Shinji Koyama

Fabrication of Aluminum Tubes Filled with Aluminum Alloy Foam by Friction Welding

Aluminum foam is usually used as the core of composite materials by combining it with dense materials, such as in Al foam core sandwich panels and Al-foam-filled tubes, owing to its low tensile and bending strengths. In this study, all-Al foam-filled tubes consisting of ADC12 Al-Si-Cu die-cast aluminum alloy foam and a dense A1050 commercially pure Al tube with metal bonding were fabricated by friction welding. First, it was found that the ADC12 precursor was firmly bonded throughout the inner wall of the A1050 tube without a gap between the precursor and the tube by friction welding. No deformation of the tube or foaming of the precursor was observed during the friction welding. Next, it was shown that by heat treatment of an ADC12-precursor-bonded A1050 tube, gases generated by the decomposition of the blowing agent expand the softened ADC12 to produce the ADC12 foam interior of the dense A1050 tube. A holding time during the foaming process of approximately tH = 8.5 min with a holding temperature of 948 K was found to be suitable for obtaining a sound ADC12-foam-filled A1050 tube with sufficient foaming, almost uniform pore structures over the entire specimen, and no deformation and minimum reduction in the thickness of the tube.

Functionally Graded Aluminum Foam Fabricated by Friction Powder Sintering Process with Traversing Tool

Functionally graded aluminum foam (FG Al foam) is a new class of Al foam in which the pore structure varies over the foam, resulting in corresponding variations in the mechanical properties of the foam. In this study, FG Al foam plates were fabricated by a friction powder sintering (FPS) process with a traversing tool that is based on a previously developed sintering and dissolution process. The variation of the mechanical properties was realized by setting the volume fraction φ of NaCl in the mixture to 60, 70, and 80%. Long FG Al foam plates were fabricated with a length equal to the tool traversing length with φ varying in the tool traversing direction. From x-ray computed tomography observation, it was shown that the density of the Al foam decreased with increasing φ. In contrast, almost uniform pore structures were obtained in each area. According to the results of compression tests on each area, the plateau stress and energy absorption tended to decrease with increasing φ. Therefore, it was shown that FG Al foam plates with varying mechanical properties can be fabricated by the FPS process with the traversing tool.

Behavior of Oxide Film in Transient-Liquid-Phase Bonding of Tin with Filler of Bismuth Film

The bond interface of a TLP (Transient Liquid Phase) bonded tin has been observed with a TEM to investigate the effect of the liquid phase on the behavior of the superficial oxide film at the interface during the bonding process. In the solid-state-diffusion bonded joint without filler, abundant oxide inclusions were observed to be distributed within a region of a few 100 nm widths along the bond interface. In comparison with this, the liquid phase introduced by the eutectic reaction of the bismuth filler with the tin substrate decreased the width of the interfacial region involving abundant oxide inclusions to form a rather layer structure a few 100 nm thick consisting mainly of SnO2. It also enhanced the annihilation of the uncontacted areas at the interface. The layer of the oxide became discontinuous and coalesced with an increase in bonding temperature and pressure, and areas where no oxide inclusion could be observed at the interface were increased, when the liquid phase was formed. Owing to these effects, the bond strength rose at lower bonding temperatures and pressures when the bismuth filler was applied.

Cu/Cu direct bonding by metal salt generation bonding technique with organic acid and persistence of reformed layer

In this study, the effect of the metal salt generation bonding technique on the strength of a direct-bonded copper–copper interface was investigated. Copper surfaces were modified by boiling in several types of organic acids, and direct bonding was performed at a bonding temperature of 423–673 K under a load of 588 N (for a bonding time of 0.9 ks). As a result of the surface modification, bonded joints were obtained at bonding temperatures of 150 K (after treatment with formic acid) and 100 K (after citric acid treatment) lower than that required for the unmodified surfaces. In addition, the duration of the modification effects was investigated by exposing the modified surface to an air atmosphere furnace kept at 323 K. The bonding strength of the citric acid-modified surface remained unchanged even after 168 h, whereas that of the surface modified with formic acid decreased within 6 h.

