Metallurgical Problems Research Articles

Effect of underwater friction stir welding parameters on AA5754 alloy joints: experimental studies

The water as a welding environment may generate serious technological and metallurgical problems but in certain cases, the physicochemical properties of water can be used effectively, e.g., to impart the specific properties of welded materials. The purpose of the work was verification of effectiveness of the water cooling of aluminium alloy AA5754 for various sets of technological parameters of underwater friction stir welding (UFSW). For the joints performed with the range of parameters of rotational speed: 475–925 rpm and welding speed: 47.5–95 mm/min, the following examinations were carried out: visual tests, radiographic tests, static tensile test, fractography (SEM, scanning electron microscope) analysis, and surface texture analysis performed with 3D measurement system. All of the joints were characterized with some amount of flash. Besides, depending on the values of selected parameters, the defects arising from inadequate stirring were found—tunnel defects and melting. The best appearance of the joint was obtained for the set of parameters of 925 rpm and 47.5 mm/min. The samples of the same joint were found to be of the highest mechanical properties—ultimate tensile strength (UTS) of 194 MPa and elongation (A) of 9.2%. The results were confirmed by the fractography analysis, which in this case indicated the ductile fracture mode. Dynamic plastic behaviour strongly depends on the process parameter values, which was reflected in the results of surface texture analysis. The parameter selection resulted in significant changes in the roughness results (from 8 to 14.2 µm depending on the sample) as well as the flow ring distance of the weld (from 20 to 50 µm depending on the sample).

Recent development of grain oriented electrical steel in Shougang steel

Shougang Steel has been pursuing the development of low iron loss and high permeability grain oriented electrical steels for more than a decade. Grain oriented electrical steel requires a very strong Goss {110}〈001〉 texture and as such a comprehensive control of thermo-mechanical processing parameters is required to achieve a strict control of texture. In this paper the key metallurgical problems associated with manufacture of grain oriented electrical steel are discussed, including the factors that affect both primary recrystallization and secondary recrystallization leading to the development of a strongly textured final sheet. The metallurgical factors affecting magnetostriction of electrical steels are also analyzed, and a technological approach for domain refinement, and its effect on magnetic properties, is described. Examples of magnetic properties under non-sinusoidal magnetization conditions are also reported and analyzed. As a result of continuous research and development efforts the high permeability low iron loss grain oriented electrical steel of thin gauge products of 0.2 mm/0.18 mm thickness have recently been developed to meet the requirements of the new China national standard of energy efficiency grades for power transformers.

Solid-State Additive Manufacturing of AA6060 Employing Friction Screw Extrusion Additive Manufacturing

AbstractSolid-state additive manufacturing constitutes a worthwhile alternative for many precipitation-based aluminium alloys that cannot be processed through fusion-based approaches due to metallurgical problems. In this work, the newly developed solid-state friction screw extrusion additive manufacturing (FSEAM) approach has been employed to study the processability of AA6060 T6 as a function of the printing velocity. Various wall-like builds were fabricated at printing velocities of 100 mm/min to 250 mm/min by deposition of 50 layers of 1 mm thickness, 14 mm width, and 150 mm length. No major defects were observed in cross section, and the microstructure showed equiaxed grains with an average size of 2–4 μm for all builds. Promising mechanical properties were obtained for all tensile test specimens extracted in the deposition direction of the layers. For specimens extracted in the build direction, only the builds fabricated with sufficiently high normal force to ensure proper bonding between successively deposited layers showed similar results to the deposition direction. The relatively high temperatures obtained during fabrication led to the dissolution of strengthening precipitates for the 150–250 mm/min samples as indicated by serrated yielding effects. Post-manufacturing heat treatment of these samples was successful, partially restoring the feedstock hardness.

Tool pin profiles effect on mechanical properties of friction stir welding of dissimilar aluminium alloys

Aluminum alloys are now widely used in a many of the engineering applications because of due to their light weight and exceptional characteristics. In many precision sectors such as automobile, railway, aerospace, and marine structures joining is considered one of the most complicated phenomena because rigid tolerances are necessary throughout distinct product assembly. Friction stir welding (FSW) of various grades of aluminium alloys has attracted significant industrial and scientific attention due to its ability to transform into a high-quality joint product. Fabricating such alloys with traditional fusion welding is a difficult process because of many metallurgical problems. In the present experimental work, the effect of different pin profiles tools on friction stir welding of AA-6061 T6 and AA-2014 T4 has been investigated. Friction stir welding has been performed using different pin profiles tools cylindrical, square and tapered and keeping the rotational speed and feed rate constant. This experimental investigation shows that by using square profile tool for friction stir welding improves the mechanical properties of the joint. It has also been observed that hardness of the weld is greater for square pin profile. Also the microstructure of the samples was observed.

