Pure aluminium and high-silicon aluminium alloy were reinforced with the discontinuous pitch-based carbon fibres by squeeze casting, then the thermal conductivity and the mechanical properties of the composites were investigated. Optical microscopy revealed that the fibres were in a random planar arrangement, and the transmission electron microscopy revealed that there is no interfacial reaction between the matrices and the fibres. The random planar arrangement of the fibres leads to the anisotropy of the composite. The fibre-reinforcement increased the thermal conductivity in the parallel direction for both pure aluminium and its alloy matrices, while the thermal conductivity decreased in the vertical direction. The increase in the elastic modulus by the reinforcement was not observed for both matrices. The proof stress of the pure aluminium increased by the reinforcement especially in the parallel direction, while that of the high-silicon alloy decreased by the reinforcement.

Magnesium alloys, in which the in-situ Mg2Si particles were dispersed, were fabricated by a casting process, and the dry sliding wear behavior of the alloys was investigated. Optical microscopy revealed that the polygonal Mg2Si particles were homogeneously dispersed in the alloys. Mg2Si particle volume fractions in the alloys were 7 and 11 vol%. Although the wear loss of the alloy decreased due to the particle-dispersion, there was no difference in the wear loss between the alloys with different volume fractions. The worn surfaces of the particle-dispersed alloys were covered with the crumbled Mg2Si particles, which would prevent seizure between the alloy and the steel counterpart, leading to an improvement in the wear resistance of the alloy. The particle-dispersion slightly decreased the scatter of the coefficient of friction during the wear for the low sliding speed and load, but the effect of the dispersion was not clearly observed for the high speed and load.

Aluminium composites reinforced with the PAN-and pitch-based short carbon fibres were fabricated by squeeze casting, then the thermal expansion behaviour of the composites was investigated. Optical microscopy revealed that the fibres were in a random arrangement on the plane parallel to the pressed plane during the melt infiltration process. TEM observation and hardness test revealed that the PAN-based fibre bonds strongly with the aluminium matrix while the pitch-based fibre bonds poorly. The difference in the bonding strength affected the thermal strain response; the heating and cooling curve approximately traced the same paths during the heating-cooling cycles for the PAN-based fibre composite, while the curve did not trace the same path for the pitch-based fibre composite. The fibre-reinforcement decreased the coefficient of the thermal expansion (CTE) of matrices in the direction parallel to the pressed plane. For example, the CTE of the pure aluminium and its composite at 333 K were 23.0 and 19.0 x 10(-6)/K, respectively.

Pure aluminum and AC8A aluminum alloy matrix composites, which were reinforced with PAN- and pitch-based short carbon fibers, were fabricated by squeeze casting, then the composites were exposed to a heat treatment. The effects of the fiber types, composition of the matrix, and heat treatment on the mechanical properties of the composites were investigated. The fibers were in a random planar arrangement in the composites. Although the aluminum carbide was formed due to the reaction between the PAN-based fiber and pure aluminum during the casting process, there was no reaction products near the PAN-AC8A, pitch-pure aluminum and pitch-AC8A interfaces. Although the ultimate compressive strength of the PAN-based fiber composite was greater than that of the pitch-based fiber composite under every condition, the strength of the PAN-based fiber composite degraded due to the heat treatment when pure aluminum was used as the matrix. Examination of fracture surface indicated that the lower reinforcing effect of the pitch-based fiber would be due to delamination at the boundary between the highly-developed graphite crystallites in the fiber. A hardness measurement of the fibers in the composites using a nano-indenter revealed that the interfacial bonding strength between the pure aluminum and PAN-based fiber degraded due to the heat treatment.

The effects of carbon fiber-reinforcement on the wear behavior of aluminum alloy under a dry sliding conditions have been investigated. Two kinds of carbon fibers, PAN-based and pitch-based short carbon fibers, were used as the reinforcements. The composites were fabricated by squeeze casting, and wear testing was carried out using the pin-on-disk method. The wear loss of the alloy and counterpart decreased due to the fiber-reinforcement. The change in the coefficient of friction during the wear test and the scatter in the roughness of the worn surface also decreased by the reinforcement. Examination of the worn surfaces and temperature change of the specimens during the wear revealed that these results were mainly attributed to the crumbled fibers forming a solid lubricant film on the worn surfaces thus preventing seizure of the matrix with the counterpart. Under a high load and sliding speed, the wear loss of the pitch-based fiber composite was lower than that of the PAN-based fiber one. The examination described above revealed that the improvement in the wear and seizure resistance was mainly attributed to the higher thermal conductivity of the pitch-based fiber composite.

