The AA 6082-T651 alloy weldments are used extensively in shipbuilding industries and offshore jacket structures. In the present research, the effects of Advanced Square Wave Alternative Current Gas Tungsten Arc Welding(ASW-AC-GTAW) process parameters on the mechanical properties and resistance to pitting corrosion of AA 6082-T651 alloy weldments welded by ER5356 filler metal were investigated. To attain this objective, positive half cycle current(PHC), negative half cycle current(NHC), frequency(F) and positive half cycle percentage(PHC%) were selected as the ASW-AC-GTAW process main parameters and were altered at three levels. An experimental design was carried out using Taguchi method and L9(34) orthogonal array. The results of tensile test, hardness test and potentiodynamic polarization test were analyzed by using Taguchi, analysis of variance (ANOVA) and regression methods. Analysis of tensile and hardness test results using Taguchi method indicated that the optimum levels of PHC, NHC, F, and PHC% were 260A, 190A, 10Hz, 60%, respectively. Analysis of potentiodynamic polarization test results using Taguchi method indicated that the optimum levels of PHC, NHC, F, and PHC% were 300A, 190A, 2Hz, 40%, consecutively. The impact of each ASW-AC-GTAW process parameters on yield tensile strength, ultimate tensile strength, elongation percentage, fracture energy, hardness and pitting corrosion were determined by using ANOVA. In order to validate analytical analyses, two optimum samples(mechanical and pitting corrosion) were welded at their corosponding optimal conditions and were tested. Equations based on mean values, Taguchi method and regression method were used to predict properties of optimum samples. The regression model results of each investigated quantity were analyzed by using ANOVA and accuracy of obtained models were determined by considering the multiple correlation coefficient(R) of each model. The results of analytical predictions were in great agreement with the results obtained from emperical work. The tensile test results of samples welded by ER 5356 and ER4043 indicated that the sample welded by ER5356 filler metal had superior tensile properties.

In this essay, deposited (Al7075/SiC/TiO2) composite coatings on the aluminum substrate has been applied by friction surfacing process. For this purpose, TiO2 and SiC particles with average size of 16 µm were put into holes in consumable rods. Characterization of microstructure, interface and particle distribution in Al7075 matrix was performed using optical and scanning electron microscopies. Microstructural investigation showed an almost homogenous distribution of SiC and TiO2 particles in Al7075 matrix. Additionally, no reaction was detected between matrix and particles. Micro hardness and pin on disk wear test results also indicated that by applying friction surfacing, mean of micro hardness and mass loss increased by 13% and decreased by 28% respectively, in comparison with Al7075 pin. Increase in micro hardness is attributed to grain refinement and dynamic recrystallization. Al7075/4.5%TiO2 specimen had the lowest resistance to wear and hybrid composite layer showed most wear resistance that is due to simultaneous existence of hard SiC particles and high hydrophobic property of TiO2. Output of Potentio-dynamic polarization corrosion test showed that current density decreased from 9.14 to 5.4 µA/m3. Among composite coatings, the Al7075/4.5%SiC had the lowest current density and corrosion rate. This reduction in current density is attributed to grain refining and proper distribution of reinforcing particles in this process. Decreasing the volume percentage and distribution of reinforcement particles in three composite layers respectively, led to more corrosion and wear rate.

<p>&nbsp;The effect of cold work and annealing treatment on the microstructure, mechanical properties and corrosion behavior of 316L stainless steel was evaluated. Microstructural investigation was done by using Optical Microscopy. Mechanical properties were examined by tensile and Vickers micro hardness tests. Potentiodynamic polarization (cyclic and non-cyclic) and electrochemical impedance spectroscopy were used to evaluate corrosion behavior of the samples. Formation of strain induced martensite caused by cold rolling shows that hardness, yield, tensile and fracture strength of the alloy is increased by increasing cold rolling percentage, while the uniform elongation of the sample is decreased. In comparison to the annealed sample, poor corrosion behavior is observed in the mixed solution of salt and acid by increasing cold rolling percentage. The chlorine ion destroys the suitable regions for the nucleation of passive layer which have been provided by cold rolling process and creates preferred sites (sub-grain boundaries and other defects due to cold work) for the attack of H+ ions and hence increases the corrosion rate. By heat treating of the 50% cold rolled sample, recrystallization phenomenon was occurred and different grain sizes were formed. By increasing of grain sizes, strength and hardness values are degraded and corrosion behavior is improved. Sensitizion of samples with different grain sizes results in precipitation of chromium carbides at the grain boundaries. By increasing of grain size in the sensitized samples, corrosion current density is also decreased and corrosion resistance is increased in the both tests.</p>

