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

In this research, the structure and mechanical properties of aluminum 6061 composite with graphene reinforcing nanoparticles produced by friction stir method (FSP) were investigated. The rotation speed of the tool was set from 112 to 280 rpm, the speed of the tool movement in the range of 31.5 to 20 mm/min and the slope of the conical tool was set at 2, 2.5 and 3 degrees.

Characterization was done by tensile tests, microhardness, field emission scanning electron microscope (FESEM) along with X-ray energy spectroscopy (EDS) and optical microscope (OM). The results show that in the presence of graphene as a reinforcement, the mechanical properties are improved.

By increasing the ratio of rotation speed to tool movement speed (advance per revolution) from 0.07 to 0.28 and increasing the tool angle from 2 to 3 degrees, tensile strength enhanced from 338 to 396 MPa, yield strength from 319 to 383 MPa and the elongation increase has increased from 10.9 to 12.3 percent. Also, the micro-hardness in the nugget area increased from 273 to 400 Vickers.

anodizing due to the significant increase in the surface performance of aluminum and its alloys is an appropriate method in the field of surface engineering. But for the application of this method as much as possible, filling the porosity of this coating is a very effective selection. On the other hand, due to the unique structure of the oxide layer, this layer can also be used to grow a variety of nanowires. In this study, 1070 aluminum anodizing was performed in oxalic acid-sulfuric acid solution. Microstructure of the coating was studied by means of field emmision scanning electron microscopy (FESEM) images. Subsequently, silver nanowires were grown in the oxid layer by electrochemical deposition method. The result of X-ray diffraction(XRD) test showed that the oxide layer has a non-crystalline structure and silver nanowires has a very high purity. . The growth of silver in the oxid coating resulted in a 55% increase in the wear resistance. The scanning electron microscopy (SEM) images of the wear surfaces showed that this increase is related to silver lubrication nature that have reduced the coefficient of friction of the coating in the presence of these fillers. The effect of these nanowires on the corrosion resistance of anodized aluminum was studied by using electrochemical impedance and TOEFL polarization tests

Hard anodizing, as one of the methods to improve surface properties, has always been considered for aluminum.But the difficulty of controlling the temperature and the formation of an anodic aluminum oxide layer at the bottom of the pores are two important problems in this method. In this investigation, by designing an anodizing reactor, precise control of the coating conditions and the use of a mild anodizing (at 40 volts) prior to hard anodizing (at 130 volts), current density changes during the coating of 1100 aluminum alloy in an oxalic acid solution were studied. The current density-time curves and field emission scanning electron microscopy (FESEM) images showed an increase of current density and a transition from mild to hard anodizing, which was accompanied by an increase in interpore distance. The x-ray diffraction (XRD) results indicate a coating with an amorphous alumina structure. Energy dispersive spectroscopy (EDS) analysis also showed that the coating only contains oxygen and aluminum due to the formation of alumina. The results of the polarization test indicated a significant improvement in the alloy corrosion resistancewith the application of aluminum oxide layer. Anodizing at three temperatures of zero, 10 and 17 ℃ showed that increasing the temperature would increase the charge density and thickness of the oxide layer, but there was no significant effect on the interpore distance, pore diameter, the thickness of the barrier layer and the pore density, indicating that these parameters are independent of current density. However, due to more corrosive intensity of solution, the range of changes in these parameters increases. The porosity of the coating also increasesfrom 15.6% to 17.3%. By comparing the anodizing of pure aluminum and 1100 aluminum alloy , it was found that the presence of alloying elements would lead to a reduction in the coating arrangement

Aluminum-ceramic metal matrix composite is a class of modern engineering materials with interesting physical and mechanical properties. These composites are used widely in many industrial (aerospace, automobile, electronic ,…). In present study, alumina granules preforms with different size (20-100 µm) were made and sintered at 1300°C and 1400°C for 2 h. Then the preforms were preheated at 700°C for 1h. Finally, molten Al was infiltrated into the preforms under load of 3 MPa by squeeze casting method. After composites making their microstructures were studied by SEM and optical microscope.The microstructure results showed that composite with higher sintering temperature has low porosities and well connected granules. Also, compressive strength, impact resistance and hardness of the composites were investigated. The results showed that sintering temperature improved compressive strength and hardness of the composites, but impact strength decreased. The strength and brittleness of the composites is higher for the composites with high sintering temperature

