High-silicon Alloy Research Articles

Effect of Al–Fe–Mn–Si particle characteristics on the growth morphology and corrosion resistance of anodic oxide film on AA 3003 aluminium alloy

This study examines the impact of Al–Fe–Mn–Si particle characteristics in AA3003 alloy on the morphology and resistance of anodic oxide films against corrosion. The results show that low-silicon-content Al–Fe–Mn–Si particles oxidise simultaneously with the matrix to form a discontinuous porous oxide film, and complex small pores are formed in the porous layer; although high-silicon-content Al–Fe–Mn–Si particles have the same oxidation rate as the alloy matrix, the growth of the oxide film is hindered by unoxidised particles in the porous layer due to the influence of particle size and chemical composition, resulting in uneven growth of the oxide film and ultimately causing defects such as enlarged pores and cracks. A mechanism model for Al–Fe–Mn–Si particles affecting the morphology of oxide film growth was established. Electrochemical test results show that compared with the oxide film of the high-silicon-content alloy, the oxide film of the low-silicon-content alloy has better corrosion resistance performance, with a corrosion potential of −0.512V (compared with −0.836V for the high-silicon alloy) and a corrosion current density of 3.34 × 10−8A/cm2 (compared with 9.614 × 10−7 A/cm2 for high-silicon alloy). The barrier layer attained an elevated impedance value and exhibited self-repairing capabilities.

Effect of laser remelting on the microstructure and properties of the aluminum high silicon alloy coating

An aluminum high silicon alloy coating with the composition of AlSi30Cu5 was prepared by the plasma spraying technology, and the coating was remelted by laser remelting process. The microstructure, mechanical properties and wear resistance of the coatings were systematically investigated. After the laser remelting, the defects of the sprayed coating were eliminated, the microstructure was dense and uniform, the porosity decreased from 3.66% to 0.37%, and the phases had not changed. The hardness and elastic modulus increased by 20.7% and 23.3% respectively, the fracture toughness increased by nearly 7 times, and the wear rate decreased by about 37.8%. Therefore, laser remelting can effectively improve the microstructure distribution and enhance the wear resistance of aluminum high silicon alloy coating.

Formation and Use of the Waste of High-Silicon Alloy Production

Formation and Use of the Waste of High-Silicon Alloy Production

Production of Special Coke for Electrofurnace Production of High-Silicon Alloys

Production of Special Coke for Electrofurnace Production of High-Silicon Alloys

Tapping Gas from the Silicon Submerged Arc Furnace: An Industrial Measurement Campaign

Producing high-silicon alloys in submerged arc furnaces (SAF) involves the generation of an intermediate process gas, consisting of silicon monoxide (SiO) and carbon monoxide (CO). Combustion of process gas from the taphole can be an environmental challenge. SiO gas burns to fine SiO2 particles which can cause poor working conditions and fugitive particulate matter emissions. The high combustion energy of SiO and CO is a source of high heat load. It is also the source of thermal NOX generation. A measurement campaign was conducted at the Elkem Thamshavn plant in Norway to investigate the composition of tapping gas from a silicon furnace. Over a 3-day period, the gas extracted from the tapping of the furnace was analyzed with Agilent Micro-GC, Protea atmosFIR, and Testo 350. The dust concentration in the gas was measured with a LaserDust instrument from NEO Monitors. Using the plant’s existing flow and temperature measurements, mass and energy flows were calculated. Linear regressions were calculated for three predictors of NOX formation in the taphole gas. From these calculations, the relation between total energy added to the tapping gas and NOX showed the best correlation.

Study of one-step and two-step quench and partition heat treatments on a medium carbon high silicon alloy using dilatometry

This study evaluated the microstructural evolution in a medium carbon high silicon steel during one-step, and two-step quench and partition (Q&P) processes using dilatometry experiments. The two-step Q&P process was carried out using different quench temperatures ranging from 180 to 260 °C. In the one-step process, Q&P heat treatment samples were held isothermally for ten minutes after quenching at specified temperatures ranging between 200 and 4°50 C. The two-step Q&P process yielded a higher fraction of retained austenite than a one-step Q&P process. During the isothermal hold step, the volume expansion due to carbon partitioning and austenite decomposition behavior was interpreted by experimentally determined strain values. For the one-step Q&P process, the austenite decomposition kinetics above and below the Ms temperature differed, as evidenced by the JMAK parameters. The TTT diagram generated for the one-step Q & P process showed a “swing back” at a temperature of around 355 °C.

