جستجوی مقالات مرتبط با کلیدواژه « stir casting » در نشریات گروه « مواد و متالورژی »

In this study, microstructure and wear properties of Al-8Zn-3Mg-2.5Cu nanocomposite reinforced with 1, 2, 3 and 5 wt.% SiC nanoparticles (SiCnp) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with 2000 W powers was used for mixing alloy and nanoparticles. Also scanning electron microscopy was used for microstructure studies. The microstructure of nanocomposite was investigated by scanning electron microscope.The microstructural studies of the nanocomposite revealed that SiCnp addition reduces the grain size, but adding higher SiCnp content (5 wt.%) does not change the grain size considerably. Further investigations on hardness revealed that the addition of SiCnp increases hardness and wear resistance. At higher SiCnp contents (5 wt.%), the presence of SiCnp agglomerate on grain boundaries was found that causes decrease the hardness and wear resistance. The optimum amount of nanoparticles before and after heat treatment is 3 wt.% SiCnp that nanocomposite exhibits best wear resistance.

In this study, microstructure and wear behavior of Al-8Zn-3Mg-2.5Cu aluminum alloy matrix nanocomposite reinforced with 0.1, 0.3, 0.5, 0.7 and 1 wt.% graphene nano plates (GNPs) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with high powers was used for mixing alloy and nanoparticles. Also the microstructure and wear surfaces of nanocomposite was investigated by scanning electron microscope equipped with EDS analysis. The microstructural studies of the nanocomposite revealed that GNPs addition reduces the grain size, but adding high GNPs content (1 wt.%) does not change the grain size considerably. Further investigations on wear revealed that the addition of GNPs increases wear resistance . At high GNPs contents (1 wt.%), the presence of GNPs agglomerate on grain boundaries was found that causes decrease the wear resistance. The optimum amount of nanoparticles is 0.5 wt.% GNPs that nanocomposite exhibits bes wear resistance.

This study investigated the effect of adding boron carbide microparticles (B4C) and titanium diboride nanoparticles (TiB2) on the microstructure, tensile strength, and hardness of A356 aluminum composite. In so doing, 2.5, 5, and 7.5 vol.% B4C reinforcements and 2.5 vol.% TiB2 reinforcement were added to the field by stir casting at 1000 °C using in situ process. The TiB2 nanoparticles were processed in situ by cryolite precursors (Na3AlF6), titanium oxide (TiO2), and potassium tetrafluoroborate (KBF4) in aluminum melt, and B4C microparticles were added directly into the melt. X-ray diffraction (XRD), optical microscope (OM), and scanning electron microscope (SEM) were used to investigate the microstructure and failure mechanism of the samples. Also, hardness and tensile tests were carried out to test mechanical properties. The results showed that addition of B4C first decreased and then increased the ultimate tensile strength compared to the sample without reinforcement. Moreover, the highest value of tensile strength was for the sample containing 2.5 vol.% of B4C and 2.5 vol.% TiB2, which showed a 235% improvement compared to the sample without an amplifier. However, the tensile strength of the sample containing 2.5 vol.% of B4C was reduced by 35% compared to the sample without reinforcement. The results of the hardness test showed a drop in properties of the samples containing 2.5% of B4C reinforcement. the highest value of tensile strength was for the sample containing 2.5 vol.% of B4C and 2.5 vol.% TiB2, which showed a 33% improvement compared to the sample without reinforcement.

