| 1. |
- Bogdanoff, Toni, et al.
(författare)
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The effect of SI content on microstructure and mechanical properties of Al-Si alloy
- 2016
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Ingår i: La Metallurgia Italiana. - Milano : Associazione Italiana di Metallurgia. - 0026-0843. ; 108:6
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Tidskriftsartikel (refereegranskat)abstract
- Al-Si alloys are the most popular casting alloys due to their excellent castability combined with high strengthto-weight ratio. This paper investigates the role of Si content in the range of 6.5 wt. % to 14.4 wt. % on the microstructure and mechanical properties of Al-Si-Mg casting alloys. All alloys were modified with 90-150 ppm Sr. No grain refiner was added. The samples were produced by directional solidification providing a microstructure that corresponds to microstructures found in die castings. From the phase diagram and coupled zone, increasing the Si level up to 14.4 wt. % is expected to start a competition between formation of α- dendrites and a fully eutectic microstructure. However, it is known that Sr-modification shifts the eutectic to higher Si contents. For the lower Si contents, the microstructure of the samples consisted of α-dendrites and a modified Al-Si eutectic. At 12.4 wt. % Si and above, a cellular eutectic microstructure was observed. No primary Si was observed even at 14.4 wt. % Si. The mechanical properties in terms of yield and tensile strength did not vary remarkably as a function of the Si level unlike the elongation to failure that dropped from 12 % at 6.5 wt. % Si to nearly 6 % at 14.4 wt. % Si; but still the material is exhibiting an elongation to failure that is far higher than normally expected.
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| 2. |
- Ceschini, Lorella, et al.
(författare)
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Al-Si-Cu alloys for high pressure die casting : Influence of Fe, Mn, and Cr on room temperaturemechanical properties
- 2016
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Ingår i: La Metallurgia Italiana. - Milano : Associazione Italiana di Metallurgia. - 0026-0843. ; :6, s. 77-80
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Tidskriftsartikel (refereegranskat)abstract
- Al-Si-Cu alloys with high Fe content are widely employed in high pressure die casting (HPDC). Even if Feis usually considered an impurity in secondary aluminum alloys, leading to the formation of harmfulintermetallic compounds, it helps in mitigating or eliminating the problem of die soldering. As a result,secondary Al alloys with Fe content of about 1 wt% are commonly employed for the production of HPDCcastings. Aiming to change the morphology of harmful Fe-bearing phases towards less detrimentalmorphologies, proper alloying elements may be added to the alloys. Mn and Cr (both present in thealuminum scrap), as instance, are reported to prevent from the formation of the acicular β-Al5FeSi phase,leading to the formation of more compact and polygonal intermetallics. Such phases are usually referredto as “sludge” particles. The influence of sludge particles on mechanical properties of Al -Si-Cu castings isstill under investigation. The present work aims at evaluating the effect of impurities (Fe, Mn and Cr)typically present in secondary Al alloys on the microstructure and mechanical properties of the A380 (Al -Si-Cu) alloy. Samples with different Fe, Mn and Cr content were produced and processed through adirectional solidification equipment to obtain specimens with controlled SDAS (~10 μm). Hardness androtating bending fatigue tests were carried out at room temperature. Mechanical properties of the alloyswere then related to the microstructure, analyzed by optical and scanning electron microscopy.
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| 3. |
- Eck, Joakim, et al.
(författare)
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Investigation of Pressure Distribution during Flow Regulation with a Stopper and Associated Mould Level Stability in a Continuous Cast-ing Simulator based on Liquid Metal
- 2022
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Ingår i: La Metallurgia Italiana. - : Associazione Italiana di Metallurgia. - 0026-0843. ; 113:1, s. 42-51
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Tidskriftsartikel (refereegranskat)abstract
- Stopper systems are widely used in the Continuous Casting (CC) process to control the steel flow from the tundish to the mould during casting of high-quality grades. The flow regulation region is subjected to severe under-pressures and generation of pressure fluctuations, especially around the narrowest gap and the tip of the stopper. This can lead to issues with air infiltration through the refractory materials, adverse flow regimes or even cavitation, which can lead to inclusions and level instabilities in the mould. Acquiring knowledge of such pressure distribution requires data from measurements which are difficult to conduct in the hostile high-temperature and corrosive environment of liquid steel in the plants.In this work, the pressure distribution is investigated in a Continuous Casting Simulator (CCS) based on a eutectic Bismuth-Tin alloy (Bi 58%-Sn 42%) with a low melting point (137 degrees C) equipped with a stainless-steel stopper rod. The pressure distribution is investigated through direct pressure measurements at two different points; a) Direct pressure measurement by sensor installed flush at the stopper-tip side and b) Indirect pressure measurements of back-pressure in the stopper argon line. The argon flow varied between 0 to 6 l/min, while casting speed varied between 0.6 to 1 m/min for a 1200 x 220 mm mould size.Results show that considerable under-pressures take place in the flow regulation region, reaching levels as low as 6.6 and 80 mbar absolute pressure at the stopper tip side and argon line. There was a detectable difference in pressure between the direct pressure measurements and additional argon line measurements. Ultimately, it could be concluded that the argon line pressure measurements; often used as industrial standard for ensuring positive pressures in the casting system, generally overpredicts the pressure in the system. This could lead to inappropriate argon settings for a caster, generation of unwanted inclusions and mould level instabilities. It was additionally possible to acoustically detect the onset of cavitation in the liquid metal.
