Journal of Advanced Materials in Engineering (Esteghlal)

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Aluminum matrix composites reinforced with Al2O3 and SiC particles (5 Vol%) were produced using the hot powder extrusion method. Extrusion temperature and extrusion reduction in area were chosen in the range of 500 to 600°C and 90 to 95%, respectively. The physical and mechanical properties of the extruded composites such as density, tensile strength, elongation and microhardness were evaluated and discussed as a function of extrusion parameters. The microstructure and fracture surface of the products were examined using SEM. The results showed that the composites were fully densified and reinforcement particles were distributed uniformly in the matrix. Presence of Al2O3 and SiC particles increased both strength and microhardness, but decreased the ductility of the composites. Experimental results for hot extrusion of the compacted powder billets also showed that the extrusion pressure was dependent on the ram speed or deformation strain rate.

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Solid Assisted Melt Disintegration (SAMD) is a relatively new method for producing metallic powder particles in which the kinetic energy transferred from a rotating impeller to the melt via a solid medium causes melt disintegration. These droplets are then solidified and separated from the media to obtain metallic powder particles. In the present study, sodium chloride (NaCl) was used to produce Al-6wt%Si powder particles. A specified amount of NaCl was introduced into the aluminum alloy melt and the slurry was stirred following a specified time-temperature regime to disintegrate the molten alloy into droplets. This blend was quenched in water to solidify Al powder particles and to dissolve NaCl in water. The Al powder particles were then collected, washed, dried, and subjected to laser particle size (LPS) analysis and scanning electron microscopy (SEM). The effects of different time-temperature regimes on the size and morphology of the resultant Al-6wt%Si powder particles were investigated and the optimum conditions for obtaining the finest spherical particles were established. It was concluded that the finest and most spherically shaped Al powder particles could be produced by stirring the slurry at 690 °C for 5 min followed by water quenching.

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In cast aluminum and its alloys, the microstructure varies under different solidification conditions, causing variations in their mechanical properties. These materials are basically produced in sand and metallic molds or through die casting, each of which is associated with a unique solidification regime with significantly different cooling rates so that the resulting microstructure strongly depends on the casting method used. In the present study, the effects of such important solidification parameters as cooling rate, solidification front velocity, and thermal gradient at the solid-liquid interface on secondary dendrite arm spacing were investigated. By a directional solidification system, the mathematical relation between cooling rate and dendrite spacing was extracted for several commercially important aluminum alloys. A neural network model was trained using the experimental values of cooling rates and secondary dendrite arm spacing. Reliable prediction of these values was made from the trained network and their corresponding diagrams were constructed. A good agreement was found between simulation and experimental values. It is concluded that the neural network constructed in this study can be employed to predict the relationship between cooling rate and dendrite arm spacing, which is difficult, if not iompossible, to accomplish experimentally.

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In this research, the reaction kinetics of TiH2 powder in contact with pure aluminum melt at various temperatures on the basis of measuring the released hydrogen gas pressure was studied. To determine the mechanism the reaction, after Solidification of samples, interface of TiH2 powder in contact with melt was studied. The results showed that PH2-time curves had three regions. In the first and second regions, the rate of reaction conforms to zero and first order, respectively. In the third region, hydrogen gas pressure remains constant and the rate of reaction becomes zero order. In the first and second regions, the main factors controlling the rate of reaction are diffusion of hydrogen atoms within titanium lattice and chemical reaction of titanium with aluminum melt, respectively. Based on the main factors controlling the rate of reaction, three temperature ranges can be considered for reaction mechanism, a) 700-750ºC, b) 750-800ºC and c) 800-1000ºC. In the temperature range (a), the reaction is mostly chemical reaction control. In the temperature range (b), the reaction is diffusion and chemical reaction control, and in the temperature range (c), the reaction is mostly diffusion control.

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In the present work, molecular dynamics simulation method was used for determining Young's modulus, Shear modulus and Poisson’s ratio of Al-SiC nanocomposites, with different volume fractions of the reinforcements. For simulation, the open source package, LAMMPS, was used. After putting Aluminum and Silicon Carbide atoms in their initial positions, interatomic potentials between them were defined. EAM potential was used for Aluminum atoms, Morse potential was used for Al-C and Al-Si, and for C-C, Si-C, and Si-Si Tersoff potential was used. According to the elastic bounding principal, and the comparison between the simulations results and Voigt, Ruess and Halpin-Tsai micromechanical models showed that the results were close to the upper bound Voigt model.

