Al Volume Fraction Research Articles

Excellent Dielectric Properties and Finite Element Simulation of Al-Epoxy Composites with Constructed Ultrathin Al2O3 Parallel-Plate Microcapacitors.

Metal-polymer dielectric composites show promising potential as embedded capacitors, whereas it remains a great challenge to achieve a high dielectric constant (εr) and low dielectric loss (tan δ) simultaneously. This work demonstrates a strategy for overcoming this challenge. Al nanoparticles with self-passivated ultrathin Al2O3 shells are compacted under the uniaxial pressure (P), and Al-epoxy composites are prepared by curing the liquid epoxy monomer that infiltrates into Al compacts. The contacting regions between adjacent Al nanoparticles are flattened and enlarged during the compacting process, so that the ultrathin Al2O3 parallel-plate microcapacitors are constructed by the insulating Al2O3 shells and conductive Al cores. The composite with P of 100 MPa and Al volume fraction (υAl) of 53.7% exhibits the εr of 189 at 10 kHz, which is much higher than the εr (48-102) of 0-3 type Al-polymer composites with similar υAl and even higher than the highest εr (160) reported in the Al-polymer composite with υAl > 80%. Furthermore, the present composites show low tan δ (<0.03) and good frequency and temperature stability of εr. The finite element simulation proves that the construction and enlargement of ultrathin Al2O3 parallel-plate microcapacitors dramatically increase the electric energy stored in Al2O3 and therefore greatly improve the εr.

Microstructure and Mechanical Properties of Adding Adhesive-Layer Laser-Welded Joints of DP590 Dual-Phase Steel and 6061 Aluminum Alloy

In this study, the experiments of laser weld bonding for DP590 dual-phase steel and 6061 aluminum alloy were carried out. Plasma shape and welding spectra were collected and analyzed, and the effect of adding adhesive layer on the microstructure and mechanical properties of laser-welded joints was also investigated. Some defects, such as pore, crack and softening in heat-affected zone, can be avoided in the weld, the increased weld penetration and width are obtained by adding adhesive layer, and the average tensile–shear strength of joint exceeds than that of no-added joint. In laser weld bonding, the Al content reduces weld penetration depth, but increases both sides of weld, Fe-rich Fe–Al ICMs with better ductility are formed in steel/aluminum interface, the Al diffusion from the lower aluminum to the upper steel side is suppressed, and transverse area of joining steel to aluminum is increased due to increasing Al volume fraction on weld width. In addition, the uniform-sized grains are distributed in the weld, shear load is shared by adhesive layer and weld, and hence, mechanical properties of laser-welded joints are improved.

Current Distribution Model and Control Principle of MgAlON Composites by Spark Plasma Sintering (SPS)

The current distribution had remarkable effect on the microstructure and properties of MgAlON composites in the process of spark plasma sintering (SPS). MgAlON composites, using alumina, magnesia and aluminum as starting materials, were prepared by SPS. Based on the current distribution method, the current distribution model on samples and single grain was established, and the basic electric current control principle was analyzed. It was found that the current conveyance by sample or single Al grain could be expressed by a formula including B and I.In the formula, B was the Al volume fraction and I was the total current. When the Al volume fraction was controlled within 12%, the current conveyance by sample increased significantly with the Al addition increasing. Meanwhile, the current conveyance by single Al grain decreased significantly. The sintering speed and properties of MgAlON composites by SPS would show a significantly change.

