Journal of Welding Science

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FeCo-V alloys are one of the most important groups of magnetic material which currently used in high speed engines due to their excellent magnetic and mechanical properties. Welding of these alloys is a great challenge since various phase transformation result in significant changes in magnetic and mechanical properties. In this research ultra-thin FeCo-V magnetic foils were welded using laser and electron beam welding processes. After development of mathematical models, working limits of process parameters were chosen to obtain welded joints which have simultaneously appropriate maximum energy product and mechanical strength.

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In this study the microstructure and mechanical properties of super duplex stainless steel UNS S32750 welding was studied. For this purpose, the method of gas tungsten arc and filler metal AWS ER2594 with a diameter of 4.2 mm was used. In order to investigate the microstructure light microscopy and electron microscopy equipped with backscatter electron diffraction were used. Mechanical properties were studied by hardness and tensile tests. Weld metal had  Cast structure with austenite in the dendrite form  located in ferrite matrix. It was also observed in the melting zone after welding, the ferrite volume fraction decreased to 50 percent 60% base metal ferrite) ,Due to the low cooling rates and  high heat input method in the gas tungsten arc welding. Vickers micro-hardness test method was carried out on the samples showed that average about 285 Vickers hardness of base metal; however, hardness in the fusion region due to increased austenite fraction fell to 250 Vickers. But hardness in the heat-affected zone due to lower volume fraction of austenite and ferrite phase formation of chromium carbide intermetalic compounds increased to 340 Vickers. The results of the tensile test showed that the tensile strength decreased with increasing heat input, because of increase the size of grains due to the increased heat input.

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In this study, microstructural features and mechanical properties of Incoloy 825-316L stainless steel dissimilar joints have been investigated. For this purpose, pulsed gas tungsten arc welding method was employed and 316L, Inconel 82 and Inconel 625 alloys were used as filler metal. First, specimens were cut. Pulsed gas tungsten arc welding was performed using peak and base currents of 220 A and 110 A, respectively. Microstructure of welded joints was studied using metallographic observations and energy dispersive spectroscopy (EDS) analysis. In order to evaluate the mechanical properties, tensile and microhardness measurements were done on the joints. In all specimens, dendritic and equiaxed and/or cellular growth of austenite phase was observed. Incoloy 625 weld metal had the finest dendritic structure. Tensile test results revealed the ductile fracture with a high percent of elongation for all specimens. The highest tensile strength and percent of elongation of 610 MPa and 48% were obtained for specimen welded using Inconel 625 filler metal. Inconel 625 and 316 stainless steel weld metals showed the highest and lowest microhardness with values of 232 HV and 224 HV, respectively.  

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High-strength low alloy steels are a class of steels used in applications that require high strength and good weldability, including ship hulls, gas pipelines and oil industry. One way to build parts is fusion welding that create areas with a large grain size in the heat-affected zone and increased susceptibility to hydrogen cracking. One way to solve this problem is to use solid state friction stir welding process. In this study, microstructural evaluation and mechanical properties of friction stir welding X-60 cross sections examined by optical microscope and by tensile and micro-hardness tests. The results indicate that changing welding parameters and thereby, change the heat input during friction stir welding have a great impact on maximum temperature and cooling rate that cause creating ferrite and bainitic ferrite in the weld zone. This change in microstructure of weld zone cause to improve mechanical properties that increase yield strength from 380 MPa to 420 MPa .Also, the friction stir process cause increasing hardness of 220 Vickers to an average of 280 Vickers and uniform distribution of hardness in the cross-section of friction stir joints.

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The fine grain structure of friction-stir welded aluminum alloys is unstable during post weld heat treatment and some grains abnormally grown. In this study, the sequence of abnormal grain growth during T6 heat treatment of Al-7075 friction-stir weld and its effect on mechanical properties of the weld was studied. The results showed that heat treatment in 510 ˚C resulted in drastic grain growth in stir zone and fine equiaxed grains in the stir zone of as-welded joint were substituted by millimeter-scale irregular grains. Post weld heat treatment resulted in decrease in the tensile elongation from about 10% to 1.5% although the joint tensile strength improved by 28%. In addition, post weld heat treatment changed the fracture location from the 
heat-affected zone to the stir zone.

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In this study, the corrosion behavior of super duplex stainless steel UNS S32750 and tungsten arc welding with filler metals AWS ER2594 duplex stainless steel in acidic solution containing chloride ions have been investigated. Microstructure of weld joints evaluateby light and electron microscope and corrosion behavior examine by open circuit potential and cyclic polarization tests.The results showed that increas in heat input leads to a change in the distribution of alloying elements, formation of intermetallic phases around grain boundaries and the shifting balance between austenite and ferritein phases in weld region. Based on the cyclic polarization tests, cross-weld and base  metal active behavior and have good corrosion resistance due to the presence of high alloying elements. As well as increase in heat input leads  to  an increase in current density and decrease in the pitting potential.