Turning machinability of aluminum alloy composites reinforced with carbon fibers was examined using a carbide tool. Pitch-based short carbon fiber was used as the reinforcement. The composites were fabricated by squeeze casting. Optical microscopy revealed that the fibers were randomly arranged in the alloy matrix. The fiber reinforcement decreased the hardness of the alloy. The fiber reinforcement also decreased the cutting resistance of the aluminum alloy, and the resistance values of the composite was lower than that of a composite reinforced with short alumina fibers. The roughness of the machined surface was significantly decreased by the fiber reinforcement under every cutting condition. No carbide tool wear was observed even if the composite underwent a machining of 2 km, whereas the tool wear was clearly observed for the alumina fiber-reinforced composite. These results indicated that the carbon fibers in the alloy act as a solid lubricant. Chips formed by machining the composite were powdery, whereas the chips formed by machining the unreinforced aluminum alloy was long.

Alumina fiber-reinforced aluminum alloy composites were prepared by squeeze casting, and the effect of the reinforcement on the machinability of the alloy was investigated. Two kinds of short alumina fibers, which have the same fiber size but different hardness, were used. Preform in which the fibers were in a random arrangement was formed with SiO2 binder, and then was infiltrated with the alloy melt to prepare the composite. The fiber-matrix interfacial bond via the binder is sufficient and no reaction product was detected. The cutting force of the alloy was reduced by the fiber-reinforcement. The lower the hardness of the fiber in the composite, the lower the cutting force of the composite. The roughness of the machined surface was drastically decreased by the reinforcement. Observation of the chip formed on the machined surface indicated that the fiber suppressed the formation of the built-up-edge, and this fact would lead to the reduction in the surface roughness by the reinforcement. The chips were shortened by the reinforcement. The difference in hardness of the alumina fiber hardly affected the roughness and the chip morphology. The hardness of the fiber has a strong effect to decrease the tool life.

The effects of reinforcement with the potassium hexatitanate short fiber on the machinability of the alloy under various cutting conditions were investigated. JIS-AC8A alloy was used as the matrix metal, and two kinds of potassium hexatitanate short fibers were used as the reinforcements. The composites were fabricated by squeeze casting. The machinability of the composites was compared with that of the composites reinforced with various reinforcements such as potassium titanate whisker and aluminum borate whisker. The reinforcements were randomly arranged in the alloy matrix, and no agglomeration of the reinforcements or porosity was observed, indicating that the melt infiltration into the reinforcement preform was perfectly accomplished. The cutting force and feed force of the alloy was reduced by the reinforcement. These force values when the potassium hexatitanate short fiber- reinforced composite was machined was smaller than that when the composites with other reinforcements were machined. The roughness of the machined surface of the alloy drastically decreased by the reinforcement under every cutting condition, and the surface roughness of composites was close to the theoretical roughness. Significant difference in roughness values between the composites was small. From the surface roughness values, the observation of the chip formation in the cutting process and the observation of machined surface, we have concluded that the reinforcements in the composite suppress the formation of the built-up edge during the cutting process. The machined surfaces and chip forms indicated that the reinforcements in the composite facilitated the shear deformation of the chips because the fibers were easily sheared by the cutting. The tool life when the potassium hexatitanate short fiber- reinforced composite was machined was significantly longer than that of aluminum borate whisker - reinforced composite.

Fiber-reinforced aluminum alloy composites were fabricated by squeeze casting, and the effects of the fiber reinforcement on the machinability of the alloy were investigated. Al-Si-Cu-Ni-Mg alloy was used as the matrix metal, and two kinds of short alumina fibers were used as the reinforcements. The cutting force values of the alloy were reduced by the fiber reinforcement under every cutting condition. The lower the hardness of the fiber in the composite was, the lower the cutting force of the composite was. The roughness of the machined surface decreased by the fiber reinforcement. This result and the in situ observation of cutting process revealed that the fibers in the composite suppress the formation of the built-up edge. The observation of chip forms indicated that the fibers in the composite facilitated the shear deformation of the chips because the fibers were easily sheared by the cutting. Continuous chips were formed after cutting the unreinforced alloy, while serrated chips were formed after cutting the composites. The lower the hardness of the fiber in the composite was, the lower the tool wear was.