Effects of silicon and manganese content on the oxidation behavior of FeMnSiCrNi alloys and the correlation between Mn-depleted zone, surface roughness and oxidation resistance

Manganese and silicon effect on high-temperature cyclic oxidation was evaluated in three austenitic shape-memory FeMnSiCrNi alloys, including a novel high-silicon alloy (Fe-17Mn-8Si-10Cr-4Ni-NbC). Mass variation, Mn-depleted zone and metal/oxide interface roughness analyses were used to study the oxidation behavior. Renewed mass gain after spallation was observed for Fe12Mn5Si and Fe17Mn5Si alloys, while Fe17Mn8Si continuously lost mass, associated with low metal/oxide interface roughness and the ferritizing potential of Si. Low manganese availability led Fe12Mn5Si to suffer internal oxidation and iron oxide formation. Here, neither increasing silicon nor reducing manganese increased cyclic oxidation resistance of the alloys.

Surface formation of plasma-electrolytic cobalt-containing coatings on piston alloys of aluminum

Based on the review of functional coatings on piston alloys of aluminum, a conclusion was made on the feasibility of using oxide coatings to increase the strength and durability of parts of the piston group of internal combustion engines. It is shown that the synthesis of the oxide layer on alloys of the Al-Si system (silumins) can be carried out by plasma electrolyte treatment in alkaline electrolytes with the addition of salts of dopant metals, in particular cobalt. This will allow to obtain coatings that have activity in the processes of catalytic combustion of fuel. It is proposed to form cobalt-containing oxide coatings on piston alloys by plasma-electrolytic oxidation in the electrolyte of 0.4 mol/dm3 K4P2O7, 0,1 mol/dm3 CoSO4 at current densities of 3–5 A/dm2 in the “decreasing power” mode. It is established that under these conditions during 15 min of oxidation on high-silicon alloys AL30 and AK21 an oxide layer with a content of up to 4.7 at.% Co is formed. The presence of up to 6.4 at.% of phosphorus in the synthesized coating will increase the heat resistance of the oxidized surface. At the same time, the silicon content in the surface layers decreases 4–5 times compared to the source material. It is shown that the morphology and phase composition of the coating changes with the incorporation of the additive component into its composition. The inclusion of cobalt occurs in the form of thermodynamically stable oxide Co3O4 (CoO·Co2O3), which crystallizes in the spinel crystal cell. This, along with a high degree of surface development is a prerequisite for improving the functional properties of the obtained oxide layers. The developed method was used for applying a cobalt-containing coating on the surface of a piston made of alloy AL30. It is established that in order to obtain a uniform oxide layer, certain technological parameters should be observed. The predicted use of a piston coated with cobalt-containing oxide coating will reduce the amount of toxic substances with exhaust gases and hourly fuel consumption, which is promising for intracylinder catalysis.

Mechanical Properties and Impact Toughness of Molybdenum Alloyed Ductile Iron

Grades of high silicon ductile iron offer excellent combinations of static strength and ductility as well as good machinability due to their fully ferritic, solution strengthened matrix. As a result of elevated silicon contents, however, the ductile-to-brittle transition temperature in the Charpy impact test is significantly increased. Thus, minimum required Charpy impact energies cannot be met for many applications by using high silicon ductile iron. Therefore, alloys with lower strength and higher toughness properties are commonly used for many technical applications. The enormous lightweight construction potential of high silicon ductile iron can therefore not be fully exploited. The present investigation pursues the metallurgical approach of partially substituting silicon with molybdenum as an alternative strengthening element in order to improve the toughness properties while maintaining similar static mechanical properties. Molybdenum serves as a carbide-stabilising element in ductile iron, while simultaneously promoting ferrite formation and is therefore regarded to be suitable alloying element. In Charpy impact tests, the ductile-to-brittle transition temperature could be reduced by about 55 °C by reducing the silicon content to 2.95 wt% and adding 0.21 wt% molybdenum compared to a high silicon alloy. Additionally, it was possible to mathematically describe the transition behaviour of the studied alloys using nonlinear regression functions and to achieve a sufficient correlation of empirically determined and calculated data. This present metallurgical concept offers a promising metallurgical tool for further improving the toughness properties of alloyed ductile iron.

