Alumina Short Fiber Research Articles

The load transfer effect in the true threshold creep behaviour of an Al-8.5Fe-1.3V-1.7Si alloy reinforced with alumina short fibres

The creep in an Al-8.5Fe-1.3V-1.7Si alloy dispersion strengthened with fine Al12(Fe,V)3Si phase particles and reinforced with alumina short fibres—Composite in the following—is investigated at temperatures 648, 698 and 748 K. The results are compared with those obtained for the composite matrix Al-8.5Fe-1.3V-1.7Si alloy (Alloy in the following) at the same temperatures. Both, the Alloy and the Composite exhibit true threshold creep behaviour; the true threshold stress decreases rather strongly with increasing temperature. However, independently of temperature, it is about twice as high in the Composite than in the Alloy. This is explained employing the concept of the load transfer effect in the true threshold creep behaviour. The results strongly suggest that rather dramatic enhancement of creep resistance of an Al-8.5Fe-1.3V-1.7Si alloy can be reached introducing into it mechanically strong short fibres of micrometer dimensions, provided the aspect ratio of the fibres and their volume fraction are large enough.

Properties of squeeze cast Mg-10Al-Mn alloy and its alumina short fibre composites

Magnesium alloys are very suitable for applications that require materials with high strength-to-weight ratio. However, the use of magnesium alloys is limited due to their low elevated temperature properties. Magnesium matrix composites are the possible alternatives. The present work involved the production and subsequent property evaluation of AM100 magnesium alloy and its alumina short fibre reinforced composites. Studies on microstructure, hardness, density, stiffness, tensile properties, impact strength, wear resistance and corrosion resistance were carried out. Results indicate the significant improvement in the properties achieved by making composites. The findings also highlight the dominant roles of the base alloy matrix and the fibre volume fraction in determining the above properties.

Thermal Fatigue Resistance of Discontinuously Reinforced Cast Aluminum-Matrix Composites

The thermal fatigue resistance of AlSi alloys and discontinuously reinforced Al-matrix composites containing graphite, silicon carbide, and fly ash particulates, and short alumina (Saffil) fibers was characterized by measuring the total length of microcracks on gravity-cast and squeeze-cast test specimens as a function of number of thermal cycles (1000–5000 cycles, 270 K amplitude). In each thermal cycle, the test specimens were heated and stabilized in air at 375 °C, water quenched, and air stabilized. In all specimens, the total crack length on a specified region increased with increasing number of thermal cycles. Whereas among monolithic alloys, squeeze-cast Al-12SiCuNiMg alloy exhibited better resistance to thermal cracking than Al-25Si and Al-20SiNi alloys, among the composites, squeeze-cast Al-alumina and Al-fly ash composites exhibited the best thermal fatigue resistance. The theoretical estimates of the thermal fatigue resistance of these composites are consistent with the experimental observations.

Temperature dependence of Young's Modulus of alumina short fiber reinforced Zn–Al MMCs produced by pressure die-casting

Abstract Conventional pressure die-casting was used to produce δ-Al2O3 (Saffil) short fiber reinforced Zn–Al based metal matrix composites, containing 10, 15, 20, 25 and 30 vol.% fibers. The temperature dependence of the elasticity modulus of the composites and the matrix material were measured at temperatures from 20 to 200°C, at 20°C intervals. It was found that the modulus of elasticity of the composites gradually increased with increasing fiber volume, but decreased with increasing temperature. The rate of change in both, however, differed depending on the fiber volume content of the composites in such a manner that the higher the volume content of fibers the lower the rates of decrease in the modulus of elasticity values with increasing fiber volume and temperature. In addition, the data obtained from the Young's modulus measurements over the temperature range studied were compared with theoretical results predicted by the shear-lag and Nielsen–Chen models and found to be in a better agreement with t...