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In this study, pure powders such as molybdenum, silicon, aluminum and titanium carbide were utilized to produce MoSi2 compound, MoSi2 /20 Vol % TiC composite, MoSi2-x Al alloyed compound and MoSi2-x Al/20 Vol % TiC alloyed composite. The initial powders were mixed in specified ratios, and then, were activated by mechanical milling. Milled powders were compacted, synthesized and sintered in the temperature range of 1100 -1400 oC. SEM was used to investigate the microstructural change and XRD for identification of phases. Effect of aluminum addition on phase formation was investigated. Addition of aluminum by over 9 atomic percent resulted in the formation of Mo(Si,Al)2 in alloyed matrix.

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In the present study, pure Aluminum powder with 5%wt Titanium Dioxide was mechanically milled at different times. Using phase analysis through X-ray diffraction (XRD), it was found that increasing of the milling times over 10 hours causes the reduction of Titanium by Aluminum and formation of Al2O3 in the structure. Also, it was shown that if the process persists, Aluminum reacts with Titanium and causes the formation of Al3Ti in the composition. The reactions were studied through the thermodynamic relations. Furthermore, after distribution of reinforcement particles in the matrix, using X-ray diffraction peak broadening, according to Williamson-Hall equation, the mean crystallite size and lattice strain were determined, and by scanning electron microscopy (SEM), the structure and morphology of the powder particles were studied.

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In this paper, the behavior of energy absorption of crush-boxes, made of Aluminum foam advanced material, was investigated based on foam cellular structure homogeneity. Therefore, thin-walled tubes of Cu-Zn30wt.%.brass alloy with 27 mm diameter and 1 mm thickness were filled with A356-10vol.%SiC-Xwt.%. of TiH2 foam liquid. Foam samples with 1, 1.5, 2wt.%. of TiH2 were prepared by Form Grip into the brass tubes in order to produce crush-box .Then the crush-boxes as energy absorber elements were compressed by un-axial loading and then behaviors of progressive buckling foams were measured. Results showed by decreasing A356-10vol.% SiC foam density from 0.93 to 0.88 and then 0.43 g/cm3, the energy absorption would be changed from 12955 to 13465 and then to 11192 J, respectively. The sample with 1.5wt.% of TiH2 and density of 0.88 g/cm3 had the maximum energy absorption. Also, the results of foams cellular structure images showed that foams of homogenous cellular structure had a sizeable effect on the progressive buckling behavior. We developed a new parameter as "sorting coefficient", which can release the foams cellular structure non-homogeneity, and change the crush-boxes energy absorption during the progressive plastic buckling.

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Nickel ferrite based cermets and their relevant composites have been widely used as inert anodes for aluminum electrolysis due to their good combination of chemical resistance, thermal stability and mechanical properties. In this study, various NiO/NiFe2O4 composites consisting of 5, 10 and 15% NiO in conjunction with Cu/NiFe2O4 cermets containing 0.5, 10 and 15% Cu were prepared by powder metallurgy method. The degradation resistance of the developed inert composites was examined under hot corrosion condition by plunging samples in to the molten electrolyte at 1000ºC. The strength, toughness, hardness, relative density, microstructural observation, phase analysis and electrical resistivity were evaluated by 3-points bending tests, Vickers method, Archimedes method, scanning electron microscope, x-ray diffraction and conventional direct current four-probe techniques, respectively. The experimental results for NiO/NiFe2O4 composites showed that a significant improvement of toughness and degradation resistance continuously occurred with a moderate decrease in strength by increasing NiO content, while the relative density was increased only up to 5%NiO content. By increasing the Cu content in the cermet samples, all the properties such as strength, toughness and electrical conductivity were improved considerably but the degradation resistance decreased.

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This study was intended to investigate the effect of injection of aluminium into the crystallizator on type, composition and activity of inclusions in low carbon steel grade USD7. The steel is made in Zob-e-Ahan Isfahan factory and its porosities and inclusions results in the problem of rupturing during rolling process. To improve the quality of this steel, 2.4 mm diameter pure aluminum wires were injected in to the crystallizator at the rate of 2, 4, 6 or 8 m/min in certain periods and then sampling was done. The results indicated that much of the added aluminum changed to aluminum oxide slag, and the remaining part altered the chemical composition of the inclusions. Increased aluminum caused an increase in the activity of alumina and reduction in the activity of other oxides in the slag and existing inclusions in the melt. By increasing Al2O3 activity from 0.313 to 0.649, the Al2O3 formation and oxygen exclusion probability increased in the system. Scanning electron microscopy showed that without aluminium injection, most of inclusions were FeO-MnO type placed around existing porosities in the ingot. The optimum rate of aluminum injection was found to be 4 m/min.