Effect of filler content on tensile properties of underfill material for flip chip bonding

The effects of the filler content and temperature on tensile properties of underfill were investigated using underfill materials which are composed of bisphenol F-type epoxy resin and spheroidal SiO2 filler. Youngs modulus of underfill increased and fracture strain decreased with increasing the SiO2 filler content. The effects of the SiO2 filler content on Youngs modulus and fracture strain were relatively large. However, the effect on tensile strength was negligible. Tensile strength was strongly affected by the strength of matrix resin itself. When the temperature was above Tg, Youngs modulus decreased and fracture strain increased remarkably. Fracture mainly occurred in matrix resin below Tg and in the interface between matrix resin and filler above Tg.

Effect of the Organic Acid Surface Modification on Bond Strength of Tin and Copper

The effect of citric-acid surface modification on the bond strength of the solid-state bonded interface of tin and copper has been investigated by SEM observation of the interfacial microstructures and fractured surfaces. Citric-acid surface modification was carried out in a vacuum chamber at a bonding temperature of 383–473 K and a bonding pressure of 7 MPa (bonding time: 1800 s). The citric-acid surface modification decreased bonding temperature by 70 K at which bonded joints could be obtained and bond strength comparable with the base metal was achieved.Copyright

Reproducibility of Aluminum Foam by Combining Sintering and Dissolution Process with Precursor Foaming Process

A preliminary study of the reproducibility of aluminum foam was performed. Aluminum foam was fabricated by a sintering and dissolution process. It was found that aluminum foam containing a blowing agent can be fabricated without the decomposition of the blowing agent, namely, the densified aluminum foam can be used as a foamable precursor for refoaming. By heat treatment of the densified aluminum foam containing the blowing agent, pores were reproduced in the aluminum.

Effect of high temperature and humidity treatment on adhesion properties and bulk properties of structural adhesive

To investigate effects of high temperature and humidity treatment on adhesion properties and bulk properties of structural adhesive, a tensile test was conducted and the results were compared with those of a lap shear test. In the stress-strain curves, the changes in fracture strain and elastic modulus with increasing aging time at 80 oC in 95% R. H. were negligible. On the other hand, the extension of adhesive was 1.0% before aging, and it decreased to 0.5% by aging over 200 h. The reduction of the extension with aging was caused by hydrolysis of urethane which is added for flexibility. In aging at 80 oC in 95% R. H., the tensile strength decreased with increasing aging time until 200 h, after that the strength was stable. In the fracture surfaces of bulk specimen, fracture with elongation of matrix resin occurred in the unaged specimen. On the other hand, the crack mainly progressed at the boundary between the filler and the matrix in the aged specimen. Comparing the results with those of a lap shear test, the decrease of the lap shear strength was much larger than that of tensile strength of adhesive itself in aging at 80 oC in 95% R. H. The difference of deterioration of both strength depends on the change of the fracture mode. In the lap joint specimen, the main fracture mode changed from cohesive fracture to interfacial fracture upon aging. The result shows that the deterioration of interface was faster than that of adhesive resin itself.

Electrochemical corrosion of copper and copper alloy in aqueous propylene glycol containing rust inhibitors

The effects of rust inhibitors in brine on corrosion behaviors of copper and brass have been investigated by measurement of cathode and anode polarization curves and immersion test. As rust inhibitors, benzotriazole, sodium benzoate and sodium nitrite solutions were prepared. As a result, it was found that benzotriazole and sodium benzoate solutions have rust-inhibiting effect for both copper and brass. In contrast, sodium nitrite has poor rust-inhibiting effect on both copper and brass, compared to other rust inhibitors.

Effect of aging and test temperature on adhesion strength of copper and epoxy resin

The aim of this study is to investigate the effect of aging and test temperature on adhesion strength of the resin (bisphenol F-type epoxy resin)/Cu interface. The adhesion strength of the Cu joint with the resin was investigated by the tensile test. The tensile test was conducted at a tensile rate of 0.1 mm/s. Tensile strength was 8.9 MPa before aging and it gradually decreased with aging at 175 °C and fell to half or less after aging for 1000 h. Tensile strength and fracture strain decreased with increasing test temperature. The fracture occurred mainly at the adhesion interface. At the temperature above glass transition temperature of resin material, the interface strength decreased.