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Transient liquid phase bonding of  UNS S32750 super duplex stainless steel to AISI 304 austenitic stainless steel using BNi-2 interlayer was carried out at 1050 oC for 45 min. Microstructure analyses of the joint were carried out using optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Microhardness indentation and shear strength test were performed to assess mechanical behavior of the joint. No eutectic contents was seen at the joint and thus Isothermal solidification was completed at 45 min bonding time. The shear strength of the joint was about 0.7 of duplex stainless steel shear strength. Froctographic studies revealed that the fracture mode was completely ductile in the case of the joint made at bonding time of 45 min.

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Solid state joining of powder metallurgy (P/M) processed and sintered by spark plasma sintering through friction stir welding (FSW) was studied. The nanocomposites were prepared via mechanical milling followed by spark plasma sintering. The microstructural and mechanical of the joints were evaluated as a function of the different processing parameters such as rotating and advancing speeds of the tool. The achieved finding revelled that the FSW of the nanocomposites produced by P/M containing bimodal sized Al2O3 reinforcement have a working window are affected by the heat input. The joint evolution revelled that the microstructure and mechanical properties of those was related to the generated heat input during the welding. It is known that dynamic recrystallization (DRX) caused grain size refinement of aluminium into stir zone. Meanwhile, it was revealed that the pinning effect of Al2O3 nanoparticles retarded grain growth of the recrystallized grains caused by dynamic recrystallization (DRX)

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In present study, the effect of heat treatment after friction stir welding dissimilar welds T6-7075 and T4-2024 aluminum alloys were investigated. Friction stir welding was performed at a constant rotation speed of 1140 rpm and welding speed 32 mm/min. After welding samples are taken under various heat treatment processes at different aging temperature and time period. Microstructural observations, phase analysis characterization and mechanical properties were performed on welded before and after heat treatment in cross section of welds joint. The results showed that post-weld heat treatment causes abnormal grain growth turns destructive effect on the mechanical properties, while formation of fine and uniform precipitation recovery strength and ductility of welds joints. It is found heat treatment based on T6-7075 and T6-2024 procedure has highest and lowest impact on the restore of weld strength. Tensile test indicate that fracture occurred on the interface between TMAZ and HAZ in retreating side (7075) at as-weld joint, if that failure happens in the stir zone by applying PWHT. Surface fracture suggested fractures in PWHT samples are predominantly inter-granular, while in as-weld joint the fractures of joints are mostly trans-granular.

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The structural and hardness developed in advanced high-strength steel DP590 have been investigated with the help of optical microscopy and scanning electron microscopy on resistance spot welded specimens. The hardness diagram of the weld sections was prepared by microhardness test and the temperature peak and heat distribution were simulated by menas of the Abaqus software. The results show that according to the temperature generated in each region of the weld nugget, the HAZ and base metals have different microstructures, and these difference affects the hardness of the regions. The presence of tempered martensite islands with a fraction of 44% in ferrite matrix in base metal, mainly martensitic structure in the nugget, and martensitic structure along with scattered areas of ferrite in the HAZ was observed. The results of the microhardness tests showed difference in hardness values of the regions, and also it was observed that the hardness values increased in the HAZ and weld zone. The hardness values measured in the nugget, base metal, and HAZ were around 400, 200, and 450 HV which were in accordance with the observed structures

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Nowadays, the use of advanced high strength steels (AHSSs) in body-in-white is one of the hot applied strategies which is followed by the most of the automakers. The study of weldability and weld challenges facing these steels in resistance spot welding process as the most widely used process in the assembly lines of the automotive industry is essential to use the outstanding mechanical responses of AHSSs. This study can result in improvement of mechanical performance of the resistance spot welds of AHSSs. Our results indicate that AHSSs experiences different welding challenges which this work aims to study them by discussing their causes, mechanisms involved and potential ways to address them.

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Joining of Hastelloy C276 nickel-base superalloy to AISI316 Stainless Steel using BNi-2 interlayer performed by transient liquid phase process (TLP) at 1150°C for 5 and 30 minutes. Bonding microstructure was studied using an Optical microscope and a scanning electron microscope (SEM). Vickers hardness test and shear strength test have been used to evaluate the mechanical properties. Microstructural studies showed that at 5 and 30 minutes of bonding time, isothermal solidification is completely formed, and the Center of the joint is free of any eutectic intermetallic compounds. Also, Findings showed that the DAZ of Hastelloy C276 nickel-base superalloy contains rich borides of Ni, Cr, Mo, and W, and the DAZ of 316 austenitic stainless steel contains borides rich in Fe, Cr, and Ni.

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