Al Si System Research Articles

Corrosive Effect of Wood Ash Produced by Biomass Combustion on Refractory Materials in a Binary Al-Si System.

In terms of its chemical composition, biomass is a very complex type of fuel. Its combustion leads to the formation of materials such as alkaline ash and gases, and there is evidence of the corrosive effect this process has on refractory linings, thus shortening the service life of the combustion unit. This frequently encountered process is known as “alkaline oxidative bursting”. Corrosion is very complex, and it has not been completely described yet. Alkaline corrosion is the most common cause of furnace-lining degradation in aggregates that burn biomass. This article deals with an experiment investigating the corrosion resistance of 2 types of refractory materials in the Al2O3-SiO2 binary system, for the following compositions: I. (53 wt.% SiO2/42 wt.% Al2O3) and II. (28 wt.% SiO2/46 wt.% Al2O3/12 wt.% SiC). These were exposed to seven types of ash obtained from one biomass combustion company in the Czech Republic. The chemical composition of the ash is a good indicator of the problematic nature of a type of biomass. The ashes were analyzed by X-ray diffraction and X-ray fluorescence. Analysis confirmed that ash composition varies. The experiment also included the calculation of the so-called “slagging/fouling index” (I/C, TA, Sr, B/A, Fu, etc.), which can be used to estimate the probability of slag formation in combustion units. The corrosive effect on refractory materials was evaluated according to the norm ČSN P CEN/TS 15418, and a static corrosion test was used to investigate sample corrosion.

Effect of the structure and properties of welded zones made of Sv-AK5 welding wire at robotic surfacing

The study covers the effect of welding arc current (47, 57, and 67 A) on the structure and properties of deposited samples obtained by robotic electric arc surfacing. Sv-AK5 (ER4043) welding wire of the Al-Si system was used as a filler material. Surfacing was carried out on a substrate in the form of a 6 mm thick plate made of AMg6 alloy (Al-Mg system). During surfacing, a typical two-phase structure of a hypoeutectic composition is formed in samples typical for Al–Si alloys with a silicon content of 5 %. Along the height of deposited layers, there is a tendency to structure enlargement in the direction from the substrate, which is associated with the accumulation of heat in layers deposited along the height. As welding arc current increases, α-Al-based dendrites and eutectic silicon crystals are refined with an increase in the density and a decrease in the microhardness of deposited samples. The increase in density is due to the reduced proportion and size of gas pores, as well as refined structural components. The decrease in microhardness is associated with the increased proportion of the soft phase (α-Al dendrites) and decreased quantity of hard eutectic silicon crystals. The average content of silicon in samples deposited in three modes is in the range of 5.46–5.91%, which corresponds to the chemical composition of Sv-AK5 (ER4043) welding wire. Higher welding arc current contributes to an increase in the tensile strength and a slight decrease in the offset yield strength and relative elongation. The features of changes in the mechanical properties of deposited samples are determined by of the specific cast structure of deposited layers formed under conditions of directional solidification in the direction from the substrate.

Hereditary Influence of Deformed Waste on the Efficiency of Modification of Alloy Systems Al–Si–Mg and Al–Mg

Hereditary Influence of Deformed Waste on the Efficiency of Modification of Alloy Systems Al–Si–Mg and Al–Mg

Phase Prediction, Microstructure and Mechanical Properties of Fe–Mn–Ni–Cr–Al–Si High Entropy Alloys

The selection of high-entropy alloys (HEAs), which are relatively lightweight and have unique mechanical properties, remains a substantial challenge. In this study, six new HEAs were designed from the relatively low-cost Fe–Mn–Ni–Cr–Al–Si system using Thermo-Calc software, and then manufactured using a casting process. The effects of the atomic ratio of the alloying elements on the microstructures and mechanical properties of these alloys in the as-cast condition were systematically investigated. Brittle body-centered cubic BCC/B2 and silicide phases were found in relatively large amounts in the form of dendritic structure within large equiaxed grains with fine needle-shaped phases in the Fe30Mn15Ni20Cr15Al10Si10 and Fe35Mn15Ni20Cr15Al10Si5 alloys, in addition to the face-centered cubic (FCC) phase. When the contents of Mn and Ni were increased in the Fe35Mn25Ni15Cr15Al5Si5 and Fe35Mn20Ni20Cr15Al5Si5 alloys, the amounts of brittle phases were reduced; however, the ductile FCC phase is not significant. The FCC phase amount, which appeared as a honeycombed structure, was more than enough when the Si content was decreased to 3%. Broad relationships between the chemical composition of the alloys, especially the Si content, and the hardness and compression properties’ measurements were established. As the Si content decreased, both the hardness and compression properties of the resulting alloy also decreased. The experimental observation of the six HEAs matched the equilibrium phases predicted by the Thermo-Calc calculations.

