Aluminum matrix composite preforms containing silicon carbide whisker (SiCw) were directly fabricated by use of wire and powder flame spray guns. In the case of the wire flame spraying method, SiCw were supplied into the spray flame by suction pressure from a modified air cap. The suction pressure depended on the opening angle of the air cap at the top of the gun. Although a larger opening angle generated higher suction pressure, an excessive opening angle caused a separation of the spray flame and hence a heterogeneous piling-up of SiCw in the preform. In contrast, the powder flame spraying did not have a high flame velocity so that the suction pressure was quite low compared to that of the wire flame spraying. Consequently the air jet containing SiCw was blown into the spray flame which consisted of molten aluminum droplets and hot flame gases. After hot forging of the perform to align SiCw two-dimensinally, SiCw/Al composites were tensile-tested. The strength has been found to be improved with increasing volume fraction of SiCw.

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The wettability of graphite by the molten Al-Li alloy was measured using the sessile drop method, and the relationship between the thickness of reaction layer at the interface and the wettability was discussed. The contact angle of the molten aluminum on the graphite decreased with the increase in temperature, and the thickness of reaction layer increased with the rise in temperature. The wettability of graphite by the molten aluminum was considerably improved by the addition of lithium in aluminum. The addition of lithium suppressed the formation of reaction layer. The contact angle of the molten aluminum on the graphite in He-H₂ atmosphere was larger than that under reduced pressure.

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Microstructures and mechanical properties of silicon carbide whisker (SiCw) reinforced aluminum alloys fabricated by the pressure casting method were investigated. The SiCw reinforced aluminum alloys fabricated under the pressure of 90MPa are superior to those fabricated under the lower pressure than round 90MPa in the mechanical properties. The failure of SiCw reinforced aluminum alloys is associated with the failure of SiCw and the interface decohesion between whiskers and matrix. These composites are strengthened by increasing the interface bonding between SiCw and matrix, i.e., the interface cohesion is strengthened by the accelerating the interface reaction. The proper addition of the highly reactive lithium to aluminum matrix makes the interface cohesion tight and results in lower density and greater strength composites.

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The effect of alloying elements on the dispersions of α-SiC, β-SiC, Al₂O₃ and SiO₂ into molten aluminum was investigated. The dispersion time of β-SiC particles in the molten aluminum was considerably longer than that of α-SiC particles at 1073K. However, at higher temperature, it became short and the difference in the dispersion time between α-SiC and β-SiC particles decreased. The dispersion time for β-SiC was decreased by adding the alloying elements such as titanium, zirconium and vanadium. Moreover, the dispersions of α-SiC and β-SiC were improved by adding calcium in aluminum. The dispersions of Al₂O₃ and SiO₂ in aluminum were difficult, but by adding calcum in the aluminum those particles were dispersed easily. The calcium or titanium concentrated layer was detected by EPMA at the interface between particle and metal matrix.

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To clarify the fatigue properties of fiber-reinforced metals, 4-point bending tests and plane bending fatigue tests were carried out on Al₂O₃ fiber/Al composites at temperatures between 295K and 673K. The behavior of elastic and plastic deformation of this composites was shown by stress-strain curves in the bending tests to be closely associated with that of the matrix. In the cyclic bending stress, stress-strain curves of the loading-unloading tests were accompanied by plastic strain within the ranges which depended on the maximum bending stress and the testing temperature. In the fatigue tests, the relationship between the plastic strain range and fatigue life was expressed well by the Coffin-Manson relation. Microstructural observations suggest that the cyclic plastic deformation in the matrix is a dominating factor in the properties of fatigue for this composites.

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Alumina short fiber reinforced aluminum alloy (FRM) is expected to have the potential to provide high strength and great durability as the automotive engine components. However, the dimensional changes of FRM under cyclic heating condition is not so well established that it is important to study the thermal stability of dimension in FRM in advance in designing the automotive engine components. In this study, thermal stability of dimension in FRM on heating and cooling has been examined with the following experimental results. (1) On rapid cooling its dimension along the fiber orientation decreased compared with the initial dimension. (2) The decrease in dimension is enhanced when the matrix contains the alloying elements or the cooling rate is high. (3) At elevated temperatures, its dimension increased gradually. (4) In-situ observation with the Ultra High Voltage Electron Microscope shows that the dislocation tangles in the matrix are released on heating, and that new dislocation tangles are formed on cooling. It is concluded that the thermal stability of dimension in FRM depends on the stress due to the mismatch of thermal expansion coefficient between fiber and matrix, and on the amount of stress relaxation induced by slip deformation in the matrix on cooling.

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An electrostatic method for fabricating uniaxially oriented ceramic discontinuous fiber preforms has been developed. Alumina short fibers suspended in an insulating liquid (Freon R-113) are aligned to form long agglomerates and sedimented to form a preform in the DC field. SiC whiskers, on the other hand, form into similar agglomerates in the AC field. A fabricated preform is incorpolated into an aluminum alloy JIS AC1A melt by squeeze casting. This FRM contains uniaxially aligned short fibers or whiskers and is free from defects. Uniaxially oriented FRM have higher bending strength than FRM with 2-dimensional and 3-dimensionally random orientations at the same volume fraction of short fibers or whiskers. Uniaxially oriented SiC composits have the highest bending strength 1.07GPa at room temperature, showing a great advantage of using uniaxially oriented preforms.

