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The primary cause of the decrease in thermal conductivity of conventional thermal conductive magnesium alloys is electron scattering brought on by solute atoms. However, the impact of phase interface on thermal conductivity of magnesium alloys is usually disregarded. This study has developed a Mg-Si-Zn-Cu alloy with high thermal conductivity that is distinguished by having a very low solute atom content and a significant number of phase interfaces. The thermal conductivity of the Mg-1.38Si-0.5Zn-0.5Cu alloy raises from its untreated value of 133.2 W/(m·K) to 142.2 W/(m·K), which is 91% of the thermal conductivity of pure Mg. This is accomplished by subjecting the alloy to both 0.8wt% Ce modification and T6 heat treatment. The morphology of eutectic Mg2Si phase is changed by Ce modification and heat treatment, and as a result, the scattering of electrons at the Mg2Si/Mg interface is reduced, resulting in increase of the alloy's thermal conductivity.

In this work, the influence of pulse voltage on the corrosion resistance of Al-4.5Mg-3Si alloy was investigated using an electrochemical workstation, scanning electron microscope, x-ray diffraction, and laser scanning confocal microscope. The results have shown that the Mg2Si phase in Al-4.5Mg-3Si alloy changed from a long strip to a short rod after electric pulse treatment, which was discontinued in grain boundary, thereby increasing the corrosion resistance of Al-4.5Mg-3Si alloy. Through theoretical calculation and derivation, the approximate quantitative relationship between the nucleation rate and the pulse voltage is obtained, that is, an e-exponential relationship between the square of the nucleation rate and the pulse voltage. Compared with the sample without electric pulse treatment, the average corrosion rate of the treated sample was reduced from 329.4992 to 119.1134 g/m2 h, the corrosion potential of Al-4.5Mg-3Si alloy increased from − 1.3271 to − 1.2764 V, and the corrosion current density decreased from 1.2726 × 10−5 to 1.0160 × 10−5 A cm−2. [ABSTRACT FROM AUTHOR]

• A novel Mg-Si-Zn-Cu alloy with high thermal conductivity of 142.2 W/(m·K) was obtained by minimizing electron scattering at Mg/Mg 2 Si interface. • It was discovered that Cu and Ce can synergistically metamorphose Mg 2 Si, and the heterogeneous nucleation theory of CeCu 2 Si 2 was proposed. • The quantitative relationship between the thermal conductivity of the alloy and the phase morphology was constructed, and the validity of the model was demonstrated. The primary cause of the decrease in thermal conductivity of conventional thermal conductive magnesium alloys is electron scattering brought on by solute atoms. However, the impact of phase interface on thermal conductivity of magnesium alloys is usually disregarded. This study has developed a Mg-Si-Zn-Cu alloy with high thermal conductivity that is distinguished by having a very low solute atom content and a significant number of phase interfaces. The thermal conductivity of the Mg-1.38Si-0.5Zn-0.5Cu alloy raises from its untreated value of 133.2 W/(m·K) to 142.2 W/(m·K), which is 91% of the thermal conductivity of pure Mg. This is accomplished by subjecting the alloy to both 0.8wt% Ce modification and T6 heat treatment. The morphology of eutectic Mg 2 Si phase is changed by Ce modification and heat treatment, and as a result, the scattering of electrons at the Mg 2 Si/Mg interface is reduced, resulting in increase of the alloy's thermal conductivity. [ABSTRACT FROM AUTHOR]

Recent research has shown that some intermetallic compound particles with high interfacial hydrogen trap energies (e.g., Mg2Si) are prone to damage at high hydrogen concentrations. In this study, the acceleration of particle damage in an A6061 alloy was observed in-situ via X-ray CT. The damage behavior of the particles that are located in the crack tip stress field, where high stress triaxiality causes a local increase in the hydrogen concentration, was analyzed. The influence of hydrogen on the damage behavior of the dispersed Mg2Si particles was investigated by preparing a material charged with hydrogen to achieve extremely high hydrogen concentration, and further hydrogen enrichment in a crack tip region was also utilized. Interfacial debonding of Mg2Si particles was frequently observed in the vicinity of a crack tip immediately prior to tensile fracture. Even though the fracture is typical of ductile fracture, hydrogen accelerates particle damage and reduces the macroscopic ductility of the aluminum alloy. This can be considered as a form of hydrogen embrittlement of aluminum alloys. Even in materials with relatively low hydrogen concentrations (0.85 mass ppm), interfacial debonding occurred in the hydrogen-enriched crack tip regions. A higher hydrogen concentration promoted interfacial debonding over a wider range of particle sizes and particle shapes. It can be inferred that localized hydrogen enrichment, which is expected to occur due to external hydrogen exposure, stress corrosion cracking, corrosion or crack tips, can directly contribute to debonding at the Mg2Si particle/aluminum matrix interface. According to the analysis, reduction of the diameter and simplification of the shape of Mg2Si particles are effective method for suppressing such hydrogen-induced debonding. [ABSTRACT FROM AUTHOR]