To develop a machinable aluminum alloy composite with high strength, high rigidity and low thermal expansion rate, potassium hexatitanate short fibers were selected as the reinforcements for the composite. JIS-AC8A alloy was used as the matrix metal, and two kinds of potassium hexatitanate short fibers were used as the reinforcements. The composites were fabricated by squeeze casting. The microstructure, thermal conductivity, thermal expansion behavior, and mechanical properties under compressive stress of the composites were investigated. These properties of the composites were compared with those of the unreinforced AC8A alloy and the composites reinforced with various reinforcements such as potassium titanate whisker and aluminum borate whisker. Optical microscopy revealed that the reinforcements were three-dimensionally arranged in the alloy matrix, and no agglomeration of the reinforcements or porosity was observed, indicating that the melt infiltration into the reinforcement preform was perfectly accomplished. The thermal conductivity of the composite decreased as the reinforcement volume fraction increased, and the value of the short fiber-reinforced composite is similar to that of the potassium titanate whisker-reinforced composites. This tendency can be roughly estimated by Landauer's model. The average thermal expansion coefficient of the composite decreased as the volume fraction increased, and the experimental values were in good agreement with the theoretical values calculated using the Shi's model. Although the compressive elastic modulus and 0.2% proof stress increased due to the reinforcement at both room temperature and 523 K, the increase in the volume fraction from 25 vol% to 45 vol% had a small effect on improving these mechanical properties for the short fiber-reinforced composite.

The possibility of turning fiber-reinforced aluminum alloy composites using a carbide tool was examined. Two types of short alumina fibers, which have the same fiber size, but a different chemical composition and hardness, were used as the reinforcements. The composites were fabricated by squeeze casting. Optical microscopy revealed that the fibers were randomly arranged in the alloy matrix. Fiber reinforcement decreased the cutting force and feed force of the aluminum alloy. The lower the hardness of the fiber in the composite, the lower the cutting force and feed force of the composite. The roughness of the machined surface was significantly decreased by the fiber reinforcement under every cutting condition. Observation of the chip formed on the machined surface indicated that the decrease in the surface roughness by the reinforcement was due to the suppression of the built-up-edge formation. Roughness values of the machined surface of the composite were similar to those when a diamond tool was used. The decrease in the hardness of the fibers in the composite had a significant effect on providing the long tool life.

Short potassium titanate fibers were selected as the reinforcements to obtain the machinable aluminum alloy composites. The composites were fabricated by squeeze casting, and the turning machinability of the composites was investigated. The whisker-reinforced composites were also fabricated to compare their properties with the fiber-reinforced composites. The cutting force was lowered by the reinforcement, and that of the fiber-reinforced composite was lower than that of the whisker-reinforced composites. The roughness of the machined surface was lowered by the reinforcement. This result and the in situ observation of cutting process indicate that the reinforcements in the composite suppress the formation of the built-up edge. Continuous chips were formed after cutting the unreinforced alloy, while serrated chips were formed after cutting the composites. Under the standard condition for the finishing cut of nonferrous metals, the composite can be machined for a long time without changing the carbide tool.

Short potassium titanate fibers were selected as the reinforcements to obtain the machinable aluminum alloy composites. The composites were fabricated by squeeze casting, and the turning machinability of the composites was investigated. The whisker-reinforced composites were also fabricated to compare their properties with the fiber-reinforced composites. The cutting force was lowered by the reinforcement, and that of the fiber-reinforced composite was lower than that of the whisker-reinforced composites. The roughness of the machined surface was lowered by the reinforcement. This result and the in situ observation of cutting process indicate that the reinforcements in the composite suppress the formation of the built-up edge. Continuous chips were formed after cutting the unreinforced alloy, while serrated chips were formed after cutting the composites. Under the standard condition for the finishing cut of nonferrous metals, the composite can be machined for a long time without changing the carbide tool.

