Yoshiaki Osawa

Material design for magnesium alloys with high deformability

Magnesium alloys are very promising structural material, especially because of their low density, but their poor deformability at room temperature is making their commercial application impractical. Some alloying elements have been shown to improve the ductility dramatically, and a search for the yet better alloying elements is now a pressing task. In this study, we investigated the effects of several alloying elements on the mechanical and deformation behaviour of magnesium alloys using both first-principles calculations as well as experiments. The first-principles calculations indicate that the influential key factor for the activation of non-basal slips is the electronegativity and atomic radius. The experimental result proves that the alloys with a similar electronegativity as magnesium and a little larger atomic radius than that of magnesium, such as Ca, Sr and some rare earth elements, show superior ductility due to activation of non-basal dislocation slips. These results propose a promising design principle for the alloys with the improved deformability at room temperature ranges.

Production of fine spherical lead-free solder powders by hybrid atomization

Considerable R&D efforts in last decade have identified several promising lead-free tin alloys for the replacement of lead-containing solders in microelectronic applications. However, it is difficult or uneconomical to produce high-quality solder balls industrially by means of conventional atomization methods. To produce acceptable lead-free solder balls efficiently and industrially, a novel powder-making process change to active voice. Hybrid Atomization that combines free fall gas atomization and centrifugal atomization effectively, was invented and developed recently by us. This new technique can produce very fine, spherical tin alloy powders with mean diameters of about 10 mm, very narrow size distributions, few satellites and low production costs. Taking Sn-9mass%Zn alloy as an example, process experiments were carried out and the optimal processing conditions obtained. Results show that the influences of processing parameters and optimum conditions are very different from those in conventional atomization processes. The spherical powder with a mean particle size of 10.6 mm and a standard deviation of 1.3—1.7 mm was obtained in the determined optimum condition.

Improved Processing of Mg-Zn-Y Alloys Containing Quasicrystal Phase for Isotropic High Strength and Ductility

The stable quasicrystal phase in Mg-Zn-Y alloys has been proved to be beneficial for strength and ductility and has also been shown to impart high fracture toughness. However, the strength of these alloys has been limited to 300MPa with an average grain size of about 1 µm. We show here a simple procedure in which a Mg93Zn6Y alloy was chilled cast and then extruded. Yield strengths of up to 400 MPa in tension and compression, accompanied by ductility of ~14% were obtained with grain of size of about 1 µm. Compression to tension yield anisotropy ratios were in the narrow range of 0.95 to 1.03. These alloys also showed ageing response with two peaks. The effect of precipitation ageing on the mechanical properties has been studied.

Application of 3-Dimensional Powder Laminating Fabrication to Metallic Components

Production of dense metal products by a three-dimensional inkjet printing system was developed. Carbonyl nickel powder with a mean particle size of 5μm was used as a raw material and two binder supply methods, (i) coating a water soluble polymer on the powder and then supplying thin polymer-dissolved water from the inkjet head; (ii) supplying a binder directly from the inkjet head were examined. The layered green product was sintered in a hydrogen atmosphere at a temperature in the range of 1073-1623K. Microstructure observation was done and sintering procedure was discussed. Sintered samples fabricated from the coated powder had non-uniform microstructure with different densities due to agglomeration of the coated powder. The inhomogeneous microstructure was improved by screening the agglomerated particles, or agglomerating most of the powder to the contrary. However, the elimination of the density variegation was not achieved in the method using the coated powder. In samples made from the powder bonded by the binder directly, microstructure was fairly homogeneous. The homogeneous microstructure helped uniform sintering, and the macroscopic shape was retained after high temperature sintering at 1623K, and a high density of over 90% was achieved.

Effect of Alloy Composition on Microstructure and Strength of Fine Grained Extruded Mg-Zn-Y Alloys Containing Quasicrystal Phase

Earlier, we reported very high yield strengths of 400 MPa accompanied by total elongations of over 12% in Mg-6xZn-xY alloys, where x=1.0, 0.5, 0.35 and 0.2 in at%, dispersed with quasicrystalline phase and processed by extrusion. Here we report on the effect of low amount of alloying elements zinc and yttrium on the texture and anisotropy of the Mg-Zn-Y alloys. With decreasing amount of the alloying elements, the yield strength of the extruded alloys remains close to 400 MPa with total elongation to failure of about 12%, while the anisotropy keeps increasing. Thus very high tensile strengths with moderate ductility are achieved even in very dilute alloys. With lesser amount of alloying elements the degree of dynamic recrystallization is reduced and the intensity of the basal texture is increased, resulting in higher yield anisotropy.

Evaluation of Damping Property of Aluminum-Alloyed Cast Iron by Several Methods

In this research, the effect of the aluminum addition to cast iron on damping property was investigated by central vibration method, dynamic mechanical analysis, ultrasonic attenuation measurement and impact sound method. All measurement results indicated that the addition of aluminum improve the damping property of cast iron.

Fabrication of Nano-Laminar Glass/Metal Composites by Sintering Glass Flakes

Fabrication of nano-laminar ceramic composite by a simple sintering technique was examined. Glass flakes with a thickness of 0.7μm coated with silver were used as model materials, and were consolidated by pulsed current sintering with a uniaxial press of 7.1MPa or 30MPa. By sintering the flakes at 943K, we obtained a fairly dense composite where the flakes were aligned by uniaxial press. The silver coating remained on the flakes through the sintering, and an interface layer between the flakes was formed. The sample’s indentation test demonstrated its high resistance to crack propagation through the transverse direction of the lamellar; this result was attributed to crack deflection at the interface and the accumulation of microfractures around the indentation mark.