This study focused on investigating the wear properties of a T6 heat-treated A6082 composite reinforced with Yttria-stabilized zirconia (YSZ). The primary objective was to assess how the reinforcement and heat treatment affected the wear parameters of the composite material. The base material chosen for the composite was A6082 alloy, which possesses excellent mechanical and tribological qualities. YSZ, known for its high hardness and wear resistance, was selected as the reinforcing phase. The T6 thermal treatment was applied to the A6082 composite to enhance its mechanical properties and induce precipitation hardening. To evaluate the wear characteristics of the composite, a pin-on-disc tribometer was utilized. This test setup represents real-world sliding contact conditions that the composite material might encounter. Several parameters were measured during the wear testing, including wear loss, friction coefficient, and wear mechanism, to assess the composite's durability under abrasion. The results of the study demonstrated that increasing the YSZ concentration in the base alloy led to a reduction in material loss and friction coefficient. This improvement can be attributed to the hardness and wear-resistant properties of YSZ. The addition of YSZ reinforcement significantly enhanced the wear resistance of the T6 heat-treated A6082 composite. Furthermore, the T6 heat treatment process also improved the wear properties of the composite. Precipitation hardening occurred, resulting in improved mechanical qualities such as strength and hardness, ultimately leading to increased wear resistance. Microscopic analysis of the worn surfaces revealed that the wear mechanism of the composite shifted from severe abrasive wear to moderate adhesive wear after undergoing the T6 heat treatment. The transformation in wear mechanism is believed to be facilitated by the formation of strengthening precipitates during the heat treatment. These precipitates limited the amount of material lost during the wear test, thereby decreasing both material loss and friction coefficient. In summary, this study demonstrates that the addition of YSZ reinforcement and the T6 heat treatment process effectively enhance the wear properties of the A6082 composite. The presence of YSZ reduces material loss and friction coefficient, while the T6 heat treatment produces precipitation hardening, leading to improved wear resistance. [ABSTRACT FROM AUTHOR]

Purposes In order to refine the coarse Mg2Si phase in Mg-Al-Si alloy, the Mg-5Al-5Si alloys are modified by adding Al-5Ti-1B and rare earth Y. Methods The Mg-Al-Si alloys with different compositions were prepared by smelting. Various means were used to analyze the composition, microstructure, and mechanical properties of alloys before and after modification, and discuss modification mechanism. Findings The results show that, adding Al-5Ti-1B to the Mg-5Al-5Si alloy transforms the morphology of the primary phase from coarse bulk to fine dendritic or polygon, the number of eutectic phases decreases with the increase of Al-5Ti-1B, while the hardness of the alloys increases significantly, which is attributed to TiB2 phase acting as the heterogeneous nucleation sites for primary Mg2Si phase. On the foundation of adding 1.0% Al-5Ti-1B, rare earth Y can further modify the size and morphology of Mg2Si. When 1.0% Al-5Ti-1B and 1.0% Y are added together, the average size of the primary Mg2Si is decreased to 10.2 μm, the morphology of primary Mg2Si is fine polygonal, and the alloy has the best tensile mechanical properties, with the modification mechanism of rare earth Y mainly adsorption and poisoning.

Metal‐based additive manufacturing can make complicated parts that are complex or expensive to cast and process. Rapid cooling rates increase laser powder bed fusion (LPBF's) mechanical properties during manufacturing. The objective of this study is to examine the impact of process parameters in the L‐PBF technique on the characteristics of microstructure and mechanical properties, specifically, on the nanohardness influenced by Si segregation. The microstructures of the produced specimens are examined using field‐emission scanning electron microscopy and the analysis identifies the existence of bimodal equiaxed α‐Al grains, accompanied by Si phases located within their grain boundaries. In addition, the solidified sample exhibits the segregation of secondary precipitates, particularly Mg2Si, which results in enhanced mechanical properties. Both cellular walls and Si precipitates impede the motion and generation of dislocations, thereby influencing the overall behavior of dislocations. The examination of segregation at the top layer is conducted in a comprehensive manner, subsequently using energy‐dispersive X‐ray spectroscopy for analysis. The presence of Mg2Si, Al2MgSi2, and other phases in all samples is confirmed through X‐ray diffraction. The as‐built samples' residual stress under different process conditions is also investigated. Additionally, the obtained microstructure is compared to a phase‐field model to forecast the evolution of the microstructure. [ABSTRACT FROM AUTHOR]

Pb plays an important role in determining the morphologies and mechanical properties of the Mg2Si phase in Mg-2.5Si-xPb alloys. As the amount of Pb increases from 0.4 wt.% to 1 wt.%, the primary Mg2Si phase is refined during solidification. Its morphologies transform from equiaxed-dendrite to polygonal and finally to roughly circular. The key reason for morphology evolution is the preferential adsorption of Pb atoms on Mg2Si {100} surfaces to suppress the growth rate along the ⟨100⟩ directions, which is demonstrated by the adsorption model based on first principles. In addition, the hardness of the Mg2Si phase decreases with the increasing solution content of Pb according to the results of the nanoindentation. With the addition of Pb at 1 wt.%, Pb content in the primary Mg2Si phase reaches a maximum of 0.4 wt.%, and the hardness of the primary Mg2Si phase reaches a minimum of 3.64 GPa. This reduction in hardness is attributed to the augmented ionic bond ratio resulting from the solution of Pb, which concurrently enhances the toughness of the Mg2Si phase. [ABSTRACT FROM AUTHOR]

The effect of Mg addition (0.5–2.0%) on the as-cast and thixoformed microstructures, hardness and tribological properties of A319 aluminium alloy was investigated. The investigations highlight the dry sliding wear test behaviour using a pin-on-disk tester configuration under the applied pressures of three loads of 10, 50 and 100 N at a constant sliding speed of 1 m/s and a sliding distance of 9 km. The detailed microstructural morphology studied for these alloys is correlated with the obtained wear properties. Results in the as-cast A319 alloy reveal that Mg addition transforms the Al2Cu phase and Si particles to form the Al5Cu2Mg3Si5 and Mg2Si intermetallic phases during solidification. Moreover, the platelet-like morphology of the β-Al5FeSi intermetallic completely converts to a Chinese script-like morphology and π-Al8Mg3FeSi6 phase with the addition of up to 1.5 wt.% Mg. By adding Mg and performing thixoforming, the microstructure of the α-Al phase shows a fine globular primary phase surrounded by uniformly distributed Si and refined fragmentation of intermetallic phases. The morphology of Mg2Si particles is modified from large, polygonal particles into relatively smaller and more globular particles, whereas the Chinese script-like morphology of π-Al8Mg3FeSi6 changes to a compact shape. Adding up to 2 wt.% Mg increases the hardness at 100 Hv. The increase in Mg content enhances the wear resistance, friction coefficient and volume loss of thixoformed A319 alloys. A combination of abrasion and adhesion for alloys with low Mg dominates the wear mechanism. By contrast, excessive subsurface fracturing and delamination with minor abrasion are mainly observed for alloys with high Mg. [ABSTRACT FROM AUTHOR]