Effect of Tempering Temperature on Microstructure and Properties of Low Carbon High Silicon Alloy Steel Treated by Q-P-T Process

The mechanical properties and microstructure of low-carbon high-silicon alloy steel were examined under various tempering temperatures using the quenching, partitioning and tempering (Q–P–T) process. The performance changed with the variation in tempering temperature. The results show that the microstructure of low carbon high silicon alloy steel treated by Q-P-T process was mainly ferrite, martensite, carbide-free bainite and film-like retained austenite. This alloys exhibited good mechanical properties at tempering temperature of 300 °C. The product of strength and elongation were 33.7 GPa%. Specifically, the Ultimate tensile strength were 1508 MPa, the yield strength were 1048 MPa, and the elongation were 22.4%. At this temperature of 300 °C, the volume fraction of retained austenite reached 10.4%.

Wear behaviour analysis of medium carbon high silicon alloy steel at different process parameter

ABSTRACT In railway wheel, track and mechanical component major issue losses of material due to rolling contact and sliding contact. A dual-wear type wear testing machine has been designed and developed, in which two discs rotate perpendicular to each other in the same direction with different velocity. In this machine bot type of wear, we can calculate rolling as well as sliding. As a result, the outer most peripheries of these discs are in symmetrical rolling contact. Discs were made up of medium carbon high silicon alloy steel with different treatments performed and were rubbed against each other rolling and sliding wear test performed in dissimilar metal also. All combinations of discs were tested including the same metal pairs. In similar metal combinations, the wear characteristics depended on the surface properties and microstructure, but not on the material hardness. Wear characteristics of material test performed on different surface treated sample by self-developed dual-wear testing machine Experimental data listed in this research paper. Characterisation of material/samples with field emission scanning electron microscopy and atomic force microscopy.

Tensile behaviour of thermally-stable nanocrystalline bainitic-steels

The deformation behaviour of two nanostructured bainitic steels designed specifically to ensure the thermal stability of the retained austenite present alongside the bainitic ferrite, has been studied as a function of test temperature. One of the alloys is especially rich in silicon whereas the other in nickel. Surprisingly, the alloys are found to have greater ultimate tensile strengths and ductility when tested at 200 °C, compared with corresponding tests at ambient temperature. This is demonstrated to be a consequence of the more gradual deformation-induced transformation of the retained austenite at 200 °C. In contrast, there is a dramatic reduction in both strength and uniform ductility during testing at 450 °C. Some carbides precipitate during testing of the high-silicon alloy, thus making the austenite less stable to both thermally and mechanically. The high-nickel alloy suffers from the same fate but for different reasons, that the austenite actually grows at the 450 °Ctest temperature, leading to a reduction in its thermodynamic stability.The experimental data on the stability of the retained austenite both at the test temperature and during cooling from that temperature have been modelled.

Effect of Silicon and Graphite Degeneration on High-Temperature Oxidation of Ductile Cast Irons in Open Air

The use of high silicon ductile irons is increasing as they offer some advantages with respect to conventional pearlitic–ferritic grades such as high elongation at rupture for a given tensile strength value and a fully ferritic matrix. Besides addressing mechanical requirements, some castings must fulfil corrosion and high-temperature oxidation requisites. Two different ductile cast irons with silicon contents of 2.04 and 5.21 wt% were used so as to comparatively study their mechanical properties and high-temperature oxidation responses. The structure of both alloys contains nodular graphite and a fully ferritic matrix. Some samples of the alloy with 5.21 wt% silicon also contain abundant degenerated graphite which was identified as Chunky graphite. Oxidation resistance of both materials was evaluated by exposures to air at 650 °C for 720 h using a tubular furnace. The alloy with 5.21 wt% silicon showed an oxidation resistance about three times higher than the low silicon alloy. Although both alloys showed similar oxidation mechanisms, the oxidation scale formed on the high-silicon alloy stands out for having lower thickness, higher silicon content in the metal/oxide interface and more compact and adherent layers. Samples with Chunky graphite showed a similar evolution to those with graphite nodules, so no negative effect from this graphite degeneration on oxidation process was observed. The analyses performed by XRD revealed the presence of fayalite in the 5.21 wt% Si alloy, which is responsible for the better oxidation resistance.