Structure and properties of short alumina fibre reinforced AlSi18CuNi produced by stir casting

In this study, AlSi18CuNi-based metal matrix composites (MMCs) containing up to 12 wt.% of alumina short fibres were successfully synthesized using casting route. The structure of the produced composites and matrix alloy was examined using optical microscopy. At the same time, specimens from these alloys were machined and used for mechanical and wear tests. The results revealed that Al 2O 3 fibres refined the structure of AlSi18CuNi alloy. Also, metallography of the composites showed that the Al 2O 3 fibres were essentially uniformly distributed throughout the matrix. At the same time, the results showed that the mechanical properties and wear resistance of the as cast alloys were improved by the additions of alumina fibres. The composites showed an increase in tensile strength and hardness at ambient temperature over that of the matrix alloy. On the other hand, a decrease in tensile properties at elevated temperature of both matrix and composite alloys was noticed, but still the composites showed higher values compared with the matrix alloy. Pin on ring dry sliding test was carried out to study wear behaviour of the prepared alloys. Higher wear resistance was observed for the composites compared to the unreinforced alloy.

An evaluation of the creep characteristics of an AZ91 magnesium alloy composite using acoustic emission

Creep experiments were undertaken to determine the potential for using acoustic emission (AE) to monitor the high temperature deformation of an unreinforced AZ91 magnesium alloy and a similar alloy reinforced with short alumina fibers after a conventional T6 heat treatment. Samples of each material were tested to failure and the fracture surfaces of selected specimens were examined using scanning electron microscopy. The results show there is an improved creep resistance in the composite by comparison with the unreinforced alloy. It is demonstrated that the use of AE provides a sensitive procedure for monitoring the nature of the creep deformation.

Novel MMC microstructure with tailored distribution of the reinforcing phase.

Saffil short fibre agglomerates with diameters of 0.4 mm to 1 mm have been prepared using a tumbling technique. These were packed and infiltrated with molten 6061 Al alloy to make a metal matrix composite (MMC) with a novel microstructure in which the composite spheres are randomly distributed in the fibre-free aluminium matrix. In parallel, a commercial preform made of identical Saffil alumina short fibres and having the same fibre volume faction was used to prepare a conventional MMC by the same technique. Microstructural observation indicates that, within the composite spheres, the local volume fraction of fibre decreases from the outer layer to the centre region. The energy absorption during fracture was estimated by using a three point loading test on notched samples and was compared with that for conventional MMCs. Preliminary results suggest that this novel MMC possesses higher energy absorption capability and hence better damage tolerance. The fracture surfaces were examined by scanning electron microscopy in order to inform these experimental results.

Clad-extrusion for producing SiCw/6061Al composite tubes

Plastic forming is one of the most important techniques of discontinuously reinforced aluminum matrix composite (DRA) applications [1–4]. Hot-extrusion is one of the important technologies of plastic forming of DRA. Many attempts have been put on extrusion technologies and their influence on microstructures and properties of DRA for the plastic purpose. A semisolid extrusion process of aluminum alloys with alumina short fibers (FRM) has been developed to produce the composite bars by using a cladding method at the temperature above the solidus of the matrix [1]. However, it should be mentioned here that deformation at the temperature above the solidus of the matrix may deteriorate the composite properties because of the superburning of the matrix alloy [5]. Thus, most of extrusion processes of DRA have been performed at the temperatures below the solidus of the matrix. At the temperature below the solidus of the matrix, if the extrusion parameters are improper, then the surface quality of the extrudate is rather poor. SiCw/Al composite tubes would be made by using a forward extrusion method. Even if SiCw/Al composite are extruded at the temperature below the solidus of the matrix, the surface quality of SiCw/Al composite tubes made using the forward-extrusion method is difficult to be controlled and there often is tearing on the surfaces of the composite tubes. To suppress this, in this work, a clad-extrusion method is used for producing SiCw/6061Al composite tubes at the temperature below the solidus of the matrix 6061 alloy. In this way a solid extrusion could be performed without tearing. The SiCw/6061 Al composites used here were fabricated by the squeeze casting technique using the β-SiC whisker (TWS-100) as a reinforcing element and the commercial 6061Alloy as a base metal. Mold and whisker perform temperature, pouring temperature and applied pressure were 450 ◦C, 750 ◦C, 60 MPa, respectively. The whisker volume fraction (Vf) was 20%. The solidus temperature of the matrix 6061 alloy in the SiCw/6061 Al composite was measured to be 580 ◦C by the DSC technique. The SiCw/6061 Al composite tubes were made by using a forward extrusion method. Fig. 1 shows a schematic illustration of the clad-extrusion for producing the SiCw/6061Al composite tubes. The extrusion temperature was 520 ◦C . The extrusion ratio was about 15. A flat die made of tempered steel was used. Matrix 6061 alloy was selected as the cladding layer. To decrease the friction between the die and the billet, all the extrusion tests were carried out under lubricating with the graphite-oil. Before extrusion, the composite billets were held for 20 min at the extrusion temperature of 520 ◦C, which was below the solidus temperature of the matrix 6061 alloy. Simple solid-state extrusion causes tearing on the surface of extruded SiCw/6061Al composite tubes. Fig. 2 shows the appearance of a SiCw/6061Al composite tube made by using a simple hot-extrusion method at 520 ◦C. It can be seen that, from this figure, there are fir-tree-like cracks on the surface layer of the composite tube. The tearing cracks on the surface of the composite tube are shown in detail in Fig. 3.