Aluminum alloy composites reinforced with short potassium titanate fibers were fabricated by squeeze casting, and the effects of the fiber volume fraction and cutting conditions on the machinability of the composites were investigated. Composites reinforced with potassium titanate whisker and aluminum borate whisker were also fabricated to compare their machinability with the short potassium titanate fiber reinforced composite. The reinforcements were randomly arranged in the alloy matrix, and no agglomeration of the fibers or porosity was observed. While the change in cutting force values during the cutting was sometimes pronounced for AC8A alloy, it was relatively small and stable for the composite. The average cutting force was lowered by the reinforcement. This is probably due to the fact that the potassium titanate fibers or whiskers in the composite facilitated the shear deformation of the alloy. The cutting force of the potassium titanate fiber reinforced composite was lower than that of the whisker reinforced composites. The roughness of the machined surface was lowered by the reinforcement. The roughness of the AC8A alloy was considerably greater than theoretical roughness. On the contrary, the roughness of the composites was close to the theoretical roughness. This indicates that the reinforcements in the composite suppress the formation of the built-up edge. Continuous chips were formed after cutting the AC8A alloy, while serrated chips were formed after cutting the composites. These results lead to the conclusion that the machinability of the potassium titanate fiber reinforced composites is superior to that of the AC8A alloy and not less than that of the whisker reinforced composite.

Although the thinning of spheroidal graphite cast iron castings has been promoted to reduce the weight of the castings, the thinning tends to cause chilling. Due to the chilling, the required mechanical properties can not be obtained. The addition of certain elements is a way to solve this problem. In this study, the spheroidal graphite cast iron melt containing minor Bi, 3.3 to 3.7 mass% C and 2.0 to 3.2 mass% Si was poured into a stepped plate mold to obtain the thin wall castings, and observation of their graphite and matrix microstructure, thermal analysis during the solidification process of the melt in the mold and the qualitative analysis of elements inside the spheroidal graphite by FE-EPMA were carried out. It was found that an increase in the Si/C mass ratio in the spheroidal graphite cast iron was effective for decreasing the amount of cementite (chill) in the matrix, and the chill was further inhibited by adding 0.01 mass% Bi even for the thin wall castings of 2 mm. Amounts up to 0.01 mass%Bi promoted refinement of the graphite, increased the graphite nodule, and promoted ferritizing of the matrix. It was also found that a high Si/C mass ratio in the spheroidal graphite cast iron promoted the effects of Bi. The temperature of the eutectic start and that of the eutectic solidification end increased due to the 0.01 mass%Bi. The temperature of the eutectoid transformation start increased and the stability eutectoid transformation of the thin wall castings was promoted by containing a minor amount of Bi. It was confirmed that substances including Bi and Mg existed in the graphite containing Bi. These results lead to the conclusion that the Bi compound and the Mg compound acted as heterogeneous nuclei of the graphite, and the nuclei promoted the crystallization of the graphite, and then the graphite nodule increased. [doi: 10.2320/matertrans.M2009255]

Short alumina fiber-reinforced aluminum alloy composites were fabricated by squeeze casting, and the effects of the fiber reinforcement on the machinability of the alloy under various cutting conditions were investigated. Al-Si-Cu-Ni-Mg alloy (JIS-AC8A alloy) was used as the matrix metal. The mean values of the cutting force of the AC8A alloy were reduced by the fiber reinforcement. The lower the hardness of the fiber in the composite, the lower the cutting force of the composite. The range of the variation in the cutting force during the cutting of the composite reinforced with lower-hardness alumina fibers was almost the same as that of the AC8A alloy. The roughness of the machined surface decreased by the fiber reinforcement under every cutting condition, and the roughness of the composites was almost the same as the theoretical roughness when the cutting speed and feed rate were high. This result indicates that the fibers in the composite suppress the formation of the built-up edge. The machined surfaces and chip forms indicated that the fibers in the composite facilitated the shear deformation of the chips because the fibers were easily sheared by the cutting. These results lead to the conclusion that the machinability of the composites is superior to that of the AC8A alloy. [doi: 10.2320/matertrans.M2009263]