 Microalloyed steels have allocated a special attention as pipeline steels due to high strength and proper toughness.The former properties can be practically improved by using thermo-mechanical controlled processing (TMCP). This process includes controlled hot-rolling and subsequent cooling stage. API 5L X60 is one of the most important microalloyed steel that have been primarily used to transport crude oil and natural gas in Iran. It is nessesary to investigate the crystallographic texture of this steel after production by thermomechanical processing. Besides, for design thermomechanical schedules and achieving favorable microstructure, it is important to know non-recrystallization temperature (Tnr). In this study, morphological and crystallographic anisotropy, grain boundary and recrystallization fraction of API 5L X60 and effect of annealing on the mentioned properties was investigated. Results indicate formation of layers of ferrite and Perlite in the processed sample. Although, there is no dominant texture in this steel. With increasing of the annealing temperature, texture intensity increases to 19.1. In the next part of the study, hot torsion test as a powerful tool to simulation of thermomechanical process was employed to determine Tnr and the effect of thermomechanical parameters (strain and strain rate) on this temperature. The determined Tnr using real schedule approach is 930°C. Tnr calculated by real schedule approach is very close to average schedule approach. Further results of hot torsion test show that decreasing of strain and strain rates variables leads to increment in the Tnr.

The composition of aluminum and copper with iron oxide (Fe3O4) particles as a matter of reinforcing, makes the production of metal matrix composite, with higher mechanical properties. Composite samples of aluminum with 1, 5, 10 and 20 %Wt. of the reinforcing particles, and Composite samples of copper with 1, 5 and 10 %Wt. of the reinforcing particles manufactured with stir casting method and using mechanical stirrer. In order to evaluate the effect of particle size distribution, the Nano-particles with 0.25, 0.5, 1 and 2 %Wt. of Fe3O4 for two metal Matrix was casting. In this study, to evaluate the microstructure characterization of composites, optical and scanning electron microscope was used. After that, some of the mechanical properties of the composite samples were compared to each other by tensile and hardness tests. In addition to mechanical properties, electromagnetic properties and corrosion resistance, respectively by potentiodynamic polarization test and VSM device for both samples were studied.
The results showed that the use of the mixer cause a homogenous distribution of particles in both aluminum and copper composites. On the one hand, the uniform distribution along with the increase in the percentage of reinforce particles and on the other hand, proper connection between the particles and matrix, improve hardness and tensile strength. The corrosion resistance of aluminum composites and Nano-composites, due to the presence of reinforcement particles and tension around the particles, reduced and as a result it, pitting corrosion happened. In the case of copper composite and nano-copper composite materials, corrosion resistance due to the formation of a strong and adhesive layer of the copper oxide and hydro-oxide with iron oxide on the surface, is increased. Also, the magnetic permeability in both composite materials has increased.
 

 In this study, heat transfer and fluid flow during Gas Metal Arc Welding using 3D model were simulated. For this purpose, the conservation equation of mass, momentum and energy by Flow-3D software solved. Buoyancy and surface tension forces and effects of mass, momentum and energy transfer of the filler droplets into the weld pool were considered. To there was a good agreement between simulation and experimental results in a similar conditions. By solving the model, the temperature distribution and flow pattern for different samples, different times were obtained. The results showed increasing in welding speed or decreasing in welding current lead to decreasing in maximum temperature and velocity across the weld pool. In the same time, height of the weld reinforcement and width and depth of the weld pool decrease too. Because of less heat input in these conditions, the thickness of HAZ were reduced and lower Peclect, Grashof and Reynolds surface tension numbers were resulted.

