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Murakami Y.,Japan National Institute of Advanced Industrial Science and Technology | Miwa K.,Aichi Science and Technology Foundation | Kito M.,Aisan Industry Co. | Honda T.,Aisan Industry Co. | And 2 more authors.
Materials Transactions | Year: 2016

In semi-solid forming processes for metals, it is important to make slurries with fine, round solid particles. In this study, we investigated the effects of mechanical vibration on the size and shape of solid particles. The slurry was prepared by pouring molten AC4CH aluminum alloy into a vibrating stainress container, and the vibration of the container was controlled. The solid particles in the slurry became finer and rounder with increasing acceleration amplitude at the same frequency, or with decreasing frequency at the same acceleration amplitude. However, at the same velocity amplitude and different frequency and acceleration amplitude, the solid particles formed a dendritic structure at high or low frequencies. The solid particles were the finest and roundest at a frequency of 50 Hz. The calculation results for the particle diameter and the particle roundness also showed that the solid particles became finer and rounder with increasing velocity amplitude. Additionally, the shapes of solid particles were affected by the frequency and displacement amplitude. Mechanical vibration with a frequency and displacement amplitude above certain threshold values produced fine, round solid particles. Slurry containing sufficiently fine, round particles was obtained by applying mechanical vibration at 50Hz with an acceleration amplitude higher than 49.0m/s2. © 2016 The Japan Institute of Metals and Materials. Source


Murakami Y.,Japan National Institute of Advanced Industrial Science and Technology | Miwa K.,Aichi Science and Technology Foundation | Kito M.,Aisan Industry Co. | Honda T.,Aisan Industry Co. | And 2 more authors.
Materials Transactions | Year: 2016

The semi-solid process is promising as a near-net-shape method for producing high performance products. However, the method is hampered by poor formability because of low fluidity, and difficulty in making the semi-solid slurry. In previous work, we made semi-solid slurries containing small, spherical solid particles by applying mechanical vibration. In this study, we evaluated the fluidity of AC4CH aluminum alloy slurries made by applying mechanical vibration. In addition, we improved the slurry fluidity by applying shear stress to the slurry at the mold gate, and investigated the effect of the shear rate on the fluidity. The slurry was prepared by applying mechanical vibration at a frequency of 50 Hz and an acceleration amplitude of 166.6m/s2 (17 G). The fluidity was evaluated by injecting the slurry through a gate into a metallic mold with a spiral cavity, and measuring the fluidity length. The shear rate at the gate was controlled by changing the thickness of the gate (1.0, 2.2, and 4.0 mm). The fluidity of the slurry made by mechanical vibration was 25% to 40% that of liquid aluminum. Applying shear stress at the gate increased the fluidity by approximately 30%. The i-phase particles in the specimen became finer and rounder as the shear rate increased. Therfore, semi-solid slurry with high fluidity can be obtained by applying mechanical vibration and increasing the shear rate. Moreover, the slurry prepared by mechanical vibration had similar fluidity to the electromagnetically stirred slurry prepared at high shear rates and casting pressures. Our method could be used to to fabricate complex products by the semi-solid forming process. © 2016 The Japan Institute of Metals and Materials. Source


Murakami Y.,Japan National Institute of Advanced Industrial Science and Technology | Miwa K.,Aichi Science and Technology Foundation | Omura N.,Japan National Institute of Advanced Industrial Science and Technology | Tada S.,Japan National Institute of Advanced Industrial Science and Technology
Materials Transactions | Year: 2012

Semisolid injection molding is expected to be increasingly utilized as a forming process applicable to highly flammable magnesium alloys, since it can be carried out at temperatures lower than those of die casting. In this study, we investigated the effects of molding conditions on the tensile strength and internal casting defects of AZ91D magnesium alloy. Semisolid injection molding was conducted at injection speeds of 220, 300 and 400 mm·s 11 and fraction solids of 0.0, 0.3, 0.4 and 0.5. Whereas the volume fraction of casting defects decreased together with the decrease of injection speed, the mechanical strength reached a maximum at an injection speed of 300 mm·s 11. The investigation results show that in the solidification microstructure, i-Mg and c-Mg 17Al 12 phases, which were liquid during injection, were refined at higher injection speeds, suggesting that the tensile strength increases together with the injection speed if there are no casting defects. This trend might be due to the increased heat transfer coefficient between the mold and the slurry from the higher flow rate. On the other hand, the volume fraction of casting defects increased together with injection speed, and as a result the tensile strength deteriorated. When the injection speed was increased, the effects of decreased strength due to the increase in the volume fraction of casting defects counterbalanced the effects of increased strength due to the refinement of i-Mg + c-Mg 17Al 12 mixed phase. For this reason, the mechanical strength is considered to reach a maximum at an injection speed of 300 mm·s 11. Thus, we demonstrated that the tensile strength of semisolid products is affected not only by the volume fraction of casting defects, but also by the microstructure of the residual mixed phase precipitated, which is refined by increasing the injection speed. Source


Murakami Y.,Sustainable Development Technology | Miwa K.,Aichi Science and Technology Foundation | Kanetake N.,Nagoya University | Tada S.,Sustainable Development Technology
Magnesium Technology | Year: 2013

Semi-solid process is useful for magnesium alloys because processing temperatures lower than conventional casting processes result in decreased combustibility. Additionally it can decrease casting defects by the increased viscosity and decreased solidification shrinkage. In this study, casting defects of semi-solid injected AZ91D specimens were observed by X-ray CT tomography and tensile test was carried out. Thus, relations between casting defects and fracture starting point were investigated. As a result, the specimens were not always fractured at the site of the largest defect; meanwhile the defects situated near the surface or perpendicularly elongated to the tension axis exerted a potent influence on fracture. Source


Murakami Y.,Japan National Institute of Advanced Industrial Science and Technology | Miwa K.,Aichi Science and Technology Foundation | Kito M.,Aisan Industry Co. | Honda T.,Aisan Industry Co. | Tada S.,Japan National Institute of Advanced Industrial Science and Technology
TMS Light Metals | Year: 2016

In the semi-solid high-pressure die casting process, the slurry flows as a solid-liquid two-phase flow. In this study, the effect of the shape of solid particles on their distribution in the slurry was investigated. The solid particles were concentrated in the center of the flow direction in the case of globular-shaped solid particles and high-flow-velocity conditions. Moreover, the concentration ratio of the solid particles increased with an increasing Reynolds number. This phenomenon was explained as follows. The shape of the solid particles affected the viscosity of the slurry; the viscosity was decreased by the globular particles. The solid particles applied Saffman force, which is generated by the velocity gradient, and moved in the direction away from the solid-liquid interface. The Reynolds number increased with decreasing viscosity or increasing flow velocity; therefore, the Saffman force increased with an increasing Reynolds number. Source

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