Al-Al2O3 Composites Research Articles

Effect of alumina particle size and thermal condition of casting on microstructure and mechanical properties of stir cast Al–Al2O3 composites

Metal matrix composites are considered as a distinct category of the advanced materials, which have low weight, high strength, high modulus of elasticity, low thermal expansion coefficient and high wear resistance. Among them, Al–Al2O3 composites have achieved significant attention due to their desired properties. In the present research, Al–Al2O3 composites with 5 vol.-% alumina were produced by stir casting at a temperature of 800°C. Two different particle sizes of alumina were used as 53–63 and 90–105 μm. The microstructure of the samples was evaluated by SEM. In addition, the mechanical properties of the samples were measured, and hence, the optimum temperature and particle size of alumina to be added to the Al matrix were determined. The results demonstrated the positive effect of alumina on improving the properties of Al–Al2O3 composites.

Extruded Al–Al2O3 composites formed in situ during consolidation of ultrafine Al powders: Effect of the powder surface area

Abstract Twenty-five samples of commercially available, gas-atomised Al (99.5%) powders with particle sizes 2 O 3 composites formed in situ during extrusion. The effect of particle size, surface area, oxygen content and atomisation atmosphere of the powder on the microstructure and mechanical properties of the extruded compacts were studied by Brunauer, Emmett, Teller (BET) analysis, hot gas extraction, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests. Thermal stability of the compacts and the individual strengthening mechanisms operating in the compacts were discussed. It was found that the properties of the compacts stemmed from the extraordinary grain boundary strengthening effect of the ultrafine-grained compacts due to their microstructures. The efficiency of the grain boundary strengthening was significantly enhanced by the presence of nano-metric Al 2 O 3 dispersoids introduced in situ. The strength of the compacts was closely related to the surface area of the powder particles. In addition, the entrapped gasses and chemically bonded humidity had a negative effect on the mechanical properties of the compacts.

Effect of Hot Working on Structure and Tribological Properties of Aluminium Reinforced with Aluminium Oxide Particulates

Al-Al2O3 (18%) composite was prepared by stir-cast melt technique. The microstructures showed uniform distribution of particulates, dispersed in the matrix. There exists discontinuity (~0.25 μm) in the interface between particulates and matrix. The composite was hot forged. Hot working resulted in fine recrystallized microstructure with particulates dispersed along grain boundaries. Formation of pancake microstructure with some inhomogeneity in the microstructure along three faces of the forged composite was observed. The discontinuity across the interface between Al-Al2O3 was reduced to 0.125 μm after forging. The as-cast and forged Al-Al2O3 composites showed higher wear resistance than pure Al. In lubricant media, there was no significant wear observed for either the as-cast or forged composite, whereas Al had shown higher wear at 50 N load.

Wear Behavior of Al-Al<sub>2</sub>O<sub>3</sub> Reinforced Composites

Aluminum composites containing 10wt. % of Al2O3 with 3 µm size of particles have been produced using powder metallurgy (PM) method and wear behavior of the composites were tested under dry condition. A comparison is also made with SiCp reinforced Al composite produced at the same conditions. The wear rate of both types’ composites increased with all applied loads, but wear rate of the composites was a strong function of normal load rather than that of type of particles used for the manufacturing MMCs. Furthermore, the wear rate of Al-Al2O3 composite was smaller than that of Al-SiCp reinforced composite, but not indicating significant differences on it. Moreover, SEM examination showed that plastic deformation was the dominant type of wear for the Al2O3 particle reinforced MMCs, but the fragmented-deformed layer of particles was more effective for the SiCp reinforced MMCs due to more fracturing of particles.

Fabrication and Aging Behaviour of In-Situ Aluminum Composites

Abstract Commonly applied in situ procedures with the aim of producing alumina particles or whiskers include the reactions between a metal oxide and aluminum. The metal, reduced with the alumina formation reaction, afterwards generally reacts with Al and transforms into an intermetallic form which will act as a reinforcing member in the composition of the matrix. In this study, by adding CuO powder in ratios of 5, 10 and 15 wt.-% composite billets were produced by the in situ procedure of stir casting. XRD patterns and microstructures of the produced Al-Al2O3 composites were examined by using optical and electron microscopy (SEM). Following the homogenization procedure on the composite material, hot deformation and thermal aging procedures were applied. The changes in the mechanical properties were compared with commercially pure Aluminum.

