Yoshinori Nishida

Superplasticity of whisker reinforced 2024 aluminum alloy composites fabricated by squeeze casting

Some ceramic whisker reinforced aluminum alloy composites having high specific tensile strength, good resistance to thermal fatigue and to wear have been commercialized as components of automobile etc.. However, since ceramic whiskers having high hardness are distributed in soft aluminum alloys, it is extremely difficult to machine them to produce complicated shape components. In order to overcome this difficulty, near-net shape production processes have been employed to produce metal matrix composite components. Squeeze casting is one of the most excellent production methods for near-net shape production in respect of production technique. Most of MMC products commercialized are being produced by squeeze casting. In squeeze casting, a preform made of fibers or whiskers is used as a reinforcement, and a molten metal is infiltrated into it by pressure. However, it is difficult to make a complicated shape preform and to infiltrate a molten metal into it without any damage. Therefore, there is a limit in the application of squeeze casting.

Superplasticity of a AIN/Mg-5wt%Al alloy composite made by a vortex method

Magnesium (Mg) matrix composites has a great potential to apply to automobile, aerospace industries since the density of magnesium is low as compared with other metal alloys and the composite is expected to achieve excellent mechanical, physical and thermal properties. High Strain Rate Superplasticity (HSRS) is expected to offer the efficiently near-net shape forming method for magnesium matrix composites, since HSRS materials usually exhibit an elongation of 250--600% at a high strain rate of about 0.1--10s{sup {minus}1}. The purpose of this study is to reveal the HSRS in a AlN particulate reinforced Mg-5wt%Al alloy composite fabricated by a vortex method. In addition, the superplastic deformation mechanism of the Mg matrix composite will be discussed.

Infiltration of fibrous preform by molten aluminum in a centrifugal force field

The pressure to infiltrate molten aluminum into alumina short-fiber preforms was generated by centrifugal force, and it was proved that centrifugal force is effective as a motive force for the infiltration and sound composites that are produced. The initiation pressure of the infiltration was also calculated and obtained clearly. The start pressure agreed well with the threshold pressure obtained theoretically. The characteristics of the infiltration in the preform was discussed using a one-dimensional solution of D’Arcy’s law in a centrifugal force field. It was made clear that when preform surface pressure is low, the region having lower pressure than the threshold pressure appears in the infiltrated region.

K2O · 6TiO2 whisker-reinforced aluminium composite by a powder metallurgical method

Amelioration de la resistance du materiau composite par une methode de metallurgie des poudres. Etude de la relation entre la resistance a la traction et la fraction volumique de barbes dans le materiau

High strain rate superplasticity of Si3N4 whisker reinforced 7075 alloy matrix composite fabricated by squeeze casting

The {alpha}-Si{sub 3}N{sub 4} whisker reinforced 7075 aluminum alloy composite which exhibits superplasticity was produced by squeeze casting, followed by hot extrusion to pursue industrial advantages, and following results were obtained: (1) the production of {alpha}-Si3N4 whisker reinforced 7075 aluminum alloy composite which exhibits superplasticity was succeeded by squeeze casting; (2) the composite exhibited a total elongation of 260% at strain rates 0.18 s{sup {minus}1} at 773 K; (3) the superplasticity occurred in the wide range of strain rate from 0.1 to 1 s{sup {minus}1}; (4) the superplasticity occurred in the industrially useful whisker volume fraction range of 20%--30%.

Superplasticity of ceramic particulate reinforced magnesium alloy composite made by a vortex method

High Strain Rate Superplasticity (HSRS) in metal matrix composites offers an efficiently near-net shape forming method to automobile, aerospace industries. HSRS materials usually exhibit an elongation of 250-600% at a high strain rate of about 10 -1 ∼10 s -1 . The purpose of this study is to develop a thermomechanical processing route to produce a fine microstructure and to further produce HSRS in a ceramic particulate reinforced Mg alloy composite fabricated by a vortex method. The superplastic behavior at high strain rate was observed a TiC/Mg-5wt%Zn and TiC/ZK51Mg composite, fabricated by a vortex method, extrusion, and hot-rolling. The strain rate sensitivity (m value) of the composites is about 0.3∼0.4. TiC/Mg-5wt%Zn exhibits the total elongation of 340% at strain rates 0.067s -1 at 743K, although the hot-rolled TiC/ZK51 Mg composite indicates total elongation of 100% at a strain rates of 0.5x10 -1 S - 1 at 673∼713K.

