Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass (bulk amorphous alloy) have unique properties such as highly resistant to corrosion, high strength and elastic deformation over whole deformation range, so that it is expected to be the next-generation machine materials. To develop further industrial applications, joining technology for the metallic glass is necessary. In this study, surface modification with Cu on Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass using laser cladding and the consequent solderability improvement were studied. As a result, the interface between Cu thin film and Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass were continuously welded by the laser cladding. XRD showed that there are no crystalline and reaction layer in the weld interface. Furthermore, it was found, by XPS, that the Cu modified layer on the Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass surface inhibited the formation of a strong oxide film. Consequently, the Cu modified layer played an important role in improving the solderability to the Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass.

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In seismic-active area, the buried pipeline is subjected to the axial tensile load exceeding the yield stress of pipe material due to the lateral flow induced by soil liquefaction. Designing a girth weld joint that does not fracture at girth weld but base metal which has high elongation capacity is feasible to ensure adequate ground displacement absorbing capacity of the girth weld joint. However, as for fine grain steel, the heat-affected zone (HAZ) is softened by welding heat input, and then, the zone of softened HAZ can be the origin of fracture under tensile load. The apparent strength of softened HAZ is affected by the plastic constraint from the surrounding weld metal and base metal during tensile loading, and the fracture location depends on the apparent strength of HAZ. This study investigates the tensile strength and fracture location of girth weld joints with softened HAZ in the static tensile test. The effect of geometric and mechanical heterogeneity of HAZ, strength overmatching of weld metal, and the width-thickness ratio of tensile test specimen on tensile strength are elucidated using parametric finite element analysis. Subsequently, an equation is proposed to predict the tensile strength and fracture location of the welded joint. Using the proposed equation, the condition of geometric and mechanical heterogeneity of the weld to confirm the girth weld joints that fracture at base metal under tensile load is clarified. The proposed equation can be used to design a girth weld joint with liquefaction earthquake resistance.

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Friction Stir Welding (FSW), which was developed at TWI in 1991, is a solid-phase welding process capable of joining linear and point welds, and is being put to practical use in the automotive, aerospace, and other industries for the purpose of weight reduction and multi-materials. In this paper, the effects of each factor on joint strength in friction stir spot welding are clarified using statistical methods, and optimized joint conditions are proposed. Specifically, the optimal joining structure is experimentally clarified for aluminum materials with composite coatings by utilizing the design of experiment method in terms of the degree of influence of tool geometry and tool motion. Only the shape of the tool's probe is triangular prism because it is known to be effective in bonding composite films to the material.

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A simple technique of restraining fatigue crack growth utilizing wedge effects of corrosion products was newly proposed and experimentally tested. Crack growth restraining sheets with a high water content gel were manufactured by way of trial and applied to notched plate specimens of steel, and the efficacy of the sheets to restrain crack growth was evaluated by fatigue tests. In the fatigue tests, the crack growth restraining sheet was renewed at proper timing to maximize its performance. In order to find a local humid (or wet) corrosive environment, which is most suitable for the crack growth restraint by wedge effects of corrosion products on the crack surfaces, water components absorbed in the gel and effects of a cathode layer as promoting factors of the corrosive reaction were comparatively examined. As a result, it was found that all the proposed crack growth restraining sheets were effective and extend the failure life in the range of 2.1 ~ 9.6 times as compared with the bare base metal specimen. Especially, the efficacy of the gel sheets with 3% salt water and synthetic sea water was remarkable (4.1~9.6 times extension in failure life), and the cathode layer (copper-leaf tape) produced certain additional positive effects in those gel sheets. From fracture mechanical analyses with FE analyses, it was found that the crack restraining effect of the gel sheet greatly varies depending on the water gel content and the existence of cathode layer. In situ observations around the growing cracks and macro- and microscopic observations of the fracture surfaces were also performed for a comparative study between the different types of crack growth restraining sheets.