Characterization of microwave processed aluminium powder

Commercial Al powder was exposed to microwave radiation for 45min. The as received and microwave heated Al powders were characterized by X-ray diffraction analysis (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and transmission electron microscopy (TEM). XRD of the microwave treated Al powder confirmed the formation of Al–Al2O3 composite. FTIR studies and EDX analysis indicated the transformation of Al powder into Al–Al2O3 core–shell composite powder after microwave processing. SEM showed that the morphology of the microwave processed Al powder was quite different from that of the as-received Al powder. TEM image of the microwave treated Al powder supported the FTIR and EDX data.

Effect of Al2O3 amount on microstructure and wear properties of Al–Al2O3 metal matrix composites prepared using mechanical alloying method

This paper reports the outcome of an investigation into the effect of Al2O3 content on the microstructure and wear properties of Al–Al2O3 metal matrix composites. The Al–Al2O3 composites are prepared by a mechanical alloying method using Al2O3 powders up to 20 vol.% as reinforcement. Alloying is performed in a vibration mill using a ball-to-powder ratio 10:1 and a milling time varying from 30 to 100 min at a rate of 710 Hz. The prepared compositions are cold pressed at 630 MPa with a single action and sintered at 560°C for 30 min under Ar gas atmosphere. The experimental results show that the reinforcing phase Al2O3 is homogeneously dispersed in the Al matrix and the interface between Al matrix and Al2O3 is well formed. Wear tests are carried out under dry sliding conditions using a pin-on-disk testing machine at three different loads of 10, 25, and 50 N and at a sliding speed of 2.08 m/sec. Total sliding distances are selected as 400, 800, 1200, and 1600 m. It is seen that the wear rate decreases with increasing Al2O3 content and sliding distance at a sliding speed of 2.08 m/sec.

Investigation of particle size and amount of alumina on microstructure and mechanical properties of Al matrix composite made by powder metallurgy

Al matrix composite is well known, in which Al2O3 is the most widely used reinforcement. The aim of this study is to investigate the effect of alumina particle size and its amount on the relative density, hardness, microstructure, wear resistance, yield and compressive strength and elongation in Al–Al2O3 composites. To this end, the amount of 0–20wt.% alumina with average particle sizes 48, 12 and 3μm was used along with pure aluminum of average particle size of 30μm. Powder metallurgy is a method used in the fabrication of this composite in which the powders were mixed using a planetary ball mill. Consolidation was conducted by axial pressing at 440MPa. Sintering procedure was done at 550°C for 45min. The results indicated that as the alumina particle size is reduced, density raises at first, then, declines. Moreover, as the alumina particle size decreases, hardness, yield strength, compressive strength and elongation increase and factors such as wear resistance, microstructure grain size and distribution homogeneity in matrix decreases. For instance, as the alumina particle size gets smaller from 48 to 3μm at 10wt.% alumina, hardness rises from 50 to 70BHN, compressive strength improves from 168 to 307MPa and wear rate rises from 0.0289 to 0.0341mm3/m. On the other hand, as the amount of alumina increases, hardness and wear resistance increase and relative density and elongation is decreased. However, compressive and yield strength rise at first, then drop. For example, if the amount of alumina with 12μm particle size increases from 5 to 10wt.%, hardness increases from 47 to 62BHN and compressive strength rises from 190 to 273MPa. Nevertheless, erosion rate after 300m decreases from 0.0447 to 0.0311mm3/m.

Wear and friction of Al–Al2O3 composites at various sliding speeds

The present study addresses the dry wear behavior of Al2O3 6061 Aluminum particulate composite under different sliding speeds and applied load using pin-on-disk tribometer at room temperature. Three grades of the submicron particle composites containing 10, 20, and 30 vol.% Al2O3 were tested. The results illustrate that higher load and higher concentration of Al2O3 particles lead to higher wear rates. For 10 and 20% Al2O3 concentrations, the wear rate decreases with increasing sliding speed, while it increases for 30% Al2O3. The surface morphologies of the worn composites indicate that at lower sliding speeds abrasion is dominant, while at higher sliding speeds delamination and adhesion increases. Results also indicate that the friction coefficient between the composite and the mating steel surface decreases with increasing sliding speed to a steady state.