Experimental investigation of Ti–Al–Si phase equilibria at 800–1200 °C

Five partial isothermal sections of the Ti–Al–Si system up to 70 at% Al and 40 at% Si have been determined experimentally between 800 and 1200 °C. Seven alloys were heat-treated for 24–1504 h and characterized utilizing scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential thermal analysis. No ternary phase was found and αTi, βTi, Ti3Al, TiAl, TiAl(1d-APS), TiAl2, TiAl3 are in equilibrium with Ti5Si3. A partial vertical section at 9 at% Si shows that all determined data are consistent with each other.

Structure and corrosion behaviour of CrxAl(Si)yC coatings fabricated by the vacuum arc discharge technique

The composition, structure and corrosion behaviour of CrxAly(Si)C coatings fabricated by the arc discharge techniques using Cr-Al-Si and graphite cathodes were studied. X-ray photoelectron spectroscopy, X-ray energy-dispersive spectroscopy, nuclear reactions, and Rutherford backscattering methods were applied to determine composition of the coating, X-ray diffraction and transmission electron microscopy — to investigate the structure of the coating. Corrosion tests were performed in an electrochemical cell in a 3.5 % NaCl solution. Depletion of the cathode surface of chromium, screening of Cr+ by C+ in plasma, and selective etching of the coating upper layers are accompanied by a decrease of Cr / (Al + Si) ratio in the coatings compared to the cathode. The carbon content (CC) in CrxAl(Si)yC, determined by XPS, EDS and NR, differs by several times. The CC measured by NR correlates with the results of Raman spectroscopy and confirms the existence of a continuous carbon matrix in CrxAly(Si)C. Cr is chemical bonded with carbon, silicon — with carbon and aluminum. The Al-Si system provides the structure feature of CrxAl(Si)yC: a network of aluminum intersects the amorphous matrix. The mechanical mismatch and weak bond between the Al structures and the amorphous matrix may be the reason for the formation of defects in the form of cracks and microchannels along the boundaries.

Atomic Composition and Structure Evolution of the Solid-Liquid Boundary in Al-Si System During Interfacial Diffusion and Contact Melting

Atomic Composition and Structure Evolution of the Solid-Liquid Boundary in Al-Si System During Interfacial Diffusion and Contact Melting

Temperature-Stimulated Morphological Features of Advanced High-Strength Medium-Mn TRIP Steel.

Advanced High-Strength Steels (AHSSs) are one of the most rapidly developing group of Fe-based metallic materials. Their excellent combination of high strength, ductility and formability is due to their complex microstructure and strain-induced martensitic transformation of metastable retained austenite (RA), which favors extra ductility of the sheet steels. A deformation temperature is one of the most important factors affecting the phase transformation behavior in these Fe–C–Mn–Al–Si systems. Therefore, the present study aimed at understanding the temperature-dependent phase transformations and structural phenomena in an advanced medium-Mn–Al-alloyed steel. The 3Mn steel was thermomechanically processed and subjected to tensile testing in a temperature range from 20°C to 200°C. The different extent of the strain-induced martensitic transformation and some softening phenomena of bainitic ferrite matrix were revealed using transmission electron microscopy and electron backscatter diffraction techniques. It was found that the thermal stability of RA is strongly dependent on the deformation temperature. Moreover, the dynamic recovery and carbide precipitation play a key role when the deformation temperature is increased to 140°C and higher temperatures.