Estimation of thermophysical properties of solid propellants based on particle packing model

A method for the estimation of thermophysical properties of two- and multi-phase solid propellants is proposed in this paper. The theoretical solutions for thermal conductivity and specific heat of a homogeneous solid propellant cell in the transient thermal conductivity process are deduced on the condition that one boundary of the cell is heated while others are adiabatic. A homogenization theory and the finite element method are employed to compute the mean temperature and heat flux of a representative volume element (RVE). According to the mean results and the theoretical solutions, the effective thermal conductivity and specific heat of solid propellant can be estimated. A packing algorithm, considering the solid particles (ammonium perchlorate (AP) or aluminum) as spheres or discs, is used to match the size distribution and volume fraction of solid propellants, and some mesoscopic models of two-phase and three-phase solid propellants are established. According to the estimation theory proposed in this paper, the effective thermal conductivity and specific heat of solid propellants are predicted. The effect of AP or Al volume fraction is also discussed in this paper.

Effect of Al components on the properties of CuAlO2 thin films deposited by RF magnetron sputtering

CuAlO2 (CAO) thin films with Al volume fraction of 1–5% were prepared by RF magnetron sputtering and were annealed at 1173K for 4h in the air. The microstructures, optical and hydrophily properties of the as-deposited films were studied. XRD measurement shows that all films are polycrystalline and present as Cu–Al–O phase. 3D profilometer measurement shows the minimum of surface roughness is 11.6nm for 1%Al–CAO film, and the maximum is 38.6nm for 5%Al–CAO film. The transmittance in the visible range decreases from 60% to 40% after the annealing process as a result of impurity and rough surface. The minimum value of average refractive index and extinction coefficient is about 1.41 and 0.031 for 1%Al–CAO film. The estimated direct band gaps of CAO films are 3.37–3.53eV. CAO films changes from hydrophobicity to hydrophily after annealing, and water contact angle of the annealed film increases from 31.1° to 70.5°.

Sustainable High Capacitance at High Frequencies: Metallic Aluminum–Polypropylene Nanocomposites

The high-frequency dielectric response of 0-3 polypropylene nanocomposites prepared with the activated metallocene polymerization catalyst [rac-ethylenebisindenyl]zirconium dichlororide absorbed on the native Al(2)O(3) surfaces of metallic aluminum nanoparticles is characterized. The nanocomposites produced are randomly dispersed in the polyolefin matrix with no visible defects that might degrade film dielectric properties. Electrical measurements show that as the volume fraction of Al nanoparticles is increased, the effective permittivity of the nanocomposites increases, with ε(r) values reaching ~10 at relatively low frequency (1 MHz). Because of the high permittivity and conductivity contrast between the metal nanoparticles and the polypropylene matrix, Maxwell-Wagner-Sillars theory can be applied to model the loss at high frequencies and provide insight into how the nanocomposite high frequency response scales with Al volume fraction. At higher Al nanoparticle volume fractions, mixing theories predict greater densities of nanoparticle aggregates, consistent with the experimentally observed shift of the dielectric relaxation to lower frequencies. Although these nanocomposites undergo the predicted initial dielectric relaxation with increasing frequency, the metallic nanoparticle complex permittivity imbues the higher Al volume fraction materials with relatively high, sustainable permittivities, 6, at frequencies as high as 7 GHz.

Empirical Relationship between Relative Electrical Conductivity and Relative Density of the Al-Foam Fabricated through Pressure Assisted Sintering/Dissolution Process

The viability of electrical conductivity as a tool for evaluating variations in morphology of pressure assisted sintering/dissolution Al-foam compacts was investigated. In the preparation of foam specimens, the Al powder and the NaCl (leaching agent) were dry-mixed together in order to prepare homogenously mixture. The blended mixture was then subjected to pressure assisted sintering in which a pressure beyond atmospheric level is externally applied to the specimen during high-frequency induction heated sintering. The embedded leaching agent was then dissolved in order to leave behind an open-celled Al with the same chemical composition as that of the original Al powder. The final material is highly porous and has an interconnected porosity network. The structure of the resulting material has three levels of porosity (i.e. main cells, windows and microporosity). The cell morphology and the size of Al foam closely match those of the leaching particles used. The influence of processing parameters: volume fraction of leaching agent, compaction pressure at elevated temperature, sintering temperature, sintering time and heating rate on the electrical conductivity of the final foams were studied. It was found that all the chosen factors have significant effects on the physical and mechanical properties of the foam and Al volume fraction is the most important parameter affecting the relative electrical conductivity and relative density of the resultant foam. The findings also suggests that the relationship between relative electrical conductivity and density of the specimen does not follow the mathematical description given by Skrohod and Solinin, instead the power law seems to be a good characterization of the relationship between experimental data of electrical conductivity and density of the resultant foams.

