Shuji Tada

Synthesis and consolidation of TiAl by MA–PDS process from sponge-Ti and chip-Al

Abstract Low cost sponge-Ti and recycled chip-Al were used as starting materials for the synthesis and consolidation of TiAl alloy via a mechanical alloying (MA) and pulse discharge sintering (PDS) process. Amorphous structured TiAl powder was obtained by MA process from sponge-Ti/chip-Al and was sintered and concurrently consolidated with the PDS process. The obtained TiAl alloy consists of γ-TiAl and α2-Ti3Al and additional Ti2AlC phase. The microstructure of the alloy can be controlled by the sintering temperature. It was found that fine equiaxed grains were obtained by low temperature sintering while fine duplex structures formed at high temperature sintering. Compared with alloys fabricated from high cost elemental Ti/Al powder with a similar process, the alloys sintered at high temperature with this process possess much higher strength at both room temperature and elevated temperatures.

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.

Properties of New TiC/TiB2/Fe-Al Cermet Alloy

Effect of TiB2 substitution on thermal conductivity and hardness in TiC / Fe-Al cermets was investigated. The (70-x)TiC / xTiB2 / 26Fe-4Al mass % cermets were fabricated by mechanical milling and subsequent pulsed current sintering method. The high relative density compacts was formed by sintering at 1423 K under 25 MPa for 60 s. The sintered materials were mainly composed of TiC, TiB2 and Fe-Al intermetallic compound. In addition, small amounts of Fe2B surrounding TiB2 were formed. The thermal conductivity of the sintered compact lineally increased with increasing TiB2 volume fraction. However, the hardness of the sintered compacts of x = 20 – 40 were higher than that of x = 0. Therefore, the substitution of TiC to TiB2 in the TiC / Fe-Al based cermet is effective to improve the thermal conductivity without the degradation of hardness.

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.

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.

Effects of Water Content of Frozen Mold on Fluidity of Aluminum Alloy

The frozen mold that is fabricated by refrigerating the mixture of sand and water has many advantages to improve the working environments such as noise, vibration, dust and bad smell. The fluidity might be the key issue to spreading this technique to light metals such as aluminum and magnesium because a frozen mold has the possibility to accelerate solidification due to its large cooling ability. In this study, the fluidity of an aluminum alloy (AC4CH) cast in the frozen mold, and the effect of water content of frozen mold on the fluidity was investigated. It is revealed that the AC4CH aluminum alloy has better fluidity against the frozen mold rather than the conventional green sand mold. The flow length of aluminum alloy cast into the frozen mold was influenced by the water content of frozen mold, and increased with decrease in the water content. The good fluidity can be achieved by the mold with the low temperature decrease property.

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.