1,721,007 research outputs found
Corrosion Resistance of 3D-Printed and Conventional Die Steels in Contact with Molten Aluminum Alloys
No full textThis study investigates the corrosion resistance of maraging steel produced via additive manufacturing and conventional forging when exposed to molten aluminum alloys used in high-pressure die casting (HPDC). The H11 tool steel, typically used in such applications, was also studied for comparison. Static immersion tests were conducted in three different aluminum alloys for HPDC (AlSi7Mg, AlSi10Mg, AlSi10MgFe). SEM-EDS analysis revealed differences in the formation of intermetallic layers on the metallic surfaces, mainly depending on the material considered. The laser-power bed fused maraging steel, often used for conformal cooling inserts, exhibited the formation of a stable high Fe intermetallic layer without a liquid phase, contributing to superior corrosion resistance compared to the forged maraging steel. The H11 tool steel demonstrated the highest corrosion resistance, especially due to its composition free from Ni and the presence of Cr and Cr-carbide. Thermo-Calc equilibrium simulations identified the phases present in the intermetallic layers at the test temperature, highlighting the effects of different steel compositions on interfacial intermetallic layers. These findings underline the critical role of manufacturing processes and alloy composition on the performance of steels in contact with molten aluminum alloys, with implications for die casting applications
The effect of partial recrystallization on the corrosion resistance of EN AW6082 forged components evaluated with different tests
No full textStructural automotive components are extensively made of aluminum alloy forgings, due to the elevate strength and low weight required. These products are frequently subjected to recrystallization. Recrystallization, often limited to surface or forging portions, is expected to reduce its tensile strength and corrosion resistance, but the literature is scarce on this subject. For a more comprehensive understanding, the present research studied the corrosion behavior of samples collected from EN AW 6082-T6 forged components, designed to expose both recrystallized and not recrystallized surfaces to the corrosive environment. Several standardized corrosion tests (i.e., PV 1113, ISO 11846, and VW 96380) were applied to assess the most representative with respect to real field exposure. Tensile tests were performed in four different conditions, recrystallized and not recrystallized specimens in an as-forged state or after corrosion. The recrystallization led to a reduction in tensile properties, but this gap was compensated by a higher corrosion resistance than the not recrystallized samples. Consequently, the mechanical properties became comparable after the corrosion test.The main purpose of the paper is to study the effect of recrystallization phenomenon, typically encountered in aluminum alloy forgings, on tensile and corrosion resistance. The results highlight the fact that recrystallization reduced the tensile properties, but the corrosion resistance is higher than that of not recrystallized samples. Consequently, the mechanical properties are comparable after the corrosion test. imag
Effect of chromium plating and decorative PVD coatings on the corrosion resistance of AA6060 components
No full textFor duplex coatings (plating + PVD) several studies have shown the criticality of rather inaccessible zones like small holes and undercuts for the corrosion damage. Also sharp edges are reported as dangerous zones for their capability of stress localization and, therefore, as cause of premature coating cracking due to inappropriate local stress distribution. In the present study the effect of holes and undercuts present on a component in AA 6060 alloy (fig. 1) obtained using four different mechanical finishing (wet vibratory finishing, dry vibratory finishing, manual polishing and mechanical polishing respectively) and then Ni plated and PVD coated using two different types of coating (Ni/Cr/ZrCN and Ni/Cu/Ni/Cr/ZrCN) have been evaluated in terms of corrosion resistance. The samples characterized by different mechanical finishing have been analyzed by Scanning Electron Microscopy to investigate the surface morphologies next to or inside the holes (fig. 2, fig. 3, fig. 4 and fig. 5). Then the specimens have been coated by decorative Chromium plating (Ni +Cr - nominal depth 20 μm) and by a ZrCN PVD layer (0.4 μm). The so obtained samples have been investigated by a neutral salt fog testing using 5% sodium chloride solution and a pH range of 6.5 to 7.2; the temperature of the salt spray chamber was controlled to maintain 35 ± 2°C according to the ASTM B 117 standard (fig. 6 and fig. 7). The duration of the test ranged from a minimum of 2 hours to a maximum of 24 hours. The Cu interlayer characterizing the Ni/Cu/Ni/Cr/ZrCN coating showed a significant improvement in the corrosion resistance of the coated part. The coating architecture, and in particular the introduction of an interlayer having a coefficient of thermal expansion intermediate between the Al value and the Ni data affected the residual stress distribution as measured using X-ray technique and, therefore had also an effect on the mechanical behavior of the coating as resulted by nanoindentation test. The four different polishing procedures used did not influence the coating adhesion; no particular effect can be also reported in terms of corrosion resistance
Wear Behavior of AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion and Gravity Casting
Full text linkHerein, the sliding wear behavior of AlSi10Mg samples realized using laser-based powder bed fusion (LPBF) is investigated via pin-on-disc (PoD) tests, before and after T6 heat treatment. The changes in the microstructure, density, and hardness induced by heat treatment are correlated with the tribological behavior of the alloy. Furthermore, short wear tests are conducted and the resulting wear tracks are investigated through scanning electron microscopy (SEM), equipped with an energy-dispersive spectroscopy (EDS) microprobe to elucidate how the wear mechanisms evolve with sliding distance. For comparison, gravity cast (GC) AlSi10Mg samples are also characterized and tested. The as-built additive manufacturing (AM) sample exhibits the lowest wear rate and coefficient of friction because of its high hardness and relative density, whereas the heat-treated sample shows the worst behavior in comparison with the GC samples. The results suggest a significant influence of porosity on the wear behavior of AM alloys
