Sharif Digital Repository

Metal matrix composites (MMC) and metal foams (MF) have been the topic of numerous researches during the last decades. The appropriate mechanical and physical properties of these materials make them useful in various industries. In this research, a unique approach is introduced for producing MMCs and MFs in which accumulative roll bonding (ARB) is employed in order to achieve a homogeneous distribution of ceramic particles in the metal matrix. Also, foamed structures can be made by subjecting Al/TiH2 composite to an appropriate annealing heat treatment where TiH2 particles decompose to hydrogen and titanium. In this work, the effect of number of ARB cycles on the size and distribution of... 

A new method for production of bimetallic rods, utilizing the equal channel angular extrusion (ECAE) process has been introduced before by previous researchers, but no attempt has been made to assess the effect of different temperatures and holding times in order to achieve a diffusional bond between the mating surfaces. In present research copper sheathed aluminum rods have been ECAEed at room temperature and subsequently held at a constant ECAE pressure, at different temperatures and holding times to produce a diffusional bond between the copper sheath and the aluminum core. The bonding quality of the joints was examined by shear strength test. The microstructure examinations were carried... 

Several SPD methods have been invented for processing rods and sheets, and their physical and mechanical properties have been investigated so far. The materials processed by these methods have not been industrialized thoroughly. Moreover, in previous investigations, few works have been carried out on tubular types of materials. Thus, in this study, aluminum tube goes through a tubular channel in order to achieve different values of strains. This method is named Tube Channel Pressing. The mechanical and microstructural investigations on aluminum tubes which have been processed up to 5 passes shows that ultimate strength increases 1.7 times and sub-grains size reaches to 360 nm. Applying final... 

Severe Plastic Deformation (SPD) Processes have drawn lots of attention due to their ability to refine grain size and develop some properties of bulk metals and alloys. After deformation, however, ductility and formability of metals are reduced. Annealing has been used as a solution for improvement of these characteristics after deformations even after SPD processes. On the other hand, there is a possibility that during annealing grains could grow, therefore it can neutralize the effect of SPD process. Consequently, predicting behavior and evolution of microstructure during annealing finds an important role. In this research, accordingly, vertex model have been used in order to predict... 

Al 5083 is a non-heat treatable alloy that widely used in the aerospace and automotive industry due to its low density and high strength. However, poor wearing behavior and low elastic modulus restrict its engineering applications. Metal matrix composites (MMCs) have advantages of high strength and modulus by reinforcement of second phase. Also, MMCs have excellent dimensional stability, damping capacity and wear, creep and fatigue resistances as compared with the corresponding monolithic alloys. Vast loss in ductility and toughness occurs by non- deformable ceramic reinforcements. For the surface engineering purposes, ceramic particles are added in the surface layers of components, whereas... 

One of the limitations of friction stir welding process is joining of sheets with low thickness. Interference ways for these limitations are joint in higher thicknesses and thickness reduction in included joint samples. In this study, in the first process, with the optimization of the variables affecting the process, joint was performed using visual inspection, mechanical properties and micro structural studies. In the next process, using the rolling operation for the reduction percent of different thicknesses, the most appropriate route was chosen. 1050 aluminum sheets (1050 and 6082-T6) with a thickness of 3 mm were welded using friction stir welding in tool rotary speeds of 1200 and 800... 

In this study, Al-TiO2 composites layer were produced on Al 1100 substrate using friction stir processing technique. The variation of process parameters such as tool rotational and substrate advancing speed as well as number of FSP passes were adjusted to achieve quite uniform dispersion of Nano-particles in the Al matrix of the fabricated surface layer. Microstructural observations were carried out using optical and scanning electron microscopes. By increasing the FSP passes, uniform distribution of TiO2 particles in the matrix improved. Surface composition layer exhibited a micro-hardness value of 49 HV which was around twice of the as-received substrate. In addition wear resistance of... 

Lots of investigations have been focused on dissimilar friction stir welding of aluminum and copper plates. Sever plastic deformation is a way to produce nanostructure materials, without changing in their appearance. The size of sever plastic deformed sheets in light of restriction in load capacity and equipments is limited and less industrial application can be found. Joining is the best solution for this problem. Therefore in this study, dissimilar friction stir welding of severely plastic deformed aluminum and copper sheets has been investigated. Friction stir welding is one of the best methods to join ultrafine grain materials.In this study, 3 mm-thick 1050 aluminum alloy and... 

Friction stir welding (FSW) is an appropriate method for joining Aluminum structures. In this method lots of defects involved in other methods are not formed and good properties are achieved for Aluminum joints. The metal sheets joined by this method are used to manufacture metal structures bodies. One of the important issues in the structure bodies used in transportation is the amount of energy absorbed in collision with other objects. One of the methods to investigate the energy absorption is wedge tearing test and one other is tensile test. In the preset study two sheets of Al 1050 were joined using FSW method in different tool rotational and welding speeds. Firstly, the microstructure of... 

The purpose of the present study was to investigate the effects of friction stir welding parameters on the fatigue life of friction stir welded sheets of Aluminum 7075 alloy. The welding process was carried out under three different rotational speeds and three different welding speeds and specimens were extracted transversely to be used for rotating-bending fatigue tests. Optical microscope and SEM images were used respectively for studying the microstructure of the weld zone and fractography. It was the indicated that an increase in the welding speed or a decrease in the rotational speed will result in an increase in the fatigue life  

The rapid pace of development of nanoscience and nanotechnology and their applications in various fields have made the study of materials in smaller scales more important than any time ever. Having an insight of materials’ microstructure and the mechanism of different phenomena in the atomic scale will be very beneficent in designing new and advanced materials or modifying the current manufacturing processes. Since molecular dynamics (MD) method has been well known as a mean of studying materials in atomic scale, it has been used in this study to investigate two different phenomena. The selection of the appropriate interatomic potential is of great importance in MD; Embedded Atom Method... 