Features of thermal expansion of special-purpose aluminum alloys after treatment of melt and heat treatment

A combination of corrosion resistance, low specific gravity, and high dimensional stability over a wide temperature range is necessary for alloys for special purpose. The dimensional stability is determined, first of all, by the low temperature coefficient of linear expansion (TCLE). The paper presents the results of studies on the effect of melt treatment on TCLE of aluminum alloys for special purpose on the basis of the system Al-(11÷40)%Si. It is shown that melt treatment with an aqueous solution of CuSO4 and modification of melt with a mixture of (CaCO3⋅MgCO3) leads to the decrease in TCLE for all alloys under consideration in the low-temperature test interval ttest = 50÷150 °C. Treatment of the melt by CO(NH2)2 vapours leads to the decrease of TCLE of alloys Al-40%Si in the whole temperature range from 50 to 450 °C. For high silicon alloys it is established that the decrease in TCLE occurs in the interval ttest = 350÷450°C after additional heat treatment

On-line electrolytic dissolution for soluble aluminium determination in high-silicon steel/electrical sheet by ED-FIA-ICP-OES

Soluble aluminium (Al(sl)) in high silicon alloys is determined by electrolytic dissolution flow injection analysis (ED-FIA) and inductive coupled plasma with optical emission spectrometry (ICP-OES). Skipping the time consuming sample preparation known from acid hydrolysis reduces the required time per determination from 15 to 4 min. A new calculation procedure is used to compensate the discrepancy in matters of dissolution between acid hydrolysis and electrolytic dissolution. Samples with a known silicon content (2,5 and 3,1 wt%) are used to determine the differences of dissolved material and to calculate a correction factor. In a working range of 200–350 ppm aluminium in high silicon steel, there is a standard deviation of 7 ppm for a measurement series of 19 samples (max deviation 19 ppm).

Basic parameters in the operation and design of submerged arc furnaces, with particular reference to production of high-silicon alloys

Basic parameters in the operation and design of submerged arc furnaces, with particular reference to production of high-silicon alloys

Carborundum-bearing reducing agents in high-silicon alloy production

The creation of a new class of carbon reducing agents containing 40–95% carborundum is considered. The carbon is derived from a wide range of natural and industrial materials, including mill siftings, coke, semicoke, high-ash coal, and coal-enrichment wastes. By two-stage production—first of carborundum-bearing reducing agents and then of high-silicon alloys—the range of possible raw materials may be markedly expanded, and the costs of materials and energy in alloy production may be significantly reduced.

Improved Performance and Reduced Cost through Advanced Electrode Drying Technology