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In resistance spot welding, which is widely used for assembling automobile bodies, reduction of weld spacing (short-pitch welding) has been put to practical use to improve the strength and stiffness of the welded assemblies and to advance collision safety and ride comfort. In short-pitch welding, shunt current going through the previously welded points is inevitable and delays nugget formation and growth, but it is difficult to know the degree of shunting because it varies depending not only on the weld spacing but also on the sheet combination. In order to study the shunt phenomenon, several theoretical models have been proposed, but they have some critical problems in practical use, such as overestimation of the shunt resistance and many parameters to be determined from experiments. In this study, a mathematical model is established which can easily predict the ratio of effective weld current (or non-effective shunt current) to the total input current with only one experimental parameter, in the case of two-sheet stack-up with a single existing (shunting) weld. By using this model, delayed nugget growth curve of the second weld can be predicted taking the shunting effects into account, from the known nugget growth curve of the first weld. Furthermore, the efficiency of the shunt current to ease some three-sheet stack-ups welding was shown experimentally, and the optimal weld-spacing to maximize the welding current range was estimated by the proposed model.

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In brazing of Ti-containing stainless steel as a substrate, even under hydrogen atmosphere conditions that reduce the passive film on the stainless steel surface, Ti oxides are not reduced and numerous Ti oxides remain on the entire surface. These are the factors that cause the decrease in wettability, which was clarified from the surface analysis of the substrate. In order to improve the wettability, it is effective to increase the surface free energy of the entire brazed joint surface. As a method to improve the surface free energy of the entire joint surface, we have confirmed that the wettability of a difficult to braze stainless steel was improved by using a material with good wettability as one of the brazing pair substrates.

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Dissimilar materials A7075-T6 and S45C were joined by center-driven double-sided linear friction welding (LFW) using SUS304 as the center material. The effect of joining pressure on the joint properties was investigated, and it was found that when the joining temperature was extremely low, the joining interface could not be formed, even if sufficient deformation of both materials occurred. Upset pressure was introduced under conditions that the joining temperature was high, and it was confirmed that the joint strength increased with increasing upset pressure. The highest joint efficiency was obtained under conditions that the upset pressure exceeded the material strength of SUS304 at the joining temperature. Microscopic observations of the obtained joints revealed the absence of defects or thick intermetallic compounds at both the A7075-T6/SUS304 interface and the SUS304/S45C interface, with the presence of a thin and uniform atomic diffusion layer.

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Friction stir welding (FSW) has been widely used in welding of metal. However, it is difficult to weld high melting point metal by FSW because of short life or high price of FSW tools. Silicon nitride tool can have both long life and low cost. Although the silicon nitride tool, which has high temperature mechanical properties, could have a long tool life for FSW of steel, it is not clear how FSW conditions affected the tool life. In this study, changes in the shape of the FSW tool was focused. A comparative verification of the tool shape changes due to the FSW conditions was carried out, and specific shape changes in silicon nitride tools were verified. The silicon nitride tool was worn only at the shoulder and not at the probe. Furthermore, the wear shape was different depending on rotation speed and welding speed of the tool. The factors that cause them were analyzed using temperature and stress simulations for silicon nitride tools. Increasing the rotation speed broadened temperature distribution, increased the peak temperature and narrowed the stress distribution. When the welding speed was increased, the temperature distribution became narrower and peak temperature was lower, and the thermal asymmetry increased, while the stress distribution expanded and the stress asymmetry increased. When the welding speed was high, the agitation in the plastic flow zone was insufficient, and there were places where the stress and temperature were low around the shoulder. It is considered that these decrements of the stress and temperature lead to the concave part remaining on the outer circumference. Therefore, it is important to control both the welding speed and the rotation speed of the silicon nitride tool in order to suppress the protrusion which is main reason of the tool breakage.