Aluminum alloy composites reinforced with the short potassium titanate fibers were fabricated to obtain a material having a low thermal expansion rate and good machinability. The composites were fabricated by the squeeze casting. The microstructure, thermal conductivity and thermal expansion behavior of the composites were investigated. Optical microscopy revealed that the fibers were homogeneously distributed in the alloy. However, the fibers were somewhat in a random planar arrangement parallel to the pressed plane when the fiber volume fraction was high. This is due to the forming of the preform by pressing the top and bottom of it. The composites were easily machined using both super alloy and diamond cutting tools. The thermal conductivity of the composite decreased as the fiber Volume fraction increased. At the higher volume fraction, the thermal conductivity of the composite in the direction parallel to the pressed plane was higher than that in the transverse direction due to the random planar arrangement of the fibers. The thermal conductivity can be roughly estimated by Landauer's model. The average thermal expansion coefficient of the composite decreased as the fiber volume fraction increased. The difference in the thermal expansion coefficient between the parallel and transverse directions to the pressed plane was slight, and the experimental values were in good agreement with the theoretical values calculated using the rule of mixture. [doi: 10.2320/matertrans.F-MRA2008933]

Aluminum alloy composites reinforced with short potassium titanate fibers were fabricated by squeeze casting, and the effect of the fiber reinforcement on the machinability of the alloy under various cutting conditions were investigated. The fibers were randomly arranged in the alloy matrix, and no agglomeration of the fibers or porosity was observed. Although the cutting force of the AC4A alloy decreased as the cutting speed increased, that of the composites little changed even though the cutting speed increased. When the cutting speed was 50 m/min, the cutting force of the AC4A alloy significantly decreased due to the fiber reinforcement. When the cutting speed was 100 and 150 m/min, the cutting force of the composites was equivalent to or less than that of the AC4A alloy. The variation in the fiber volume fraction only slightly affected the cutting force values of the composites. The roughness of the machined surface of the AC4A alloy increased as the feed rate increased, and decreased as the cutting speed increased. The fiber reinforcement diminished the variation in the roughness due to the feed rate and Cutting speed. When the feed rate was high, the roughness of the composite having a high fiber volume fraction was almost equivalent to the theoretical roughness. This indicates that the fiber reinforcement suppresses the formation of the built-up edge. The machined surface and chip forms indicated that the fibers in the composite facilitated the shear deformation of the chips because the fibers were easily sheared by the cutting. These results lead to the conclusion that the machinability of the composite is superior to that of the AC4A alloy. [doi: 10.2320/matertrans.MER2008180]

In order to develop a process to obtain a functional layer on the surface of a magnesium alloy, the composite layer including in situ Mg2Si was formed on the surface by a gravity die-casting. The optimum fabrication condition to form the composite layer and the formation mechanism of the layer were clarified by observing the microstructure, and then the wear properties of the composite layer were also investigated. By casting the magnesium alloy melt into the permanent mold on which the slurry mainly consisting of Si particles was coated, the magnesium alloy composite layer in which the in Situ Mg2Si particles were dispersed was formed. The melt temperature and mold temperature required to form the composite layer, which perfectly covers the casting, were above 1073 K and above 673 K, respectively. The composite layer was a magnesium alloy in which the fine Mg2Si particles of approximately 40 vol% were dispersed. The thickness and hardness of the layer was about 600 pm and 180 HV, respectively. Under the dry sliding wear, the weight loss of the composite layer was lower than that of the magnesium alloy. These results lead to the conclusion that the wear resistant magnesium alloy composite layer in which the in situ Mg2Si particles were dispersed can be formed in the present process. [doi:10.2320/matertrans.MER2008198]

Although it is known that the addition of bismuth refines the graphite nodule in spheroidal graphite cast iron, the refinement mechanism has not yet been clarified. In this research, the effect of bismuth on the refinement has been investigated by examining the microstructure of the spheroidal graphite cast iron containing a small amount of bismuth. Bismuth was added at 0.01 mass% to the spheroidal graphite cast iron melt containing 3.5-3.7 mass% carbon and 2.0-2.8 mass% silicon, then the melt was poured into the mould to obtain the stepped test bar with 2, 3, 5 and 10 mm thicknesses. The graphite nodule increased as the bismuth content increased. The diameter of the graphite nodule decreased as the thickness decreased, namely, as the cooling rate increased. The graphite nodule was further refined by the addition of bismuth. The increase in silicon content increased the graphite nodule count and the ferrite in the matrix. It postulated that bismuth exists as simple substance or a compound in the vicinity of the nucleus of the graphite.

