 and AgNi contacts on a simulation test device. Waveforms of contact displacement, contact voltage, and current were recorded with LabVIEW during the tests, and changes in a contact gap and heights of pips with increases in operation cycles were observed through charge-coupled device cameras. The resultant test results show that welding in separation is accompanied with a preceding voltage pulse which represents arc rather than contact bounce arc.

The jointing of 2G coated conductor (CC) tapes, which has a low joint resistance, is essential in fabricating coils, magnets, and power devices that need several kilometers in length. Although manufacturers of CC tapes can now produce 1 km in length at best with high critical current, i.e., $I_{c}$ , it is still not sufficient to fabricate coil windings. Although various techniques such as solder and diffusion joining have been recently reported, a practical and cost-effective joint method for CC tapes with low joint resistance should be established. In this paper, the ultrasonic welding (UW) method and a hybrid welding method that incorporates soldering onto the UW were tried to improve specific joint resistance at the joint part of the Cu-surround GdBCO CC tapes with a stainless steel substrate. Different horn tip patterns having large contact area ratio were adopted and their effects on joint characteristics were investigated for UW and hybrid-weld CC tape joints.

During high-power fiber laser welding, molten pool thermal radiation contains plenty of information which is related to the welding quality. In order to study the relationship between the molten pool characteristics and the welding stability during high-power (10 kW) fiber laser butt joint welding of type 304 austenitic stainless steel plates, the laser beam spot was controlled to move along the weld joint center, parallel to the weld joint with deviation, and cross the weld joint with two different slopes. Under these four different experimental conditions, the infrared radiation characteristics of a molten pool infrared image in laser welding process was investigated based on welding thermal radiation and heat conduction mechanism. An infrared-sensitive high-speed camera was used to capture the molten pool dynamic infrared images during laser welding. The image processing and pattern recognition algorithm were applied to analyze the molten pool characteristics. The molten pool width, keyhole area, keyhole swing, keyhole sharp degree, and position coordinates were defined as the characteristic parameters of a molten pool to analyze the welding stability. It was found that the joint deviation would affect the welding stability which could be reflected by the welding thermal balance, temperature distribution of a molten pool, and the shape of the corresponding infrared thermal image. Welding experimental results showed that the stability of high-power fiber laser welding process could be estimated by the proposed infrared characteristic parameters.

There is a lack of sufficient understanding regarding resistance spot welding behaviour of multi-layer structure. This paper investigates the weld nugget development and failure characteristics of four-sheet joint of dissimilar sheet thickness (0.7/1.2/1.2/0.9 mm) made on low carbon steel. The heat dissipation via water-cooled electrode hinders the weld nugget penetration into the thin/thick sheet interface. It was shown that increasing heat input led to bonding mechanism transition from solid-state welding to fusion welding at thin/thick sheet interface. Increasing welding current beyond a critical value changed the failure mode from interfacial to pullout leading to improvement of energy absorption of the joint. Fusion zone size along middle sheet/sheet interface proved to be the most important controlling factor for mechanical properties of four-sheet resistance spot welds.

Investigations were carried out into the special features of thermal and deformation processes in single- and twin-arc welding of joints with different edge reparation. On the basis of the experimental results it was established that deformation of all types when using the constricted shapes of the welding gap is lower than when using the standard welding gaps. The level of strain in the component can be additionally reduced by the application of twin-arc welding. The investigation results also show that in the final stage of welding it is necessary to correct the welding conditions in the immediate vicinity of the edge of the welded component in order to eliminate the superheating effect caused by the reflection of the heat flow from the welding edge.

This research concerns a dissimilar metal joining of steel and aluminium (Al) alloys by means of zinc (Zn) insertion. The authors propose a joining concept for achieving strong bonded joints between Zn-coated steel and Al alloys. A eutectic reaction between Zn in the Zn coating and uniform Al–Fe intermetallic compound (IMC) layer at the joint interface, leading to a strong bonded joint. The ultimate aim of this research was to apply this joining concept in the resistance spot welding process for manufacturing vehicle bodies. As a practical issue characteristic to joints of dissimilar metals, anticorrosion measures against electrochemical corrosion must be undertaken. If there is moisture near a joint interface of dissimilar metals, electrochemical erosion will progress. Therefore, a sealing function that could prevent moisture intrusion is required. By applying the above-mentioned welding process to a set of metals with thermosetting resin spread in between, we realized seal spot welding, which no...

