Reinforced Aluminum Metal Matrix Research Articles

Transient liquid phase bonding of 2124 aluminium metal matrix composite

The transient liquid phase (TLP) bonding of particle reinforced aluminium metal matrix composites (MMCs) using copper interlayers often results in the segregation of SiC particles to the bond region, and this has the effect of producing bonds with poor mechanical strengths. In this preliminary study, the TLP bonding of a 2124 aluminium alloy MMC is investigated using nickel interlayers, and the initial results show that good bonds are produced with no effect on the SiC dispersion in the matrix. The absence of segregation is attributed to the high diffusivity of the nickel in the aluminium MMC, which produces rapid isothermal solidification at the bonding temperature. Bond shear tests show that near parent metal strengths are possible when thin nickel interlayers are used, and failure occurs at the MMC/bond interface. When thick interlayers are used, failure is predominately through the centre of the bondline.

Effect of thermal stress on the microstructures of aluminium metal matrix composites

Discontinuous reinforced aluminium metal matrix composites have been synthesized using nanocrystalline mullite and zirconia of diameters ranging between 20–30 nm prepared by a sol–gel route. Uniaxial hot pressing technique was used to prepare the composites in the temperature range varying between 450–610°C, close to the matrix metal solidus. The thermal stress-induced evolution of microstructures of the AI metal matrix were characterized by applying X-ray diffraction line profile analysis in terms of the defect parameters such as particle (domain) sizes, root mean square strains, lattice parameters changes, dislocation densities etc. The microhardness (Vickers) values of the composites have been measured and correlated with the values of thermal stress along with other parameters depicting the matrix microstructures.

Modeling steady wear of steel/Al 2O 3Al particle reinforced composite system

Considering that harder asperities on one surface would plastically deform the contact areas of a softer counterpart surface, a theoretical model has been developed to describe the steady sliding wear in a system of an alumina particle reinforced aluminium metal matrix composite pin on a steel disk. The model predicts that the volumetric wear of the pin-on-disk system is proportional to the applied load, and depends on the particle volume fraction of the composite and the relative hardness of the rubbing pair. Experimental results obtained from the steady wear of a particulate Al 2O 3-6061 Al composite/carbon steel system are in reasonably good agreement with theoretical predictions. However, many more experimental data are needed to confirm the general applicability of the proposed wear model for metal matrix composites.

Effect of Heat Treatment and Interfacial Characteristics on the Work Hardening Behaviour of a SiC Reinforced Aluminum Metal-Matrix Composite

An understanding of the work hardening behavior of particulate reinforced metal-matrix composites is crucial in optimizing the parameters for deformation processing of these materials. The microstructure and interfacial properties of these composites can be altered by the choice of the heat treatment used. These interfacial properties in turn determine the mechanical behavior of these materials. In this study, a SiC reinforced aluminum metal matrix composite was subject to two different heat treatments to modify the matrix/reinforcement interfacial characteristics. A model, developed earlier, was then used to relate the work hardening behavior to microstructural parameters. It is shown that the model is applicable for both the heat treatments studied.

Effect of aging on work hardening behaviour of SiC reinforced aluminium metal matrix composite

Effect of aging on work hardening behaviour of SiC reinforced aluminium metal matrix composite

Effect of aging on work hardening behaviour of SiC reinforced aluminium metal matrix composite

An understanding of the work hardening behaviour of particle reinforced metal matrix composites is crucial in optimising the parameters for deformation processing of these materials. The microstructure and mechanical properties of these composites can be altered by a suitable aging treatment In particular, aging can be used to maximise the strength or the ductility of the composite. The strength is maximised in the peak aged condition while the as solutionised condition has relatively higher ductility. In this paper a modified continuum model is used to relate the work hardening behaviour of the composite to microstructural parameters. The model is also used to predict the fracture strain of the composite for the two aging conditions and is quite accurate for both aging conditions.

A One-Dimensional Model of a Shape Memory Alloy Fiber Reinforced Aluminum Metal Matrix Composite

A one-dimensional model of a shape memory alloy fiber reinforced aluminum metal matrix composite is developed based on a linearized shape memory alloy constitutive model. The requirements of stress equilibrium and strain compatibility within the composite couple the constitutive variables of the shape memory alloy reinforcement. The shape memory alloy reinforcement's state trajectory resulting from a particular external thermal-mechanical process is therefore sensitive to the external process, the constitutive properties of the composite matrix, and fiber volume fraction. Three distinct thermal-mechanical processes are treated in this paper; the first is an isothermal tensile loading-unloading process at the stress free martensitic transformation start temperature; the second is an external stress free thermal process to a temperature above that required for the shape memory alloy reverse transformation; and, the final process is an isothermal loading at the thermal process finish temperature. The model predicts that the composite will exhibit a large longitudinal compressive strain during the heating process, and will retain a large matrix residual compressive stress at the end of the heating process. The model also predicts that the composite elevated temperature flow strength will be significantly higher than that of the unreinforced matrix alloy.