Performance of Aluminium / Vinylester Particulate Composite

The performances of aluminum /vinylester particulate-composites were studied in detail in order to investigate its suitability for engineering applications. This study examined the suitability of atomised aluminum particles for particulate reinforcement of a vinyl ester resin. Mechanical properties were obtained for the composite by testing various percentages of aluminium powder (75-150 m) and vinylester resin. It has been found that the inclusion of Al powder has not significantly changed the properties of vinylester resin, however an improvement in the ductility of the composite has been recorded. The optimal performances of the composite were exhibited by 15% Al composition. The properties of the particulate composites were modeled using numerous empirical models. Unfortunately a significant difference was found between some of the experimental and predicted properties of the Al/vinylester particulate composite. This paper intends to detail the variation of mechanical properties with the change of Al volume fraction in the composite and the performances of empirical models in prediction of the properties of particulate composites.

In situ synchrotron X-ray diffraction experiments on Al–15%BN mechanically alloyed powder: Observation of AlN nanoparticles precipitation and enhanced thermal stability of nanostructured Al matrix

Two different in situ experiments using high energy X-ray diffraction from synchrotron source were performed in order to understand carefully the phase transformation in nanostructured Al–15%BN mechanically alloyed powder. After milling at room temperature for 10 h, a solid solution of Al, B and N was achieved. During the heating, the formation and the evolution of the metastable trigonal Al 2B 3 and a very fine precipitation of hexagonal AlN ( d < 8 nm) within Al grains were detected quantitatively. We found a stabilization of Al 2B 3 between 225 °C and 550 °C and, only around 600 °C the hexagonal AlB 2 starts to form. A detectable decreasing of the Al crystallite size between 420 °C and 470 °C was attributed to the precipitation of AlN nanoparticles that reduce the Al volume fraction and, at the same time, hinder the grain boundary propagation. The powder loses the nanostructure above 600 °C exhibiting an exceptional thermal stability at temperatures close to 0.9 T m .

Processing, Microstructure, and Properties of a Mg/Al Bimetal Macrocomposite

A bimetal magnesium/aluminum (Mg/Al) macrocomposite containing millimeter-scale Al core reinforcement was fabricated via casting and hot-extrusion. Characterization revealed that the Al volume fraction was not uniform along the extruded rod length. Major defects were absent, minimal porosity was present and Mg—Al interfacial integrity was good. The thermal stability of macrocomposite sections was marginally improved when compared to pure Mg. Results revealed that the presence of Al core leads to an improvement in average hardness and stiffness of Mg, and an overall improvement in tensile behavior (beyond 7% Al) assessed using work of fracture (WOF) of Mg. For macrocomposite sections containing more than 7% Al, shift in load bearing from Mg to Al at stress levels corresponding to the plastic deformation zone of Mg was indicated in the stepped tensile stress strain curve. An attempt is made to study the effect of presence of mm-scale Al and its variation on the microstructure and mechanical properties of the bimetal Mg/Al macrocomposite.

Solidification processed Mg/Al bimetal macrocomposite: Microstructure and mechanical properties

Abstract A new bimetal magnesium/aluminium (Mg/Al) macrocomposite containing mm-scale Al core reinforcement was fabricated via casting and hot coextrusion. Characterization revealed fairly uniform Al volume fraction along the extruded rod length attributable to mechanical interlocking between Mg shell and Al core. Major defects were absent and Mg–Al interfacial integrity was good. Thermal stability of the macrocomposite was marginally improved when compared to pure Mg. Results revealed that the presence of the Al core leads to a decrease in strength of Mg, but an improvement in stiffness as well as significant increase in failure strain (144%) and work of fracture (73%) of Mg. An attempt is made in the present study to investigate the effect of presence of mm-scale Al core on the microstructure and mechanical properties of the bimetal Mg/Al macrocomposite.

