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A variety of materials have been used to assemble transportation equipment in order to realize both securement of high strength and weight reduction in recent years. In the manufacturing fields, various joining methods are used, and there are as many methods as material variations. Among those joining methods, mechanical joining can join without heating or melting materials. We have proposed a high-speed nailing method using a spiral nail in order to improve the joining strength in this study. The proposed method is characterized by spiral grooves provided on nails, which bite joined parts to improve joining strength. Using nails with several spiral groove angles, this study has verified effectiveness of the spiral groove angles of the nail and also revealed the mechanism of the method that affects joining strength. Incidentally the proposed method can joint dissimilar materials at high speed without supporting behind clamped plates. Since the nail has the spiral grooves, we can easily remove the nails by rotating the nail in the opposite direction. Therefore the method is suitable for recycling and maintenance.

Joining of 5083 and 6063 aluminum alloys to 304 stainless steel was successfully achieved by high-frequency linear friction welding working at 245 Hz with varied friction pressure and time, which affect the heat input. Increasing the friction pressure and friction time resulted in the softening of aluminum alloys, which facilitated plastic flow and subsequent squeezing behavior. The morphology of the intermetallic compound layer, dependent on the plastic flow, determined the performance of 5083 aluminum alloy/steel joints. Excessive friction pressure and time led to inefficient welding in 6063 aluminum alloy/steel joints because the softening and squeezing behavior of the heat-treatable alloy was susceptible to the heat input. Highly efficient joints were obtained in a short duration, i.e., 1 s, through the formation of a thin intermetallic compound layer at the interface below 500 and 50 nm for 5083 and 6063 aluminum alloy/steel joints by controlling the appropriate friction pressure. High-frequency linear friction welding was demonstrated to be effective for the sound joining of various materials by controlling the friction pressure.

We succeeded in improving the fatigue properties of friction stir welded 7075-T73 aluminum alloy, e.g., prolonging the fatigue life at lower stress amplitude as compared to the base metal, using femtosecond laser peening, which was performed in air without any overlays such as a protective coating and plasma confinement medium, which are necessary for conventional nanosecond laser peening. The results of the plane bending fatigue tests with a stress ratio of R= -1 demonstrated that femtosecond laser peening enhanced the fatigue strength of the friction stir welded specimen at 106 cycles by approximately 15 MPa compared with that of the base metal, and prolonged the fatigue life of the friction stir welded specimen under cyclic loading at a stress amplitude of 200 MPa by approximately 3.7 times compared with that of the base metal. We suggest that dislocation generation, which occurs behind the shock front under femtosecond-laser-driven shock compression owing to its large shock amplitude, induces surface hardening and compressive residual stresses in a near-surface volume. They prevent the initiation of fatigue cracks on the surface of the specimen, resulting in improved fatigue properties.

High-frequency linear friction welding (HFLFW) with a 250 Hz oscillation frequency was applied on similar joining of AA5052 and AA6063, i.e., work- and precipitation-strengthened Al alloys, with 11 × 11 mm2 friction surface. Sound joints were achieved under a 30 MPa friction pressure and with processing times longer than 1 s. The thermomechanically affected zone (TMAZ) of AA6063 joints suffered from softening at a distance of 2–3 mm from the joined interface in contrast to the TMAZ of AA5052 joints. The pressure reduction to 7 MPa narrowed down the thickness of the softened TMAZ to 1 mm from the interface. A thermal finite element (FE) model was calibrated against in situ temperature measurements. Significant temperature differences of up to 300 °C at the welding interface were assigned to the process parameters as well as to the different thermal and mechanical properties of the Al alloys. Linear hardening and softening effects in AA5052 and AA6063, respectively, were quantified in hardness vs. temperature diagrams, and a pressure-hardening phenomenon was identified. A user subroutine was fed with these correlations, which visualized the hardness distribution over the near-interface volume for a low- and a high-pressure process.