Friction stir welding is a widely used welding process for aluminum alloys because it avoids many of the problems of conventional fusion welding. This process is beneficial especially for lithium containing aluminum alloys in which the reactive property of element Li causes porosity and hot cracking during melting and solidification. In friction stir welding process, each region undergoes different thermo-mechanical cycles and produces a non-homogeneous microstructure. In the present study, the mechanical properties and microstructure of a 2195-T8 aluminum alloy joined with friction stir welding were investigated. The change in microstructure across the welded joint was found to correspond to microhardness measurement. The microstructure was characterized by the presence of severely deformed grains and fine recrystallized grains depending on the region. Tensile tests shows the optimum condition was obtained at the tool rotating speed of 600rpm and the traveling speed range from 180 to 300mm/min.

Aluminum-copper-lithium alloy is a light weight metal that has been used as substitute for conventional aerospace aluminum alloys. With addition of Li element, it has lower density but higher strength. However these aluminum alloys are hard to weld by conventional fusion welding, since they often produce porosities and cracking in the weld zone. It is known that solid state welding like friction stir welding is appropriate for joining of this alloy. In this study, friction stir welding was performed on AA2195 sheets, in butt joint configuration in order to understand effects of process parameters on microstructure and mechanical properties in the weld zone. The results include the microstructural change after friction stir welding with electron microscopic analysis of precipitates.

Glass welding with femtosecond lasers is now ready for industrial practice. Clever heat management prevents tension and cracks occurring in the material. Laser welding supersedes earlier joining methods such as glueing as well as offering a number of advantages: no additional materials are necessary, no evaporation and embrittlement of materials, and greater durability. Laser welded glass protective caps for laser light cables are one demonstration of it. Furthermore, glass welding by laser opens up new design options.

Mechanical alloying (MA) is a powder metallurgy processing technique involving cold welding, fracturing and rewelding of powder particles in a high-energy ball mill. In the present study, the intermetallic matrix composites (IMCs) of Ni-Al reinforced by M7C3 were produced by powder metallurgical routes via solid state reaction of Ni, Al and M7C3 particulates by mechanical alloying processes. Ni, Al and M7C3 powders having 100 μm were mixed, mechanical alloyed and the compacts were combusted in a furnace. The mechanically alloyed (MAed) powders were investigated by X-ray diffraction (XRD), microhardness measurement, optic microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The presence of the carbides depressed the formation of unwanted NiAl intermetallic phases. The mechanical alloyed M7C3 particles were unstable and decomposed partially within the matrix during alloying and sintering, and the morphology of the composites changed with the dissolution ratio of M7C3 and sintering temperature.

Aerospace vehicle requires structures to withstand intense aerodynamic heating and propulsion system to provide very high effective heat exchange. In order to satisfy both requirements of effective thermal exchange and mechanical properties, high temperature materials, or sometimes dissimilar metals with different properties must be joined together. In this study, it is demonstrated that diffusion welding process can be applied to manufacturing lightweight integral structures of aerospace structural parts with titanium and stainless steel. The results show that the technology to design and develop the diffusion welding process of high temperature metals can be applied for manufacturing of aerospace components for high temperature application.

A tandem gas metal arc welding system was utilized for narrow gap welding in three welding positions: flat, vertical down, and overhead welding position. The two arcs worked in two independent molten pools respectively. The molten pool behaviors were investigated and the weld forming characteristics were revealed. The results suggest the molten pool behaviors in different welding positions are different due to the action of gravity. In flat welding position, the molten pool surface is concave. In vertical down welding position, more fusion metal flow to the head of molten pool, and the molten pool is asymmetric, and the molten pool surface is more concave than that in flat welding position. In overhead welding position, more fusion metal flow to the tail of the molten pool, and the surface of the pool is convex. High quality welds for various welding positions can be acquired with an appropriate ratio of welding speed to wire feed speed.

The problem of heat conductivity in arc and electron beam welding of rings and bars (parallelepiped) with a rectangular cross section with and without rapid cooling of the surface is investigated. The problem is solved analytically taking into account the dimensions of the component and welding technology (welding conditions and the sequence of making sections of the multilayer welded joint). A method is proposed for the determination of the welding conditions taking into account restrictions for the maximum temperature of heating the reference zone of the component. It is shown possible to replace the large-scale ring by a small-scale parallelepiped when investigating temperature fields in fusion welding.

Material-flow behavior during friction-stir welding of 6082-T6 aluminum alloy has been visualized by marker insert technique. Four stacked layers were evolved in welding nugget zone (WNZ) in the transverse section. The material-flow behavior in vertical direction was detected by observing the distribution of Cu foil fragments and Al-Cu intermetallic compounds. The downward and upward flows encounter each other at the advancing side in the material depositing process, changing the morphology of WNZ. A conceptual balanced-flow model and a plastic material-flow model were used to describe the material-flow behavior, and the origin of the downward material flow in the advancing side was discussed. The excess-material flow derived by the welding tool due to the existence of the tilt angle is crucial to the weld formation.