The effect of fatigue microcracks on rapid catastrophic failure in AlSiC composites

The fatigue resistance of discontinuous reinforced aluminum metal matrix composites is greatly influenced by the rapid nucleation and growth of a very large number of microcracks. These microcracks, which result from an abundance of potential crack initiation sites, are often retarded in growth by the presence of reinforcement through crack trapping. With continued fatigue, microcracking becomes so extensive that it induces widespread coalescence leading to increasingly larger microcracks. Inevitably, some of these large microcracks link together to form the fatal crack and instability takes place very shortly afterwards at unusually small critical crack sizes. The present study examines the form of catastrophic failure in smooth specimens of a 2124 aluminum alloy reinforced with silicon carbide whiskers. Experimental observations of microcrack initiation and stage-by-stage growth through to final failure are reported. Effort is directed at characterizing the distribution and orientation of microcracks present, particularly when linkage(s) result in the formation of the fatal crack, and developing a geometric probability method for predicting coalescence. Results show that microcracks initiate and grow preferentially in arrays which maximize the energy release rate. Near the end of life, the interaction of some microcracks brings about large increases in their stress intensity factor leading to coalescence and fatal crack formation.

Machinability of a silicon carbide reinforced aluminium metal matrix composite

Machinability of a silicon carbide reinforced aluminium metal matrix composite

Machinability of a silicon carbide reinforced aluminium metal matrix composite

The machinability of a DURALCAN ® aluminium metal matrix composite (A359/SiC/20p) has been studied in this paper. Continuous turning of round composite bars using tools with 25 mm polycrystalline diamond (PCD) inserts has been selected as the test method. The matrix of test conditions included cutting speeds of 300, 500 and 700 m min −1 and feed rates of 0.1, 0.2 and 0.4 mm rev −1 while the depth of cut has been kept constant at 0.5 mm. The performance of the tools is based on development of 0.25 mm maximum flank wear, which has been monitored by optical and scanning electron microscopy. The tool life data have been analyzed using regression techniques and a general form of the Taylor equation has been developed to describe the tool performance on this composite. The time required to reach the tool wear limit decreased with increases of speed and feed. However, the volume of material removed before reaching the wear limit actually increases with the higher feed rate. These phenomena have been reconciled by rewriting the Taylor equation in a modified form. Practical implications of this deviation are discussed and comments are made on the effects of cutting parameters on surface finish and chip formation.

Improvement of mechanical properties of HIP aluminium alloy by extrusion : K. Hanada et al (University of Electro-Communication, Tsukuba Ibaraki, Japan.)

Metal matrix composites provide new materials with superior properties. They give high strength and stiffness. In this study, a stainless steel fiber reinforced aluminum metal matrix laminated simple supported plate is loaded transversely. Elasto-plastic stress analysis is carried out in the laminated plate by using finite element technique. The expansion of plastic zone and residual stresses are determined in the symmetric and/or antisymmetric cross-ply and angle-ply laminated plates for small deformations. Iteration numbers are chosen as 100, 150 and 200. The yield points in symmetric laminates are higher than those in antisymmetric laminates.

Diamond/Al metal matrix composites formed by the pressureless metal infiltration process

Diamond particles are unique fillers for metal matrix composites because of their extremely high modulus, high thermal conductivity, and low coefficient of thermal expansion. Diamond reinforced aluminum metal matrix composites were prepared using a pressureless metal infiltration process. The diamond particulates are coated with SiC prior to infiltration to prevent the formation of Al4C3, which is a product of the reaction between aluminum and diamond. The measured thermal conductivity of these initial diamond/Al metal matrix composites is as high as 259 W/m-K. The effects of coating thickness on the physical properties of the diamond/Al metal matrix composite, including Young's modulus, 4-point bend strength, coefficient of thermal expansion, and thermal conductivity, are presented.

The performance of aluminium alloys and particulate reinforced aluminium metal matrix composites in erosive-corrosive slurry environments

A range of aluminium alloys and particulate reinforced aluminium metal matrix composites has been tested in an apparatus which simulates the erosive-corrosive action of a slurry. The slurry used in the investigation is composed of synthetic mine water and silica sand. The corrosion component of the mass loss was found to be an important synergistic factor. The addition of ceramic reinforcement particles to the matrix alloys has a detrimental effect on the slurry erosion resistance.