ホットプレス法によるアルミナ短繊維強化チタン複合材料の作製

ホットプレス法によるアルミナ短繊維強化チタン複合材料の作製

Dry sliding wear behavior of Al 2O 3 fiber reinforced aluminum composites

Dry sliding wear behavior of die-cast ADC12 aluminum alloy composites reinforced with short alumina fibers were investigated by using a pin-on-disk wear tester. The Al 2O 3 fibers were 4 μm in diameter and were present in volume fractions ( V f) ranging from 0.03 to 0.26. The length of the fiber varied from 40 to 200 μm. Disks of aluminum–alumina composites were rubbed against a pin of nitrided stainless steel SUS440B with a load of 10 N at a sliding velocity of 0.1 m/s. The unreinforced ADC12 aluminum alloy and their composites containing low volume fractions of alumina ( V f ≈ 0.05) showed a sliding-distance-dependent transition from severe to mild wear. However, composites containing high volume fractions of alumina ( V f>0.05) exhibited only mild wear for all sliding distances. The duration of occurrence of the severe wear regime and the wear rate both decrease with increasing volume fraction. In MMCs the wear rate in the mild wear regime decreases with increase in volume fraction, reaching a minimum value at V f=0.09. Beyond V f=0.09 the wear rate increases marginally. On the other hand, the wear rate of the counterface (steel pin) was found to increase moderately with increase in V f. From the analysis of wear data and detailed examination of (a) worn surfaces, (b) their cross-sections and (c) wear debris, two modes of wear mechanisms have been identified to be operative, in these materials and these are: (i) adhesive wear in the case of unreinforced matrix material and in MMCs with low V f and (ii) abrasive wear in the case of MMCs with high V f.

Short thermal fatigue crack propagation behavior of alumina short fibre reinforced aluminum matrix composites

Thermal fatigue resistance is one of the most important parameters to design engine materials. The thermal fatigue crack growth behavior of alumina short fibre (Vf = 18 vol.%) reinforced AlSi12CuMgNi aluminum alloy composite has been investigated under thermal cycling condition between room temperature and 280 °C. Initiation and propagation of thermal fatigue crack have also been discussed. The results show that in the range of short crack, the fibres play an important role in the path of thermal fatigue crack, and the crack propagation rate of composites is much larger than that of the matrix alloy.

Temperature dependent strength analysis of short fiber reinforced Al–Si metal matrix composites

Abstract Metal matrix composites (MMCs) were produced by a pressure infiltration technique, using Saffil ( δ -Al 2 O 3 ) alumina short fiber preforms as the reinforcement, and the alloy Al–12 wt% Si (LM 13) as the matrix material. The matrix alloy and the composites were subjected to a standard T6 heat treatment and consequently tensile tested. The room temperature strength of the composites were seen to increase up to 15 vol.% fiber and then deviated sharply from the linear behavior and decrease continuously as the fiber volume increased. As the test temperature was raised, all composites showed excellent retention of strength up to 300°C. Furthermore, the experimental results of tensile strength were compared to a modified rule of mixtures (ROM). The high temperature strength analysis showed that the strength of planar-randomly oriented short fiber reinforced material can be explained through combined effects of load transfer, dispersion strengthening, and dislocation strengthening. The reinforcement behavior of these type of composites is seen to be controlled by the elevated temperature properties of the matrix alloy. The theoretical tensile strength values, calculated with a temperature dependent modified rule of mixture equation, showed an excellent agreement with experimental data at room temperature and also at elevated temperatures of up to about 200°C.