Mechanical and adhesion properties of Al/AlN multilayered thin films

An investigation was conducted on the mechanical properties of compositionally modulated Al/AlN thin films deposited by r.f. magnetron sputtering on Si(100) substrates. The films were made to have modulation periods ranging from 40 to 200 nm. The volume fraction of Al was varied from 0.125 to 0.625 for films with the minimum modulation period of 40 nm, but it was set to 0.5 otherwise. Hardness and adhesion of the deposited films were examined by nanoindentation and scratch test method, respectively. Residual stress of monolithic Al and AlN films with varying thickness and multilayered films was also measured by a conventional beam-bending technique. As compared with a monolithic AlN film, films of various modulation periods with the Al volume fraction of 0.5 were found to have lower hardness. On the other hand, high hardness comparable to and 12% higher than that of monolithic AlN film was registered for films that have the modulation period of 40 nm and the Al volume fraction 0.125 and 0.25, respectively. All the modulated films were found to have critical loads almost twice as high as that of a single AlN film, except the one with the lowest Al volume fraction. From the scratch test, a cohesive failure was observed for films with alternating layers in residual stress state of opposite signs whereas an adhesive failure was noticed otherwise. These observations indicate that a load-carrying capacity of a modulated film depends not only on the modulation period and individual layer thickness but on the residual stress states of alternating layers.

Effect of Volume Fraction on Mechanical and Fatigue Crack Growth Properties of SiC Particle Reinforced AL Alloy Composites

In order to save the energy and protect the environment, it were studied about ecomaterials with the developed countries as central figure. In the Metal Matrix Composites(MMCs), this trends appeared the development of the MMCs which had excellent mechanical properties in spite of the low volume fraction of reinforcement. Therefore, in this study, fatigue crack growth test, tensile and hardness test were conducted in order to investigate the mechanical and fatigue properties of 5 %, and 10 % /Al composites. As the results, in the tensile and hardness test, tensile strength and hardness increased but fatigue crack growth rate decreased with /Al volume fraction. And in the view of fatigue failured surface through the SEM, fatigue crack initiated around the SiC particle and in low regions, fatigue creck detoured the SiC particle but crack propagated through the SiC particle in the high regions.

The temperature and volume fraction dependence of the resistivity of granular Al-Ge near the percolation threshold

Extensive measurements of the temperature and of the Al volume fraction dependence of the resistivity of granular Al-Ge have been made near the percolation threshold phi c. The results at 295 K are analysed using the percolation equations, as modified by Efros and Shklovskii, and by Straley, for systems where the two components have finite conductivity ratios, and by fitting the results to the general effective media (GEM) equation, which also takes into account the finite conductivities of both components. The parameters of these equations are the conductivities (resistivities) of the two components, the critical conductivity exponents s and t, and the critical (percolation) volume fraction phi c. The experimental value of phi c, obtained from resistivity and magnetoresistivity measurements at and below the superconducting transition temperature for Al, agrees remarkably well with the values obtained from the percolation and GEM equations. The observed exponents are found to be high, and the width of the critical region surprisingly large. Attempts to extend this type of analysis to lower temperatures proved unsuccessful, and it is concluded that the resistivity of the more insulating component, namely of the amorphous Al-doped Ge, depends on the total Al content of the sample. It is shown that phi c cannot be identified from the resistivity versus temperature curves between 5 and 295 K, nor from temperature derivatives of these curves. Graphs of the resistivity versus temperature of the amorphous Al-doped Ge for individual samples are extracted using the GEM equation.