Sharif Digital Repository

In this research, Friction stir welding (FSW) of 7075-O and 7075-T6 aluminum alloys was performed to investigate the effects of the base material conditions, effects of process parameters on the FSW characteristics and optimum parameters which lead to best mechanical properties of joints. The experimental results indicated that the base material condition has a significant effect on weld morphologies, weld defects, and mechanical properties of joints. The optimum parameters were 1230 rpm and 60 mm/min for 7075-O and 1230 rpm and 100mm/min for 7075-T6. Also, Double welded friction stir welding of 7075 aluminum alloy was performed to investigate the effects of the second pass of weld on the... 

The aim of this research is to fabricate Mg based nanocomposite by friction stir processing and investigation of the process parameters on the microstructure and mechanical properties of the nanocomposite. In order to this aim, alumina nanoparticles as reinforcement were poured in the groove, with 5mm depth, and due to rotation of friction stir tool, these nanoparticles were mixed with the matrix and nanocomposite was produced. To reach to the best condition in nanocomposite fabrication, the effect of friction stir processing parameters such as, tool rotation speed, tool design, number of friction stir passes, cooling media and reinforcement percent on microstructure, hardness, tensile... 

Flux-cored arc welding has become prevalent in the recent decades worldwide. One of the variants of this welding method is self-shielded welding which requires no external shielding, neither with mineral flux nor with shielding gases. In this study, the variation of microstructure and mechanical properties of flux-cored self-shielded welds was investigated and optimization of this properties was also carried out. For this purpose, a basic combination of powders was chosen from the literature to fabricate the flux-cored wire. These powders contain fluorine, calcium carbonate, aluminum, magnesium and iron. Then, same amount of alloying elements such as molybdenum and nickel was added to this... 

Friction stir soldering (FSS) or brazing (FSB) as an emerging joining process, was first developed to resolve some shortcomings in FSLW and FSSLW such as excessive IMC layer thickness and confined bond area. Although it has advantages over conventional furnace soldering and/or brazing, including localized heating, less detrimental thermal effects on the substrates and capability to reduce the amount of voids at the joint interface. The aim of this study is to investigate the effects of rotational speed, traverse speed and plunge depth of the pinless tool on the shear strength and electrical resistivity of the copper-coated graphite-copper FSSed joints with the aid of Sn-37Pb solder alloy. At... 

Ultra-fine and fine-grained aluminum matrix nano-composites were fabricated by friction stir processing (FSP) of 1050 Al alloy sheets containing 6 vol% volume fractions of pre-inserted MMO nanoparticles. Annealed sheets were processed at different rotational (w=800-2000 rpm) and traverse speeds (v-50-200 mm/min). A special design tool (concave shoulder and cylindrical pin with regular threads) without changing the rotation and traveling directions was utilized. It is shown that the best and highest desired mechanical properties of the base metal is attained at w=1600 rpm and v =100 mm/min through one single pass. The structure of grains are changed due to the applied severe plastic... 

In this research, aluminum matrix composites (AMCs) reinforced by different contents of zirconium dioxide nanoparticles, graphite microparticles, and a mixture of both with various hybrid ratios, into a cold-rolled Aluminum1050 as base metal, fabricated by 4-passes friction stir processing. Observations show that the processing of composites reinforced by Gr particles is significantly hard due to the low friction coefficient of graphite resulting in the decline in the maximum temperature during the process and the type of base metal. The mixtures of graphite and zirconia resulted in more homogenous dispersion of particles in the matrix due to deterring a drastic drop in friction coefficient... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

Friction Stir Spot Welding (FSSW) with ability of refilling weld’s keyhole, is one of the new solid state joining processes which have gained many applications, especially in automobile industry. Considering newness of the process, first part of this study has been dedicated to design and manufacture of a FSSW machine which is done entirely by author of this study. Second part was survey on effect of parameters such as Tool rotation speed, Weld time, and Forge time for refilling the hole, on properties of an aluminum joint. After welds were made, specimens were subjected to Lap-shear tensile test, after that, studies on macro and microstructure have been carried out. Generally an increase in... 

The objective of this investigation was obtaining sound Friction Stir Welded (FSWed) Commercially Purity Titanium using suitable Tool’s Materials (for Shoulder and Pin) in order to be able to work in high temperature (>1000 ˚C) with great mechanical properties and minimum wear during process. Consequently, different materials and designs for Tool, such as High Speed Steel tool, Tungsten based tool, Tungsten Carbide (WC-Co) based tool and diverse tool geometry and designs like simple design, threaded design, fixed pin and inserted pin (adjustable pin) was used. The results demonstrated that using simple cylindrical WC-Co for pin and Tungsten for shoulder resulted in joints with the best... 

In this research, for optimization of repair welding of control valve and flange that use in East Oil& Gas Company, effect of chemical composition, microstructure, hardness and stress relive on sulfide stress cracking (SSC) investigated with select of four electrodes. All welds were prepared by shielded metal arc welding (SMAW) and investigated with optical microscope, hardness test, tensile test and SSC test. The results showed that increase of nickel content in the range of 0.032–1.58 wt. % in weld metals, decrease of acicular ferrite and increase of side plate ferrite, grain boundary ferrite and M/A micro constituent in microstructure. Ni3S2 decrease SSC resistance and (FeCu).S increase... 