In this paper, synergy effect of various bismuth contents and cooling rates on performance of ‎Al-8Si-0.3Mg cast alloy after applying T6 heat treatment was evaluated. Cooling rate was ‎measured based on analyzing cooling curve and its second derivative curve. A step mould with ‎different casting thicknesses was designed to obtain four different cooling rates (0.55 to 6 ‎‎°C/s). Microstructures of sample were evaluated by optical microscopy and scanning electron ‎microscopy (SEM). Results showed that sample modified with Bi and solidified at higher ‎cooling rate required less time for annealing and spherodising of eutectic silicon. Moreover, ‎tensile test results indicated that the highest yield strength (142.2 MPa), ultimate tensile ‎strength (235 MPa) and elongation percentage (6.1%) obtained for the sample containing 0.5 ‎wt% Bi and solidified at the highest cooling rate (6 °C/s). Fracture surface of samples cooled at ‎low cooling rate comprised of cleavage indicating brittle fracture mode resulted in low ‎ductility. Likewise, fracture surface of samples solidified at highest cooling rate exhibits ‎dimples and ductile fracture mode. The counter graph of quality index used to predict the ‎quality of heat-treated samples with different levels of Bi and solidified at various cooling rates ‎showed that the highest index (352.8 MPa) obtained for specimen containing 0.5wt% Bi ‎solidified at 6 °C/s cooling rate.‎

Excellent features including high elastic modulus and thermal expansion coefficient associated with low weight and the ability to manufacture with conventional techniques were developed Aluminium composites reinforced with cremic particles at recent decades. In this work, Al2024/SiC composites with different SiC percentages (1,2,3%) were produced by Accumulative Roll Bonding (ARB) process. In order to produce composite samples 60% reduction rolling were applied to the samples firstly and then rolled strips cutted out into two parts and again subjected to 50% reduction for 3 passes. Mechanical properties of samples were investigated. Creep tests were done at temperature and stress range about 250-350°C and 30-40 MPa respectively. According to the results, Al2024%SiC composite had higher hardness degree than the other composites because of appropriate adhesion of raw strips together due to lower volume of SiC powder in this composite and acceptable consistency of particles into the matrix. Moreover, creep life of this sample was higher than the other. It is obvious that the creep life of All composites produced were several times less than the Al2024-T3 original raw sample.

In this research, cooling curve thermal analysis and interrupted quenching technique were employed to examine interactive effect of Sr-Bi on porosity characteristics of the Al-7Si-0.4Mg alloy commonly used in industry. Based on obtained cooling curve profile and plotting the first and second derivative curves, solidification process of the alloy was studied. Solid fraction curves were calculated and corresponding exact temperatures for precipitation of 20, 45 and 80% solid for alloys with different Sr/Bi ratios, namely 0.1, 0.34 and 0.46 were determined. Subsequently, alloys were quenched rapidly at determined temperatures in the same solid fraction. Porosity characteristics consist of size, area and density were measured using an optical microscope equipped with image analyzer software. Results show that the size, area and density of porosity were affected by Sr/Bi ratio and solid fraction percentage. Area percentage and size of porosity increased by 75% and 141% respectively with increase of Sr/Bi ratio from 0.1 to 0.46. Critical solid fraction for the nucleation and growth of porosity in the alloys were determined at 70% and 80%respectively while Sr and Bi co-existed.