Effect of microstructure on the electrical conductivity of p-type Fe–Al–Si thermoelectric materials

Developing cost-effective thermoelectric (TE) materials that do not rely on toxic and expensive elements is crucial to widespread use in practical applications. Earth-abundant Fe3Al2Si3-based thermoelectric materials exhibit moderate thermoelectric properties near room temperature. Hence, improving the thermoelectric properties of these materials may lead to practical applications. In this study, we investigated the microstructural factors controlling the electrical conductivity (σ) in p-type Fe3Al2Si3-based thermoelectric (FAST) material to find ways to improve the TE performance. The σ of a large-grained stoichiometric τ1-Fe3Al2Si3 compound is low, ~1 × 104 Ω–1 m–1 at room temperature, whereas a high σ of ~6.7 × 104 Ω–1 m–1 is obtained in Al-lean alloys. Microstructure observation revealed that the formation of a composite structure consisting of FeSi (ԑ-phase) precipitates dispersed in the τ1-matrix results in an increase in σ while maintaining thermal conductivity and sufficiently high Seebeck coefficient to improve the power factor. We found that the Ohmic-contacted ԑ-phase can modify the surrounding τ1-matrix to an Al-lean τ1-phase, which contributes to the carrier concentration increment and brings six times the enhancement of σ. This led to a power factor of ~880 µW m–1 K–2, more than three times larger than that of the single-phase compound (~250 µW m–1 K–2), the highest for the earth-abundant Fe–Al–Si system. This work demonstrates that the control of τ1-Fe3Al2Si3/ԑ-FeSi composite microstructure is critical to developing a higher power factor in p-type FAST materials.

The Tb‒Hf‒Al‒Si system (600 C)

Information about systematic investigations of quaternary intermetallic systems with rare-earth elements is scarce, therefore studies of such systems are relevant. Alloys of the Tb‒Hf‒Al‒Si system are promising for the creation of new functional materials thanks to their mechanical (due to the presence of Al in the samples), heat-resistant (Hf), semiconductor (Si), magnetic, superconducting, catalytic, and sorption (Tb) properties. The aim of this work was to investigate the Tb‒Hf‒Al‒Si system: establish the phase composition of alloys, search for new phases and determine their crystal structures. Samples of the Tb‒Hf‒Al‒Si system were prepared by arc-melting the elements under a purified argon atmosphere. The alloys were annealed at 600 °C for 7 months in evacuated quartz ampoules, and subsequently quenched in cold water. X-ray powder diffraction data were recorded on a DRON 2.0M diffractometer, Fe K α radiation, a Panalytical X’Pert, Cu K α radiation, and a STOE Stadi P diffractometer, Cu K α 1 radiation. Energy-dispersive X-ray analyses were performed on a Tescan Vega 3 LMU scanning electron microscope. During the investigation of the Tb‒Hf‒Al‒Si system the formation of the quaternary phase (Tb 0.74 Hf 0.26 )(Al 0.48 Si 0.52 ) was established based on X-ray diffraction and energy-dispersive X-ray analysis. The crystal structure of this phase belongs to the TlI type (Pearson symbol oS 8, space group Cmcm , unit cell parameters: а = 4.312(1), b = 10.793(3), c = 3.973(1) Å) with a statistical mixture of Tb and Hf atoms on the I site and a statistical mixture of Al and Si atoms on the Tl site. Based on the results obtained here, the existence in the quaternary system Tb‒Hf‒Al‒Si of extended solid solutions based on other binary, Hf 5 Si 3 (structure type Mn 5 Si 3 , Pearson symbol hP 16, space group P 6 3 / mcm , 10 at. % Tb and 7 at. % Al – (Tb 0.1 6 Hf 0.8 4 ) 5 (Al 0.1 9 Si 0.8 1 ) 3 ), TbAl 2 (MgCu 2 , cF 24, Fd -3 m , 7 at. % Si – (Tb 0 . 94 Hf 0 . 06 )(Al 0 . 90 Si 0 . 10 ) 2 ), TbAl (DyAl, oP 16, Pbcm , 8 at. % Hf and 5 at. % Si – (Tb 0 . 85 Hf 0 . 15 )(Al 0 . 89 Si 0 . 11 )), HfSi (FeB, oP 8, Pnma , 9 at. % Tb and 7 at.% Al – (Tb 0 . 17 Hf 0 . 83 )(Al 0 . 15 Si 0 . 85 )), and ternary, Tb 2 Hf 3 Si 4 (Sc 2 Re 3 Si 4 , tP 36, P 4 1 2 1 2, 18 at. % Al – (Tb 2 . 4 Hf 2 . 6 (Al 0 . 42 Si 0 . 58 ) 4 ), compounds was established. Within the homogeneity ranges of the solid solutions, the value of the valence electron concentration does practically not change. Keywords : Tb‒Hf‒Al‒Si system, X-ray diffraction, energy-dispersive X-ray analysis, solid solution, TlI structure type.