Alloy coatings protect steel from corrosion in various applications. We investigated the effects of Si addition on the microstructure, electrochemical behavior, and corrosion resistance of steel sheets coated with a hot-dip Zn–Mg–Al–Si alloy using a batch-type galvanization process. Microstructural analysis revealed that the Zn–Al–Mg alloy coating layer contained a significant amount of Fe that diffused from the substrate, leading to delamination due to the formation of brittle Fe–Zn intermetallic compounds. However, the introduction of Si resulted in the formation of a stable Fe2Al3Si inhibition layer at the substrate–coating interface; this layer prevented interdiffusion of Fe as well as enhanced the coating adhesion. Additionally, the formation of acicular Mg2Si phases on the coating surface improved the surface roughness. As the Si content increased, the corrosion resistance of the coating improved. Specifically, the Zn–Al–Mg coating layer with 0.5 wt.% Si exhibited excellent anti-corrosion performance, without red rust formation on its surface even after 2600 h, during a salt spray test. [ABSTRACT FROM AUTHOR]

The transfer matrix method (TMM) was used to investigate the tunability of the transmittance with an external magnetic field and temperature within the photonic bandgap in the terahertz range. Mg2Si and CoSb3 defect layers (D) were used for this in the symmetric (Si/SiO2)N D (SiO2/Si)N and asymmetric (Si/SiO2)N D (Si/SiO2)N one-dimensional photonic crystals. Using the Faraday model, different results were obtained for the responses of symmetric and asymmetric structures to magnetic fields for the right- and left-handed polarized dielectric constants. Our findings demonstrate that the defect mode is only seen in the CoSb3-contained structure when a magnetic field between 0 and 1 T is used. For both symmetric and asymmetric Mg2Si-contained structures, the peak was not apparent in the presence of magnetic field. The Drude model was used to analyze the temperature dependency of the defect mode for the structures mentioned above. For asymmetric and symmetric constructions, various frequencies and heights were found. The frequency of the CoSb3 defect peak varies considerably as temperature rises from 100 to 300 K, whereas the Mg2Si defect frequency remains unchanged. The asymmetric Mg2Si structure at different temperatures did not exhibit any defect modes. The defect mode heights of all structures fall as the temperature rises. [ABSTRACT FROM AUTHOR]

Hot dip galvanized products are widely used in various aspects of production and life due to their excellent corrosion resistance. Some studies have added a fourth trace alloying element to the zinc aluminum magnesium coating to form a quaternary alloy for better performance. This article prepared two different types of Zn−Al−Mg alloy ingots with trace amounts of Si added by induction melting, consisting of Zn1Al1Mg0.01Si and Zn1Al1Mg0.05Si, and solidified them in a heating furnace with argon gas protection atmosphere. The precipitation process of Zn1Al1Mg(0.01,0.05)Si alloy components under non equilibrium and equilibrium solidification conditions was calculated. The initial crystalline phase of the alloy and the initial solidification temperature were predicted through phase diagram calculations. The microstructure and phase types of the alloy were analyzed using scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM). The electrochemical Tafel curves of Zn1Al1Mg(0.01,0.05)Si with different Si contents showed that the Zn1Al1Mg0.05Si has the highest corrosion potential and Zn1Al1Mg0.01Si has the lowest corrosion current which means the 1Al1Mg0.01Si alloy possesses the highest corrosion resistance. The Nyqust curves and bode curves also showed that the practical impedance of 1Al1Mg0.01Si alloy is higher than that of 1Al1Mg0.05Si. Moreover, electron probe X-ray micro-analyzer(EPMA) reveals the distribution of Si elements in the Zn1Al1Mg(0.01,0.05)Si. At present, there is little research on the microstructure and properties of quaternary alloys containing silicon. Therefore, studying the influence of silicon content on the microstructure and properties of alloys is of great significance. [ABSTRACT FROM AUTHOR]

Owing to efficient thermoelectric conversion, non-toxicity, low density and cost, Mg2(Si,Sn)-based solid solutions hold potential for mid-to-high temperature waste heat recovery. Yet, challenges arise from n-Mg2(Si,Sn) degradation at ≥400 °C caused by Mg loss and charge carrier reduction, particularly in Sn-rich compositions. To build a thermoelectric generator (TEG) stable up to 400 °C, we propose binary Mg2Si as the n-type leg. Using Ni45Cu55 and Ni yields low electrical contact resistance (