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The morphology, microstructure, hardness change, and co-deposition mechanism of electrolytic Ni–metal sputtered cellulose composite plating were investigated. Composite plating experiments were conducted using various cellulose powders as co-deposited materials, including natural wood derived cellulose (CF), sodium carboxymethyl cellulose (CMC), and those treated with Au-Pd sputtering (AP CF and AP CMC, respectively). It was found that cellulose composite Ni plated films are successfully fabricated with AP CF, CMC and AP CMC, while CF does not almost achieve co-deposition. Ni plated films with CMC and AP CMC showed approximately twice the surface Vickers hardness compared to the Ni film without cellulose. In contrast, Ni plated films with CF and AP CF showed similar hardness to that without cellulose. At cross-section of the specimen with AP CF, co-deposited sites where AP CF is fully covered with nickel with gold presence were observed. This suggests that Ni deposition from metal particles on AP CF surface forms co-deposition with “cladding” mode. On the other hand, the specimen with AP CMC showed that the cellulose as if pierced the Ni film as seen in that with CMC. This indicates that the Ni deposition mechanism via chelate complexes between carboxylate of CMC and Ni ions is dominant, and the effect of Au-Pd sputtering is negligible. Although Au–Pd sputtering treatment on the cellulose is effective in enabling co-deposition, such as with CF, it is not always necessary for cellulose co-deposition. The presence of conductive particles that act as a nucleus for Ni deposition is probably sufficient for co-deposition. This indicates potential that various types of the conductive cellulose are able to be applied as co-deposited materials for composite plating for such as the wear resistance coatings or the surface treatment on electrodes of electronic substrates.

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In recent years, low-melting-temperature solders are required in electronics packaging. Among them, Sn-Bi alloys are expected to exhibit good wettability and strength. However, they have difficulty in ductility due to the brittle nature of Bi. In some research, to improve the mechanical property of Sn-Bi alloys, Zn and In are added. The modified alloy had better mechanical properties and the low-melting-temperature equivalent to Sn-58Bi. However, its ductility is not comparable to that of typical lead-free solder, Sn-3.0Ag-0.5Cu. Therefore, in this study, by reducing the content of Bi, we attempt to improve the ductility of Sn-Bi-Zn-In alloy. To investigate the effect of Bi content on the melting temperature, microstructure, and tensile strength were evaluated using Sn-xBi-2.6Zn-1.0In (x=45, 40, 35, 30, 25, 20 mass%) alloys. In addition, the fracture surfaces and nearby microstructures were observed to analyze the effect of the Bi content. As a result, the melting onset and offset temperatures increased with reducing the Bi content. In all alloys, the microstructures had Sn-rich phases, Bi-rich phases and Zn phases. As the Bi content was reduced, the morphology of Bi phase changed from layer-like eutectic phases to small round shape. Reducing the Bi content from 45 to 35 mass%, the ductility improved. However, with the decreasing Bi content from 35 to 20 mass%, the ductility was getting worse. The fracture surface analyses indicated that, their ductility was affected by the Bi-rich phase morphologies. Based on these results, the ductility enhancement with the enhancement with the 35 mass% Bi content would be understandable with the strain dispersion by the refined Bi-rich phases. The strength slightly increased decreasing the Bi content due to the decrease in the Sn-rich/Bi-rich phases interface.

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Copper and aluminum were bonded at 298 K by electrodeposition of copper. The faying surface of the aluminum was anodized to improve the interface strength between the deposited copper and aluminum. Many tubular pores with diameters of several tens of nm were formed in the anodic oxide (alumina) film on the aluminum surface along the film growth direction, and the higher the anodic oxidation voltage, the larger the pore diameter and the thicker the wall between the pores. Electrodeposited copper and aluminum were bonded through the porous oxide film, forming a bonding interface where copper was electrodeposited in the pores in the oxide film. Although the joint was made through the oxide film at the bonding interface, it was found that there was electrical conductivity between the copper and aluminum. No intermetallic compounds were observed at the interface between the electrodeposited copper and aluminum. Electrodeposited copper in the tubular pores in the oxide film on the aluminum surface caused an anchoring effect at the joint interface, resulting in a sound joint with base metal fracture on the aluminum side.