We developed High-Frequency Linear Friction Welding (HFLFW) operating at 250 Hz, which is larger than conventional LFW methods, to realize welding aluminum alloys. In order to establish the fundamental HFLFW process for the welding of Al alloys, the relationship between the mechanical properties and microstructure of the HFLFW joint was investigated for both 6063 and 5052 Al alloys, which have different strengthening mechanisms. Sound welds were achieved for both 6063 and 5052 Al alloys. The change in the shape of flash with increasing process time indicated that the material flow in the joint was largely affected by the material properties such as proof stress at high temperature and thermal conductivity. Further, the hardness increased and refined grains were observed at the interface of the 6063 Al alloy joints welded in the low-heat-input condition, which led to a higher joint strength at a shorter process time. The size of the refined grains was about 100 nm, as observed by transmission electron microscopy. Our findings reveal that a high frequency is effective and HFLFW is a promising process for the welding of precipitation-hardening aluminum alloys with a high joint strength owing to the less heat effect during the process. Keywords: Linear friction welding, Aluminum alloy, Precipitation hardening, Frequency, Microstructure, Mechanical properties

One of the mechanisms for the dissimilar materials joining is the formation of interfacial reaction layers. However, this reaction is disrupted owing to the presence of oxide layers and voids, leading to lower strength, and the elimination of these factors is essential. Thus far, studies on linear fraction welding (LFW) with regard to the relationship between the joint strength and the microstructure of the base alloy and interface are lacking. Therefore, herein, the influence of microstructural changes in base alloys and interfacial structures on the joint tensile strength was investigated for the dissimilar joint between the stainless steel and an A5083 alloy after high-frequency linear friction welding at 245 Hz. After the initial joining process up to 1 s, the joint strength decreased as the friction increased. The crystal orientation analyses using electron backscatter diffraction demonstrated a minimal change in the microstructure of the A5083 alloy, particularly in the grain size in the geometric dynamic recrystallization region. This variation in the microstructure was minimal, regardless of the friction time, which was consistent with the result of the hardness distributions. The observation of microstructure using transmission electron microscopy revealed the formation of metastable Al-Fe intermetallic compounds and Al-Mg-Cr compounds derived from the reaction between the oxide layer and alloying elements in the A5083 after experiencing friction for a short time. Conversely, we confirmed the formation of a fragile boundary within the interfacial reaction layer after the exposure to friction for an extended period due to differences in the formation process of the layer: mechanical mixing or interdiffusion. Hence, it was proposed that mechanical removal as well as the interfacial reaction between the oxide layer and the Mg contained in the aluminum alloy function in removing the surface oxide layer, which plays a significant role in designing the interfacial structure and joint properties.

In Order to Improve the Joining Strength of Friction Stir Spot Welded PVC Joint, Sic Particle was Compounded by the Stirring in the Welding Process. the Influence of Sic Particle Sizes on the Joining Strength was Investigated in this Study. in Case of the Specimen Compounded Sic Particle with Size of 14.6μm, Heat Generated during the Process Significantly Increased and Resulted in Increasing Width of Welded Region. however, According to Result of Hardness Test, Excessive Heat Generated during the Process Led to Degradation of Mechanical Property of the Welded Area in the Specimen Compounded Sic Particle with Size of 14.6μm. on the other Hand, in Case of the Specimen Compounded Sic Particle with Size of 6.5μm, Width of Welded Area was Smaller than that of the Specimen Compounded Sic Particle with Size of 14.6μm and was Similar as that of the Specimen Compounded Sic Particle with Size of 0.5μm. it was Observed that Hardness of the Welded Area was Uniformly Higher in the Joint Compounded Sic Particle with Size of 6.5μm. Specimen Compounded Sic Particle with Size of 6.5μm Showed the Highest Strength among the Joints Tested. it is Considered that the Joining Strength was Affected by both Width and Mechanical Property of the Welded Area.

Summary High-speed MIG welding is an effective process for reducing welding distortion and increasing the weld strength of aluminium alloys. The effects of welding conditions and the pulse duration of the pulsed current on the occurrence of pit-like surface defects in weld beads are examined to improve weld bead stability and to suppress the occurrence of surface defects during high-speed MIG welding. The formation mechanisms of surface defects are studied by observations of arc phenomena and weld bead appearances. The occurrence of surface defects during short arc and long arc welding respectively corresponds to changes in the welding current and arc voltage. Surface defects are considered to be formed by explosive scattering of the welding wire during short arc welding and solidification shrinkage during long arc welding. Surface defects can be suppressed through optimisation of the welding conditions. Reduction of the pulse duration of the pulsed current is effective for improving the appearance of wel...

