Papers by Keyword: Welding Process

Abstract: In this work, the microhardness of 7075 aluminum alloy friction stir welding (FSW) joint was measured by a micro vickers hardness tester, the microstructure of the joints was characterised by microscope, the precipitated phases among the welding nugget zone (WNZ), thermal mechanical affected zone (TMAZ), heat affected zone (HAZ) were affirmed by X-ray diffractometer (XRD) and the lattice fringe of transmission electron microscopy (TEM) high resolution image. Based on this, the precipition behavior of precipitated phases was studied. The results show that the microhardness distribution of the 7075 aluminium alloy FSW joints is heterogeneous in comparison with the base metal (BM). The precipitates in the joint mainly include MgZn rod shape and AlCuMg in elliptical shape. In the WNZ, the main precipitate is AlCuMg, and the fine grain strengthening effect is better, so the microhardness in this zone is relatively high. In the TMAZ, the quantity of AlCuMg decreased while the MgZn₂ increased relatively in comparison with the WNZ. At the same time, the effect of the fine grain strengthening was weakened, though the strain hardening increased. Therefore, the microhardness in the TMAZ still decreased. In the HAZ, the quantity of MgZn₂ increased furtherly, and there is no strain hardening and fine grain strengthening, so the microhardness of the HAZ was the lowest among the FSW joints. Besides, through comparative tests, the optimal process parameters of friction stir welding of 7075 aluminum alloy were obtained.

Abstract: In this paper, the properties of the base metal of the low-alloy high-strength steel 20MnTiB, the welding process and the microstructure and properties of the welded joints were studied. The results are as follows: post-heat treatment below 400°C, the strength change of the steel decreases slowly, the elongation does not change significantly, and the metallographic structure is not obvious. When the temperature is above 400, the strength is greatly reduced. And its plasticity increases remarkably, and precipitates on the grain boundary are precipitated and grown on the metallographic structure. When the line energy is in the range of 9.6~12.0kJ/cm, the mechanical properties and microstructure of the welded joints meet the requirements, and the welding process that meets the requirements is studied. Finally, the mechanical properties and microstructure of the welded joint are studied. Provide a reference for the research and application of steel.

Abstract: 9Ni steel is a low temperature serving ferrite steel, providing high strength and excellent low temperature toughness, which could serve well at-196°C. Therefore 9Ni steel is widely used in storage tanks and transport ships for liquefied natural gas (LNG). Nevertheless there are some challenges in the industrial application, such as hot cracking, cold cracking, magnetic arc blow, etc.. In this paper, the study on the welding technology of 9Ni steel developed by Baosteel is carried out. Firstly the weldability is analyzed through welding thermal simulation using Gleeble 3500 system, Y-groove cracking test, maximum hardness in weld heat-affected zone test. The results prove that 9Ni steel could be welded without preheating. The welding consumables have also significant influence on the performance of the welded joints. In this paper the characteristics of different types of welding consumables, including ferrite base type, austenitic stainless steel type, Ni-base alloy type and Fe-Ni base alloy type are analyzed, then the selecting principle for welding consumables is proposed. Furthermore welding process experiments are undertaken using various welding procedures such as SMAW, GTAW, FCAW and SAW. The results indicate that heat input and interpass temperature should be controlled to ensure a sound weld joint. Finally fracture toughness at-196°C of 9Ni steel and its joint is studied using CTOD test. In conclusion, 9Ni steel developed by Baosteel has good weldability and can meet the requirements of industrial application.

Abstract: Utilizing submerged arc welding under heat input 50 kJ/cm on 60 mm thick marine engineering structure plate F550, the effect of preheating and post welding heat treatment on the microstructure and impact toughness of coarse-grained heat-affected zone (CGHAZ) has been investigated. The original microstructure of the steel plate is tempered martensite. The yield and tensile strength is 610 and 660 MPa, respectively. The impact absorbed energy at low temperature (-60 °C) at transverse direction reaches about 230~270 J. Welding results show that the preheating at 100 °C did not have obvious influence on the microstructure and toughness; whereas the tempering at 600 °C for 2.5 h after welding could significantly reduce the amount of M-A components in the coarse-grained heat-affected zone and thus improved the low temperature impact toughness.