Solving the selectivity problem in magnetic random access memories using configurations that form C-states

Abstract The selectivity problem in magnetic random access memory is caused by processing problems that are metallurgical in origin. In honor of the 70th birthday of Professor Kronmüller, who has made so many contributions to magnetism and metallurgy, a solution of the selectivity problem is presented in which the metallurgical problems are circumvented by the design of the patterned thin film element to make it insensitive to processing problems. The solution is theoretical, using micromagnetics, the limitations of which call for experiments to support the conclusions.

Influence of InterPulsed TIG Welding Parameters on the Evolution of Microstructure and Tensile Properties of Su-718 Alloy Sheets

Abstract Superalloy 718 (Su-718) is a high-performance nickel-based alloy typically employed in high-temperature applications of aero-engine components. It is mostly joined by the Tungsten Inert Gas (TIG) welding process for clean and precise joints. However, the joints are more prone to premature failure owing to the metallurgical problems during solidification, such as constitutional segregation in the fusion zone (FZ) and microfissuring in the heat affected zone (HAZ). To overcome these problems, in this investigation, a recently emerged InterPulsed TIG (IP-TIG) welding process was utilized for joining Su-718 alloy. It is the advanced variant of the TIG welding process principally differentiated by electromagnetic condensation of the arc and high-frequency pulsation up to 20 kHz. The primary objective of this study is to make the potential use of electromagnetic condensation of the arc and pulsation for minimizing the Laves phase growth in FZ and enhancing the tensile strength of joints. To achieve this, the effect of IP-TIG welding parameters on evolution of the microstructure and tensile properties of Su-718 alloy joints is investigated and the results are analyzed in detail in this paper. The analysis of microstructural features was done using optical microscopy, scanning electron microscopy, and Energy Dispersive X-ray Spectroscopy techniques. The influence of Laves phase morphology on the strength and elongation of joints is revealed and correlated to the fracture surface. The principal mechanism responsible for changes in microstructural features and consequential influence on tensile behavior of joints is explained briefly and correlated to the cooling rate and heat input conditions during welding.

Machine learning for metallurgy I. A neural-network potential for Al-Cu

High-strength metal alloys achieve their performance via careful control of precipitates and solutes. The nucleation, growth, and kinetics of precipitation, and the resulting mechanical properties, are inherently atomic scale phenomena, particularly during early-stage nucleation and growth. Atomistic modeling using interatomic potentials is a desirable tool for understanding the detailed phenomena involved in precipitation and strengthening, which requires length and timescales far larger than those accessible by first-principles methods. Current interatomic potentials for alloys are not, however, sufficiently accurate for such studies. Here a family of neural-network potentials (NNPs) for the Al-Cu system are presented as a first example of a machine learning potential that can achieve near-first-principles accuracy for many different metallurgically important aspects of this alloy. High-fidelity predictions of intermetallic compounds, elastic constants, dilute solid-solution energetics, precipitate-matrix interfaces, generalized stacking fault energies and surfaces for slip in matrix and precipitates, antisite defect energies, and other quantities, are shown. The NNPs also captures the subtle entropically induced transition between ${\ensuremath{\theta}}^{\ensuremath{'}}$ and $\ensuremath{\theta}$ at temperatures around 600 K. Many comparisons are made with the state-of-the-art angular-dependent potential for Al-Cu, demonstrating the significant quantitative benefit of a machine learning approach. A preliminary kinetic Monte Carlo study shows the NNP to predict the emergence of GP zones in Al-4at%Cu at $T=300$ K in agreement with experiments. These studies show that the NNP has significant transferability to defects and properties outside the structures used to train the NNP but also shows some errors highlighting that the use of any interatomic potential requires careful validation in application to specific metallurgical problems of interest.

