Seiichiro Tsutsumi

Microstructural Characteristics and Mechanical Properties of Friction Stir Welded Thick 5083 Aluminum Alloy

Joining thick sections of aluminum alloys by friction stir welding (FSW) in a single pass needs to overcome many challenges before it comes to full-scale industrial use. Important parameters controlling the structure-properties relationships both across weld cross-section and through thickness direction were investigated through mechanical testing, electron backscatter diffraction technique, transmission electron microscopy, and occurrence of serrated plastic flow. The evolution of the properties in the weld cross-section shows that the presence of undissolved and fragmented Al

Friction Stir Welding of Thick Aluminium Welds—Challenges and Perspectives

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A numerical study of the return mapping application for the subloading surface model

6MnFe particles cause discrepancies in establishing the Hall-Petch relationship, and derive the strengthening from the Orowan strengthening mechanism. A ‘stop action’ friction stir weld has been prepared to understand the role of geometrical features of the tool probe in the development of the final microstructure after complete weld. Sectioning through the ‘stop action’ weld with the probe in situ displays the individual effect of thread and flat on the grain structure formation. The material at the thread surface experiences more severe deformation than the material at flat surface. Both the high-angle boundaries and mean grain size are found to be higher at the thread surface. The strain hardening capacity, stress serration amplitude, and frequency are observed to be higher in the stir zone than other weld regions.

Bonding process without pressure using a chestnut-burr-like particle paste for power electronics

The authors have successfully performed femtosecond laser peening on a 2024 aluminum alloy without any sacrificial overlays. Laser pulses were directly irradiated to the surface of specimens in the air without water film as a plasma confinement medium during the peening treatment. The fatigue life was improved as much as 38 times in comparison with base material at a stress amplitude of 195 MPa. The fatigue strength of the peened specimen after 2 × 106 cycles was 58 MPa larger than that of the base material. The femtosecond laser peening process has a great potential to be applied in various fields where conventional peening methods cannot be used, as this process can be performed under ambient conditions without the use of a plasma confinement medium such as water or transparent materials.

Prediction of Fatigue Crack Initiation Life Based on the Extended Cyclic Plasticity Model

The present paper describes the main challenges faced by the heavy metal industries in the adoption of the friction stir welding of thick section. The requirement of higher forge axis load necessitates the use of a massive and expensive FSW machine, powerful fixtures and improved tool material technology to withstand the higher bending stresses. The thicker sections are also responsible for the significant variations in the joint properties such as grain size, precipitates morphology, distribution of secondary phase particles and hardness due to the noticeable differences in the temperature distribution along the weld thickness. To address these typical challenges in the friction stir welding of thicker sections, a preheating technique along with a composite backing plate is developed. The main advantages of the present approach are to reduce the requirements of the higher forge axis load, power consumption of the FSW machine, tool wear, and improved weld productivity and joint properties through a thermal balance along the thickness of the weld. The present approach can also be extended to the thicker plates of the high strength materials.

High performance computation of residual stress and distortion in laser welded 301L stainless sheets

Ti and solution treated Mg alloys such as AZ31B (ST), AZ61 (ST), AZ80 (ST) and AZ91 (ST) were successfully bonded at 475 °C by spark plasma sintering, which is a promising new method in welding field. The formation of Ti3Al intermetallic compound was found to be an important factor in controlling the bonding strength and galvanic corrosion resistance of dissimilar materials. The maximum bonding strength and bonding efficiency at 193 MPa and 96% were obtained from Ti/AZ91 (ST), in which a thick and uniform nano-level Ti3Al layer was observed. This sample also shows the highest galvanic corrosion resistance with a measured galvanic width and depth of 281 and 19 µm, respectively. The corrosion resistance of the matrix on Mg alloy side was controlled by its Al content. AZ91 (ST) exhibited the highest corrosion resistance considered from its corrode surface after corrosion test in Kroll’s etchant. The effect of Al content in Mg alloy on bonding strength and corrosion behavior of Ti/Mg alloy (ST) dissimilar materials is discussed in this work.

Pressureless Bonding by Micro-Sized Silver Particle Paste for High-Temperature Electronic Packaging

Purpose Many practical problems in engineering require fast, accurate numerical results. In particular, in cyclic plasticity or fatigue simulations, the high number of loading cycles increases the computation effort and time. In this work, it is demonstrated that the return mapping technique in the framework of unconventional plasticity theories is a good compromise between efficiency and accuracy in finite element analyses. Design/methodology/approach The accuracy of the closest point projection method and the cutting plane method implementations for the subloading surface model are discussed under different loading conditions by analysing the error as a function of the input step size and the efficiency of the algorithms. Findings Monotonic tests show that the two different implicit integration schemes have the same accuracy and they are in good agreement with the solution carried out with an explicit forward Euler scheme, even for large input steps. However, the closest point projection method seems to...

A return mapping algorithm for elastoplastic and ductile damage constitutive equations using the subloading surface method

High-lead-containing solder has been pushed to the limit of high-temperature stability and eco-friendly technology for next-generation power electronic devices. Silver is an attractive material as alternative of high-lead solder due to its high melting point and good electrical and thermal properties. However, silver nanoparticle paste is high cost, and contains a number of organic materials such as solvent and dispersants. These tend to produce unexpected large voids in the sintered layer after heating, and this affects the properties and reliability of devices. In this study, silver pastes composed only micro-sized particles were used for joints and a bonding without applied pressure was tried. Chestnut-burr-like silver particles was prepared for bonding without pressure and the effect of addition of small and spherical silver particles on bondability was investigated. The addition of spherical particles in chestnut-burr-like particle paste was promoted the sintering behavior. The joint using mixed silver particle with the weight ration of 5:5 showed the shear strength of 18.6 MPa, which was comparable to those of silver nanoparticle pastes by pressureless process.