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Liquid-phase diffusion bonding was performed in air at a bonding temperature of 400°C, a bonding pressure of 20 MPa, and a heat holding time of 15 min. The specimens for liquid-phase diffusion bonding were AC2C and ADC12, aluminum alloy for casting. After liquid-phase diffusion bonding, solution annealing and aging treatments were also performed on the joints. As a result, the joint strength was improved by about 2 times and the joint efficiency was 90% by using the 3-layer insert material as compared with the Zn single-layer insert material. This was because the Si concentration in the liquid phase decreased by using the 3-layer insert material and Si was discharged to the outer circumference of the joint. By using the 3-layer insert material, the interfacial fracture factor after T6 heat treatment changed from Si particles to Mg oxides.

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Multiple regression analysis, neural networks (NN), and other methods are used as approximate computation methods for physical phenomena. However, multiple regression analysis has the problem of overlearning due to factors that cannot be formulated, and NN has the problem of overlearning due to the diversity of its representational capabilities. In response to this problem, we have proposed an integrated neural network (INN) that integrates a simple perceptron and an NN, which mimic multiple regression analysis. In this paper, we show that INN can reduce overlearning of the simple perceptron part (multiple regression analysis) and achieve higher accuracy by compensating for errors caused by NNs through weight analysis. Furthermore, it was revealed that the correction of the NN part is effective under adaptive control according to the approximation accuracy of the simple perceptron part.

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Dissimilar joining between carbon fiber reinforced thermoplastic (CFRTP) and metal has attracted attention of transportation equipment industry for reduction of weight and cost by multi-material structure. Friction stir spot welding (FSSW) between anodized A5052 (AO-A5052) and carbon fiber reinforced thermoplastic (CFRTP) was investigated for the improvement of joining strength. Average tensile shear strength of AO-A5052/CFRTP joint was 2505N and more than 500N higher than that of untreated-A5052/CFRTP joint. In the AO-A5052/CFRTP joint, probe plunge induced cracks and microwrinkles in the anodic oxide layer on the weld surface. Matrix resin was immersed into the cracks and the microwrinkles underneath of the shoulder of the welding tool. Reinforced carbon fiber and matrix resin was immersed into large crack at the outer peripheral corner of probe. Thus, those increased the joining strength by mechanical anchoring effect. Thermal stress test and machining stress test were performed for revealing the mechanism of cracking of anodic oxide layer. Although thermal stress did not generate cracks in the anodic oxide layer, machining stress by probe plunge generated cracks in the anodic oxide layer. The generated cracks in anodic oxide layer underneath of the shoulder were distorted to the rotating direction of welding tool by the friction stirring.

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Viscosity of pure Bi and Bi-10Sn molten alloy were measured in a low shear rate range. The flow curves of pure Bi and Bi-10Sn alloys were prepared from the torque data obtained by rotational viscometer, and the interaction between these metals and copper contact interface was investigated. When graphite cone was used, the viscosity of pure Bi was 3.29 mPa∙s and of Bi-10Sn was 86.7 mPa∙s. In the other hand, in case of copper cone, the viscosity of pure Bi was 5.65 mPa∙s and that of Bi-10Sn was 278 mPa∙s. It was considered that, in the range, the flow characteristics of pure Bi was Newtonian fluid and that of Bi-10Sn alloy was Non-Newtonian fluid. The surface adhesion was observed by XRD and EPMA analysis. Chemical interaction between Cu and Sn was confirmed from analysis results. Sorosite(Cu(Sn,Sb)) peak pattern was obtained for the pure copper cone after Bi-10 Sn viscosity measurement by XRD. The sorosite peak pattern was identified with a reaction product of Cu_1+x(Sn,Bi), and Bi atoms were substituted for Sb atoms in the sorosite. Reaction products Cu₃Sn was not detected by XRD. Cu₆Sn₅ peak pattern was observed in the XRD patterns obtained from an adhesive on pure copper cone near the edge. Bismuth atoms were removed from a sorosite ; Cu_1+x(Sn,Bi) (0.1<x<0.2) then the composition of Cu₆Sn₅ was derived.