Short alumina fibre and in situ Mg2Si particle reinforced hybrid composites were fabricated by infiltration with the molten magnesium alloy into the preforms consisting of the fibres having Si particles attached to their surfaces. P or CaF2 particles were used as the refiners of the Mg2Si particles. All of Si particles reacted with the Mg alloy and melt to form Mg2Si particles. As the melting temperature decreased or the cooling rate after the infiltration increased, the Mg2Si particles became finer. The introduction of P or CaF2 further promoted the refinement of the Mg2Si particles. When the composite was fabricated by squeeze casting in the permanent mould, fine Mg2Si particles with a grain size of similar to 5 mu m were formed regardless of introducing the refiners due to the rapid solidification. The strength of the hybrid composites was higher than that of the conventional fibre reinforced composite at both room temperature and high temperature.

SiC particle preforms were infiltrated with spheroidal graphite cast iron melt by vacuum assisted casting in the sand mould, and spheroidal graphite cast iron composites in which the particles were dispersed in the surface region were fabricated. Although the melt infiltration was not accomplished when the melt was poured under atmospheric pressure, the infiltration was accomplished by the vacuum assisted casting when the SiC particle volume fraction and preform thickness were optimised. When the Si content of the cast iron was 2.5 mass%, the phase consisting of mainly Fe3Si was formed at the particle/matrix interface due to the reaction between the cast iron melt and the particles during the infiltration. The matrix of the composite consisted of fine spheroidal graphite particles, ferrite, pearite and chill crystal. Although the increase in the Si content suppressed the reaction and chill, no infiltrated area was observed in the composite.

Short alumina fiber- and in situ Mg2Si particle reinforced magnesium alloy composites were fabricated by squeeze casting. The in situ Mg2Si particles were formed during the infiltration with the melt into the preforms consisting of the fibers having Si particles attached to their surfaces. The microstructure of the composites and their tensile strength and Young's modulus in the range from 293 K to 523 K were investigated. The effect of the Mg2Si particles on the tensile properties was examined by comparison with the properties of the fiber-reinforced composite without the Mg2Si particles. Fine Mg2Si particles with a grain size of approximately 5 mu m were formed due to the rapid solidification in the permanent mold. The dispersion of the Mg2Si having a high Young's modulus was found to be effective for improving Young's modulus of the fiber-reinforced magnesium alloy composite. The experimental value of the composite was in good agreement with the calculated value based on a previously proposed model. The tensile strength of the composite with 18 vol% fibers and Mg2Si particles was higher than that of the conventional fiber-reinforced composite at both room temperature and high temperature. Examination of the fracture surfaces indicated that stress transmission between the fiber and the matrix became easy due to the particles, which reduced the fiber-to-fiber contact.

In order to develop a new aluminum alloy composite which has a low thermal expansion rate and is machinable, the aluminum alloy composites reinforced with short potassium titanate fibers were fabricated. The fiber preform was fabricated and then infiltrated with the AC4A aluminum alloy melt by squeeze casting to fabricate the composite. The microstructure and thermal properties of the composites were investigated. Optical microscopy revealed that the fibers were homogeneously distributed in the alloy. However, the fibers were somewhat in a planar random arrangement parallel to the pressed plane when the fiber volume fraction was high. This is due to the forming of the preform by pressing the upper and bottom of it. The composites were easily machined by the commercial super alloy cutting tools: the composites have good machinability. The thermal conductivity of the composite decreased as the fiber volume fraction increased. At higher volume fraction, the thermal conductivity of the composite in the parallel direction to the pressed plane was higher than that in the transverse direction because of the planar random arrangement of the fibers. The thermal conductivity can be roughly estimated by Landauer's model. Average thermal expansion coefficient of the composite decreased as the fiber volume fraction increased. The difference of the thermal expansion coefficient between the parallel and transverse direction to the pressed plane is slight, and the experimental values are in good agreement with the theoretical values calculated by the rule of mixture. These results show that the reduction in the thermal expansion of the aluminum alloy can be accomplished by the reinforcement with the short potassium titanate fibers.

