جستجوی مقالات مرتبط با کلیدواژه « آلومینیم » 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.

In the joining of aluminum and polyethylene sheets with friction stir spot welding method, various factors affect the strength of joints. In this study, the effect of surface conditions and the dwell time of tool have been investigated. The results indicated the increased shear tension load with the prolonged dwell time due to the higher frictional heating, more molten polyethylene formation and an increased adhesion area. The use of mandrill that created more scratches with smaller dimensions was more effective to increase the strength. The highest shear tension load of joints was 785 N. Macroscopic and microscopic studies revealed that the mechanical interlocking and adhesion of molten polyethylene on the aluminum surface were the main joining mechanisms.

In this study, the effects of molten Al temperature and immersion time of steel samples on the joining of Al and steel and the formation and growth of intermetallic compounds, at the interface, were examined. Following surface pretreatment, steel rods were immersed into the pure aluminum melt (in an Alumina crucible) at temperatures of 680, 720, 760 and 800 Celsius and kept for different times of 5, 10, 15 and 20 minutes, at each temperature followed by air cooling after being taken out of the melt. (Then were taken out and cooled in airwhere.) Afterwards, the microstructure of interface between steel substrate and aluminium was examined by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Vickers hardness tests. The results showed that the main (two) intermetallic compounds formed at the Al/steel interface are FeAl3 and Fe2Al5 (were observed in reaction interface of steel substrate and aluminium. These intermetallic compounds were FeAl3 and Fe2Al5.) with a larger part of the intermetallic layer being the Fe2Al5 layer with a tongue- like morphology. As the temperature and time of immersion increase, only the thickness of the intermetallics changed without changing their composition. Thus, with increasing melt temperature and immersion time, the thickness of the intermetallic layer, especially Fe2Al5 layer, increased to a maximum value and then reduction of the thickness of the intermetallic layer was observed with further increase in temperature and time.

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

For the first time, nitrogen gas was used in friction stir processing (FSP) to form an Al/AlN composite surface layer on aluminum plate. Investigating the microstructure of the layers by X-ray diffraction, scanning electron microscopy and optical microscopy showed the formation of aluminum nitride particles on the surface layer of commercially pure aluminum. These particles found to have non-uniform distribution in the layer. While the percentage of composite reinforcements is not more than 10%, the aluminum grain size reduced from 100 to 70 μm due to restoring processes resulting from severe plastic deformation and significant improvement in surface properties observed. Due to extreme thermo-mechanical process, the surface layers have a finer grain size and high levels of hardness. As a result, the grain size ranged from an average of 100 μm to 70 μm and a hardness of 22 to a maximum of 38 Hv, which is about 1.7 times the base metal hardness. The wear resistance of the sample also improved up to 1.1 times with respect to fine graining of the surface layer and the presence of hard nitride particles. The coefficient of friction reduced from 1.2 to 0.9, indicating an improvement in the tribological properties of the sample

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

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.‎

In recent years, methods based on sever plastic deformation have been considered to improve the structure and mechanical properties of various metals, especially aluminum. Among the different methods, accumulative roll boding process is appropriate to improve the structure of metals sheet. Using this method, nanostructured aluminum alloys and aluminum nanocomposites reinforced by particles can be manufactured and simultaneously improve mechanical properties such as tensile strength and hardness. In most researches, after applying of 6 to 8 cycle of accumulative roll boding process the average of grain size reduced to less than 500 nm and the tensile strength increased to more than 2 times of the strength of the annealed aluminum. Accumulative roll boding process can be applied to different sheets in different routes, which will have a different effect on structural modification and mechanical properties. In this paper, the effect of various methods of accumulative roll boding process on microstructure and mechanical properties of aluminum alloys and aluminum based composites has been investigated.

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.

To reach an acceptable bimetallic composite product from two metals, interface characteristics needs to be investigated. In this work joining of commercial aluminium and a plain carbon steel and the formation and growth of intermetallic compounds at the interface was investigated. Steel rods were immersed into the pure aluminium melt at temperatures of 680, 720, 760 and 800 Celsius and kept for different times of 5, 10, 15 and 20 minutes, respectively and then were taken out and cooled in the air. After cross sectioning and sampling, the microstructure of interface between steel substrate and aluminium was studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Vickers hardness tests. The results showed that two intermetallic compounds, FeAl3 and Fe2Al5 are formed in the interface. Increasing the holding time and temperature changed the interface thickness and had no clear effects on the intermetallics types. Vickers hardness tests showed that the hardness of reaction interface was higher than aluminum and steel substrate due to presence of the above mentioned intermetallics. Kinetic of intermetallics formation are discussed.

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.

In this research, the effect of various amounts of aluminum on morphology of graphite in ductile cast irons produced by in-mold casting process is investigated. For this purpose, spherical graphite cast iron containing 0, 3.7, 5.5, 6.4 and 7.5 wt. % aluminum, respectively, were prepared in Y-block form via in-mold process. After casting, samples were prepared for microstructural studies, using conventional methods, followed by optical microscopy (OM) examination. Chemical composition of samples were determined using quantometer, x-ray fluorescence spectroscopy (XRF) and carbon/ sulfur determination method. Increasing the number of spheres from 168 to 668 per square millimeter, reducing the grain size from 21.4 to 8.8 micrometers, and changing the percentage of spherical graphite from 65 to 48 percent was observed.Hardness of samples show increase from 284 to 482 Vickers by increasing aluminum content from 0 to 7.5 weight percent.