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In this study, AlN whiskers were prepared in a tube furnace at 1000˚C for 1h with 500 nitrogen gas flow. Al powders with particle size of 3 μm and 45 μm and NH4Cl were used as raw materials. SEM, TEM and XRD analysis were used to characterize AlN whiskers. The results showed that the diameters of AlN whiskers would range from 140 nm to 340 nm if different amounts of NH4Cl and 3 μm Al powder were used. In the case of using NH4Cl more than 40wt%, pure AlN without any unreacted Al was formed as the final product. Using NH4Cl and Al with particle size of 45 μm led to AlN whiskers with 630 nm to 870 nm in diameter. By adding 50%wt NH4Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing NH4Cl content in starting materials (about 200 nm). Also, an increase in the diameter of AlN whisker resulted from coarse Al powder. By adding NH4Cl to Al, thermodynamically spontaneous cholororination - nitridation reactions were increased in vapor phase and whiskers and pure AlN powder were produced.

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Sodium molybdate (Na₂MoO₄) as a grain refiner was used to refine the microstructure of Al-0.7Fe alloy. Al-Fe samples with the addition of 0.1, 0.2, 0.3, 0.4 and 0.5 wt.% sodium molybdate were fabricated by casting in sand molds at 750 ͦC. The microstructures of the as-cast samples were investigated by scanning electron microscopy (SEM) and the present phases were revealed by X-ray diffraction (XRD). The effect of sodium molybdate on the microstructure was examined by measuring the average grain sizes of the alloys, determining the widths of intermetallic compounds and carrying out hardness and tensile tests. The results showed that the addition of sodium molybdate modified the microstructure of Al-Fe alloy by reducing the average grain sizes. Also, it was found that the optimum amount of sodium molybdate to add to Al-0.7Fe alloy melt was 0.3 wt.% in this study.

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This study aims at investigation of the hydrogen damage after dissolution annealing and two-stage aging in aluminum 7075 alloy. Dissolution annealing was performed at 500 to 575 ^°C for duration of 1 to 20 hours. The first stage of two-stage aging was performed at 180, 200 and 220 ^°C for 30 minutes. The second stage was carried out at 120 and 150 ^°C for 10, 15 and 20 hours. Structural characteristics and chemical composition of precipitates was investigated using SEM and EDS methods, respectively. Reduction of the tensile strength in T6 process after hydrogenation reached to 150 MPa, although it decreased only, about 50 MPa in the two-stage process. Overall, tensile strength after hydrogen charging was significantly increased in the two-stage aging compared to the T6 process.

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In this study, microstructure and mechanical properties of diffusion joints between 5754, 6061 and 7039 aluminum alloys and AZ31 magnesium alloy were investigated. Diffusion joints were done between the alloys at 440 °C, for duration of 60minutes, at 29 MPa pressure and under 1×10^-4 torr vacuum. The interface of joints was studied using optical (OM) and scanning electron microscopy (SEM) equipped with EDS analysis and the line scan. According to the results of EDS analysis, the presence of intermetallic compounds including Al₁₂Mg₁₇, Al₃Mg₂ and their mixture was observed at the diffusion zone. Also, according to the results of the line scan, the hardness value of aluminum alloys has a considerable effect on diffusion of the magnesium atoms toward aluminum alloy and the greatest diffusion of magnesium was observed when 6061 aluminum alloy was used. More diffusion resulted in a stronger bond between atoms of magnesium and aluminum, and maximum strength of approximately 42 MPa was obtained when 6061 aluminum alloy was used.

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In the present article, RRA, T73 and T6 heat treatments were carried out to improve mechanical properties of 7075 aluminum alloy and its hardness, tensile and bending strengths were evaluated. For this purpose, solution annealing was performed at 530 ºC for 16 h. For T6 treatment, aging was executed at 150 ºC for 24 h after solution annealing. In T73, aging treatment was done in two stages after solution annealin, at 120 and 180 ºC for 7 and 20 h, respectively. RRA treatment was performed in three stages. The first stage was the same as T6 treatment, the second stage constitutes tempering at 200 ºC for
20 min and in the third stage aging process was repeated like T6 treatment. Evaluation of the microstructures and fractured surfaces were performed with optical microscopes (OM) and scanning electron microscopes (SEM). Energy dispersive spectroscopy (EDS) was used to study the chemical composition of precipitates. Hardness, tensile and bending strength were evaluated according to ASTM E384-11e1, ASTM B557-06 and DIN 50121 standards. RRA treatment increased tensile strength from 466 to 485 MPa and hardness from 110 to 165 Vickers. After T6 treatment, tensile strength increased from 466 to 505 MPa and hardness from 110 to 160 Vickers. In T73 process, the tensile strength remained almost constant (465 MPa) but yield strength increased from 394 to 410 MPa and hardness decreased from 110 to 84 Vickers. The bending strength increased from 797 to 844, 920 and 1030 MPa in T73, RRA and T6 processes, respectively. By applying RRA process in optimized temperature and time, hardness, tensile and bending strengths of 7075 aluminum alloy were enhanced from 5 to 15% compared to that of T6 and T73 processes.