In order to obtain a lightweight material having an excellent high-temperature strength, Mg alloy composites reinforced with short alumina fibers and ill situ Mg2Si particles were fabricated. The composites were fabricated by pressureless infiltration of the Mg alloy melt into the preform consisting of the fibers and attached Si particles. The volume fraction of Si particles in the preform, the melting temperature of the Mg alloy, and the cooling rate after the infiltration were varied. P and CaF2 particles were also used as refiners of the Mg2Si. Based on the results, the conditions dispersed the Mg2Si particles finely and homogeneously and the formation and dispersion mechanism of the Mg2Si were clarified. Although the Si content exceeds its equilibrium Solubility in the Mg melt when the volume fraction of the Si particles was 9.5 vol%, all of the Si particles reacted with the Mg alloy melt to form Mg2Si particles. The Mg2Si particles were homogeneously dispersed in the matrix, because the segmentation Of Mg2Si particles in the infiltration was prevented due to the presence of fibers. As the melting temperature decreased or the cooling rate after the infiltration increased, the Mg2Si particles became finer. The introduction of P or CaF2 further promoted the refinement of the Mg2Si particles.

Aluminum alloy matrix hybrid composites reinforced with particle-attached continuous alumina fibers were fabricated by squeeze casting, and the effects of the particle-dispersion on their strength in the temperature range 293 to 623 K were investigated by microscopy and fractography. It was found that the particle-dispersion among the fibers minimizes the preform contraction and fiber-to-fiber contact due to melt infiltration during the squeeze casting, resulting in a homogeneous distribution of the fibers in the composite. The tensile strength, 0.2% proof stress and elastic modulus of the composites in the longitudinal direction increased due to the particle-dispersion over the whole temperature range measured. The fracture surface of the particle-free composite was flat and close-packed fibers were frequently observed, indicating that stress concentrated in the neighboring fiber, then the cracks initiated at the points of fiber contact, followed by progressive fracture of the touching fibers. In contrast, the surface of the hybrid composite was irregular and close-packed fibers were rarely observed, showing that the matrix around a fiber relieved the stress concentration and the strengthening by the fibers was satisfactory. The transverse tensile strength and proof stress of the particle-free composite were lower than that of the unreinforced alloy. Many fibers and grooves remaining in the matrix were observed on its fracture surface. This is considered to be due to the initiation of the cracks at the points of fiber contact and their propagation mainly along the fiber-matrix interface. In contrast, the strength of the hybrid composite was close to that of the unreinforced alloy. The matrix was dominant on its fracture surface. This is attributed to the strong fiber-matrix interface and the propagation of cracks mainly throughout the matrix.

Alumina short fibre preforms were fabricated using an Al2O3 binder and infiltrated with aluminium piston alloy melt by squeeze casting. Al2O3 binder is thermodynamically more stable than the conventional SiO2 binder and reduces the fibre/ matrix interfacial reaction. The effects of fibre volume fraction, temperature and heat treatment on the yield strength and tensile strength of the composite were investigated. The Al2O3 binder provided a satisfactory interfacial bond between the fibre and the matrix without any interfacial reaction or fibre damage. Aging behaviour was not changed by reinforcement. At every temperature, the composites showed the highest strength with a fibre volume fraction of 18%. The strength of the composite was improved by T6 heat treatment. Examination of the fracture surfaces and calculation of the tensile strength using the rule of mixtures indicated that the 18% fibre reinforced composite had a strong interfacial bond even at high temperatures.

Aluminum alloy matrix hybrid composites, in which alumina particles were dispersed among continuous alumina fibers, were fabricated by squeeze casting, and the influence of temperature and the effects of the particle-dispersion on the strength of the composites were then investigated. The particle-dispersion among the fibers minimized preform contraction and fiber-to-fiber contact due to the melt infiltration during the squeeze casting. The tensile strength, 0.2% proof stress and elastic modulus of the composites in the longitudinal direction increased with increasing the fiber volume fraction, retaining nearly the same values up to 623 K. These values of the hybrid composite were larger than those of the particle-free composite at every temperature. This is because the fibers were distributed uniformly owing to the particles that prevented the fiber-to-fiber contact, leading to the reduction of stress concentration at the points of direct fiber contact, and stress transmission between the fiber and the matrix becomes easy. At every temperature, the transverse tensile strength and proof stress of the particle-free composite was lower than that of the unreinforced alloy, because the fracture was initiated at the fiber-to-fiber contact point and the cracks propagated mainly along the fiber-matrix interface. In contrast, the strength of the hybrid composite was close to that of the unreinforced alloy even at high-temperature, because the cracks propagated mainly throughout the matrix owing to the uniform distribution of the fibers and the strong fiber-matrix bond.