Abstract: X80 pipeline steels were employed to investigate the effects of two different welding processes (swing welding and row welding) on the quality of weld joints. The welding thermal cycles of multi-pass welding were tested and the microstructures of the two kinds of weld joints were studied by optical microscope. The hardness tests as well as low-temperature impact tests combined with fracture analysis with scanning electron microscope (SEM) were carried out to evaluate the properties of weld joints. The results showed that under the similar condition of heat input, the grain of swing welding joint is bigger than that of row welding. The joint of row welding has lower hardness and better toughness, suggesting that the process of row welding can improve the properties of weld metal. Consequently, though swing welding is simple in operation and good in production efficiency, row welding is better in terms of microstructure and properties of weld joints.

Abstract: Modelling and numerical simulation of technological welding processes is the creative experimental method. Simulation replaces a real system computer model. To create the model can be applied to many experiments under predetermined conditions and analysis of the results. The results can be optimized and implemented to a real system. In a relatively short time, it is possible to solve complex processes occurring in the melting phase of the welding process, using the most advanced computer technology. Appropriately selected algorithm of model experiments can help study the course of temperature fields and formation of stresses and strains in solving the problems in the field of welding. The result of thermal and structural tasks of numerical simulation using FEM are the temperature fields, stress fields and strain generated in the process of welding and welded parts during cooling. Procedure of solving the tasks can be applied to any weld shape and any material of welded parts. The results published in the paper were obtained by solving the thermal and stress- strain tasks in the ANSYS program. Modelling and numerical simulation open possibilities for the three dimensional analysis of the phenomena studied. Based on the development of numerical methods and their application, it is possible to create computational models. Their implementation in software systems opens new possibilities for the area of numerical simulation of technological welding processes. The paper described simulation fillet and butt weld made of stainless steel 17242.

Abstract: This research introduces a new approach of using Failure Mode and Effect Analysis (FMEA) and Genetic Algorithm to improvement of manufacturing process – welding process. FMEA analysis is used to measure the weight of failures by calculating the Risk Priority Number (RPN) value for welding process. By FMEA we have identified precisely the main causes which lead to the appearance of many failures for which the RPN value is highest. Then we have established the parameters which are directly responsible of these causes. By using these parameters we have got a function that actually has to be improved optimized. This is going to be the objective function for the Genetic Algorithm.

Abstract: Alloy IN718 is a nickel based precipitation hardened material and it has the necessary strength over a range of temperatures which includes the operating range for many rocket propulsion systems and jet engines. This performance is accomplished by a combination of solid-solution strengthening, precipitation strengthening and grain-boundary strengthening. However, it is common for precipitation hardened nickel based superalloys to have a problem of post-weld cracking. In this study, several welding processes are investigated to obtain the optimum welding method of IN718 for elevated temperature forming. These include LBW(Laser Beam Welding), EBW(Electron Beam Welding), HIP(hot isostatic pressing), and solid state diffusion bonding. The result shows that the LBW specimen performs the highest formability at 980°C so that this process can be applied to superplastic forming of IN718 sheet. It is demonstrated that the elevated temperature superplastic forming of nozzle extension with internal cooling channels was possible with laser beam welded IN718 sheet.

Abstract: This paper presents an experimental investigation of heated tool welding of polypropylene matrix composite. The goals of this paper are to investigate the issues of local changes of welding strength that depends on heating time. For experimental procedure, specimens were injection molded as ISO tensile test specimens and matrix was reinforced by organic and inorganic materials. In addition, welding of specimens was carried out by non-contact heated tool butt welding process. Within the range of the weld process parameters were investigated, the highest weld strength dependent on heating time was achieved of the order of 94% to the base strength of the material. And then these specimen’s maximum welding strengths and energy at break point properties that were depend on heating time have been compared.

Abstract: 10mm thick aluminum alloys 5A02 plates were welded using MIG beam in this paper.The MIG weld formation and microstructure morphology were studied,the hardness in the weld were measured, the tensile test were made.The test result shows that the cooperation of welding current,speed and root gap can lead to perfect welds.There are equiaxed grain in the central welds and cloumnar grain structure near the fusion line.The maximum hardness is in the fusion zone of joints,and the minimum is in the softening zone.