The conventional cold welding concept was extended to nanoscale, in which silver nanowires were welded together by large plastic deformation. A nanoindenter was employed as a cold welding tool to visualize and conduct welding. The MD simulation shows that unlike single crystal nanowire, sufficient plastic deformation is key to realize successful welding when the two nanoobjects have large orientation mismatching. The lattice orientation of joint interface is complex but no defects were found in both experimental and simulation.

Application of high strength steel is one of the most promising solutions to the problem of vehicle weight reduction. However, weldability problems occur when three sheet metals of the high strength steel are welded. This is because under such situation, the suitable welding range in the lobe diagram is too narrow and the strength between the contact zones is lower than the required value, and also, expulsions between the sheets occur. In this work, a conically shaped hollow electrode was applied at the lower electrode to improve resistance spot weldability of three-sheet welding including high strength steel. Shear strength test and analysis of welding signal and weld cross section were conducted. It was found that the proposed lower electrode has some advantages in welding the three-sheets welding compared with conventional electrodes or hollow electrodes. Consequently, a welding process using the proposed electrode was studied and verified with numerical analysis.

This work reports on an improved ultrasonic welding process for the direct joining of thermoplastic and metal. A metal thin plate was structured with grid arrays on a micro-scale level by laser irradiation. A thermoplastic part was placed on the structured region, and ultrasonic welding or ultrasonic hot welding was applied. The thermoplastic was locally melted and re-solidified in the structured grooves with very low energy input due to the tiny initial contact area of the grid tips. Single lap shear specimens and boss specimens were used to study the feasibility and performance of hybrids made by this joining method. Both shear strength and normal tensile strength were affected by changes in the grid structures and welding parameters, and the experimental results show that the micro-structure geometry of the metal plate is a major factor in the joining strength. Successful welds required that process cycle times be less than 1 s. Furthermore, the mold holding the metal sheet was heated in the ultrasonic hot welding experiments, and the heated mold significantly enhanced the joint quality. Ultrasonic hot welding appears to be a fast, low cost, and reliable method to produce plastic/metal hybrid products for electronics and other industrial applications.

The drive toward fulfilling weight reduction obligation, superior weld quality requirement, and industrial manufacturing rationale has sprung up considerable interest in applying laser welding technology on aluminum alloys. Nevertheless, porosity, solidification cracking, and surface reflectivity have been the major banes of laser welding of aluminum alloys. However, literature has shown that positive efforts have been accomplished in reducing these fundamental concerns by adopting careful selection of welding procedure, modification of pure laser welding techniques, and the use of appropriate filler metal. Albeit, there is still upbeat progression on the application and improvement of laser welding of aluminum alloys. At present, laser welding technology has the potential of fulfilling industrial requirements in joining lightweight aluminum alloys because of its capacity for automation and intrinsic flexibility, precision and repeatability, low general heat input, high welding speed, and low weld distortion. As a result, this report examines the available and current status of laser technologies in welding aluminum alloys. It further categorizes the laser technologies of aluminum alloys into four assemblages, namely, pure or single-beam laser welding, laser-arc hybrid welding, tailored heat source laser welding, and other innovative laser welding technologies, respectively. Mechanical, corrosion, and microstructural behaviors of laser welded aluminum alloys are also studied. Conversely, some of the research areas that need further investigations are proposed. Corrosion behavioral properties, influence of micropores on fatigue and quasi-static tensile strength, and toughness characterization of laser welded aluminum alloys are insufficient in literature.

The dispersion homogeneity of particles has a significant influence on the mechanical properties of particle reinforced metal matrix composites. In this study, a new Cu matrix composites with uniform dispersion of submicron and nanoscale MXene reinforcement particles were fabricated by the methods of high energy ball milling and hot pressing sintering. The microstructure evolution of MXene-Cu composite powders were studied in detail. When the initial MXene content is less than 3 vol%, the MXene particles can be dispersed homogenously in Cu matrix after 12 h ball milling. The refinement and dispersion of the MXene particles are mainly achieved by the cold welding and plastic deformation of composite particles in ball milling process. The XRD and TEM results reveal that these MXene reinforcement particles have been transformed to cubic TiCx in the final MXene/Cu composites. The tensile test results indicate that the UTS and elongation of the MXene/Cu composites are closely related to the dispersion homogeneity of the MXene particles. The UTS and elongation of the 1MXene/Cu and 3MXene/Cu composites increase with increasing the ball milling time. The UTS of the 3MXene/Cu-12 h can reach to 314 MPa with an elongation of 11.1%. The maximum UTS of the 5MXene/Cu-6 h can reach to 354 MPa. However, further increase in milling time would result in the UTS and elongation decline. The fracture surface analysis further testifies that the 3MXene/Cu-12 h composite presents a typical plastic fracture feature, while the 5MXene/Cu composite with various ball milling time all present brittle fracture characteristic for the severe agglomeration of MXene particles.