For Al-Mg-Si alloys, cooling after homogenisation is a crucial step because the precipitation of the equilibrium β-Mg2Si phase determines the processing capabilities in subsequent steps, as well as the subsequent precipitation age hardening potential, and thus, the final properties. It is therefore important to understand how microstructural variations affect the transformation of β-Mg2Si during cooling after homogenisation. In the present work, alloys with similar effective solute contents of Mg and Si, but with different microstructures and a different amount of primary Al-Fe-Si phases, were produced. Characterisation of the precipitation reaction was performed using interrupted quench experiments with cooling rates of 1–6 K/min, monitored by light optical microscopy (LOM), scanning electron microscopy (SEM) and conductivity measurements. Precipitation kinetics for β-Mg2Si was found to increase in microstructures with shorter secondary dendrite arm spacing (DAS). However, despite measuring both a higher density and volume fraction of the primary phases, no effect on the phase transformation from an increased iron content was found in terms of precipitation kinetics or particle count statistics. Furthermore, comparisons with iron-free high-purity-based alloys revealed that the precipitation reaction for β-Mg2Si was identical in the two different microstructures both in terms of onset temperature and overall kinetics. The present results show that nucleation of β-Mg2Si is not dependent on the larger constituent phases and indicates that overall transformation kinetics is governed by bulk diffusion rates. [ABSTRACT FROM AUTHOR]

Silicon nitride ceramics were prepared by plasma-activated sintering at 1550 °C with 2−5 wt% Mg 2 Si as a sintering agent. The effects of the Mg 2 Si content on the phase, microstructure, and thermal conductivity of the ceramics were studied. Mg 2 Si reacts with SiO 2 to form MgO and Si, benefiting to the transformation and densification of Si 3 N 4. After heat treatment at 1700 °C for 6 h in a flowing N 2 , the residue Si reacted with N 2 and lattice O to form Si 3 N 4 and SiO, resulting in decreases in the grain-boundary phase and lattice O content. After the heat treatment, the sample prepared with 3 wt% Mg 2 Si achieved a relatively good balance between the thermal conductivity and strength, with values of 110 W/(m⋅K) and 705 ± 30 MPa, respectively. [ABSTRACT FROM AUTHOR]

One of the most important parts used in various industries is the pipe, whose inner surface can be exposed to wear (especially sliding wear). In this study, increasing the wear resistance of the inner surface of the Al-15 Mg2Si composite tube, which is a suitable alternative to the most widely used aluminum alloy in the industry, (Al-Si alloy) has been investigated by optimizing the thermal parameters. In this study, the simultaneous effects of pouring temperature, solutionizing temperature, aging temperature, mold preheating temperature, wear force, and wear temperature on the sliding wear resistance of the inner surface of the above tube made by the centrifugal casting method was studied, and the results using Design Expert software were analyzed. The most effective parameter on the wear resistance of the above alloy was the dissolution temperature; the best temperature was 570 °C. The effect of aging temperature was found to be insignificant. The best pouring temperature was determined in the range of 750–700 °C, and the suitable temperature for preheating the mold was determined to be 300 °C. [ABSTRACT FROM AUTHOR]

We attempted to calculate the hydrogen trapping energies at the incoherent interfaces of MgZn2 precipitates and Mg2Si crystallites in aluminum alloys from first-principles calculations. Since the unit cell containing the incoherent interface does not satisfy the periodic boundary condition, resulting in a discontinuity of crystal blocks, the hydrogen trapping energy was calculated in a region far from the discontinuity (vacuum) region. We found considerable trapping energies for hydrogen atoms at the incoherent interfaces consisting of assumed atomistic arrangement. We also conducted preliminary calculations of the reduction in the cohesive energy by hydrogen trapping on the incoherent interfaces of Mg2Si in the aluminum matrix. [ABSTRACT FROM AUTHOR]

Metal–oxide–semiconductor field-effect transistor (MOSFET) faces the major problem of being unable to achieve a subthreshold swing (SS) below 60 mV/dec. As device dimensions continue to reduce and the demand for high switching ratios for low power consumption increases, the tunnel field-effect transistor (TFET) appears to be a viable device, displaying promising characteristic as an answer to the shortcomings of the traditional MOSFET. So far, TFET designing has been a task of sacrificing higher ON state current for low subthreshold swing (and vice versa), and a device that displays both while maintaining structural integrity and operational stability lies in the nascent stages of popular research. This work presents a comprehensive analysis of a heterojunction plasma doped gate-all-around TFET (HPD-GAA-TFET) by making a comparison between Mg2Si and Si which serve as source materials. Charge plasma technique is employed to implement doping in an intrinsic silicon wafer with the help of suitable electrodes. A low-energy bandgap material, i.e. magnesium silicide is incorporated as source material to form a heterojunction between source and silicon-based channel. A rigorous comparison of performance between Si-based GAA-TFET and HPD-GAA-TFET is conducted in terms of electrical, radio frequency (RF), linearity, and distortion parameters. It is observable that HPD-GAA-TFET outperforms conventional Si-based GAA-TFET with an ON-state current (I ON), subthreshold swing (SS), threshold voltage (V th), and current switching ratio being 0.377 mA, 12.660 mV/dec, 0.214 V, and 2.985 × 1012, respectively. Moreover, HPD-GAA-TFET holds faster switching and is more reliable than Si-based device. Therefore, HPD-GAA-TFET is suitable for low-power applications. [ABSTRACT FROM AUTHOR]

Alloy coatings protect steel from corrosion in various applications. We investigated the effects of Si addition on the microstructure, electrochemical behavior, and corrosion resistance of steel sheets coated with a hot-dip Zn–Mg–Al–Si alloy using a batch-type galvanization process. Microstructural analysis revealed that the Zn–Al–Mg alloy coating layer contained a significant amount of Fe that diffused from the substrate, leading to delamination due to the formation of brittle Fe–Zn intermetallic compounds. However, the introduction of Si resulted in the formation of a stable Fe2Al3Si inhibition layer at the substrate–coating interface; this layer prevented interdiffusion of Fe as well as enhanced the coating adhesion. Additionally, the formation of acicular Mg2Si phases on the coating surface improved the surface roughness. As the Si content increased, the corrosion resistance of the coating improved. Specifically, the Zn–Al–Mg coating layer with 0.5 wt.% Si exhibited excellent anti-corrosion performance, without red rust formation on its surface even after 2600 h, during a salt spray test.