Effect of thermal cycling on the properties of SiC whisker-reinforced aluminium alloys

This study was carried out to examine whether the same degradation occurred in the case of SiC whisker-reinforced aluminium alloy fabricated by squeeze casting, when it was subjected to thermal cycling

High Strain Rate Superplasticity in 10vol.% SiC Particulate Reinforced AZ31 Magnesium Alloys

AZ31 magnesium matrix composites reinforced with 10vol.% SiC particulate (2 μ m) were prepared by stirring-cast under high purity argon atmosphere, then extruded with a reduction ratio of 49:1 at 663K. Superplasticity of the composites was investigated at temperature range from 638K to 838K and strain rate from 2,08 x 10 S - to 5.21 × 10 -1 S -1 . High strain rate superplasticity has been obtained in the composites at 798K with a strain rate of 2.08 × 10 - s -1 and at 813K with a strain rate of 5.21 × 10 -1 S -1 , respectively. The maximum total elongation of 228% was obtained at a strain rate of 2.08 × 10 -1 S -1 , The strain rate sensitivity exponent (m) which was higher than 0.3, were observed when the strain rate was higher than 10 - S - at 798K. Increasing the test temperature to 813K, the maximum total elongation exceeding 195% was achieved at a higher strain rate of 5.21 x 10 -1 s -1 than at 798K. It indicates that superplasticity in such a kind of composite can be obtained by adjusting the strain rate and tensile test temperature. One kind of magnesium matrix composites may show high strain rate superplasticity under two tensile strain rates, and correspondingly at two optimum test temperatures. The higher the tensile strain rate is, correspondingly, the higher the optimum temperature is, too.

Anisotropy of the charpy impact value of carbon steels and corrective heat treatment

Abstract The anisotropy of ductility, toughness, etc., of rolled steels has a great effect on the forming limit and on formability in forging or press forming. In this paper, how the anisotropy can be reduced by different heat treatments has been explored, making use of an instrumented charpy impact machine. It has been found that the presence of elongated manganese sulphide (MnS) in spherodised steels with more than 0.017% sulphur has a great effect on the anisotropy. Though the elongated MnS was modified to globular by homogenising, the array of inclusions remained and the anisotropy of the steels could not be completely removed: however, by homogenising, the anisotropy of steels with less than 0.009% sulphur could be almost completely eliminated. In the case of a specimen orientation of 22.5° (with respect to the rolling direction) for as-received and spherodising steels with more than 0.017% sulphur, the absorbed energy became remarkably high — since ductile cracks are easily initiated along the original longitudinal direction — but this did not appear for steels with large amounts of pearlite because of the effect of the latter in reducing anisotropy. It was established that the anisotropy arises chiefly from inclusions and is also influenced by pearlite, and it was found that heat treatments are available to eliminate the anisotropy.

Fabrication of gradient distribution alumina short fibre reinforced aluminium alloy

Gradient distribution alumina short fibre reinforced 6061 aluminium alloy have been fabricated by taking advantage of preform compressive deformation during squeeze casting. Pressure was applied mechanically by a punch. Velocity of the punch, pre-heat temperature of the preforms and pouring temperature were controlled during the infiltration of molten 6061 alloy into alumina short fibre preforms. The distribution of hardness along the infiltration direction in the composites was measured and the distribution of volume fraction along the infiltration direction was calculated by the hardness. Velocity of the inflow, pre-heat temperature of the preform, pouring temperature of the molten metal, binder content of the preform and volume fraction of fibres, all have a very great effect on the gradient distribution of alumina short fibres in the aluminium alloy composites.