Thermo-mechanical simulation of ultrahigh temperature ceramic composites as alternative materials for gas turbine stator blades

The efficiency of the Bryton cycle strongly depends on the maximum temperature of the cycle. However, restrictions on metallurgical problems deprive engineers from the benefit of high temperatures. Ultrahigh temperature ceramics can be considered in such cases, instead of traditional materials like M152 superalloy. In this study, SiC reinforced HfB2 and ZrB2 ultrahigh temperature ceramics were proposed as gas turbine stator blades. The heat transfer and stress-strain equations were solved numerically by the finite element method to obtain temperature and stress distributions. The results showed that the maximum thermal stress occurs in vicinity of the cooling ducts where the temperature gradient is maximum. The maximum displacements of 1.2 mm (for HfB2–SiC) and 1.14 mm (for ZrB2–SiC) occur in the upper wall. It can be noticed that the ZrB2–SiC made blade showed lower maximum stress and displacement than those for the HfB2–SiC made one, as a result of lower expansion coefficient of ZrB2–SiC system. The addition of SiC to monolithic HfB2 and ZrB2 ceramics decreases their thermal conductivity and following that, the temperature uniformity in blades reduces. Although the thermal stresses and the probability of failure in these stator blades enhance, the ZrB2–SiC material presented the best performance among the other investigated samples. Both Coulomb-Mohr and Von Mises failure analyses were employed. It was understood that both blades made of HfB2–SiC and ZrB2–SiC composites simply withstand the applied stresses with the safety factors of about 1.5.

Influence of magnetically constricted arc traverse speed (MCATS) on tensile properties and microstructural characteristics of welded Inconel 718 alloy sheets

The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding (GTAW) of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone. This paper reports the direct effect of magnetically constricted arc traverse speed (MCATS) on bead profile, tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding (GTCAW) process. The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing. It is correlated to the solidification conditions during welding. The relationship between MCATS and Arc Constriction Current (ACC) was derived. Its interaction effect on the magnetic arc constriction and joint performance was analysed. Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties (98.39% of base metal strength with 31.50% elongation). It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer, discrete laves phase in interdendritic areas.

Effect of Delta Current and Delta Current Frequency on Microstructure and Tensile Properties of Gas Tungsten Constricted Arc (GTCA)-Welded Inconel 718 Alloy Joints

The magnetic arc constriction technique was used to control the heat input-related metallurgical problems such as segregation of Nb and laves phase formation in the weld metal region of gas tungsten arc welding (GTAW) of Inconel 718 alloy. The delta current (arc constriction current) and delta current frequency are the two important parameters in controlling the arc characteristics. The main effect of the delta current and delta current frequency on the microstructural modification and corresponding influence on the tensile properties of a gas tungsten constricted arc (GTCA) welded 2-mm-thick Inconel 718 alloy sheet was investigated systematically and presented in this article. Superior tensile properties were exhibited by the joints made using a delta current of 50 A and delta current frequency of 4 kHz because of the grain refinement in the fusion zone and finer, distinct laves phase formation.

Effect of Heat Input on Evolution of Microstructure and Tensile Properties of Gas Tungsten Constricted Arc (GTCA) Welded Inconel 718 Alloy Sheets

The significant effect of heat input on the microstructural characteristics and tensile properties of 2-mm-thick Inconel 718 alloy sheets joined by gas tungsten constricted arc welding process was investigated systematically. It involves the application of magnetic arc constriction technique to solve the heat input-related metallurgical problems in gas tungsten arc welding of Inconel 718 alloy such as segregation of Nb and laves phase evolution in weld metal region which drastically reduces the weld mechanical properties. Heat input range was used from 495 to 585 J/mm by varying Main Current from 60 to 80 A at distinct levels of 5 A. The average secondary dendrite arm spacing was increased from 6.31 to 8.92 μm, revealing the corresponding cooling rate between 2087 and 720 °C/s. Superior tensile properties were obtained at an optimum heat input of 518 J/mm. It exhibited 98.16 and 78% of base metal strength and ductility. It is attributed to the grain refinement in fusion zone microstructure and the evolution of lower amount of laves phase with finer and discrete morphology. The average size and volume fraction of laves phase for the current sample were 3.12 μm and 7.68%. The benefits of magnetic arc constriction and Delta Current pulsing were not achieved at higher heat input.

Inoculation Solutions Against Metallurgical Problems

Inoculation can be used to fight many complex iron defects. Five cases will be developed to illustrate in different metallurgical conditions how beneficial some elements can be to solve specific metallurgical issues.