Review of corrosion studies on aluminium metal matrix composites: Turnbull, A. National Physical Laboratory (UK) Report No DMM (A) 15 Nov. 1990 27 pp

Silicon carbide whisker or particulate reinforced aluminum metal matrix composites, especially attractive because of their superior strength, stiffness, low cycle fatigue properties, corrosion fatigue behavior, creep resistance and wear resistance compared with the corresponding wrought aluminum alloys, have shown promise for various critical structural applications. The major drawback of these materials, however, is their less than ideal ductility, fracture toughness and fatigue crack growth rate (FCGR) properties. Consequently, in order to develop a succinct, structural reliability prediction capability that could be easily applied by design engineers to structures manufactured from these metal matrix composites and to examine initial methods whereby the ductility, fracture toughness and crack growth resistance of these materials might be improved, room temperature tensile, fracture toughness and FCGR tests were conducted on 20 v/o SiCw/2124Al (T6), 25 v/o SiCp/6061 Al (F and T6) and 25 v/o SiCw/6061 Al (T6) metal matrix composites. Compared with the corresponding wrought aluminum alloys, the three subject metal matrix composites demonstrated increased yield and ultimate strengths, substantially inferior ductility and fracture toughness, a lower crack propagation resistance and essentially equivalent values of threshold stress intensity range, ΔKth.

Study on the Effect of the Surface Treatment on the Residual Stress Gradient in Silicon Carbide (SiC) Reinforced Aluminum Metal Matrix Composites

Silicon carbide (SiC) whiskers and particule-reinforced aluminum alloys show promise as metal matrix composites (MMC) stiff and in high-strength lightweight applications. When a MMC is cooled down to room temperature from the fabrication or annealing temperature, residual stresses are induced in the composite as a result of the mismatch of the thermal expansion coefficients between the metal matrix and fibers. The magnitude of the residual stresses has a very important effect on the yield stress and fatigue strength of the MMC. Many techniques are available for residual stress measurement on mechanical parts. X-ray diffraction, bending deflection, and hole drilling are three techniques that are commonly used.

The Elevated Temperature Response of Silicon Carbide and Boron Reinforced Aluminum and Titanium Metal Matrix Composites

AbstractThe elevated temperature modulus and strength of aluminum, titanium, and hybrid aluminum/titanium metal matrix composites were investigated. Aluminum (6061-F) and titanium (Ti-6AI-4V) metal matrix composites reinforced with AVCO silicon carbide or boron fibers were vacuum hot pressed and their tensile properties evaluated to temperatures in excess of 300°C. Microstructure, fracture modes and mechanical properties were characterized to assess the effect of fibers and matrix on composite strength and modulus as a function of temperature. Finally, a comparison of specific strength and modulus is provided as a function of temperature. In general, the metal matrix composites exhibited low density (<2.8 g/cm3), high modulus (200 GPa), and strengths equivalent to 1250 MPa at 250–300°C. The effect of fiber orientation on axial stiffness was investigated using boron fiber reinforced aluminum (6061-F).

Fractography of a SiC particulate reinforced aluminium metal matrix composite

Etude par microscopie electronique a balayage des materiaux a matrice metallique d'alliage Al-6061 renforces par SiC rompus par traction. Analyse et comprehension du mecanisme de rupture

Tensile, fracture toughness and fatigue crack growth rate properties of silicon carbide whisker and particulate reinforced aluminum metal matrix composites

Silicon carbide whisker or particulate reinforced aluminum metal matrix composites, especially attractive because of their superior strength, stiffness, low cycle fatigue properties, corrosion fatigue behavior, creep resistance and wear resistance compared with the corresponding wrought aluminum alloys, have shown promise for various critical structural applications. The major drawback of these materials, however, is their less than ideal ductility, fracture toughness and fatigue crack growth rate (FCGR) properties. Consequently, in order to develop a succinct, structural reliability prediction capability that could be easily applied by design engineers to structures manufactured from these metal matrix composites and to examine initial methods whereby the ductility, fracture toughness and crack growth resistance of these materials might be improved, room temperature tensile, fracture toughness and FCGR tests were conducted on 20 v/o SiCw/2124Al (T6), 25 v/o SiCp/6061 Al (F and T6) and 25 v/o SiCw/6061 Al (T6) metal matrix composites. Compared with the corresponding wrought aluminum alloys, the three subject metal matrix composites demonstrated increased yield and ultimate strengths, substantially inferior ductility and fracture toughness, a lower crack propagation resistance and essentially equivalent values of threshold stress intensity range, Δ K th .