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Generally, brazing is completed when the brazing filler metal permeates the gap by uniform wetting. It is believed that the joining process is completed with the formation of joint defects “voids” in the process of uniform wetting. However, previous studies have shown that what occurs when brazing is performed is non-uniform wetting. It is suggested that this non-uniform wetting is the cause of void generation. Wetting and spreading of brazing filler metal is tested on a metal plate, as described in JIS Z 3191. This is used to investigate the wetting of the brazing filler metal. However, this method does not cover the wetting of the molten brazing filler metal as it moves into the gap. Therefore, it is suggested that the JIS Z 3191 experiment is insufficient to evaluate the wetting of the molten brazing filler metal that penetrates into the gap. In this experiment, we created new specimen. It is called us “V-groove specimen”. Specimens were created with two base metals. They are pure copper and lead-free brass in which bismuth was used as an alternative element. In order to do in situ experiments, it was not possible to observe the inside of a conventional electric furnace. Therefore, we produced a furnace with a window for in-situ observation and experimented with it. As a result of experiments with V-groove specimens, it was found that there are two types of wetting of brazing filler metal. They are called “primary wetting” and “secondary wetting”. The shape of the specimen was measured and evaluated for two types of wetting. The results showed that the primary wetting was measurable in shape and spread evenly. However, the shape of the secondary wetting could not be measured, and it was found to be non-uniformly spread.

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Exhaust gas recirculation (EGR) coolers composed of stainless steel brazed with Ni-based brazing filler metals for motor vehicles are a standard technology. The ferritic stainless steels have been used in the EGR coolers because of the requirement of low material cost compared to austenitic stainless steels for the last decade. On the other hand, Ni-based amorphous brazing foils produced with rapid solidification technology have been increasing since the foils are ductile and do not contain organic binders. Few studies were conducted on the mechanical properties of ferritic stainless steels brazed with Ni-based amorphous brazing foils. This study investigated the shear strength and microstructure of ferritic stainless steel single-lap joints brazed with commercially available Ni-based amorphous brazing foils. As a result, it appeared that the SUS444 single-lap joint brazed with MBF67 brazing foil containing phosphorus had relatively lower shear strength than those brazed with MBF20 and MBF50 brazing foils because of the formation of the Cr-Ni-P intermetallic compounds with higher Vickers hardness within the brazed layer.

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Laser peening (LP) is a well-established technique for introducing compressive residual stress (RS) near the surface of metal components to improve their high-cycle fatigue properties. In this study, butt-welded joint specimens of SBHS500 steel with angular distortion were prepared and treated with LP. X-ray diffraction showed that the maximum compressive RS over 400 MPa was introduced near the surface by applying LP with an irradiated pulse energy of 7.5 mJ, a spot size of 0.42 mm, and a pulse density of 800 pulses/mm2. The effect reached a depth of approximately 0.15 mm from the surface. The specimens were subjected to a uniaxial fatigue test with a stress ratio of 0.1 together with specimens without LP. The results showed that the fatigue life was prolonged by LP. However, in the stress range of 300 MPa, the detrimental effect of angular distortion predominates over the beneficial effect of LP, showing that the fatigue life extension by LP is not evident.

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Al alloy sheet and galvannealed steel sheet were joined by Sc-RFSSW, and the bonding process was analyzed by observing the microstructure of the bonded interface. The interface was divided into three regions. Al, Zn, and IMC flowed into the GA steel sheet at the interface produced under the inner and outer circumferences of the tool shoulder. Zn and Fe discharged by the scrubbing process were rolled into Al from the anchor at the interface produced under the outer periphery of the shoulder and expelled from the interface.

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For extending the application of hybrid welding to the fabrication of steel bridge structures, a series of experiments were performed. One-pass full-penetration corner joints of SBHS500 with 12 mm thickness were fabricated by laser-arc hybrid welding. Four passes were required to produce the same-dimensional full-penetration corner joints by conventional arc welding. Monotonic compressive loading experiments were performed to investigate the load-carrying performances of hybrid-welded and arc-welded corner joints. Compared to arc-welded specimens, the elastic stiffness of hybrid-welded specimens was greater by 24%, and the maximum compressive load of hybrid-welded specimens was greater by 5%, demonstrating that the load-carrying performances of hybrid-welded corner joints may outperform arc-welded corner joints.

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