Rapid precipitation of intermetallic phases during isothermal treatment of duplex stainless steel joints produced by friction stir welding

The propensity of duplex stainless steels to form secondary phases that harm their main properties is a metallurgical problem that continues to be studied. Friction stir welding has shown excellent results when applied to duplex stainless steels, enabling the formation of joints that maintain the austenite-ferrite balance, without the presence of secondary phases. Welding processes cause significant microstructural reformulation in the joint microstructure, so the properties and metallurgical behavior of welded joints differ significantly from those of the corresponding base metals. The formation of secondary phases in duplex stainless steels occurs by diffusional transformation processes that are dependent on the transformation time, with the kinetics being influenced by the previous microstructure. Although friction stir welding makes it possible to obtain joints free from secondary phases, it is important to study the propensity of welded joints to subsequently form secondary phases, in order to be able to understand the behavior of these joints when they are subjected to hot operations, such as weld repairs. In this work, friction stir welded joints were treated isothermally at 850 °C and were analyzed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Ferritoscope measurements, and X-ray diffractometry. The results revealed that the friction stir welded joints presented much faster formation of intermetallic phases, compared to the base metals, with the appearance of regions showing advanced stages of intermetallic phase precipitation after only 5 min exposure at 850 °C.

Microstructural study in AA7075 alloys welded with different filler metals

ABSTRACTEven though AA 7075 is an aluminum alloy with high mechanical properties, it is not often applied in manufacturing. This is so, because it is considered as very difficult to produce defect free welded joints. This is so, because this alloy has a tendency to hot cracking. The metallurgical problems that appear during welding of AA 7075 have not been fully solved but they have been reduced by applying alloys such as: 4043 and 5356 as filler metals. However, in literature there is little information about the metallurgical effects of these types of filler metals applied in arc welded joints of AA7075. This is especially true for Tungsten Inert gas welding. Therefore, this work is focused in comparing the microstructure and Vickers microhardness in weldments of AA 7075 with ER4043, ER5356 and AA7075 as filler metals. Besides, a set of welded joints with the three different filler metals were quenched after welding in order to modify the final microstructure. The results were evaluated by microstructural analysis focused on the Heat Affected Zone and Vickers microhardness and they were compared among them.

Numerical analyses of heat transfer and thermal stress in a ZrB2 gas turbine stator blade

Abstract Temperature of burned gases is a key parameter in output works of gas turbines. Nevertheless, high temperatures cause metallurgical problems in the turbine parts, specially the blades. Hence, ZrB2 as an ultra-high temperature ceramic (UHTC) with a melting point of 3246 °C , considerable high-temperature strength and relatively high thermal conductivity can be a proper candidate for manufacturing of gas turbine parts. In the present work, heat transfer and related thermal stresses of a gas turbine stator blade made of ZrB2 ceramic is investigated numerically by means of Comsol Multiphysics software and the obtained data are compared with M152 (UNS S64152) alloy. The results showed that ZrB2 has more uniform temperature distribution than M152, which is corresponded to its lower thermal gradient. Due to its lower thermal expansion coefficient, ZrB2 showed lower total displacement than M152 which is an important parameter in blade performance. Also, the Von Mises stress of ZrB2 showed higher value than M152.

Finding the Most Efficient Way to Remove Residual Copper from Steel Scrap

The supply of end-of-life steel scrap is growing, but residual copper reduces its value. Once copper attaches during hammer shredding, no commercial process beyond hand-picking exists to extract it, yet high-value flat products require less than 0.1 wt pct copper to avoid metallurgical problems. Various techniques for copper separation have been explored in laboratory trials, but as yet no attempt has been made to provide an integrated assessment of all options. Therefore, for the first time, a framework is proposed to define the full range of separation routes and evaluate their potential to remove copper, while estimating their energy and material input requirements. The thermodynamic, kinetic, and technological constraints of the various techniques are analyzed to show that copper could be removed to below 0.1 wt pct with relatively low energy and material consumption. Higher-density shredding allows for greater physical separation, but requires proper incentivization. Vacuum distillation could be viable with a reactor that minimizes radiation heat losses. High-temperature solid scrap pre-treatments would be less energy intensive than melt treatments, but their efficacy with typical shredded scrap is yet unconfirmed. The framework developed here can be applied to other impurity-base metal systems to coordinate process innovation as the scrap supply expands.