Dry-sliding wear and friction behaviors of Al–15Mg2Si–5TiB2–4TiAl3 in-situ hybrid composites were evaluated at different temperatures (100–300 °C) and loads (10–60 N). The addition of TiB2 and TiAl3 particles enhanced the wear resistance. Moreover, the severe wear transition condition was changed from 300 °C to 10 N for the as-received Al–15Mg2Si composite to 300 °C - 60 N for the as-cast Al–15Mg2Si–5TiB2–4TiAl3 hybrid composite. This change was ascribed to the presence of thermostable particles and refined/modified Mg2Si particles via nucleation mechanism. Applying thermomechanical processing and hot deformation by the extrusion process necessitated higher loads and temperatures for this transition. Indeed, fragmentation and more homogeneous dispersion of reinforcements, higher hardness and toughness of composite due to grain refinement by dynamic recrystallization (DRX), reduction and closure of casting defects, and stability of tribolayer were recognized as leading reasons for replacing severe adhesive/plastic deformation wear with the abrasive mechanism. Accordingly, this study introduced an Al matrix hybrid composite with excellent performance at elevated temperatures.

This study aims to investigate the microstructural alterations, mechanical properties, sliding wear behavior, and corrosion properties of Al-15%Mg2Si composites with different contents of yttria-stabilized zirconia (YSZ). Al-15%Mg2Si composites with the different contents of YSZ (0, 3, 6, and 9 wt.%) were fabricated using the stir-casting technique. The fabricated composites were characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), Vickers hardness tester, linear reciprocating tribometer (LRT), and electrochemical test. The results showed that with the introduction of YSZ particles, the average size of the primary Mg2Si particles in the base composite was 137.78 µm, which was reduced to 88.36 µm after adding 9 wt.% YSZ. The aspect ratio of Mg2Si particles also decreased from 3, for the base composite, to 1.27 in the composite containing 9 wt.% YSZ. Moreover, the hardness value displays an incremental trend from 102.72 HV, as recorded for the base in situ composite, to 126.44 HV in the composite with 9 wt.% YSZ. On top of that, the Al-15%Mg2Si-9%YSZ demonstrates exceptional wear resistance, with the lowest wear rate of 0.46 mm3/km under a 25 N applied load. Its average coefficient of friction (COF) was recorded at 0.42, which is lower than both the 3 and 6 wt.% of YSZ-containing composites. The smoother worn surface in Al-15%Mg2Si-9%YSZ hybrid composite implies the abrasion phenomenon, as dominant wear behavior is milder than the other fabricated composites. On top of that, the Al-15%Mg2Si-9%YSZ also possesses optimum corrosion resistance. The corrosion rate is 0.080 mmpy, comparable to the 0.164 mmpy rate obtained in the in situ composite. [ABSTRACT FROM AUTHOR]

Ultrafast high-temperature sintering (UHS) is a recently proposed technique able to synthesize and sinter dense materials within seconds. Although UHS has already proved its effectivity with a large set of materials, spanning from refractory ceramics to complex metal alloys, any application to thermoelectric materials is today still lacking. Mg2Si is a well-established thermoelectric material. It is based on wide available non-critical raw materials, it is non-toxic, lightweight and it expresses its best thermoelectric performances in the intermediate temperature range (up to about 600 °C). Mg2Si is typically produced with powder processing by Spark Plasma Sintering (SPS), partially limiting its widespread diffusion also due to the costly production technique. Here we present a simple route to sinter Mg2Si pressed powders by UHS. The process allowed to obtain dense samples (with relative densities >95%) with 20 s heating up to about 1080 °C followed by a rapid free cooling, a total thermal history below 1 min, and with energy demand at the Wh scale. The high process rate proved its efficacy in preventing grain growth and in avoiding any significant Mg evaporation. A full thermoelectric functional characterization is presented for Mg2Si and Bi-doped Mg2Si, together with a comparison with SPS-produced properties. [ABSTRACT FROM AUTHOR]

For Al-Mg-Si alloys, cooling after homogenisation is a crucial step because the precipitation of the equilibrium β-Mg2Si phase determines the processing capabilities in subsequent steps, as well as the subsequent precipitation age hardening potential, and thus, the final properties. It is therefore important to understand how microstructural variations affect the transformation of β-Mg2Si during cooling after homogenisation. In the present work, alloys with similar effective solute contents of Mg and Si, but with different microstructures and a different amount of primary Al-Fe-Si phases, were produced. Characterisation of the precipitation reaction was performed using interrupted quench experiments with cooling rates of 1–6 K/min, monitored by light optical microscopy (LOM), scanning electron microscopy (SEM) and conductivity measurements. Precipitation kinetics for β-Mg2Si was found to increase in microstructures with shorter secondary dendrite arm spacing (DAS). However, despite measuring both a higher density and volume fraction of the primary phases, no effect on the phase transformation from an increased iron content was found in terms of precipitation kinetics or particle count statistics. Furthermore, comparisons with iron-free high-purity-based alloys revealed that the precipitation reaction for β-Mg2Si was identical in the two different microstructures both in terms of onset temperature and overall kinetics. The present results show that nucleation of β-Mg2Si is not dependent on the larger constituent phases and indicates that overall transformation kinetics is governed by bulk diffusion rates.