The effect of alumina nanoparticles contents with the average size of 40 nm on the microstructure and wear behavior of A356/Al2O3 nanocomposite produced through stir casting was studied. The alumina nanoparticles with the amounts of 1, 1.5 and 2 weight percent, were incorporated into the molten matrix alloy being mechanically stirred, along with blowing an inert gas. To improve the nanoparticles wettability, 1wt% Mg was added to the molten matrix alloy. The microstructure of the nanocomposite was studied by using optical and scanning electron microscopes. The microstructural observations showed that the alumina nanoparticles have been evenly distributed within the matrix. The percent of porosity measured by the Archimedes method is increased with increasing the nanoparticles weight percent from 1.3% to 3.2 %. It was shown that, the increased percent of porosity can be attributed to the increase in the particles agglomeration with increasing particles weight percent. To study the wear behavior of the materials, nanocomposite containing 1wt% alumina, having the lowest porosity percent and even distribution of nanoparticles, was selected. The wear test showed that the addition of nanoparticles to the matrix alloy gave rise to enhance its wear resistance. Study of the worn surfaces and sub surfaces showed that the dominant wear mechanism for the materials used in the current work is probably an adhesive wear followed by the formation of a mechanically mixed layer (MML). However, this mechanism occurred with the less wear rate for the nanocomposite as a result of the presence of reinforcing particles.

The aim of current research was to examine the microstructure and mechanical properties of Aluminium matrix hybrid nano-composite reinforced with carbon nanotube (CNT) and silicon carbide whisker (SiCW) prepared by hot pressing. Hybrid nano-composites were fabricated with different amount of CNT and SiCW (0-5 weight percent) in equal proportion. In order to distribute the reinforcements, Al powder and the reinforcements were mixed in a planetary ball mill with a speed of 120 rpm for one hour, and then compressed samples were produced under the pressure of 500 MPa at 550ºC for 45 minutes. Followed by composite fabrication, Vickers microhardness and compressive strength test were performed and microstructural observations were undertaken using field emission scanning electron microscopy (FESEM). The results showed that by increasing the amount of reinforcements up to 1 percent, mechanical properties of nano-composites increase; while, by increasing the amount of reinforcements from 1 to 5 percent, mechanical properties of nano-composites decrease due to the agglomeration of CNTs and non-uniform dispersion of SiCW.

Adhesive bonding is an alternative to traditional joining systems like riveting and welding which has been used extensively in electronic, automotive, and aerospace industries. Design of such reliable bonding, requires knowledge achievement of bonding fracture resistant. In this study interface failure initiation of Al-2221 and glass/epoxy prepreg has been investigated by using acoustic emission (AE) technique. Furthermore, failure analysis simulation is done by commercial FEA software ABAQUS. Simulation was implemented by cohesive zone model (CZM) by using cohesive surface technic. Prepreg was used to reduce variation in specimen production and in order to improve adhesion between Al-2221 and composite layers. Pretreatment by a chromic acid anodizing agent was performed on the surface of aluminium. Failure initiation was identified by monitoring of force-displacement curve, online processed AE signals and using sentry function analyzing method. Critical load and fracture toughness was then calculated to be used as simulation input. Simulation result indicates that force-displacement curve obtained by sentry function method is in better agreement with the experimental result. According to present study AE online monitoring method can detect aluminium/ composite bonding failure more accurately than the other methods.

Al-ZrSiO4 composite possesses extensive applications in military، aerospace industries etc because of high mechanical properties and high wear resistance. One of the effective factors on the mechanical properties of the particulate composites is the distribution of the particles in the matrix. Stir casting is one of the proper techniques to produce such composites. In this paper، composites with various volume percents، 1. 5، 2، 2. 5، 3. 5 and 5 vol% zircon particles، have been produced at 750 and 850. The effect of reinforced particle volume percentage and casting temperature parameters on the microstructure and mechanical properties of these composites has been studied. Results show that the mechanical properties (UTS، Hardness) have been properly improved compared to that of monolithic matrix alloy. X-ray diffraction patterns of the samples exhibit the presence of zircon phase in the matrix. In addition، SEM images show that zircon particles could be uniformly distributed in the metallic matrix.

In this study, atmospheric corrosivity class of Tehran city was determined using environmental data and corrosion rate of standard specimens during one year exposure time. Accordingly, corrosion rate of Aluminum, Copper and Zinc standard helical and flat specimens were analyzed after each time intervals. Meanwhile, other influential parameters such as deposition rate of Chloride and Sulphur dioxide and time of wetness were evaluated.