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In this study, electrical wire explosion has been used to produce aluminum carbon nanotube (Al-CNT) nanocomposite particles in acetone medium. In order to synthesize Al-CNT nanocomposites, initially, CNTs were ultrasonically dispersed. Then, aluminum wire was exploded in this medium. Synthesized samples were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM) methods. The results exhibited formation of spherical nanoparticles in the medium. The average diameter of nanoparticles was 4 nm. Moreover, attained nanoparticles remained stable in acetone. Results revealed a good interaction between aluminum nanoparticles and CNTs in this medium. It is concluded that acetone is a suitable medium for synthesizing Al-CNT nanocomposite as appropriate dispersion of Al-CNT nanoparticles can be achieved in this medium.

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Despite a great thermodynamic driving force, copper cementation by aluminum from sulfate solutions involves a relatively slow kinetics due to the presence of the passive oxide film on the surface of aluminum. The previous studies have confirmed the positive effect of the presence of small amounts of chloride ion on reducing the scale of this problem. In this paper, the effect of concurrent ball milling on the kinetics of this process has been investigated. The cementation experiments were carried out in a polyamide jar with alumina balls inside by planetary ball milling. The studied parameters were ball number (0, 4), temperature (25-55 °C) and time (0-240 s). All experiments were conducted at constant condition of [Cu²⁺] = 6 g/L, [Cl⁻] = 75 mg/L, rotation speed of 160 rpm, average aluminum particle size of 279 µm and [H⁺] = 1.94×10^-3. The results showed that concurrent ball milling reduces the induction period of the cementation process to less than 120 s.  The apparent rate constant of cementation showed the positive influence of simultaneous milling on the kinetics of the studied cementation process. Moreover, activation energies of the induction and main periods were calculated to be respectively 86 and 26 kJ.mol^-1, indicating the shift of the reaction mechanism from chemical control to mass transfer control.
 

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In this study, Spark Plasma Sintering (SPS)  of both slip casted and powder specimens of alumina/ yttria core-shell nanocomposite were utilized for fabricating transparent Yttrium Aluminum Garnet (YAG) ceramics. Phase evolution, optical transmittance and the microstructure of sintered samples were compared. In slip casting process, Dolapix CE64 was used as a dispersant for preparing the stable aqueous slurry of this nanocomposite powder. The effect of Dolapix concentration and pH value on the stability of the suspension was described, and the viscosity diagrams were investigated at different pH value and different weight percents of Dolapix. The rheological behavior of the nanocomposite powder slipped at 60-70 wt% solid loading was studied by measuring their viscosity and shear stress as a function of shear rate of the slurry. The results showed that, the suspension has a minimum viscosity at pH of 10 by addition of 2.5 wt% Dolapix. Also, the slurry with solid loading of 60 wt% showed the Newtonian behavior and this rheological behavior was preserved even above this solid loading values. Slip casting technique caused the uniform size and pores distribution as well as eliminating large pores in the green body. Consequently, transparent YAG ceramic with 60% optical transmittance was achieved after SPS process of slip casted green body which was much higher than that of nanocomposite powder, i.e. about 30% at the same sintering conditions.
 

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In order to improve the oxidation and hot corrosion resistance of steels, various elements including aluminum, chromium, silicon, titanium or combination of these elements can be diffused on to the surface of steel. In this study, aluminum and titanium were simultaneously co-deposited onto the AISI 430 ferritic stainless steel substrate by the pack cementation process. Coating was examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coating consised of two layers with the thickness of approximately 14 microns. The results obtained by XRD showed the existence of FeTi, TiO₂, AlTi, Al₃Ti and Al₅Ti phases in the coating. Isothermal oxidation and cyclic oxidation were carried out at 1000^○C. It was showed that the diffusional coating of aluminum-titanium led to the improvement of cycle and isothermal oxidation resistance.