This work investigates the effect of insitu formed TiB2 particles on tribological behaviour of Al-Si/Mg2Si hybrid composites. For this purpose, different amount of TiB2 particles (0, 1, 3, 5 wt.%) have been generated through stir casting method using the halide salts K2TiF6 and KBF4. The tribology test has been performed on the pin on disc tribometer at ambient conditions with different applied load (10 N to 40 N) and sliding distance (1000 m to 3000 m) at a fixed sliding speed. The evolved worn surfaces are also analysed with the use of SEM with EDS and AFM to examine the wear mechanism. Results indicate that with an increasing TiB2 particle amount, wear rate of hybrid composite decreases while CoF increases. However, with the increase of applied load and sliding distance the wear of hybrid composite increases. Minimum wear and highest CoF is observed in the hybrid composite having 5 wt.% TiB2 particles in Al-Si/Mg2Si. The observed tribological results are also correlated with microstructure, mechanical properties, worn surfaces profile and debris analysis of the hybrid composites. These developed hybrid composites could be utilized on those places where less wear and high friction are required such as brake and clutch systems. [ABSTRACT FROM AUTHOR]

The anodic hydrogen evolution (AHE) on Mg, MgZn2 (η-phase), Al4Cu2Mg8Si7 (Q-phase), and Mg2Si (β-phase) intermetallic compounds has been investigated using hydrogen evolution technique and customized polarization schemes. Results show that at constant applied anodic current densities, the hydrogen evolution rates on pure Mg and MgZn2 are much higher than those of Q-phase and Mg2Si, indicating AHE is not very pronounced on Q-phase and Mg2Si. After anodic galvanostatic polarization, an obvious enhanced cathodic activity was observed for Mg, MgZn2, and Al4Cu2Mg8Si7 with no obvious change for Mg2Si. The stepped galvanostatic-potentiostatic tests reveal that pure Mg has the highest degree of cathodic activity enhancement with the increase of applied anodic current density, followed by Q-phase and MgZn2, while no obvious change of cathodic activity was noted in the case of Mg2Si. No single model was seen to be suitable for explaining the observed AHE of all the electrodes at the same time. However, the "incomplete film univalent Mg+ ion mechanism" and the "enhanced catalytic activity mechanism" can explain the observed experimental phenomena in many cases. [ABSTRACT FROM AUTHOR]

Full-dense B 4 C-based ceramics with excellent mechanical properties were fabricated using spark plasma sintering with Mg 2 Si as a sintering aid at a low temperature of 1675 °C while applying a uniaxial pressure of 50 MPa. The effect of Mg 2 Si addition on the densification behaviours, mechanical properties and microstructure of as-sintered ceramics were investigated. Not only did the formation of ultra-fine grained SiC using the in-situ reaction effectively inhibit the growth of B 4 C grains, but it also contributed to the strength and toughness of the resultant ceramics. Additionally, microalloying Mg imparted more metal bonding characteristics to the B 4 C matrix, thereby improving their ductility. The results indicate that the composite containing 7 wt% Mg 2 Si had excellent mechanical properties, including a light weight of 2.54 g/cm3, Vickers hardness of 34.3 GPa, fracture toughness of 5.09 MPa m1/2 and flexural strength of 574 MPa. [ABSTRACT FROM AUTHOR]

Dissolution of Si in Al-5 mass%Mg alloy melt by the reduction of SiO2 and its effect on microstructure formation of the alloy after solidification were investigated. Al-5 mass%Mg alloy without silica powder had approximately 0.05 mass%Si as an impurity. No significant difference in Si content was observed after the reaction with silica for 10 min, while the Si content increased up to about 0.12 mass% after 30 min. From the microstructure analysis and calculation of Scheil-Gulliver cooling, it was considered that as-cast microstructures of Al-5 mass%Mg-1 mass% SiO2 alloys had the distribution of eutectic phase particles, which are comprised of β-Al3Mg2 and Mg2Si phases. Based on the phase diagrams, only limited amount of Mg can be selectively removed by silica depending on the ratio of Si and Mg. Addition of silica of more than approximately 1.5 mass% in Al-5 mass%Mg alloy led to the formation of spinel and removal of both Mg and Al from the melt.

This work presents an overview on the study of Si and Mg2Si, obtained as second phases in aluminum alloys, including their modifications due to processing conditions, alloying elements and heat treatments. These micrometric phases are generally studied using optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Although they can be differentiated combining OM and SEM, a validation study using XRD is indispensable. This work studies the peculiarities of using these techniques, and the differentiation of Si and Mg2Si depending on their XRD peaks, morphologies and gray scales. This review showed that the presence of other second phases complicates the identification of Si and Mg2Si. It also revealed that their morphological modifications have been barely studied quantitatively. We are presenting some study cases related to this topic, adding our own quantitative characterizations through the use of shape descriptors and fractal dimension, demonstrating their effectiveness and importance. [ABSTRACT FROM AUTHOR]

The present work aims at understanding the microstructure and mechanical property correlation of hypo (Mg-0.5, 0.7, 1.15 wt% Si) and hyper (Mg-2, 4, 6, 8 and 10 wt% Si) eutectic binary Mg-Si alloys. The microstructures of hypoeutectic alloys consist of α-Mg and lamellar Mg-Mg2Si eutectic phases; whereas the microstructures of hypereutectic alloys consist of primary Mg2Si, Chinese script eutectic Mg2Si and α-Mg phases depending upon the Si content. Significant increase in hardness values of these alloys was observed as a function of Si content which is due to the presence of hard Mg2Si phase. In the hypereutectic alloys, the average microhardness of primary Mg2Si was about ten times higher than that of α-Mg. Compressive behaviour, tensile properties (UTS, YS and %E) at the room temperature (RT) as well as at 150 °C, elevated temperatures (ET) were analyzed and reported as follows: compressive strength of Mg-Si alloys has improved with the increase of Si content, Mg with 2 to 4 % Si shows good tensile properties at RT and ET. Alloys containing high Si content show a marginal reduction in strength at high temperatures due to the presence of the thermally stable Mg2Si. [ABSTRACT FROM AUTHOR]