Multi-criteria optimization strategies for tree-structured production chains

The aim of this paper is presentation of some optimization strategies applicable in the optimization of multi-stage and multi-thread chain structures (linear and tree-structured acyclic graphs) with multiple intermediate goal functions. The inspirations for this type of analysis are production chains often seen in industrial plants. Production in these plants consists of sequences of multiple units connected linearly or in tree-structured graphs in which, at various production stages, intermediate quality criteria, related to the semi-products, may have to be considered. Optimization strategies as well as the results of their application for different hypothetical problems and the real metallurgical problem of lead production are presented.

How Will Copper Contamination Constrain Future Global Steel Recycling?

Copper in steel causes metallurgical problems, but is pervasive in end-of-life scrap and cannot currently be removed commercially once in the melt. Contamination can be managed to an extent by globally trading scrap for use in tolerant applications and dilution with primary iron sources. However, the viability of long-term strategies can only be evaluated with a complete characterization of copper in the global steel system and this is presented in this paper. The copper concentration of flows along the 2008 steel supply chain is estimated from a survey of literature data and compared with estimates of the maximum concentration that can be tolerated in steel products. Estimates of final steel demand and scrap supply by sector are taken from a global stock-saturation model to determine when the amount of copper in the steel cycle will exceed that which can be tolerated. Best estimates show that quantities of copper arising from conventional scrap preparation can be managed in the global steel system until 2050 assuming perfectly coordinated trade and extensive dilution, but this strategy will become increasingly impractical. Technical and policy interventions along the supply chain are presented to close product loops before this global constraint.

Analysis of an Axle Failure under Torsional Load

Premature fracture of an axle under torsional load occurred after a tracked military tank had experienced field testing for only 80 kilometers. Visual metallographic examinations were performed with optical microscope (OM) and scanning electron microscope (SEM). The investigation demonstrates that the premature fracture is caused by metallurgical problems inside the axle where the primary and secondary cracks originate, propagate, and eventually result in final catastrophic rupture through torsional fatigue. The failure mechanism is summarized and improvement of the fatigue lifetime for the axle is recommended.

New Analysis Method Application in Metallographic Images through the Construction of Mosaics Via Speeded Up Robust Features and Scale Invariant Feature Transform

In many applications in metallography and analysis, many regions need to be considered and not only the current region. In cases where there are analyses with multiple images, the specialist should also evaluate neighboring areas. For example, in metallurgy, welding technology is derived from conventional testing and metallographic analysis. In welding, these tests allow us to know the features of the metal, especially in the Heat-Affected Zone (HAZ); the region most likely for natural metallurgical problems to occur in welding. The expanse of the Heat-Affected Zone exceeds the size of the area observed through a microscope and typically requires multiple images to be mounted on a larger picture surface to allow for the study of the entire heat affected zone. This image stitching process is performed manually and is subject to all the inherent flaws of the human being due to results of fatigue and distraction. The analyzing of grain growth is also necessary in the examination of multiple regions, although not necessarily neighboring regions, but this analysis would be a useful tool to aid a specialist. In areas such as microscopic metallography, which study metallurgical products with the aid of a microscope, the assembly of mosaics is done manually, which consumes a lot of time and is also subject to failures due to human limitations. The mosaic technique is used in the construct of environment or scenes with corresponding characteristics between themselves. Through several small images, and with corresponding characteristics between themselves, a new model is generated in a larger size. This article proposes the use of Digital Image Processing for the automatization of the construction of these mosaics in metallographic images. The use of this proposed method is meant to significantly reduce the time required to build the mosaic and reduce the possibility of failures in assembling the final image; therefore increasing efficiency in obtaining results and expediting the decision making process. Two different methods are proposed: One using the transformed Scale Invariant Feature Transform (SIFT), and the second using features extractor Speeded Up Robust Features (SURF). Although slower, the SIFT method is more stable and has a better performance than the SURF method and can be applied to real applications. The best results were obtained using SIFT with Peak Signal-to-Noise Ratio = 61.38, Mean squared error = 0.048 and mean-structural-similarity = 0.999, and processing time of 4.91 seconds for mosaic building. The methodology proposed shows be more promissory in aiding specialists during analysis of metallographic images.