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An attempt to fabricate particle dispersed Al-4mass% Cu alloy composites was made by compocasting. The recovery of particles introduced in the molten metal is governed by the particle size, fraction solid of the metal and Mg concentration in the metal. Mg 0.5mass% is required in the metal to ensure homogeneous dispersion of SiC particles 40μm in size in the molten metal. A spinel product MgAl₂O₄ is observed at the Al₂O₃ particle-Al interface, but no reaction product is found at the SiC-Al interface. The wear loss of the composites decreases with increases in size and content of dispersed Al₂O₃ particles so significantly that 2017 alloy containing 2.5mass% of Al₂O₃ particles is equivalent to FC25 cast iron in wear loss. Rolling of Al₂O₃ particle dispersed 2017 alloy composites results in a decrease in tensile elongation with increases of size and content of particles. The strength of the alloy containing dispersed Al₂O₃ 20μm in size from 0 to 7.5mass% decreases only slightly by rolling.

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SiC whisker/Al composites fabricated by high pressure infiltration were extruded and rolled at high temperatures. The length and orientation of whiskers in the hot worked composites were measured. A relationship between the strength and working ratio of the composites was discussed. Tensile properties of extruded composites greatly depend on the whisker orientation and decrease at lower extruding temperatures because of shortening of whiskers during extrusion. The elastic modulus of SiCw/6061 composites is expressed as
E=255V_f+72 (GPa)
As the extruded flat bars are cross-rolled, the whisker orientation turns at greater rolling reductions resulting in moderating anisotropies in structure and tensile strength.

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The combined extrusion method was applied to the fabrication of SiC whisker/aluminum composites. SiC whisker and aluminum powder were mixed and tried to be formed by the combined extrusion equipment. As the result, not only a cylindrical cup but also a more complicated shape product, such as a cylindrical cup with screw pattern on its outside surface, could be formed. In order to increase the composite strength, sufficient penetration of the matrix into the tangled whisker which remained even after mixing of the whisker and the matrix powder was necessary by increasing temperature and pressure at the both stages of compaction and extrusion. The composite strength did not depend on forming velocity in the range of 0.1-2mm/s. The composite strength proportionally increased with increasing the volume fraction of whisker up to 15%, where the strength attained twice that of matrix.

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Al-Si-X composites containing dispersed ceramics-particles were prepared by powder extrusion. Wear characteristics of the composites were investigated by pin-drum type and pin-disk type wear testing machines under an oil lubricated condition. The wear resistance of the base material is extreamly improved by dispersion of the particles. The composites containing much transition metals show further good wear characteristics even against the same composites.

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Al₂O₃-particle dispersed 2618 alloy composites were prepared by powder extrusion for sliding members use and their mechanical properties and wear characteristics were investigated. The composites show better wear characteristics and higher ductility than Al-Si alloys which are known as the most popular materials for sliding members.

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SiC whisker reinforced aluminum alloy composites with whisker volume fraction (V_f) ranging from 0 to 40% were fabricated by a powder metallurgical method. In a low V_f range, the ultimate tensile strength increases proportionally with the increase of V_f and agrees satisfactorily with the value calculated from Kelly and Tyson's equation. In a high V_f range, however, the increasing rate of strength becomes smaller than the theoretical value due to the decrease in ductility of composites. This deviation from the proportional line takes place at a lower V_f and the decrease in strength is also observed in higher strength aluminum alloy matrix composites. At elevated temperatures, the tensile strength follows the proportional relationship with the V_f to a higher V_f range due to the improvement in ductility. The elastic modulus increases as the V_f increases and is in good agreement with the value calculated from Cox's equation, assuming that the elastic modulus of whiskers is 43, 000kgf/mm². The whisker orientation factors of three dimensional random array composites for the strength and the elastic modulus are determined experimentally as 0.38 and 0.68, respectively.

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A newly developed compacting method for fabricating metal matrix composites was tested, in which superplastic Zn-Al alloy powders having preferable bondability and SiC fibers were used. Tensile testing of fabricated composites was carried out at 250°C. Requirements for fabricating sound SiC/SPZ composites by superplasticity applied powder metallurgical method include 410°C of fabricating temperature, 70MPa of pressure and duration for 5min. The composites have strength more than 80% of the ROM value. The heat treatment achieved for controlling properties of the composites includes initial heat treatment at 360°C for 1h and water quenching which improve the ductility and enable post-forming and second heat treatment at 250°C for 30min which recovers the high temperature strength once decreased by the initial heat treatment.

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SiC fiber reinforced superplastic Zn-Al alloy (SiC/SPZ) composites were fabricated by a metallurgical technique in which ultrasonic vibration was applied. Fiber breaking in the composites during tensile testing were detected by an acoustic emission technique in order to analyze the mechanism of strengthening induced by modification of microstructures. The fracture resistance of composites to failure is enhanced by homogeneous arrangement of fibers. Homogeneous arrangement of fibers and preferable penetration of matrix metals to the interstices among fibers which are induced by superplasticity and ultrasonic vibration result in strengthening of SiC/SPZ composites, even if the volume fraction of fibers remains unchanged.

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