ELNES of Al-Al2O3 Composites Produced by Mechanical Milling

ELNES of Al-Al2O3 Composites Produced by Mechanical Milling

Fluorescence spectroscopy analysis of Al–Al2O3 composites with coarse interpenetrating networks

Fluorescence microprobe spectroscopy was used to characterize the stress fields that develop within an interpenetrating Al-Al2O3 composite resulting from both the thermal expansion mismatch during sample processing, and from an external applied load. The 30 vol% Al-70 vol% Al2O3 composite that was inves- tigated had an aluminum and alumina phase feature size of 50-100 lm. The residual thermal compressive stress measured in the alumina was ~40-340 MPa. The effect of varying the metal ligament size on the residual stress distribution is discussed. Additionally, the appli- cation of an external load caused a non-uniform stress distribution to develop within the alumina regions around the crack-tip, which was attributed to micro- structure inhomogeneities. The crack was further ex- tended and the influence of the stress distribution within the alumina regions on the crack extension direction is briefly discussed.

Al–Al2O3 Composites with Interpenetrating Network Structures: Composite Modulus Estimation

The effective Young's moduli of co‐continuous Al–Al2O3 composites over the 5–97 vol% Al2O3 composition range were experimentally measured and compared with theoretical composite modulus values predicted using the methods of Ravichandran, Tuchinskii, Hashin‐Shtrikman, and the effective medium approximation (EMA). The influence of phase morphology and the modulus ratio (E1/E2) of the constituent phases on the resulting experimental and calculated Young's modulus is discussed. For two‐phased co‐continuous composites with a modulus ratio greater than 5, the EMA, with an appropriate microstructural shape factor, was the most consistent method for approximating the composite Young's modulus over the entire composition range.

PM processing of Al-Al2O3 composites and their characterisation

Aluminium based composites containing 5 to 20 vol.-%Al2O3 as the reinforcing phase were synthesised by powder metallurgy. The process consisted of blending aluminium powder with Al2O3 powder followed by hot compaction and hot extrusion. The microstructural features, mechanical properties and wear characteristics of the composites were investigated with variation in volume fraction of Al2O3 phase. The results indicated a continuous increase in yield and ultimate tensile strength with a marked decrease in ductility of the composites arising from increased Al2O3 content. High temperature tensile test data revealed that the strength of the base material Al and composite materials containing 5 and 15%Al2O3 decreased with increase in temperature. However, the rate of strength reduction was higher for the extruded compact of unreinforced aluminium than the composites. Lower wear rates were observed in the composite materials than the unreinforced aluminium compacts. An increase in Al2O3 content led to a decrease in wear rate of composites under the applied load of 5-35 N and a range of sliding velocity from 0·25 to 1·5 m s-1. The reasons for improvement in strength and wear behaviour of composite materials are discussed in light of their microstructural features.

Solidification processing of Al-Al2O3 composite using turbine stirrer

Solidification processing of Al-Al2O3 composites involves mixing of nonwetting alumina particles in molten aluminum alloy resulting in a slurry where the particles are often attached to bubbles sucked at the center of vortex below the stirrer. The internal surface of bubbles is eventually oxidized by oxygen from air entrapped in it. These bubble-particle combines may float or settle during casting depending on the overall density influencing the particle and porosity distribution in a cast composite ingot where the performance of a stirrer may be evaluated under a given condition of processing. Particle incorporation is more for turbine stirrers instead of flat blade stirrers, but the porosity also increases. Flotation of bubble-particle combines during casting of ingot results in higher particle content at the top. Microstructure shows clusters of particles along circular boundaries of thin oxides at the top of the ingot and sometimes at the bottom. This may be a consequence of filling of bubbles to different extents by surrounding liquid puncturing the oxide layer, if necessary, during solidification. When the manner of stirring is changed to 2 minutes of stirring of particles into molten alloy with an intermediate 2-minute period of no stirring before stirring the slurry again for 2 minutes, relatively uniform particle incorporation results along the height of cast ingot compared to that obtained by continuous stirring. This difference in particle distribution may be attributed to flotation of bubble-particle combines to release the particles on the top of the slurry when stirring ceases and its remixing into the slurry when it is stirred again. However, an increase in the intermediate period of no stirring and a higher processing temperature result in enhanced porosity and a more inhomogeneous particle distribution along the height of the ingot.