In the present work, primary crystallization mechanism, glass forming ability, thermal stability and formation of nano Al crystals and their effects on the mechanical behavior were investigated in various Al amorphous alloy containing misch metal including Al90-xNi10-yFeyMMx (x=2-10%at, y=0-10 %at) alloys. In order to elaborate the Cu effect on the primary crystallization mechanism Al86Ni10-xCuxMM4(x=0-2/5) alloy were prepared. The results showed that in Al90-xNi10MMx (x=2-10 %at) alloying system variation of the misch metal from 2 to 10 atomic present results in increase in glass forming ability. The crystallization onset temperature also increases from 405 K in Al88Ni10MM2 to 630 K in... 

Lots of researches have been carried out on the severe plastic deformation (SPD) and annealing of the aluminum up to now. Due to the different annealing behavior of the severely deformed metals and on the other hand the necessity to the rollig for producing the thin SPD sheets, so the purpose of the recent study is producing the thinned sheets with applying the temperature simultaneously. Dislocations density increases by SPD so it confines their movement and cause to the higher strength of the material. Rolling of the SPDed sheets increase the mechanical properties. Grain boundary energy increases with this mechanical improvement and results in lower ductility. So, it is necessary to... 

Hot deformation behavior of Al-SiC nanocomposites was investigated in this study. Aluminum powders with mean size of 60 micron and SiC nanopowders (mean size of 45nm) in amounts of 1 and 2 volume percents, as reinforced part, were mixed and milled for 40 hours by planetary ball mill. After degassing at 450 oC for 1 hour, milled powders were pressed into Aluminum cans (in Argon atmosphere) and then hot extruded. Extrusion ratio was 1:14. High density billets (with 98% of theoretical density) were produced because of that high extrusion ratio. TEM microstructure studies showed that fine distribution of reinforcements and Aluminum Oxides obtained via this procedure. Hardness and Uniaxial... 

Aluminum and its alloys have wide applications in industry and recently researches have been expanded in this area. The main reasons are unique features of aluminum corrosion resistance and high strength to weight ratio. The fundamental problem of aluminum is low wear resistance that leads to be worn in industrial applications. For more efficiency of titanium, extensive efforts have been made for solving this problem, one of the best solutions is coating. Plasma electrolyte Oxidation (PEO) is a novel method to create ceramic coatings on metals to improve wear and corrosion resistance. In this research micro and nano Si3N4 particles were added to electrolyte to create alumina-silicate... 

In current project, high purity nanoparticles were synthesized by use of Electromagnetic Levitation Melting Gas Condensation (ELM-GC) method. In this case high purity aluminum samples were melted by this method to a temperature of 1683 0C in a silica tube. High purity argon and helium gases were employed as carrier gases and cooling agents. To study particle size, morphology, and purity of obtained nanoparticles, Field Emission Scanning Electron Microscopy (FE-SEM), X-ray Diffraction (XRD), Dynamics Light Scattering (DLS), and ADS analysis were employed. The FE-SEM and DLS tests confirmed narrow size distribute of spherical shape pure aluminum nanoparticles under both inert gases. The... 

Joining metals to polymers is an increasing demand in industry mainly due to weight savings. Polymer-metal hybrid structures are widely used in aerospace and automotive industries. However, dissimilar joining of polymer to metal is very difficult due to large mechanical and physical properties differences. Since conventional methods for joining polymers to metals have various limitations, it is necessary to employ new practical and environmental friendly joining processes. In this study, the feasibility of joining an aluminum alloy (AA5052) to polypropylene (C30S) sheets via friction stir welding was examined. Lap joint configuration was determined as the optimized configuration by analyzing... 

In this study Ni-P-Al2O3-SiO2 nano composite coating developed on aluminium alloy 6061 using electroless method. Due to oxidation of aluminium, a double zincate pretreatment performed to obtain proper adhesion of coating on substrate. Effect of solution temperature and heat treatment on thickness and property of nano composite coating was studied. Furthermore, effect of concentration of nano particles in electroless solution on thickness, morphology, micro hardness, wear behavior, corrosion resistance and particle content in coating were investigated. Field emission scanning electron microscopy (FESEM, Hitachi S-4160) with energy dispersive spectroscopy (EDS) was used to evaluate morphology... 

One of the Friction Stir Welding (FSW) limitation is thinner sheets joining. To solve this limitation, sheets were welded through FSW at upper thickness and then reduced welded samples thickness. In this research, 3-mm-thick AA1050 aluminum plates were joined by FSW.For this purpose, the effect of welding parameters on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed (900,1200 rpm) to travel speed (50,90,150 mm/min) (ω/v). It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed. Subsequently, hardness reduction was observed in... 

In this study, Butt resistance welding of copper to aluminum wires was studied. In this regard, the effect of current, pressure, post weld heat treatment and using intermediate layer of tin on the microstructure, strength and special electrical resistance of welds were examined. Based on a series of initial tests to establish the connection with the appropriate strength, the diameter of the aluminum and copper wires respectively 3 and 3.5 mm and their length 9 and 3.5 cm were selected. In order to weld samples, currents 4.4 to 4.7 KA and pressures 0.3 and 0.5 MPa were used. Then post weld heat treatment at currents 0.5, 1 and 1.5 KA on the welded sample in the pressure 0.3 MPa and the...