Influence of modification with highly dispersed silicon carbide on the casting properties of the secondary alloy of the Al-Si system

One of the main areas of application of aluminum is the aerospace and transport industries, which are constantly increasing the requirements for the properties of cast products. The use of aluminum as the main material for the manufacture of various parts of vehicles can significantly reduce their weight, which leads to a decrease in fuel consumption. In order to meet the requirements of the modern world, the work considers studies to improve the quality and increase the properties of products from the secondary aluminum alloy AlSi12. Modern technologies for processing liquid aluminum alloy are analyzed. According to the results of an analytical review, it was found that modifiers that affect the size of the primary grain and the shape of inclusions of eutectic silicon are of the greatest interest. It was found that the modification processes do not change the chemical composition of the alloy, but rather contribute to a change in the size and shape of the structural components of the alloy. The paper considers the influence of an ultradispersed SiC modifier with a particle size of up to 200 nm on the casting properties of secondary aluminum alloys: fluidity, linear and volumetric shrinkage. The fluidity was studied in green sand and metal mould. It was found that the addition of 0.1 % SiC improves the fluidity of the secondary alloy from 560 to 630 mm for green sand mould and from 230 to 295 mm for a metal mould due to cleaning from non-metallic inclusions. A further increase in the SiC content to 0.2 % does not lead to an obvious increase in fluidity. The study of linear shrinkage found that increasing the content of the modifier to 0.2 % contributes to its decrease. At the same time, an increase in the pouring temperature of the alloy promotes an increase in the total linear shrinkage, which is associated with the long residence time of the metal in the liquid state. As a result of the rapid crystallization of the melt with additional nucleation centers in the role of which are particles of the ultradispersed modifier, the coefficient of volumetric shrinkage decreases from 28 to 20 %. The proposed technical solutions for the modification of alloys of the secondary alloy AlSi12 can be used in processes that will improve the quality of cast metal products with the economical use of energy resources and materials for its production.

Design, Simulation and Optimization of an Additive Laser-Based Manufacturing Process for Gearbox Housing with Reduced Weight Made from AlSi10Mg Alloy

The gas turbine engine’s (GTE) development aims for the increasing the efficiency, strength, reliability and safety of its components. To create competitive engines, housing parts and components with high functionality and reduced weight are needed. Especially difficult in the design and production are the gearboxes for aviation GTE. Traditional technologies based on precision casting or material forming operations have significant limitations due to the complexity of fulfilling multiple different requirements. Nowadays, one of the progressive production techniques is additive manufacturing. The article presents the results of computational and experimental studies that substantiate the applicability of laser additive technology to reduce the mass of body parts by up to 15% while ensuring their strength properties. The physical and mechanical characteristics of aluminum alloys acceptable for the manufacturing of housing parts were analyzed. The necessary characteristics of the powder alloy of the Al-Si system and the technological parameters of the L-PBF of the modified housing of the gear reducer are established. Using the finite element method (FEM) the L-PBF process was numerically simulated and the technological modes for synthesis of the AlSi10Mg alloy powder were optimized. With the help of a serial 3D printer ProX320DMP, the prototype of a gear housing was manufactured.