The commercial success of lithium ion batteries hinges on significant improvements in both cost and energy density. The electrode coating operation presents the highest leverage opportunity to address both challenges. Navitas ASG with Lambda Technologies has recently demonstrated and scaled up a patent-pending advanced drying process (ADP) technology that breaks through the limitations on electrode thickness and drying rate that are inherent in the present coating technology. This technology can improve electrode loading by at least 50% and accelerate coating rates by >2X. The technology is drop-in compatible with capital equipment in operation at battery OEM plants. The technology will enable cathodes that can match emerging high capacity silicon alloy anode materials. The expected impact of this technology will be >20% improvement in the cell level Wh/kg and 8% reduction in the system level EV battery cost. Microwave drying introduces key advantages over radiant and convective cooling for electrode drying (figure 1). Microwaves efficiently transfer energy through selective absorption by polar solvent (e.g. NMP) or water molecules. Microwave energy is also uniformly deposited through the bulk of the coated electrode. Electrode drying, however, introduces two barriers to use of microwave energy: avoiding arcing with the presence of metal foil current collectors, and supporting roll-to-roll coating without leakage of the microwave field through the coating web entry and exit ports. Navitas worked with a microwave processing company Lambda Technologies to resolve these barriers through the use of variable frequency microwaves (VFM). VFM-dried electrodes were validated by Navitas through accelerated life testing and failure analysis of prototype cells. Navitas worked closely with Lambda to design a VFM module able to support continuous web drying operation – a key challenge. Navitas installed a VFM module onto our Toyo WI pilot coating line and performed pilot scale electrode coating validation for several established commercial anode and cathode formulations to demonstrate accelerated drying with the absence of any deleterious effects on the electrode. The work by Navitas also involved the production of state of the art commercial baseline (i.e. non-VFM dried) benchmark electrodes. The VFM process showed significant advantages, with drying acceleration of >2X for NMP and >5X for water borne slurries. Thorough evaluation of adhesion, cohesion, conductivity, binder distribution etc. has shown the VFM electrode physical properties are as good as or better than the baseline (identical electrode coating passed through coater at lower speed with VFM module toggled off). The Navitas pilot coating trials validated potential cost savings and provided data for presentation to prospective commercial partners to establish confidence that existing coating lines can be retrofitted with VFM. In the course of the validation runs the Navitas team observed that VFM electrodes showed significantly less binder segregation than conventionally dried electrodes. This is attributed to the fact that VFM deposits the drying energy more uniformly in the bulk of the electrode. Uniform energy distribution enables transport of the solvent to the surface as vapor phase rather than as a liquid that drags dissolved or suspended binder to the surface where radiant/convective drying energy transfer predominates. Our observation of reduced binder segregation led to the realization that the critical-to-quality features that limit the ability to coat cathodes at loadings >5mAh/cm2 in high volume production are greatly improved in the VFM process. These limitations include poor adhesion to the current collector (binder deprivation), cracking due to residual stress (binder deprivation), and defects or performance limitations associated with excess binder at surface. Data will be presented comparing VFM electrodes to commercial state of the art electrodes for electrode loading ranging from 3 to 8 mAh/cm2 Figure 1

Thermal conductivity and mechanical properties of pitch-based carbon fibre reinforced aluminium composites fabricated by squeeze casting

Pure aluminium and high-silicon aluminium alloy were reinforced with the discontinuous pitch-based carbon fibres by squeeze casting, then the thermal conductivity and the mechanical properties of the composites were investigated. Optical microscopy revealed that the fibres were in a random planar arrangement, and the transmission electron microscopy revealed that there is no interfacial reaction between the matrices and the fibres. The random planar arrangement of the fibres leads to the anisotropy of the composite. The fibre-reinforcement increased the thermal conductivity in the parallel direction for both pure aluminium and its alloy matrices, while the thermal conductivity decreased in the vertical direction. The increase in the elastic modulus by the reinforcement was not observed for both matrices. The proof stress of the pure aluminium increased by the reinforcement especially in the parallel direction, while that of the high-silicon alloy decreased by the reinforcement.

An investigation into the friction and wear mechanisms of aluminium high silicon alloy under contact sliding

This paper investigates the friction and wear of aluminium high silicon alloy Al-60Si against EN26 steel. The sliding tests were conducted on a pin-on-disk tribometer and the mechanisms of deformation induced by contact sliding were analysed by SEM and EDS. It was found that subsurface deformation and cracks in silicon particles play a central role in the mechanism variation of friction and wear. Under a low load, cracks appeared beneath the wear track. Matrix extrusion over the wear track took place, resulting in ductile abrasive wear. With increasing the applied load, the matrix material was sheared more, which reduced the extrusion and changed the wear mode to brittle delamination. When the load reached a critical value, deformation and severe cracking appeared in the deeper subsurface and the matrix softened due to frictional heating, leading to accelerated wear. Upon a further increase of the applied load, mechanical mixing of finely fragmented silicon particles took place, and the wear mode experienced a number of changes from “ductile delamination + abrasive”, “brittle delamination/ploughed + abrasive” to “abrasive + ductile delamination”.