TiB2/Mg-4Al-1.5Si magnesium matrix composites were prepared by semi-solid stirring assisted ultrasonic treatment, the primary Mg2Si phases in the composites exhibit polygon with sharp corners, and the eutectic Mg2Si phases appear thin Chinese-script or short-strip shape. To reduce stress concentration around the sharp corners (tips) of the Mg2Si phases, the morphology of the Mg2Si phases was further modified by solution treatment at 420 °C for 24 h, and the effects of the morphology modification of the Mg2Si phases on the mechanical properties of the composites were investigated. The results showed that after the solution treatment, the sharp corners of the primary Mg2Si phases were blunted, and the partial branches of the eutectic Mg2Si phases were dissolved into particles. The Vickers-hardness, ultimate tensile strength, yield strength, and elongation of the composites were increased by 11.50%, 33.28%, 28.57%, and 27.17% compared with those of unmodified composites, respectively. The solution treatment exhibits a more significant strengthening effect for the composites in hardness, ultimate tensile strength, and yield strength compared with the matrix alloys. [ABSTRACT FROM AUTHOR]

In this study, open-cell Mg composite foams reinforced with in-situ Mg2Si were prepared. In order to refine the Mg2Si compound, the composite foams were co-modified with Y + Sb elements followed by solution heat treatment. The influences of complex modification and holding time of solution heat treatment on the microstructure and compressive properties of the composite foams were studied. The experimental results show that the morphology of Mg2Si is effectively changed by complex modification. The coarse dendritic primary Mg2Si (∼40 μm) is altered to the fine polygonal shape (∼10 μm); the coarse eutectic Mg2Si is transformed to a long rod or granular shape. Both compressive strength and energy absorption capacity of the composite foams are significantly increased. Additionally, with the increasing holding time of solution heat treatment, the eutectic Mg2Si undergoes obvious spheroidization, and the corner of the primary Mg2Si occurs passivation. Consequently, the compressive strength and energy absorption capacity are further improved.

Microstructural alteration and tensile properties of Al-15% Mg2Si composite specimens was examined after addition of gadolinium (Gd) and conducting solution heat treatment. Various percentages of gadolinium (0.5, 1.0, 2.0 and 5.0 wt. % Gd) were added to the composite Al-15% Mg2Si composite. The specimens then solutionized at 500 °C for 4h followed by quenching. The results showed that regular morphology and small size of primary Mg2Si particles is achieved after addition of 1.0 wt.% Gd compared to untreated composite. Due to solutionizing effect, Mg2Si dissolution occurred which led to alter the morphology of primary Mg2Si particles to round shape. Tensile testing results revealed that enhancement in UTS and El% values owns to influence of both Gd addition and solution heat treatment on the Al-15% Mg2Si composite. The fracture surface of untreated composite depicted a cellular fracture, while the fracture surface of Gd treated and heat treated composite showed a ductile surface containing fine dimples, in which alteration of fracture mode is due to the role of Gd and heat treatment on microstructural modification, which results in reduction of potential sites for stress concentration and crack initiation areas.

A small area with a large Al 6 (Fe, Mn) particle and a large Mg 2 Si particle was prepared on AA5083, and the dislocation and corrosion behaviors were compared with those of small areas containing only Mg 2 Si and Al 6 (Fe, Mn) particles in 100-times diluted synthetic seawater. Mg 2 Si discolored in both cases upon immersion, but discoloration and trenching were observed for Al 6 (Fe, Mn) only when Mg 2 Si was on the same area. The discoloration of Al 6 (Fe, Mn) started simultaneously with the dissolution of Mg 2 Si. The role of Mg 2 Si in the discoloration of Al 6 (Fe, Mn) particles and the trench formation mechanism was discussed. • Discoloration and trenching occurred for Al 6 (Fe, Mn) only upon Mg 2 Si dissolution. • Alkalization resulting from Mg 2 Si dissolution induced a compositional change on the Al 6 (Fe, Mn) surface. • Oxygen reduction activity on Al 6 (Fe, Mn) significantly increased due to alkalization. • Increased cathodic activity was identified as the cause of trenching around Al 6 (Fe, Mn). [ABSTRACT FROM AUTHOR]

The magnetic properties of Mg2Si‐based dilute magnetic semiconductors in Mg62X2Si32 systems (X = V, Cr, Mn, Fe, Co, and Ni) are investigated by spin‐polarized first‐principle calculations. The ground‐state magnetic interaction of V‐, Cr‐, or Fe‐doped Mg2Si system is ferromagnetic (FM) coupling, consistent with the double‐exchange mechanism. The Mn‐ or Co‐doped Mg2Si system is antiferromagnetic (AFM) coupling, which can be explained by the superexchange mechanism. The ground state of Ni‐doped Mg2Si is the nonspin‐polarized state. The V‐ or Cr‐doped Mg2Si exhibits half‐metallic character, Mn‐ or Co‐doped Mg2Si is a semiconductor, and Fe‐doped Mg2Si presents metallic nature. It can be seen that different 3d transition metal atom‐doped Mg2Si correspond to different potential applications. [ABSTRACT FROM AUTHOR]