Effect of Solidification Rates at Sand Casting on the Mechanical Joinability of a Cast Aluminium Alloy

Implementing the concept of mixed construction in modern automotive engineering requires the joining of sheet metal or extruded profiles with cast components made from different materials. As weight reduction is desired, these cast components are usually made from high-strength aluminium alloys of the Al-Si (Mn, Mg) system, which have limited weldability. The mechanical joinability of the cast components depends on their ductility, which is influenced by the microstructure. High-strength cast aluminium alloys have relatively low ductility, which leads to cracking of the joints. This limits the range of applications for cast aluminium alloys. In this study, an aluminium alloy of the Al-Si system AlSi9 is used to investigate relationships between solidification conditions during the sand casting process, microstructure, mechanical properties, and joinability. The demonstrator is a stepped plate with a minimum thickness of 2.0 mm and a maximum thickness of 4.0 mm, whereas the thickness difference between neighbour steps amounts to 0.5 mm. During casting trials, the solidification rates for different plate steps were measured. The microscopic investigations reveal a correlation between solidification rates and microstructure parameters such as secondary dendrite arm spacing. Furthermore, mechanical properties and the mechanical joinability are investigated.

Fe-Al-Si Thermoelectric (FAST) Materials and Modules: Diffusion Couple and Machine-Learning-Assisted Materials Development.

To lower the introduction and maintenance costs of autonomous power supplies for driving Internet-of-things (IoT) devices, we have developed low-cost Fe-Al-Si-based thermoelectric (FAST) materials and power generation modules. Our development approach combines computational science, experiments, mapping measurements, and machine learning (ML). FAST materials have a good balance of mechanical properties and excellent chemical stability, superior to that of conventional Bi-Te-based materials. However, it remains challenging to enhance the power factor (PF) and lower the thermal conductivity of FAST materials to develop reliable power generation devices. This forum paper describes the current status of materials development based on experiments and ML with limited data, together with power generation module fabrication related to FAST materials with a view to commercialization. Combining bulk combinatorial methods with diffusion couple and mapping measurements could accelerate the search to enhance PF for FAST materials. We report that ML prediction is a powerful tool for finding unexpected off-stoichiometric compositions of the Fe-Al-Si system and dopant concentrations of a fourth element to enhance the PF, i.e., Co substitution for Fe atoms in FAST materials.

The problem of crack formation in thin sublayers of silicon oxide during pulsed heating of interconnects

It is well known that in modern micro- and nanoelectronics thin-film structures are actively used as a gate dielectric, passivating layers, membranes, etc. The research is devoted to the problem of crack formation in thin sublayers of silicon oxide during pulsed heating of interconnects on single-crystal silicon wafers. The purpose of the paper is to study the effect of surface sources of thermal shock on the cracks formation in films and aspects of crack formation in SO2 films have been studied in detail. Experimental verification of the estimates made was carried out on multilayer structures of a silicon substrate-silicon oxide sublayer-aluminum film (Si-SiO2-Al). As substrates, it was used phosphorus-doped silicon single-crystal wafers oriented in the (111) direction, with a resistivity in the range p = 0.1 Ω.сm. The authors studied the temperature fields in silicon wafers (Al-Si system) and silicon oxide wafers (Al-SiO2 system) heated by a surface metallization layer both for the case of a point heat source and for the case of a long rectangular metallization path (provided that the track length significantly exceeds its width). The calculation results showed that the temperature profile of the metallization path (width 75 μm) in the transverse direction is heterogeneous. It was also shown that, in contrast to SiO2 films, the level of appearing mechanical stresses in silicon is insufficient for the formation of cracks near the source of thermal shock. This is due to a higher tensile strength than that of oxide.

Підвищення пластичності сплаву системи Al-Si зі зниженим вмістом кремнію шляхом деформаційно-термічної обробки