Friction stir processing as a relatively new and effective solid-state process is used for surface modification of metals and alloys in order to modify their microstructure and properties. In this study, the effect of friction stir processing on the microstructure and mechanical properties of an Al-0.9Ni-Fe alloy was investigated. The process was performed under the rotational speeds of 600-2000 rpm and the traverse speed of 25 mm/min. According to the results, the severe surface plastic deformation refined the intermetallic compounds present in the microstructure, improved their distribution within the matrix, and substantially reduced the amount of casting defects. As a result of these microstructural variations, the tensile strength and percent elongation of the base alloy are increased by almost 40 and 205%, respectively. The fracture toughness is also improved by 205%. It was also found that the hardness of processed alloy is about 24% higher as compared to the base alloy.

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.

Gray cast iron is among the most common and important engineering material that plays a significant role and has many applications in various industries, including the automotive and machinery manufacturing. It still attracts researchers’ interest to improve its properties and maintain its position among the engineering materials. In this research, the microstructure of plain cast iron as well as those containing 4 wt% aluminum with different amounts of silicon, 1 to 4 wt%, was studied. Pin-on-disc method was used to evaluate the wear resistance of the cast irons. The results showed that the addition of aluminum to gray cast iron brings about the formation of ferrite phase, which accompanies a decrease in hardness value. In addition, the increase in silicon content in aluminum bearing cast iron up to 2wt% intensifies the formation of ferrite phase, while the further increase to 3 wt% results in emerging a Fe-Al-Si intermetallic compound. In gray cast iron with constant 4 wt% aluminum, increasing silicon content to 3 wt% and 4 wt% leads to improve the hardness value due to the increased percentage of intermetallic phase. Confirming microstructure evolution as well as hardness values, the results of wear experiment approved lower wear rate in cast irons containing intermetallic phase. In contrast, the lowest wear resistance was observed in aluminum bearing cast iron containing 2 wt% silicon.

In this research interface of aluminum-brass bimetal composite, fabricated by a vertical centrifugal casting machine, were investigated. At first, brass bushes were preheated at 100-300 °C temperature range and then aluminum melt with 1.5 melt-to-solid volume ratio was cast into cylindrical bush rotating at 800, 1600, and 2000 (rpm), respectively. Obtained samples were studied using optical microscope (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Image J software. Results show that metallurgical joint in this work is probably due to particular dissolving condition, provided by multiple mechanical forces involved and also possible solid diffusion at the end of solidification process. Study of the EDS results show that layers formed at the achieved interface consisted of four discrete layers from the brass side, including Al3Cu5Zn4, Al3Cu3Zn, Al3Cu precipitates scattering in aluminum matrix and finally α-Al/Al3Cu anomalous eutectic structure near the aluminum side.

In this research, the effect of 2.3 wt.% aluminum addition on the microstructure and tensile properties of high manganese austenitic steel Fe-18Mn-0.6C was studied. For this purpose, the samples were investment cast, homogenized and hot rolled. Tensile testing was carried out at ambient temperature. Microstructural investigations and fractography on the steel samples were carried out using an optical microscope and a scanning electron microscope. The results showed that the aluminum addition increases the austenite grain size. In addition, 2.3 wt.% aluminum addition increases the yield strength and plastic strain, decreases the ultimate tensile strength and eliminates the serrated flow during plastic deformation.

Aluminum is one of the most common metals used in industry and aluminum composites are highly regarded by engineers because of having simultaneously the desired physical and mechanical properties. Therefore, in this study, casting of aluminum-aluminum bimetallic composite samples of A356 and 7075 which are widely used metals in the industry have been done without surface preparation. With a constant volume ratio of metals, A356 melt was casted around the 7075 insert. In this paper, the melt temperature as one of the most important parameters affecting the quality of interface as well as the insert temperature and cooling the samples was investigated. Comparing the results of the optical microscopy indicate improvement of the interface quality with increasing the melt and insert temperature, due to the destruction of oxide layer caused by thermal stress between the metals. The results show that the cooling condition of the samples, has no significant effect on the quality of the interface.

In this paper, the effect of aluminum addition on the tribological behavior of Hadfield steel in mild wear condition was investigated. The pin-on-disk test method was used on the different compositions of Hadfield steel that alloyed by three nominal compositions of zero, 1.5 and 3 weight percent of aluminum. The experimental induction furnace surrounded by Ar atmosphere and zirconia ceramic mold was used for melting and casting of samples. In the wear test, the grinding wheel as abrasive medium was used and the changes in the friction coefficient and the weight losses of specimens versus the sliding distance were measured. The tensile, hardness and impact tests were used for evaluation of mechanical properties. In addition, the microscopically studies on the deformed samples, worn surface and wear debris were done using optical and scanning electron microscopes. The results shown that in the low stress wear condition, the work-hardening of worn surface of Hadfield steel cannot well be activated, therefore it has not sufficient wear resistant. By addition of 3wt. % aluminum, the yield strength from 415MPa to 470MPa and hardness from 190HV to 215HV can be increased. In addition, depth of work-hardened on abrasive forces and worn surface hardness can be enhanced from 100µm to 200µm and from 340HV to 365HV in sequence. Thus the wear rate from 0.15mg/m to 0.11mg/m was decreased and wear resistance was improved up to 70%.