Tensile and fracture toughness properties of three typical aluminum casting alloys, A (0.7%Si)–T6, B (4%Si)–T6 and C (7%Si)–T6, were evaluated in both as-cast and as-forged conditions. Cast and forged alloys showed increased elongation and fracture toughness with increase in forging ratio, especially in A (0.7%Si)–T6 alloy. The tensile and yield strengths of cast and forged alloys of B (4%Si)–T6 and C (7%Si)–T6 increased with forging ratio, but decreased in 50% forging ratio. Mechanism of the increased fracture toughness are considered to be a decrease in the size of casting defects with forging ratio. On the other hand, it is also considered to change microstructures of α phase and eutectic Si particle. In the Al–Si–Mg alloys, Mg2Si is a major precipitate, however, it is considered that the excess Si also contributes to the increase of the strength.

Hybrid laser welding have been carried out, with bead-on-plate and butt welding setting, on Al-Mn and Al-Mn-Mg alloys, to evaluate the welding defects morphology. On bead-on-plate welding, keyhole mode was achieved without the welding defects at 60mm/s traveling speed with 2.12kW pulsed laser in Al-Mn alloy. The increase of maximum power of pulsed laser and Mg content caused a rise of welding defects, that is, porosities and cracks. Simultaneously, both penetration depth and bead width became larger, and aspect ratio of fusion zone (depth to width) also increased. X ray tomography clearly evaluated internal welding defects such as porosity. Morphology of fusion zone and welding defects were influenced by an incorrect root gap in butt welding. An increase in the root gap tended to reduce the porosity, and achieved higher aspect ratio of fusion zone, which was deeper penetration depth and wider bead width. On the other hand, underfill, as superficial welding defect, was clearly formed in both alloys. The root gap in butt welding was one of sensitive factors on the laser weldability besides Mg content and pulsed laser power.

顎機能障害患者の咀嚼筋や胸鎖乳突筋の表面筋電図検査を行うと, ほぼ一定の小さな振幅を持った自発的な持続性の筋放電が安静時, 最大かみしめ直後, あるいは咀嚼の直前直後などに記録されることがある.このような自発放電の存在についてはすでに, 筋の過緊張や疼痛との関連について論じられており, 咬合治療により自発旅電が消失するとの報告がある.これらの報告は, 咀嚼筋や側頸筋に見られる自発放電が顎機能障害の症状との関係が深いことを示唆している.我々は, 顎機能障害の症状の程度と自発放電の発生頻度, 出現率には何らかの関連があるものと考える.もしそうであれば規定された被験運動を一定の条件で行わせた場合, 一定の検査時間における自発放電の発生頻度をパラメータとすることで顎機能障害の症状の程度の判定, あるいは治療効果の判定をすることはきわめて合理的な検査となりうる.実際に自発放電の検査時間内の発生頻度の算出を効率的に行うため, コンピューターで自動的に算出を行ないたい.これには, 自発放電と随意的な筋収縮に伴う筋放電とを自動的に識別しなければならない.現在, 自発放電と随意的な筋収縮に伴う筋放電の識別は, 検者がその波形の特徴に基づいて行っている.そこで我々は自発放電を認識する方法として, その波形の特徴が随意的な筋収縮に伴う筋放電波形とは異なることに注目して新たに振幅密度分析法を開発した.振幅密度分析は, 分析対象である信号波形の一定時間内の電圧データを電圧に対する分布密度として解析する分析法である.今回はまず, 発信器による波形の特徴が既知である3種類の信号波形に本分析法を用いて分析した.その結果, 振幅密度分析により信号波形の形の違いを判別できることが分かった.次に臨床応用例として正常被験者の最大かみしめ時の筋放電と, 表面筋電図検査にて自発放電が記録された顎機能障害患者の自発放電での分析を行った.さらに振幅密度分布に半値幅, 半値幅1最大振幅という評価値を導入して, 正常な最大かみしめ時の筋放電と自発放電を区別できる事が分かった.以上より, 振幅密度分析は, 随意的な筋放電と自発放電を自動的に区別でき, 自発放電の発生頻度の算出, さらには顎機能障害患者の検査, 診断に役立つことが期待される.