Hybrid composites in which Al2O3 particles were distributed among Al2O3 continuous fibres were fabricated by squeeze casting, using Al-Cu-Mg alloy as the matrix. Their microstructures and mechanical properties were investigated, with special attention paid to the effect of the presence of the Al2O3 particles. The particles were found to minimise contraction of the preform as well as the resultant fibre-to-fibre contact caused by compression. There were few reactions at the interface between the fibres and the matrix. The tensile strength parallel to the fibre axis increased as the volume fraction of the fibres increased, and was further improved by the introduction of the particles. The tensile strength of the hybrid composite perpendicular to the fibre axis was about the same as that of the unreinforced alloy, while that of the composite without particles decreased as the volume fraction of the fibres increased. Tensile fractures perpendicular to the fibre axis occurred mainly at the interface in composites without particles, but occurred in the matrix in the hybrid composites.

  Hybrid composites, in which particles were distributed among continuous fibers, were prepared by the squeeze casting process. Aluminum alloy of AC1B was used as the matrix metal, and Al₂O₃ continuous fibers and Al₂O₃ particles as reinforcements. Their microstructures and mechanical properties were investigated and the effects of the introduction of particles were focused. The introduction of particles minimized preform contraction and fiber-to-fiber contact caused by squeeze casting. There were few reaction products at the interfaces between fiber and matrix. The longitudinal tensile strength of the composite increased with increasing fiber volume fraction, and further improved with the introduction of particles. The transverse tensile strength of the hybrid composites was approximately the same as that of the matrix alloy, while that of composites without particles decreased with increasing fiber volume fraction. Transverse tensile fracture mainly occured at the fiber-matrix interface for composites without particles, but occured in the matrix for hybrid composites.

各種砂型の通気性試験を行い、減圧吸引下での種々の砂型における通気性を明らかにした。 また、実用製品を想定してトーナメント状の鋳型に鋳鋼溶湯を注湯し、薄肉部への溶湯充てんにおける減圧の効果を明らかにした。

減圧鋳造法を用いて耐熱鋳鉄・鋳鋼溶湯を砂型鋳造した場合について、鋳型内に設置したセラミックスフィルターへの溶湯含浸挙動、渦巻き試験片を用いた湯流れ挙動の観察により、耐熱鋳鉄・鋳鋼溶湯の湯流れ性に及ぼす減圧の効果を調査した。

高硬度で耐熱性に優れるSiC粒子を用いてプリフォームを作り、これにねずみ鋳鉄溶湯、あるいは球状黒鉛鋳鉄溶湯を含浸させることにより、機械的性質や耐摩耗性に優れるだけでなく、リサイクル性にも優れた粒子分散高機能鋳鉄複合材料を開発することを目的とした。SiC粒子を用いてプリフォームを作り、これを砂型内に設置し、鋳鉄溶湯を注湯するプロセスにより、SiC粒子が鋳鉄表面部に分散した複合材料を作製することができた。また、ねずみ鋳鉄、球状黒鉛鋳鉄いずれの場合も、鋳鉄単体に比べて複合材料の摩耗量は大きく減少したことから、SiC粒子の複合化により鋳鉄の耐摩耗性も向上することが分かった。このSiC粒子分散複合材料を再加熱すると、鋳鉄マトリックスが完全に溶解する温度でもSiC粒子は溶解・分解せずに残存することが認められた。すなわち複合材料中に存在するSiC粒子は溶解工程のみで溶湯から分離除去でき、複合材料のリサイクルが比較的容易であることが明らかとなった。以上の結果から、砂型内での複合化プロセスにより、優れた耐摩耗性とリサイクル性を併せ持つ鋳鉄複合材料を容易に作製することが可能となった。