Yuichiro Murakami

Effect of Volume Fraction Solid and Injection Speed on Mechanical Properties in New Type Semi-Solid Injection Process

We have developed new type semi-solid injection process, that is, runner-less injection process which can obtain high material yield of about 90% for magnesium alloy. In this process, alloy billets are heated to the semi-solid temperature in the injection cylinder and are injected into a permanent mold. In order to investigate the effects of volume fraction solid and injection speed on microstructure and mechanical properties of AZ91D magnesium alloy injected into the permanent mold, semi-solid forming testing machine which has the same system as a runner-less injection machine, has been made on an experimental basis. The magnesium billet precisely controlled at given temperature has been injected into a permanent mold with two kinds (slow and high) of speed and plate-like specimens with each fraction solid have been fabricated. Microstructure has been observed by optical microscopy and X-ray computerized tomography (CT) scanner. Mechanical properties have been measured by tensile test. The effects of volume fraction solid of the alloy slurry and injection speed on mechanical properties have been clarified.

Microstructures and Casting Defects of Magnesium Alloy Made by a New Type of Semisolid Injection Process

We have developed a new type of semisolid injection process that allows magnesium alloys to be formed in high material yields approximating 90%. In this process, generic magnesium billets are heated into their semisolid temperature range in an injection cylinder, without cover gas, and then the material is injected into a mold.

Effect of Vibration during Solidification to Obtain High Potential Metallic Materials

We have developed vibration assisted solidification process. It is very useful and effective process to obtain high potential metallic materials which have very fine crystal. Aluminum alloys and magnesium alloys are induced electromagnetic or mechanical vibrations during solidification. Both alloys have fine grain and also decrease casting faults after solidification. In this paper, we introduce and discuss the effect and the mechanism of vibration assisted solidification process.

Investigation of Strontium-Niobium Oxides for Application to Thermal Barrier Coatings

We have been trying to find new oxide compounds with large thermal expansion coefficients and low thermal conductivities by means of a material calculation technique. Among thousands of compounds in the databases, we found that there were some materials with low thermal conductivities and large thermal expansion coefficients in the group of strontium-niobium oxides. For example, Sr4Nb2O9 has a thermal expansion coefficient of 14.510-6 / and thermal conductivity of 1.0 W/mK, although a slight amount of other phases appear during long-term annealing. These thermal properties are better than those of yttria-stabilized zirconia, which is the standard material for thermal barrier coatings. To prevent the precipitation of other phases, we prepared the solid solutions, Sr4Nb2-xMxO9. In this study, the thermal conductivities and thermal expansion coefficients of these solid solutions were measured, and their thermal stabilities were evaluated by long-term annealing.

Effect of the Shape of Solid Particles on the Distribution of Particles in JIS AC4CH (A356) Aluminum Alloy Semi-Solid High-Pressure Die Casting

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.

Effect of machining and storage conditions on hydrogen analysis for 7075 aluminum alloy

