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Friction stir welding as a joining process in solid state welding various alloys widely used metal, particularly aluminum alloys. Although the low heat generated during the process does not melt the base metal, but the thermal cycle applied to the sample, which reduces the mechanical properties of the junction. Recently, this method of welding process is used in the cooling methods. In this study the microstructure and mechanical properties of 5050 aluminum alloy weld in two conditions: with friction stir welding in the air and on underwater friction stir welding was studied. The results of underwater friction stir welding were compared with samples of friction stir welding in the air. Results showed that the structure of the underwater welding was 36% more finely than welded structures in air and its tensile strength was improved about 6%. Also, the SZ zone in underwater friction stir welding has a higher hardness than friction stir welding in air.

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The 7075-T6 aluminum alloy is one of the strongest aluminum alloys that possess excellent combination of mechanical properties such as high strength to weight ratio, good corrosion resistance and thermal conductivity but they generally present low weldability by traditional fusion welding process. Friction stir welding is a new solid state process that is function of different process parameters. In the current study, to investigate the effect of some of the main welding process parameters such as rotational speed, traverse speed and tool shoulder diameter properly, a Design of Experiment (DOE) was used with a Response Surface Methodology (RSM) approach to find the best process settings and achieve optimal performance. Results showed that to achieve sound high-grade joints parameters should be optimized. When improper welding parameters are used, problems such as defect formation, precipitates dissolution and grain growth can deteriorate the mechanical properties of the joint. So, of the twenty joints fabricated using various welding parameters, the joint fabricated at a rotational speed of 1050 rpm, welding speed of 100 mm/min and shoulder diameter of 14 mm exhibited superior metallurgical and mechanical properties in comparison to other fabricated joints.

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Presence of porosity and gas layers around the Al2O3 particles are one of the most important reasons of decreasing in mechanical properties of aluminum metal matrix composites. In this research, for decreasing of porosity, increasing of wettability and uniformly distribution of particles in matrix three method were used; using inert gas for injection powder with 5 liter/ min flow rate, particles heat treatment in 1100 ̊C for 20 min and mill Al2O3 particles with Al particles in ratio of Al / Al2O3= 1. The effect of these parameters on microstructure and mechanical properties of composite were investigated. The results showed that amount of porosity and agglomeration of particles were high in metal matrix composite with handy injection of particles. While injection with inert gas, using heat treatment and Al / Al2O3 milled Cause improve wettability and uniformly distribution of particles in molten Al. the results showed the maximum value of hardness , compression strength and impact energy have obtained in metal matrix composite reinforced with Al / Al2O3 milled with value of 78.7 BHN, 539.1 MPa and 8.2 Joule, respectively.

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Friction stir welding (FSW) has many advantages in welding dissimilar joints in comparison with fusion welding methods. In this study, weld ability of butt joint of 5052 aluminum alloy and Ti-6Al-4V titanium alloy by FSW process has been studied and discussed. The welding was successfully performed by using a tool with frustum pin. The influences of both rotational and traverse speed of welding tool on mechanical properties are investigated. The results show that the metallurgical and mechanical properties improve by choosing appropriate parameters. The highest tensile strength of 260 MPa was obtained at rotational speed of 500 rpm and a 40 mm/min traverse speed, which was ~ 94% of the aluminum base metal tensile strength. As a result of increasing the rotational speed from 500 to 1000 rpm, high heat input can forms cracks at joint area. In rotational speed of 1000 rpm, increasing traverse speed from 40 to 56 mm/min leads to a sound joint with 192 MPa of tensile strength. This decreasing in tensile strength can be related to the formation of intermetallic compounds such as TiAl3, along the entire interface between the two alloys

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In the present study, microstructure and wear resistance of in-situ composite coatings TiC-Al2O3 and TiB2-TiC-Al2O3 product by gas tungsten arc welding process on AISI 304 austenite stainless steel were investigated. For this, a paste of the mixed powders of 3TiO2-4Al-3C and 3TiO2-4Al-B4C was provided and applied on the surface of AISI 304 austenite stainless steel substrate, then fused using gas tungsten arc welding process. The microstructural features and phase characterization of the cladded samples were investigated using optical and electron microscopy and X-ray diffraction analysis. The mechanical properties of clad layers were studied by Vickers microhardness and pin-on-disk wear tests. The microstructural investigations of cladded layers indicated that high heat input during welding led to high temperature synthesis and formation of significant reinforcing particles on the surface of steel. Also, the cubic TiC particles formed separately or inhomogeneously nucleated on Al2O3 particles in the austenitic matrix of 304 stainless steel. Likewise, the formation of TiB2 particles was approved with X-ray diffraction analysis. The rei