White steel slag from ladle furnace as calcium carbonate replacement for nitrile butadiene rubber: A possible industrial symbiosis
No full textOver the years, natural resources conservation and waste management have become increasingly important
globally, leading to the promotion of systemic approaches that integrate different processes by sharing materials, energy, and services. Recycling and reuse of materials have also become an area of increasing interest. This study investigates the potential use of ladle furnace (LF) slag, a waste product of the steel industry, as a nonconventional filler for rubber compounds. LF slag is produced during the refinement stage of the steelmaking process and is almost entirely landfilled. This research compares a standard nitrile-butadiene rubber (NBR) filled with calcium carbonate to an NBR filled with 10% LF slag (by volume). The study evaluates the compounds’ processability and mechanical performance by means of rheometer analysis, hardness test, tensile test, compression test, and compression set. The use of LF slag in NBR rubber compounds could represent an example of a circular economy, where waste from one industry becomes a raw material for another
Effect of a New High-Pressure Heat Treatment on Additively Manufactured AlSi10Mg Alloy
Full text linkThe application of an innovative high-pressure T6 treatment (HPT6) to additively manufactured AlSi10Mg alloy is reported in this paper. The aim of this treatment is to obtain the effective densification of the material together with the hardening effects typical of T6 heat treatment in one step. For comparison, a two-step treatment consisting of hot isostatic pressing followed by conventional T6 treatment was applied. Standard annealing and T6 treatment alone were also considered. The microstructural and mechanical properties of alloys treated under all the studied conditions were analyzed and their density was measured to quantify their densification. Although the application of high pressure hindered the diffusion mechanisms, and thus could limit the hardening effect of heat treatment, HPT6 treatment was found to ensure suitable mechanical properties and high densification. Furthermore, it required less time; therefore, it can be considered as a time-efficient process for high-performance applications
Segregations on forged components: Their effect on defects like cracks and on the microstructure of heat treated parts
No full textSegregations on forged components: their effect on defects like cracks and on the microstructure of heat treated parts Segregation of alloying elements during the ingot solidification process and the subsequent hot forming operations are responsible for the formation of regions exhibiting different chemical composition and therefore different mechanical properties. During the casting of steel the structure of the ingot is characterized by the development of dendrites. The presence of such type of microstructure causes a high lack of homogeneity both in terms of chemical and mechanical behaviour not only in the ingot but also in the finished product obtained from it. In particular chemical heterogeneity develops during solidification, when elements having a low partitioning ratio are ejected into the interdendritic regions causing areas of high solute concentration. Therefore it can be asserted that segregations affect the service properties of the forged parts and often lead to their failure (fig. 1). Several methods for alleviating structural heterogeneity are described in the literature and, in particular, the homogenizing heat treatment carried out at high temperature (usually ranging from 1200°C to 1300°C depending on the chemical composition of the considered steel) after the ingot casting and cooling. In the present paper the effectiveness of different heat treatments in reducing the extent of segregations has been evaluated both using industrial and laboratory furnaces. A 20 Mn5 steel grade has been examined; the choice of such material was done in order to evaluate the effect of the Mn segregation which, along with the C segregation, often causes failures in the forged parts produced using low alloyed Mn steels. In literature the influence of Mn segregation was systematically evaluated by Majka [15] that showed the effect of different heat thermal treatments carried out on a tailored segregated Mn steel and in particular the effect due to the cooling procedures from austenitizing temperature simulating a normalizing heat treatment. The formation of ferrite in low-Mn areas resulted in carbon enrichment in the austenite of adjacent high-Mn zones and caused the formation of perlitic layers or bainitic or martensitic zones depending on the cooling rate and the level of local segregation. Such severe differences in the local steel chemical composition are responsible for the nucleation of microcracks causing the scraps of several forged parts produced starting from Mn low alloyed steel (fig. 2). Starting from such preliminary remarks, in the present paper samples from a scraped forged shaft produced in 20Mn5 steel were cut to be characterized in different heat treatment conditions. The scrap of the shaft was due to the ultrasonic control executed at the end of the production steps; such a control showed cracks having sizes higher than the acceptable limit defect; a microstructural analysis of samples examined in the forged condition showed an important segregation affecting a large part of the shaft (figs. 3-4). Three different set of samples were characterized in the industrial furnace according the following conditions: 1) homogenization at 1320 ° C × 80 min. + air cooling - fig. 5; 2) homogenization + normalization at 900°C × 30 min. + air cooling - fig. 6 3) homogenization + quenching (900°C × 60 min. + water cooling) and tempering (600°C × 1h + air cooling) - fig. 6. A reduction in the level of segregation was obtained after the homogenization treatment even if not all the local differences in the chemical composition were removed. The effect of two different controlled heat treatments carried