: In the present study, optimization of friction stir welding parameters, such as rotational and travel speed,shoulder diameter and pin dimeter in Al-Mg alloy (AA5083) was carried out by response surface methodology.The result of RSM have shown the tensile strength of joints was not sensitive to variation of welding parameters.And then the effect of welding parameters on 7 samples in 9 condition was crrried out.Three primary parameters was considered.microstructure, mechanical properties and corrosion behavior considered.By optical and electron microscope images as well as tests of energy-dispersive x-ray spectroscopy (EDS),vickers microhardness, tention, Nitric Acid Mass Loss (NAMLT Test), microstructure, mechanical, and corrosion properties of FSWed samples evaluation and compared with base metal. Microstructural analysis of the samples showed fine and equaxied grains in the nugget zone, elongated grains in the TMAZ and coarse grains in the heat affected zone and base metal.Compared with the base metal, all of the samples showed higher hardness properties in microhardness test.The sample with 700 rpm rotational speed,46 cm/min travel speed and 15mm shoulder diameter, had maximum tensile strength.In NAMLT test, mass loss was increased for the BM,because the β phase particles randomly formed in the matrix and remained with out any changes.In the Stir Zone, isolated β phase particles randomly formed in the matrix regardless of the sensitizing heat treatment.The results of measuring the peak temperature during FSW suggest that the precipitated β phase was dissolved and fractured by frictional heat and mechanical stirring.and resistance of intergranular croosion increase.

Shot peening is one of the severe plastic deformation that can improve the mechanical properties of materials special at welded metals. In shot peening process, the repeated impingements of the shots on the surface of the metal would result in compressive stresses in surface layers. By applying this process, the grain size, in a micrometer thickness layer would reduce to submicron and in some cases to the nanometer size. In this research, the effect of shot size, the coverage percentage and the air pressure on the grain size and thickness of the nanostructured layer of dissimilar weld of 2205 duplex stainless steel and 316L stainless steel has been investigated. In addition the corrosion resistance of the shot peened steel in the 3.5 wt% NaCl solution has been studied. The shot size of 0.023, 0.017 and 0.011 in. , the coverage of 20000%, 40000% and 60000% and the air pressure of 45psi, 65psi and 90psi have been investigated. The characterization of the nanostructured layer has been studied using FESEM and AFM. The corrosion resistance of the shot peened regions has been studied by cyclic potentiodynamic polarization. In this research the practical conditions for obtaining the nanostructure layer on the surface of weld using the shot peening process have been achieved. In addition, the results have been showed that by increasing the shot size and the coverage, the grain size decrease and the thickness of the nanostructure layer would be increase. This process would result in increasing the hardness but the corrosion resistance has been somewhat reduced.

<p>Because of the unique structure of carbon nanotubes (CNTs) they show unique properties such as lightness, high tensile strength, extremely high thermal conductivity and stability. Therefore CNTs have received considerable attention in the recent years. In common with conventional fiber composites, mechanical electrical, magnetic and optical properties of nano-composites are linked directly to the alignment of carbon nano-tubes in the matrix. So controlling the orientation and placement of carbon nanotubes is essential to exploit their outstanding electrical, optical, mechanical, and thermal properties. Application of Magnetic field is one of the ways for alignment of CNTs. However, due to the lack of natural paramagnetism in CNTs, these must be hybridized with other magnetic materials.in this research CNTs were coated successfully by nanoparticles of synthesized Fe3O4 and magnesium ferrite. Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometry (EDX) was carried out and confirmed the formation of Fe3O4 and MgFe2O4 nanoparticles on the CNTs. In addition, the magnetic, electromagnetic and electric behavior of CNTs coated by Fe3O4 and MgFe2O4 was investigated. Results revealed that the Fe3O4/CNTs have good magnetic properties. Saturation magnetization of Fe3O4/CNTs and MgFe2O4/CNTs was obtained as 15.53 emu/g and 2.22 emu/g.<br /> magnesium composites reinforced with CNT and Fe3O4/CNTswith and without applied magnetic field were fabricated and their corrosion behaviour was investigated. composites with coated carbon nanotube showed better corrosion behavior than uncoated reinforcements. Applied magnetic field resulted in better corrosion behavior in the sample with carbon nanotube/magnetite.</p>

<p style="text-align: left;">&nbsp;This study was conducted to investigate the effect of welding process on microstructure and corrosion behavior of weldment between API X80 and API X70 high strength low alloy steels. SMAW, GTAW and GMAW welding process with 8018G, E80S and ER80S filer metals are used in this study subsequently. Microstructures of welded joints were investigated using scanning electron microscopy/energy-dispersive analysis (SEM/EDAX) technique and optical microscope (OM). Polarization and impedance test used to investigate corrosion behavior. Result indicate that GMAW process, HAZ is wider and grain size increased due to higher heat input. Also corrosion resistance of GMAW weld line is lowest. Because of higher heat input in GMAW process, cooling rate is lowest. So precipitate have time to growth and size of them increased. Precipitate are nobler than matrix, so they perform as cathode in corrosion environments. By decreasing the size and increasing distribution of precipitates, corrosion resistance improved.</p>