This study was conducted to investigate the effect of adding titanium diboride (TiB2) nanoparticles on the microstructure and tensile properties of the Al5083 matrix composite. Al5083/TiB2 metal matrix composites (with 5 and 10 wt % reinforcement) along with zirconium (Zr) and cerium oxide (CeO2) additives with different wt % were fabricated by in situ-stir casting at 1000 °C. The samples were then subjected to hot extrusion for uniform distribution of reinforcements in the matrix. TiB2 nanoparticles were in-situ processed in molten aluminum using the precursors such as cryolite (Na3AlF6), titanium oxide (TiO2), and potassium tetrafluoroborate (KBF4). The microstructure, surfaces, and failure mechanism of the samples were investigated using X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM). Tensile test results showed that the addition of 10 wt % TiB2 particles increased the ultimate tensile strength by 17.7 % and decreased the strain by 19.2 % compared to the sample without reinforcement. Besides, the addition of Zr and CeO2 increased the strength by 35.8 % and the strain of the sample containing 78 % by 10 % reinforcement compared to the sample without reinforcement due to the removal of intermetallic compound Al3Ti and the incompatibility between coefficients of thermal expansion (CTE) with the matrix. Also, post-extrusion annealing in the sample with 10 wt % TiB2 reduced the tensile strength.

One of the methods to improve and achieve superior properties, is to modify and optimize the Manufacturing Process and to consider the use of nanoparticles as reinforcements in these materials. In this regard, stir casting method is considered as one of the methods of distribution of refractory particles in the melt and three percent by weight of 0.01, 0.05 and 0.1% of graphene nameplates and carbon nanotubes as reinforcements particles added to The primary alloy A356, due to the properties of carbon based nanoparticles. The optimum conditions, including the rotational speed of the graphite mixer, 500 RPM, were obtained for one-minute mixing in a row, at 740⁰C. The results of elemental, phasic and microstructural analysis, confirmed, the distribution correctly of reinforcements nanoparticles in the composite matrix. The tensile test showed, an increase in yield, ultimate and fracture strength, and also strain, so that the maximum increase in strength and strain using 0.1 wt.% graphene, was 28% and 2.6%, respectively. Also, by using 0.1 wt.% carbon nanotube, the nanocomposite hardness increased to 88.4 Vickers, indicating a 33% improvement in the ratio of non-reinforced alloy.

The low cost stir casting is one of the most applicable methods to fabricate Aluminum metal matrix composites. In this study, stir casting technique is utilized to produce Silicon carbide/Aluminum alloy composite. To achieve a homogeneous and suitable distribution, reinforcing particle surface properties is investigated by applying various thermal and mechanical treatments. SiC Oxidation performed at 950˚C for 1 hour and keeping at 650˚C for 2 hours as heat treatment. Mechanical treatment comprised milling aluminum and SiC powder. 10% vol. fraction Silicon carbide particles with average size of 2, 10 and 40 microns were gradually added to the aluminum matrix stirring at 640˚C. After stirring, the composite was cast at 700˚C in a steel mold. Observing the composite microstructure using OM and SEM reveals that reinforcing particles are dispersed in the matrix. However, heat treated reinforcing particles at 950˚C and keeping at 650˚C leads to fabricate a more homogenous composite of a specified percentage of reinforcing particles in which particles could be easily wetted by the matrix. In samples with SiC particles milled with Al powder, particles were not desirably bounded and disturbed in the matrix. Oxidation at 950˚C and keeping at 650˚C Shows better wettability and distribution of particles. This specimen also has the highest hardness of 139 HV, indicating the proper bonding of particles and their uniform distribution in the matrix.

Today, the use of nanoparticles in aluminum composite materials has attracted researchers due to their superior effects on mechanical and physical properties. Due to the poor wettability of the nanoparticles by the metal during the casting and the high ratio of the surface to the volume of the nanoparticles, it is difficult to achieve uniform distribution of the particles in the interior. In the manufacturing process, nanoparticles tend to form cluster particle masses. The mass of nanoparticles has undesirable effects on mechanical properties, including strength and resilience of the composite. In this study, stir casting process for composite manufacturing with different amount of mixed powder containing of nano Si3N4, AlMg and Al2O3 was used. For better distribution of particle reinforcement, cold rolling was used. In order to characterize the composite, microstructural, mechanical and phases studies properties were used. FESEM tests on mixture of aluminum and nanoparticles showed that after ball milling, particles are in nanometric size. Mechanical and optical result show that optimum of reinforcement is 0.5 % w.t. It is notable that the higher yield stress of the composite samples does not reduce the elongation significantly, when compared to monolithic aluminum.