The current work is carried out to characterize welding of AISI 304 Austenitic Stainless Steel to Ductile Cast Iron. The welding method was SMAW and the welds were produced using a Nickel-Buttering by a pure Nickel electrode(ENi1) on Cast Iron side, then by 4 types of filler materials the joints were produced; Ni-base electrode(Ni1), E308 and E309 Austenitic stainless steel electrodes and E7018 electrode. The preheat temperature of Cast Iron has been selected to be 250○ and 500 ○C to avoid crack of weldments. The comparative evaluation was based on metallography, chemical composition, hardness and corrosion behavior on two different preheat temperatures. According to metallography, the best... 

Microstructural characteristics and mechanical properties of a friction stir welded cast Aluminum Bronze (Cu–9Al–1Fe), produced through sand casting method, have been investigated in this study at tool rotation of 850–1500 rpm and traverse speed of 50–100mm/min. The study also describes results obtained from microstructure evolution (optical microscopy and Clemex image analysis software) and mechanical properties of Aluminum Bronze welds produced by FSW process. Refinement of the primary coarse cast microstructure and elimination of the defects in base metal due to porosity and casting was seen clearly after friction stir welding. Microstructure of the stir zone was divided into four... 

A concern in the production sour oil and gas is the corrosion caused by the acid gas H2S. Even though corrosion resistant alloys (CRA) have long been available as a material selection option that mitigates H2S corrosion, the carbon steel is in general more cost-effective for oil and gas facilities. The aim of this study is to investigate the mechanical properties of 410NiMo cladding on a low alloy steel substrate. In this investigation, two successive layers of ER410NiMo were clad on low alloy steel substrates. To reduce the likelihood of Hydrogen Induced Cracking (HIC) and producing stable hydrogen traps, Post Weld Heat Treatment (PWHT) was used. To characterize the mechanical properties of... 

The effect of alloying elements such as Chrome, Molybdenum and Chrome-Molybdenum on microstructure and mechanical properties of submerged-arc weld of structural St37 and 4135 Chromoly Steel was investigated. Addition of alloying elements was done through flux and slag-weld metal reactions. Bonded flux was used to achieve this purpose. Mechanical properties were studied by means of Longitudinal Tensile, Hardness and Charpy V-notch tests. Microstructure was studied by means of Optical and Scanning Electron Microscope. The results show that chromium increase Ultimate Tensile Strength (UTS) and impairs Impact Toughness (IT), although it increases the percentage of acicular ferrite (AF). In the... 

In this research, the strength and wear resistance of aluminum 5083 was improved by using composites with magnesium oxide nanoparticles (MgO-20nm) and friction stir processing. The effect of the number of process passes and rotational speed variables, considering the number of one, three, and five passes at rotational speeds of 700, 1000, 1300, 1600, and 1900 rpm, was investigated on the mechanical properties and wear behavior of the composite. To determine the appropriate weight percentage of MgO powder, the longitudinal tensile strength of three composites with different weight percentages of 3, 4.7, and 6 were compared. The linear movement speed of the tool was selected as a constant... 

Joining of yttria-stabilized zirconia (YSZ) to stainless steel (SS) is considered for various applications such as solid oxide fuel cells, thermal barrier coatings, and medical implants. In the present work, a series of brazing pastes utilizing silver and nickel nanoparticles (~80 nm) mixed with carboxymethyl cellulose as the organic phase were developed to join 5YSZ to 420 SS. The effects of processing parameters such as time and temperature of brazing and the composition of the paste on the microstructure of the joint and its mechanical strength were studied. The mechanism of interface formation was elaborated by scanning electron microscopy (SEM) and electron probe micro analyzer (EPMA).... 

Tungsten Inert Gas (TIG) process and different cored wires that were filled separately with nano TiC particles, micro TiC particles and graphite powders were employed to produce surface composite coating on CP-Ti substrate to improve wear resistance. At first using titanium strips, wire drawing process and different powders various cored wires were produced and then using TIG, these cored wires were coated on CP-Ti. This process was done for different current intensities and velocities. Composite coating tracks were found to be affected by the TIG heat input and the kinds of the cored wires. The microstructures of the surface composite coating showed phases of α'-Ti and primary and dendritic... 

Friction Stir Processing (FSP) was used to fabricate Al1050/Fe3O4 nanocomposite in three different weight percent (2.5%, 4% and 5.3%). The effects of rotational speed (1200-1600 rpm), traverse speed (5-15 cm/min) and the number of FSP passes (1, 2, 3 and 6 passes) on microstructure and mechanical properties were investigated. In order to study microstructure evolution, optical and field emission scanning electron microscopes were used. Micro hardness, longitudinal and transverse tensile and wear test were carried out to investigate mechanical properties of the obtained composites. Results showed that increase of the rotational speed and decrease of the traverse speed in 1 pass processed... 

Dilution is a parameter with significant effects in SMAW process. As this factor is in a range of 25-35% in SMAW process, it can increase the portion of base metal in the weld metal. During cladding carbon steel by stainless steel, this parameter causes reaching different composition as the number of weld rows increases. The aim of this project firstly is to investigate the effects of this parameter and then achieving the same properties in different welding rows. Suggested electrodes are as follows; E316-L16 three-row, KST 309-L16 for two-row and KST 310-16 for one-row welds. Corrosion behavior of each clad have been studied and the results show that; although by changing the electrodes the... 

Engineering polymers are being increasingly used in a wide number of applications related to tribological properties. Many chemical and physical methods have been utilized to modify polymer surfaces by depositing thin inorganic films. Most of these techniques are based upon the use of high energy sources that ultimately can damage polymer surfaces either chemically or physically. Incorporation of fillers as reinforcing materials significantly changes various properties of thermoplastics. Friction stir processing (FSP) is a tool to modify the surface properties of materials. It has been developed for upper surface modification of metals in recent studies, exclusively by making surface...