アルミニウム合金中の水素は,ミクロポア中にてガス状, または格子中に原子状で存在しており,材料の機械的特性に 影響を及ぼすと考えられている。また,多量に水素が存在し ている場合には,熱処理や溶接時の膨れをもたらすことも知 られている 。それゆえ,アルミニウム合金の諸特性を 所望の値とするためには,アルミニウム合金中の水素含有量 を精密に制御する必要がある。そのためには,アルミニウム 合金における水素量を精度よく分析することが不可欠であ る。アルミニウム合金における水素量の分析については,軽 金属協会規格LIS A06-1993に規定されている 。試料形状・ 寸法は,体積が比較的大きく比表面積が小さいφ8 mm程度の 円柱状試料であることが推奨されている。また,試料の前処 理として,油などを用いずに旋削した後すぐに,あるいは水 酸化ナトリウム水溶液に浸漬後,水洗,硝酸水溶液によるデ スマット処理,水洗,アルコール・アセトン洗浄後に,真空 加熱抽出,真空融解抽出,または不活性ガス融解抽出の方法 で定量分析することと定められている。しかしながら,これ らの前処理や分析方法に関する詳細な条件などは示されてい ない。さらに,実際のアルミニウム合金の水素分析において は,試料の前処理,分析方法,および分析条件によって分析 値が大きく異なることが知られている 。すなわち,現状で は,アルミニウム合金における水素量に関する報告値を同列 に議論することは困難である。 近年,軽金属学会においてアルミニウム中の水素研究部会 が立ち上げられ,測定時間が短く汎用品が普及している不 活性ガス気流融解熱伝導度測定法を対象に測定値を同列に 比較できるようにする試みが行われている 。その中で,清 水 は,前処理条件に関する調査を行い,その結果,旋盤 加工による前処理が測定値のばらつきを減らすことに最も有 効であると報告している。また,不活性ガス気流融解熱伝導 度測定法による水素分析装置を提供するメーカーの一社であ るLECO社の技術ノートにおいても,前処理として旋盤加工 が用いられている 。この技術ノートには,推奨加工条件と して回転速度600~700 rpm,送り速度~0.04 mm/rが記載され ているが,切込み量については触れられていない。さらに, 本加工条件を逸脱した場合に,水素量に影響を与えるかどう かは不明である。また,多数のサンプリングを行うにあたっ ては,より高速な加工条件が適用可能であれば作業者への負 担を軽減することもできる。そこで,本報告では,7075ア ルミニウム合金を対象として種々の条件下で旋盤加工による 前処理を行い,水素分析を実施することで加工条件の影響を 明らかにすることを目的とした。同時に,分析用試料の適切 な保管方法についても検討を行ったので,その結果を報告す る。

Development of New Type Semi-Solid Injection Process for Magnesium Alloy

We have developed new type semi-solid injection process for magnesium alloy. This process does not require to use any cover gases and the special magnesium billet such as thixo-billet. In this study, plate specimens were produced by injecting the semi-solid billet with different fraction solid. The microstructure observation, detection of casting defects by an X-ray computed tomography scanner, and tensile test were carried out. With increasing fraction solid, the size and shape of α-Mg solid particles became smaller and more spherical. In the condition of low fraction solid or forming in liquid state, the casting defects were located in the center of the specimen at the thickness direction. Additionally, the volume fraction of the casting defect decreased with increasing fraction solid. Moreover, the casting defects can be reduced by preventing solidifying and clogging of the top of the nozzle. Then, the specimen which has few casting defects could be obtained by injecting the slurry of fraction solid 0.5. However, the tensile strength and yield strength were highest in fraction solid 0.4. It is contemplated that the composition of the solid solution component element in the matrix was increased in fraction solid of 50%, therefore the matrix became brittle.

Effect of Casting Condition in Semi-Solid Aluminum Alloy Injection Process on Distribution of Defects and Density

Semi-solid process is expected as near net shape method with high quality. In this study, the semi-solid aluminum slurry was injected into a metallic mold with spiral shape cavity via some gates of several thicknesses. The effects of injection speed and gate thickness on the distribution of casting defects and density were investigated. Most of the casting defects appeared at the center of the specimen. The casting defects were generated most frequently on the tip of the spiral specimen. The amount of casting defects was decreased by semi-solid injection process than general high pressure die casting. The density of specimen made by the semi-solid injection process was approximately the same as high pressure die cast at near the gate, and increased in the other area.

Effect of Casting Defects Distribution on the Beginning of Tensile Fracture in Semi-solid Injected Magnesium AZ91D Alloy

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.

Effect of Solid Particles on Fluidity of Semi‐Solid Aluminum Alloy Slurry

Semisolid processing is considered as an attractive and promising manufacturing method for producing near net-shape metal products that have reduced porosity and shrinkage. In this study, the fluidity of Al-Si-Mg alloy slurry was evaluated by injection into a spiral metallic mold. Image analysis showed that solid particles in specimens became small and spherical with increasing shear rate on the gate. Fluidity was increased with increasing shear rate, with decreasing particle size and with particle roundness. Furthermore, particle roundness has a greater effect on fluidity than particle size.