A method of deformation-heat treatment is considered for Al-Si alloy with 4.5 % silicon, which consists in a series of small hot deformations with intermediate annealing. The proposed method allows one to achieve grinding and spheroidization of silicon inclusions, which in the cast state have the form of lamellar excreta at the grain boundaries and significantly reduce the plasticity of the material. Spheroidization, grinding and mixing of inclusions that are achieved during this deformation-heat treatment lead to significantly increase the ductility of the alloy without loss of hardness. The processes of structure change during the deformation of aluminum alloys with low Si content are insufficiently studied. In particular, of interest was the possibility of increasing the ductility of such materials by grinding and mixing silicon inclusions during hot deformation. In this case, to prevent a decrease in ductility due appearance of microconcentrators of stress in the form of acute angles of the crushed silicon inclusions, the deformation was carried out as a series of stages with intermediate annealing. In addition, it was assumed that the cyclic change of temperature in this mode will contribute to the spheroidization of fragments of crushed silicon inclusions by changing the solubility of silicon in solid solution from temperature. It is shown that the proposed mode of deformation-heat treatment of these alloys of the Al-Si system allows to significantly increase their ductility – the critical degree of deposition (deposition before cracking) from 67.8 % in the cast state to – 92.1 %. The hardness of the material can be increased by hardening under cold plastic deformation. In this case, since the material after deformation-heat treatment is more plastic, it has greater reserves for hardening in this way. It is shown that owing to hard plastic deformation, the hardness of the material of samples with 4.5 % Si, which has undergone deformation-heat treatment, can increase to values of 95 ± 17 HV, which is significantly higher than in the cast state. At the same time, the hardness (and, probably, strength) of a similar cast material can also be increased due to hardening, but to lower values – 67 ± 12 HV. Key words: aluminum, aluminum-based alloy, deformation-heat treatment, silicon inclusions, plasticity, hardness.

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.

Interfacial Heat Transfer Coefficient in Unidirectional Permanent Mold Casting: Modeling and Inverse Estimation

The thermal control of the permanent mold casting process is highly dependent on the Interfacial Heat Transfer Coefficient (IHTC). Based on that, many works proposed several models in order to estimate its behavior. This work intends to study three IHTC models present in the literature, as well as to propose and analyse two new models. The proposed models are based on two distinct methodologies: thermal resistance method and analytical comparison to the thermal gradient formulation at the metal/mold interface. All these models will be analysed in terms of their ability to reduce the error between the simulated and experimental thermal profiles by using an inverse method and verifying their respective parameter sensitivity based on the relative sensitivity coefficient. It is observed that the exponential formulation model, proposed in this paper, is able to reduce the numerical/experimental error more efficiently than the others methods in all three hypoeutectic alloys of the Al-Si system considered.

The Effect of Coatings on the Oxidation Kinetics of Intermetallic Titanium Alloys of the Ti2AlNb and γ-TiAl Systems

The results of a study of the effect of aluminide coatings of the NiCrAlY and Al(Si) systems on intermetallic heat-resistant titanium alloys VIT1 based on Ti2NbAl orthophase or TNM-B1 based on γ-TiAl on the resistance to isothermal oxidation are presented. The structures, phase, and chemical composition of the coatings after annealing and after high-temperature oxidation at temperatures of 650 and 700°C are considered. The coating layer of the Al(Si) system consisting of TiAl3, TiSi2 and Ti5Si3 sets a barrier for inhibiting diffusion of titanium into the coating layer of the NiCrAlY system, which is based on high-temperature phases of β-NiAl and γ'-Ni3Al, which provide heat resistance.

Composition-dependent dynamic precipitation and grain refinement in Al-Si system under high-pressure torsion

Understanding composition effects is crucial for alloy design and development. To date, there is a lack of research comprehensively addressing the effect of alloy composition on dynamic precipitation, segregation and grain refinement under severe-plastic-deformation processing. This research investigates Al-xSi alloys with x = 0.1, 0.5 and 1.0 at.% Si processed by high pressure torsion (HPT) at room temperature by using transmission electron microscopy, transmission Kikuchi diffraction and atom probe tomography. The alloys exhibit interesting composition-dependent grain refinement and fast dynamic decomposition under HPT processing. Si atoms segregate at dislocations and Si precipitates form at grain boundaries (GBs) depending on the Si content of the alloys. The growth of Si precipitates consumes most Si atoms segregating at GBs, hence the size and distribution of the Si precipitates become predominant factors in controlling the grain size of the decomposed Al-Si alloys after HPT processing. The hardness of the Al-Si alloys is well correlated with a combination of grain-refinement strengthening and the decomposition-induced softening.