Modelling of infiltration of molten metal in fibrous preform by centrifugal force

Infiltration kinetics of molten metal in fibrous preforms by centrifugal force is discussed theoretically. The relationship between the location of infiltration front and time is introduced for three major types of centrifugal casting processes. By the relationship, pressure distribution curves in the preform are also obtained. Some calculated examples are shown for the infiltration of molten aluminum into an alumina short fiber preform. If the speed of revolution is slightly higher than the minimum value determined by threshold pressure, infiltration is continuous. Since the second derivative of the pressure distribution curves in the infiltrated region is always positive and proportional to angular velocity in the centrifugal force field, the pressure curves are convex toward low pressure. When the surface pressure of the preform is low enough or the speed of revolution is high, the region having lower pressure than the threshold pressure appears in the infiltrated region. These results are compared with experimental data from references and by the authors.

Infiltration of fibrous preforms by a pure metal: Part V. Influence of preform compressibility

Infiltration by a pure matrix in the presence of preform deformation and partial matrix solidification is analyzed using a bounding approach for the preform rheology where solid metal is present. It is found, using parameters for the infiltration of short alumina fiber preforms by aluminum, that the two bounds are close in comparison to other factors of uncertainty in the prediction of infiltration rate. Using this approach, preform compression is shown to exert a significant influence on the infiltration rate for the system explored; in particular, the analysis shows the existence of an optimal value of applied pressure. Simplifications in the analysis are also presented, which yield fairly accurate results while easing their computation significantly.

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.

アルミナ短繊維強化Al基複合材のクリープ特性

アルミナ短繊維強化Al基複合材のクリープ特性

濡れ性評価に基づくアルミナ短繊維強化マグネシウム複合材料の作製とその圧縮強度

The wettability between molten magnesium alloys and alumina substrate was investigated by the sessile drop method in order to develop the alumina short fiber reinforced magnesium composites. It is suggested that the wettability between molten magnesium and alumina substrate became better and the contact angle decreased from 89° to 80° by adding 3% zinc to the molten magnesium. However, the contact angle increased with increasing aluminum content in the molten magnesium. Based on the results of the wettability measurements, the alumina short fiber reinforced magnesium matrix composites was fabricated by the spontaneous infiltration of molten magnesium into the alumina fiber preform. The compressive tests indicated that the compressive strength appears to be affected by the fabrication process. The compressive strength of the Mg–8%Al alloy reinforced by alumina short fiber was 2 times higher than that of the monolithic alloy at room temperature.

Thermal diffusivity of short-fibre reinforced Mg-Al-Zn-Mn alloy

The commercial magnesium casting alloy AZ91 is widely used due to its high specific strength at room temperature and good corrosion resistance. The aim of the present paper is to study the effect of annealing between 20 C and 300 C on the thermal diffusivity of AZ91 alloy reinforced by {delta}-alumina (Al{sub 2}O{sub 3}) short fibers and to estimate the temperature dependence of the thermal diffusivity. As the thermal diffusivity of the composite depends on the metallurgical state of the matrix and on the amount of short-fiber reinforcement, the authors studied the annealing effects both in the reinforced and unreinforced alloy subjected to the same thermomechanical treatment.

Mechanical Spectroscopy of Thermal Stress Relaxation in Aluminium Alloys Reinforced with Short Alumina Fibres

Mechanical Spectroscopy of Thermal Stress Relaxation in Aluminium Alloys Reinforced with Short Alumina Fibres

Mechanical Spectroscopy of Thermal Stress Relaxation in Aluminium Alloys Reinforced with Short Alumina Fibres

The mechanical behaviour under low temperature thermal cycling of aluminium-based composites reinforced with short Al 2 O 3 SAFFIL fibres has been investigated by mechanical spectroscopy (mechanical loss and elastic shear modulus measurements). A mechanical loss maximum has been observed during cooling which originates in the relaxation of thermal stresses at the interfaces due to the differential thermal expansion between matrix and reinforcement. The maximum height increases with the volumetric fibre content. In addition, if the matrix strength is increased by the appropriated choice of alloy and thermal treatment, the maximum diminishes and shifts to lower temperatures. No damage accumulation at the interfaces has been detected during long period thermal cycling in the range 100 to 500 K. A description of the damping behaviour is made in terms of the development of microplastic zones which surround the fibres.