In this study, microstructure and mechanical properties of AA7068 nanocomposite reinforced with 1, 2, 3 and 5 wt.% SiC nanoparticles (SiCnp) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with 2000 W powers was used for mixing alloy and nanoparticles. Also scanning electron microscopy was used for microstructure studies. The microstructure of nanocomposite was investigated by scanning electron microscope.The microstructural studies of the nanocomposite revealed that SiCnp addition reduces the grain size, but adding higher SiCnp content (5 wt.%) does not change the grain size considerably. Further investigations on hardness revealed that the addition of SiCnp increases hardness. At higher SiCnp contents (5 wt.%), the presence of SiCnp agglomerate on grain boundaries was found that causes decrease the hardness. The optimum amount of nanoparticles is 3 wt.% SiCnp that nanocomposite exhibits hardness of 155 BHN. According to the results of hardness for the initial samples and nanocomposites reinforced with 3 wt.% SiC, 24% increase in hardness can be seen.

In this research, the influence of various weight percentages of reinforcing particles on the microstructure and mechanical properties of composites was investigated. Aluminum alloy (A356) matrix composites reinforced with 0.5, 1 and 1.5 wt. % nano-particle SiC (about 80nm) were fabricated via stir casting method. Fabrication was performed at 610°∁ by the injection of reinforcing particles into molten alloy. The composites were characterized by field emission scanning electron microscope (FESEM) equipped with image analyzer and energy dispersive spectroscopy (EDS) and, Optical microscope (OM). Microstructure evaluation revealed a uniform distribution of nano particles with reduced in weight percentages and the average size of dendritic arms has decreased at least 50 percent. .Brinell hardness measurement showed that addition of reinforcing particles gives rise to hardness compared to matrix alloy and the highest increase was for the sample contain 0.5% SiC with 40 percent increase. The porosity percentage in the materials was calculated according to the difference between the theoretical and measured density and revealed that porosity increased about 3% by increasing in amount of SiC particles.

In the present investigation, a A356 aluminum alloy based composite has been produced by the addition of boron nitride powder with three different conditions including raw powders, coated powder using Ni-P electroless bath and coated aluminum particles with Ni-P/ BN(h) surface composite. Moreover, parameters such as impeller shape and rotation speed have been examined in order to obtain optimized conditions. The results based on scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) showed that the pre-treatment has a main role in deposition of Ni-P on the surface of BN(h) powders. Also, it was obtained that optimum pretreatment consisting of oxidation in 200 ºC for 1 hr, sensitization in 10g/l SnCl2�ꗾ HCl solution for 15 minutes and then activation in 0.25 g/l PdCl2 �ꗾ HCl solution. Moreover, results showed that the optimum value of added powders was 6% after coating on aluminum particles using the Ni-P electroless bath. Furthermore, the agitator of four-blade type with a radial flow was a good choice for the manufacture of aluminum/boron nitride composite. Also, it was shown that tensile strength of composite materials is not proportional with hardness, so that the tensile strength can decrease while hardness increases.

The effect of stir casting process on the modification of the Fe-containing intermetallics formed in a cast in-situ composite based on Al-319 matrix alloy was studied in the present work.
Microstructural observations using optical and scanning electron microscopes showed that the undesirable needle-like shape of the Fe-containing intermetallics (β) and also the coarse star-like α phase were modified into the disc and spheroid shape particles with much less length to width ratio. The effect of parameters such as stirring temperature, cooling rate and Fe contents on the shape, size and distribution of intermetallic particles and eutectic Si blades were also studied. Results showed that the best condition to improve the above-mentioned microstructural features can be achieved at a stirring speed of 1200 rpm for 5 minutes at the vicinity of β needles nucleation temperature followed by casting into a metallic mold. Based on the results obtained from the current work, it can be concluded that the harmful morphology of the β needles can be properly modified by applying a shearing force during stirring the molten alloy in the semi-solid state.