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| 4. |
- Farooq, Muhammad, et al.
(författare)
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Influence of long time ageing on ductility and toughness in the stainless steel 310 in the presence of banded microstructure
- 2012
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Ingår i: La Metallurgia Italiana. - 0026-0843. ; 104:11-12, s. 33-38
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Tidskriftsartikel (refereegranskat)abstract
- During service at elevated temperatures extensive formation of particles can take place that can have a dramatic influence on mechanical properties. Precipitation of sigma-phase and M23C6-carbides have been studied both experimentally and with thermodynamic modelling for 25Cr20Ni austenitic stainless steels (AISI 310) at 800 degrees C for up to 5000 h. Previous work has demonstrated that the modelling could describe the nucleation and growth satisfactory. After long term ageing the particles form bands in the microstructure. In the present paper the influence of these bands on ductility and toughness at room temperature is analysed. For this purpose previously developed models for ductility and toughness are utilised. Model values for banded and non-banded microstructures have been generated for casts of 310 in fine and coarse grained conditions with 0.04 and 0.12%N The model values show that in the coarse grained condition, no reduction in ductility and toughness can be expected in the banded microstructure. In the fine grained condition a modest reduction is predicted.
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| 5. |
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| 6. |
- Heikkila, I., et al.
(författare)
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Comparison Between Microstructures, Deformation Mechanisms and Micromechanical Properties of 316L Stainless Steel Consolidated by Laser Melting
- 2018
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Ingår i: La Metallurgia Italiana. - 0026-0843. ; :3, s. 5-11
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Tidskriftsartikel (refereegranskat)abstract
- A powder bed fusion laser technique (PBF-LS) was used to fabricate 316L stainless steel specimens for characterization of microstructures and micromechanical properties under uniaxial loading in-situ in a scanning electron microscope (SEM). Correlations between the microstructure, deformation mechanisms and mechanical properties were investigated. The results show that the morphology of the microstructure is very different when the sample building orientation was altered. In tensile test specimens that were machined from horizontally oriented rectangular beams, smaller grains and a more deformed microstructure were observed. Under uniaxial loading the yield strength and initial work hardening rate was highest in the horizontally built specimens. The uniform and total elongation was better for tensile test samples that were machined from vertically built rectangular specimens. Slip and twinning were the dominant deformation mechanisms with correlation to the observed texture. The observed anisotropic mechanical behavior can be explained by the differences in the distribution of deformed and sub-structured microstructures along the strain path.
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| 7. |
- Hryha, Eduard, 1980, et al.
(författare)
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Surface Oxide State on Metal Powder and its Changes during Additive Manufacturing: an Overview
- 2018
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Ingår i: Metallurgia Italiana. - 0026-0843. ; 110:3, s. 34-39
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Quality and usefulness of the powder for additive manufacturing (AM) are strongly determined by the surface composition of the powder. In addition, taking into account harsh conditions during AM process, significant changes in the powder surface chemical composition are taking place, limiting powder recyclability. Hence, knowledge concerning amount of oxides, their composition and spatial distribution on the powder surface determines further powder recycling. This communication summarizes possibilities of qualitative and quantitative analysis of powder surface chemistry by surface-sensitive chemical analyses using XPS and HR SEM coupled with EDX. The effect of alloy composition, AM process applied and powder handling on the surface composition of the powder are addressed. Results indicate significant enrichment in the thermodynamically stable surface oxides in case of high-alloyed powder for both, EBM and LS processes. A generic model for the oxide distribution, depending on the alloy composition and powder surface degradation during AM manufacturing, is proposed.