Microstructure and composition of Al-Al2O3 composites made by reactive metal penetration

The microstructure of Al-Al2O3 composites made by reactive penetration of Al (or Al alloy) into ceramic (mullite or kaolin) preforms has been investigated using transmission electron microscopy (TEM). The Al-Al2O3 composites were found to contain a mutuallyinterconnected network of Al and Al2O3. No crystallographic orientation was observed between the Al and Al2O3 phase. Impurities and pores in the ceramic preforms were found to have a strong effect on the microstructure of the composites. The impurities resulted in formation of small particles in the Al2O3 grains of Al-Al2O3 composites, whereas the porosity yielded a varied ratio of Al to Al2O3 in the composites. The growth rate of the Al-Al2O3 composites was found to depend on the microstructure and composition of the ceramic preforms as well as the composition of the reactive metals. Pure aluminium penetrated into a dense mullite faster than into a porous mullite at temperatures below 1200 °C. Addition of Mg to Al reduced the growth rate, whereas a continuous phase of amorphous SiO2 in the ceramic preforms increased the growth rate.

Microstructure, tensile properties and fracture behaviour of Al2O3 particulate-reinforced aluminium alloy metal matrix composites

The tensile deformation and fracture behaviour of aluminium alloy 2014 discontinuously-reinforced with particulates of Al2O3 was studied with the primary objective of understanding the influence of reinforcement content on composite microstructure, tensile properties and quasi-static fracture behaviour. Results reveal that elastic modulus and strength of the metal-matrix composite increased with reinforcement content in the metal matrix. With increase in test temperature the elastic modulus showed a marginal decrease while the ductility exhibited significant improvement. The improved strength of the Al-Al2O3 composite is ascribed to the concurrent and mutually interactive influences of residual stresses generated due to intrinsic differences in thermal expansion coefficients between constituents of the composite, constrained plastic flow and triaxiality in the soft and ductile aluminium alloy matrix due to the presence of hard and brittle particulate reinforcements. Fracture on a microscopic scale initiated by cracking of the individual or agglomerates of Al2O3 particulates in the metal matrix and decohesion at the matrix-particle interfaces. Failure through cracking and decohesion at the interfaces increased with reinforcement content in the matrix. The kinetics of the fracture process is discussed in terms of applied far-field stress and intrinsic composite microstructural effects.

Positron annihilation lifetime study of hydrogen-charged Al-Al2O3 composites

Positron annihilation lifetime study of hydrogen-charged Al-Al2O3 composites

Effect of magnesium on mechanical properties of alumina-fiber-reinforced aluminum matrix composites formed by pressure infiltration casting

Abstract AlAl2O3 composites containing 0.48%–6.8% Mg in the matrix alloys have been fabricated by pressure infiltration casting. Optical microscopy, scanning electron microscopy and image analysis were used to examine and to analyze the details of the microstructure and the fracture surface. Tensils tests were utilized to evaluate the mechanical properties. The addition of magnesium was found to improve the infiltration and to decrease the porosity of the composites. The tensile strength of the composites increased with increased magnesium content, while elongation remained almost constant (10%).

Measurement of Elastic Moduli from the Impact Sound of Engineering Ceramics and Composites at Elevated Temperatures.

A simple instrumentation system is developed to determine the elastic moduli of engineering ceramics and their composites from the sound produced by the impact of a sphere on a specimen which is suspended by thin metallic wires or ceramic threads in a furnace. The natural frequencies of the flexural and torsional vibration modes are measured from the impact noise using a fast Fourier transform analyzer. Elastic moduli are then computed from these frequencies using Timoshenko's beam theory and also Saint-Venant's torsion theory. The validity of the measurement method is demonstrated by room temperature tests on ceramic and metallic specimens of known elastic moduli. Sialon and Al-Al2O3 composites are tested at elevated temperatures up to 800°C. It is shown that Young's and the shear moduli of the materials tested decrease with an increase in temperature, while Poisson's ratio remains almost constant.

Microstructural refinement by thermomechanical treatment of a cast and extruded 6061 AlAl2O3 composite

Microstructural refinement by thermomechanical treatment of a cast and extruded 6061 AlAl2O3 composite