In the last few decades, the production of Aluminum Matrix Composite (AMC) has been attractive due to the enhancing the mechanical property of Aluminum. One the most important parameters in the production of metal matrix composites is the uniform distribution of reinforcing phase in the matrix. The stir casting method can produce composite by strengthening the Nano-particle in the uniform distribution of reinforcing particles in the matrix and high wettability, which is the most important parameter in determining the properties of materials on the Nano-scale. In this study, the aim is producing aluminum composites reinforced with TiC nanoparticles coated with aluminum to increase the wettability. After preparation of particles, they were added to molten aluminum alloy LM2 and after stirring over a period of time as a variable parameter, casting was done in the sand mould. To evaluate the mechanical properties of the composite the Brinell test was used for the determination of the hardness and the pin on disk test was used to measure the wear rate and the friction coefficient. The results show that the hardness of composite increases and. With the increase of stirring time, the weight loss decreased with respect to the base alloy and the coefficient of friction increases.

In the last few decades, the production of Aluminum Matrix Composite (AMC) has been attractive due to the enhancing the mechanical property of Aluminum. One of the most important parameters in the production of metal matrix composites is the uniform distribution of reinforcing phase in the matrix. The stir casting method can produce composite by strengthening the Nano-particle in the uniform distribution of reinforcing particles in the matrix and high wettability, which is the most important parameter in determining the properties of materials on the Nano-scale. The aim of this study is producing of aluminum composites reinforced with B4C nanoparticles coated with aluminum to increase the wettability. After preparation of the particles, they were added to molten aluminum alloy LM2 and after stirring over a period of time as a variable parameter, casting was done in the sand mould. To evaluate the mechanical properties of the composite the Brinell test was used for the determination of the hardness and the pin on disk test was used to measure the wear rate and the friction coefficient. The results of the present research show that the hardness of composite increases adding the strengthening Nano-particles and the weight loss with respect to the base alloy decreased when the stirring time increases. Also, the coefficient of friction increases.

In this research, the fabrication of in situ Al-Mn-Al2O3 composite samples from different composition of Al-MnO2 as starting materials have been made by stir casting method. For this purpose, a mixture of Al and MnO2 powders with weight ratio 1:7 was ball-milled. Then 1, 3, 4 and 7wt% of this mixture along with 5%wt Mg (to improve wettability) have been added to melted aluminum at 900 ° C . The disperstion of added materials in molten of Al was made by using graphite stirrer during 8 minutes. The molten of composite was casted into a preheated steel mold. Differential thermal analysis (DTA) was conducted on starting powder mixtures to study the aluminothermic reaction and the possible other reaction or phase changes. XRD analysis and scanning electron microscopy (SEM) were used to investigate the microstructure and phase composition of composite samples. The results show that the final phase composition for all composites is solid solution of Al-Mn, ceramic phase of alumina and MnAl6 intermetallic compound. The amount of MnAl6 and Al2O3 particles in composite samples were increased by adding higher quantity of MnO2 into molten of Al. Moreover there is an optimal amount of MnO2 in which haighest mechanical properties such as hardness, strength and toughness is obtained for composite samples.

In this paper, ZX51-xAl2O3 (x=0, 2.25, 4.5, and 6.75 vol%) magnesium matrix composites were fabricated by stir casting and then were hot extruded at 300, 350, and 400°C. After precise measuring of density based on Archimedes’ principle, physical properties of produced composites including apparent density, relative density, and volume percentage of porosity were investigated and also were statistically analyzed with the aid of Regression. The results showed that the apparent density and volume percentage of the porosity increase linearly and quadratically respectively for both the as-cast and extruded composites, while the relative density of the composites decreases by a second-order polynomial function when the amount of particle reinforcements increases. However, for all volume percentages of the reinforcement, the apparent and relative densities of the extruded composites were higher than those of the as-cast counterparts. In contrast, an opposite behaviour was observed for volume percentage of porosity; indicating of decreasing porosity content in consequence of extrusion processing. Contrary to serious effects of alumina particles volume percentage, physical properties of the extruded composites seemingly behaved independent of extrusion temperature.