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In the present study, the mechanical and microstructural properties of dissimilar joint of 304 austenite stainless steel and C70600-copper-nickel alloy made by Gas Tungsten Arc Welding process has been investigated. The aim of this joint is using the twin metallurgical properties such as; heat dissipation and corrosion resistance of copper-nickel alloy and mechanical properties of 304 austenite stainless steel alloy. Welding of two dissimilar metal steel to copper-nickel alloy due to differences in melting point, the difference in thermal conductivity, rapid solidification of copper nickel are facing many problems. In this research due to solubility and weldability of nickel with two both alloys, three filler metals Inconel 625, Inconel 82 and 61 were used. According to microstructural investigations welds made by Inconel 625 and Inconel 82 show a finer equiaxed dendrite structure as compare as in Inconel 61 filler metal. The tensile strength of samples welded by Inconel 625, 82 and 61 filler metals was 324, 323 and 293 MPa, while the elongation percent of three samples show small difference. According to mechanical properties of joints, the Inconel 625 and 82 filler metal are appropriate for dissimilar welding 304 austenite stainless steel and C70600-copper-nickel alloy.

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In recent years, development of polymer electrolyte membrane fuel cells (PEMFCs) has been considered to generate electricity and heat. Among main components of PEMFCs, bipolar plates (BPPs) have significant influence on cost and performance of the system. Metallic BPPs, formed using thin sheets, have been developed as alternative to conventional graphite plates because of advantages such as suitable cost, mechanical strength and power density. Flexibility of the sheets and spring back during forming process make dimensional errors inevitable and lead to inappropriate contact pressure distribution between BPPs and gas diffusion layer (GDL), resulting in decrease of fuel cell performance. Excessive accuracy in BPP production leads to increase the final cost and decrease the general usability of the technology. Therefore, to reduce unnecessary costs, managing design process and improving efficiency, analysis of BPP dimensional errors is done using finite element method and Monte Carlo simulation (MCS). First, contact model of the metallic BPP and GDL is developed and heights of each channel and each rib of BPP are fully parameterized due to stochastic variations of dimensional errors with normal distribution. Then, contact pressure distributions of GDL (Pave, Pstd) for different dimensional errors are obtained by MCSs. Increasing dimensional tolerance from 0.015 mm to 0.075 mm, average contact pressure (Pave) has decreased by 11% and standard deviation of contact pressure (Pstd) has increased up to 90%. Namely desirable distribution of GDL pressure is reduced by increasing the dimensional error and suitable dimensional tolerances for BPPs can be determined according to engineering requirements.

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In the present research, the friction stir extrusion process as a novel method for wire fabrication from AA6063 aluminum alloy was utilized. For optimization of the process parameters, the L9 standard array of Taguchi design of experiment method was used. The important process parameters include: rotational speed, force, tool face geometry and the die hole size as input variables and grain size and hardness as quality criteria was considered. The tensile test, micro hardness and metallography investigation for studding wire mechanical properties were used. The rotational speed parameter with over 63 percent and after that the force with significant contribution percentage as second parameter was determined. The tool face and the hole size do not have sizeable effect on the mechanical properties and they were introduced as minor process parameters. By investigation of samples, it were determined that with correct setup of process parameters, defect-free wire with grain size over 23 times less than the base metal could be produced. It can increase the ultimate tensile strength of 14 percent against of the base metal

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Surface engineering in many manufacturing industries plays an important role in improving product performance and increasing the operating time of parts. Pure aluminum has a very high electrical conductivity, good corrosion resistance and strength to weight ratio. However, due to very low hardness and wear resistance, its application is limited. Therefore, this paper is studied may improve the surface properties of pure aluminum using copper and nickel as alloying elements using electric discharge process. The pulse on time and pulse current as input parameters and surface hardness, alloyed layer texture and surface roughness as output parameters have been considered. According to the microhardness testing results, in this alloying method, the average hardness of the aluminum parts is about more than 8 times and in some parts of the 38.5 Vickers reached up to 450 Vickers, Based on the results of XRD analysis, the formation of intermetallic compounds Al3Ni2, ALCu, and Al4C3 increased surface hardness. The results show that by increasing the pulse on time surface hardness increased and surface roughness becomes greater. Also, Increasing pulse current the surface roughness increasing trend.

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Today, the industry's need to join dissimilar metals has increased, especially in the automotive and aircraft industries. In this regard, in order to join metals, new methods, called solid state joining, have been used, among which electromagnetic joining is performed with a lower cost and at a higher speed. In this research, firstly, the feasibility of joining copper tubes to composite tubes by electromagnetic method and the quality of the joinit have been studied. Then, the effect of the welding voltage process parameter on the mechanical properties of the strength has been investigated by the ring test. Finally, in order to examine the surface hardness of the welded samples, the Vickers hardness test was performed. The results show that the joining of the copper samples to the composite tubes has been done well. It has been observed that with the increase in voltage, due to the increase in the collision energy of the two tubes, the connection force has increased by about 2 times. In the 8 kV voltage, due to the increase in the impact speed, a more severe plastic deformation has occurred than in other samples which has caused more local deformation of the weld interface and, as a result, an increase in the hardness. The hardness of the interface in this condition was about 8% higher than that of the 5 kV voltage.