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| 8. |
- Jarfors, Anders E.W. 1963-, et al.
(författare)
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Comparison between high-pressure die-cast and rheo-cast aluminium-SICp MMC; wear and friction behaviour
- 2021
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Ingår i: La Metallurgia Italiana. - : Associazione Italiana di Metallurgia. - 0026-0843. ; :11-12, s. 13-18
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Tidskriftsartikel (refereegranskat)abstract
- Aluminium is essential in automobile industry together with cast iron. Because of its lightweight property and good mechanical properties, aluminium reinforced with silicon carbide have found application as brake discs. Aluminium reinforced with 15%and 20% silicon carbide were high-pressure die-cast (HPDC) and Rheo-HPDC cast in the current paper. Micro-Vickers hardness and Rockwell C hardness showed different trends with the increasing amounts of SiCp-particles. Scratch resistance of the surface on micro-scale was analysed using a micro-scratch test to study the mechanics of the wear process. Reciprocating sliding wear of the composites was considered, using the HPDC cast aluminium with 20% silicon carbide of liquid casting as the sliding surface. The wear showed a combination of abrasive wear and adhesive wear. The metallography of the wear surfaces showed deep abrasive wear grooves. Wear debris from both the surfaces were forming a tribolayer. The formation of this layer decided the friction and wear performance as a result of the abrasive and adhesive wear mechanisms seen both in the micromechanics of the scratch test and in the friction behaviour.
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| 9. |
- Jarfors, Anders E. W.
(författare)
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Yielding and failure of hot chamber die cast thin-walled AZ91D
- 2016
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Ingår i: Metallurgia Italiana. - Milano : Associazione italiana di metallurgia. - 0026-0843. ; 108:6, s. 53-56
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Tidskriftsartikel (refereegranskat)abstract
- Thin-walled components in AZ91D magnesium are commonly cast using hot chamber die casting. AZ91D mechanical properties commonly show scatter and its low critically resolved shear stress cause early yield with an ill-defined yield point. This may result in large differences between the true yield point or proportionality limit and the off-set proof stress. The current study takes a look at this and its relation to the failure of the component. The material investigated was a hot chamber die cast material with a wall thickness of 0.8mm. Tensile tests were made and the proportionality limit and off-set proof stress was established as well as elongation to failure and tensile strength. The overall average off-set proof stress was 154 MPa and the overall proportionality limit was 63 MPa resulting in a typical property Stress Gap of 91MPa. This difference varied from 65MPa up to 105MPa. The Apparent Toughness was also evaluated The Stress Gap and Apparent Toughness was analysed and the influence of process parameters established.
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| 10. |
- Khadhraoui, S., et al.
(författare)
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A new approach for modelling and control of dephosphorization in BOF converter
- 2018
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Ingår i: La Metallurgia Italiana. - : Associazione Italiana di Metallurgia. - 0026-0843. ; 110:11-12, s. 5-16
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Tidskriftsartikel (refereegranskat)abstract
- In the BOF process, the accurate control of Phosphorous removal up to ultra-low values is very important to ensure a high quality of the end–product. This has proven to be associated with several challenges, leading to a preferred usage of high priced low P iron ores. Thus, in the scope of the European BOFdePhos project, important thermodynamic and kinetic aspects of the dephosphorisation reaction such as the effect of solid phases on Phosphorous distribution and lime dissolution in a foamy slag were investigated. It was found that BOF slags are heterogeneous during a large period of the blow and also at the end of blow in most cases. The type and amount of solid phases is strongly affected by temperature and minor oxides content such as MgO-, MnO- and Al2O3-content. The consideration of solid phases formation in the slag, especially the P dissolving C2S_C3P phase, is crucial for a successful modelling and control of dephosphorisation. However, most of the Phosphorous distribution equations available in the literature were developed for homogeneous slags. Thus, a new approach for thermodynamic modelling of the P-distribution between a heterogeneous slag and liquid iron covering the total blowing period in converter was developed and incorporated in a kinetic dephosphorisation model. It was found that while the P distribution in a fully liquid slag was a strong function of temperature, CaO- and FeO-content, the P distribution in a heterogeneous slag depended further on temperature but also on the amount of solid phase as well as the basicity of the liquid slag phase. Even though the C2S_C3P phase can dissolve high amount of Phosphorous, the P-dissolution in the solid phase in the industrial process is associated with strong kinetic limitations. New strategies for the enhancement of dephosphorization control in the BOF converter, focusing on using the potential of the solid phase in removing Phosphorous, were developed.
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