out in laboratory was also evaluated starting from forged samples heat treated according to: • a heating at 900°C × 60 min+ air cooling (condition A); • a heating at 1320°C × 150 min+ air cooling (condition B). The microhardness distribution obtained on polished samples tested in the condition A and B can be observed in fig. 7 and 8 respectively. The sample treated at higher temperature assured a reduced scatter in the microhardness data (fig. 8) with respect to the condition A (fig. 7) and such a result can be related to a more homogeneous distribution of Carbon and Manganese. Anyway fig. 8 shows the presence of a hardness peak in correspondence of which a high level of Mn was detected by EDS microanalysis as reported in fig. 9; therefore a certain level of segregation is still present inside of the examined sample. From the whole experimental results it can be assumed that although the homogenizing treatment can be used as a reducing Mnsegregation tool, only a proper sequence of casting steps (starting from the casting temperature to the ingot cooling rate) aimed at small dendrite size and controlled Mn ingot distribution can be considered the proper solution to obtain high quality forged components. In fact the absence of severe Mn-segregations inside the ingot is fundament to obtain a forged part without cracks related to martensitic or bainitic brittle areas mainly due to chemical inhomogeneities in terms of carbon and manganese distribution. The extension of such macrosegregation zones are affected from the thermal distribution gradient imposed both during the forging phase and the heat treatment of the forged part and therefore changes in the size and distribution of macrosegregation can be also observed during the forging steps. Unfortunately such variation often cause local high level of stress and therefore can induce cracks nucleation and propagation inside the forged component
Zinc-based diffusion coating as an environmental-friendly alternative to conventional processes
No full textThe aim of the present work is to show the first results obtained in a project about an innovative and environmental-friendly galvanizing technology. This research activity is founded by Regione Lombardia. To this aim, commercial items coated by diffusion were analyzed and compared in terms of chemical composition, microstructure, corrosion and mechanical resistance. In particular two processes were considered: a conventional technique (sherardization) and an innovative technology that represents the starting point of the project. Morphology and chemical composition of the coated samples were studied, as well as corrosion resistance, hardness and coating adhesion. Moreover, an industrial pilot plant able to replicate the innovative technique was realized in order to optimize process parameters and to improve process efficiency. In these initial project steps, only small steel items were coated. However, one of the final project goal is to coat large structural parts with complex geometry
The corrosion resistance of maraging steel 1.2709 produced by L-PBF in contact with molten Al-alloys
No full textNowadays there is a growing interest in the use of secondary Al-alloys for high-pressure die casting to obtain structural parts. To guarantee appropriate performance, these alloys are characterized by a lower Fe content (< 0.15%) than conventional secondary ones, commonly used in the production of non-structural parts. This makes them more susceptible to the phenomenon of die-soldering, thus resulting in a decrease in the service life of dies and inserts. The production of complex and demanding castings requires appropriate dies and materials, especially in high stressed areas where higher-performance steel inserts are used. Recently, maraging steel has been applied for these issues. Thanks to the good weldability of maraging steels, these alloys are nowadays also processed by additive manufacturing (AM) techniques, to obtain very complex parts like inserts with conformal cooling channels, able to extend the life of the inserts themselves, increasing productivity. In this context, this work aimed at the evaluation of the dissolution of maraging steel (1.2709) samples obtained via laser-based powder bed fusion (L-PBF) into molten AlSi7Mg (B356.2) through static immersion tests carried out at 720 °C for different times, to evaluate their response to the die-soldering phenomenon. For comparison, forged maraging steel samples were also considered, to investigate the effect of the different microstructure on the dissolution behavior. As well as a conventional H11 steel, to obtain benchmark data. The corrosion resistance of the samples was evaluated by measuring the samples' dimensional variation after the tests. Furthermore, SEM-EDS analysis was carried out to investigate the extent and the composition of the intermetallic layer formed on the samples' surface
On the ageing of a hyper-eutectic Zn-Al alloy
Full text linkZinc alloys are widely used in different fields, like handles and locking, fashion and design as well as automotive or electronics, thanks to their good mechanical and technological properties combined with low cost and easy formability. A limit to a wider use of these alloys is the aging phenomenon that causes a drop in their mechanical properties in time. In order to improve their use in competition with more expensive copper and aluminum alloys, in the last years the research has been addressed to develop new Zn-alloys compositions. One of these new alloys, containing 15 wt% of Aland 1 wt% of Cu, appears to be suitable for both foundry and plastic deformation forming processes, as resulted from preliminary laboratory and industrial trials. Being a newly developed alloy, many properties have still to be investigated, to better understand the effective potentiality for a proper industrial application. In this paper the ageing behavior of die-cast Zn-15Al-1 Cu hyper-eutectic alloy was studied by means of tensile tests and microstructural analyses. It was demonstrated that the alloy suffers from a drop in mechanical properties, in particular at the very beginning of soaking at high temperature. A first analysis of the microstructure by optical and scanning electron microscope was not able to fully point out the causes of the aging phenomenon
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