A new alloy Mg-5Sn-3Zn-1Mn-xSi (x = 0.5, 1, 1.5, 2wt %) with varied composition is investigated. Morphological behavior of as-cast Mg-5Sn is studied with the addition of Zn and Mn. Mg2Sn phases are mostly present in the grain boundaries. Grain refinement is observed on the micrographs with the addition of Zn and Mn. With the different addition of Si in Mg-5Sn-3Zn-1Mn alloy, Mg2Si phase is formed along with the Mg2Sn phase. With lower addition of Si forms eutectic Mg2Si phase with Chinese script shape morphology. When Si addition exceeds 1 %, primary Mg2Si polygonal particles also formed along with eutectic Mg2Si phase. Addition of Si up to 1 % by weight sufficiently improves the mechanical property. Above 1 wt% Si, a slight reduction in tensile strength is observed, accompanied by the formation of hard and brittle primary and coarse Chinese script Mg2Si phases. [ABSTRACT FROM AUTHOR]

The types and changes of the second phases in the Mg–xAl–ySi–0.3Ca alloys and their effects on the properties of the alloys were studied. The results showed that within a certain range of Si and Al content, Si had the greatest influence on the size of the Mg2Si phase, while Al content affected the size and morphology of Mg17Al12 and Mg2Si phases. The CaMgSi phases were less affected by the Al and Si content. In a tensile test, the as-cast alloy had the best performance when it contained small Mg17Al12 and Mg2Si phases, and the Mg17Al12 phase was more likely to become the fracture source. The alloy we tested with the best corrosion resistance was Mg–4Al–0.7Si–0.3Ca alloy, the worst was Mg–6Al–0.7Si–0.3Ca alloy. [ABSTRACT FROM AUTHOR]

Thin film-based thermoelectric materials have attracted enormous research interest due to their potential to exhibit excellent thermoelectric (TE) behavior. Considering the potential of earth-abundant and nontoxic magnesium silicide (Mg2Si) to behave as a mid-temperature TE material, the present study was conducted to assess the structural evolution and electrical behavior of Mg2Si films prepared by electron beam thin film deposition technique. The films were deposited on silicon (100) substrate at room temperature with thickness ranging from 0.5 µm to 4 µm. The investigation revealed that the electrical behavior of this alloy film is considerably influenced by its thickness. The effect of film thickness on evolution of the structure was also studied by x-ray diffraction (XRD), field emission scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. It was observed that the present experimentation could produce a nanocrystalline grain structure of Mg2Si alloy with a small quantity of excess magnesium phase. Moreover, XRD results delineated that the crystallite size is influenced by the thickness of the film under the same deposition conditions. The residual stress within the e-beam-deposited film, as manifested through the measured strain values of the films, was found to be thickness-dependent. Moreover, it was confirmed that there was no influence of the substrate on the structure and properties of the studied films. [ABSTRACT FROM AUTHOR]

The goal of this study was production of an Al–15%Mg2Si metal matrix composite (MMC) containing 3 wt.% copper and also study microstructural and hardness properties. For this, pure Al, Mg, Si and Cu ingots were used to make composite via in situ route. The composite was characterised by X-ray diffraction, optical microscope (OM) and scanning electron microscope equipped with energy-dispersive X-ray spectroscopy (EDX) analysis. Microstructural observations explored that Mg2Si particles form all over the Al matrix. According to the OM characterisation, the size of primary Mg2Si particles was estimated to be ~20 μm. This amount could be decreased to ~7 μm (65% reduction) due to the presence of copper, mostly because of the formation of Cu-rich intermetallic phases during solidification, as detected by EDX analysis. Further results showed that these phases lead to an MMC with more hardness compared to the counterpart without Cu. In addition, because of Mg2Si phases in these systems which are even lighter than Al, it has high specific stiffness and strength. Therefore, it could be widely used as a lightweight material in aerospace and automobile fields, such as safety-belt pretensioner, steering wheel frame, crossbeams, wheel rims, car frame and shock absorbing cover. [ABSTRACT FROM AUTHOR]

Segregation can seriously damage the mechanical properties of the aluminum alloys. 6061 aluminum alloy wheel spokes were prepared by squeeze casting. To investigate the formation mechanism of segregation, the microstructure of the alloy was observed using scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and electron microprobe analysis methods. The Gibbs energy of each phase during solidification was calculated by JMatPro. Results show that the segregation phases in the R-joint of the wheel spokes are mainly composed of Mg2Si, β-AlFeSi and Al5Cu2Mg8Si6 intermetallics. During the solidification of the 6061 aluminum alloy wheels, Mg2Si and α-AlFeSi phases precipitate in the mushy zone at first. With the decrease of temperature, α-AlFeSi transforms into β-AlFeSi, while Al5Cu2Mg8Si6 precipitates from the solid-state aluminum alloy after solidification. Segregation at the R-joint of wheel spokes is mainly caused by insufficient cooling, so the cooling during alloy solidification should be enhanced to avoid segregation.

In this paper, by using an ultrasoft pseudopotential plane wave method based on density functional theory, the electronic structures and optical properties of four V - doped models of Mg2-x Vx Si ( x = 0, 0. 25, 0. 5, 0. 75 ) were calculated separately, and their energy band structures, densities of states and optical properties were analyzed. The results showed that V doped Mg2Si changes from its original semi-conductivity to half-metal, and the impurity levels appear at the Fermi level. The density of states also showed that near the Fermi level, the contribution of the 3d orbital of the V element dominates, and the optical properties of Mg2Si change with the doping of V. This article provides a theoretical basis for the application of Mg2Si materials in electronic devices and optical devices. [ABSTRACT FROM AUTHOR]

Mg2SiNi3, is a topologically densely packed intermetallic compound (TCP-IMC) and an excellent diffusion barrier material between nickel and Mg2Si-based thermoelectric material. However, even a little migration of the Mg atom from Mg2Si to Mg2SiNi3 under the action of a driven force promotes the formation of an Mg deficiency region on the Mg2Si side, which destroys the balance of point defects and leads to performance deterioration. In this work, by adjusting the chemical potential of Mg across the MgxSi15Ni50/Mg2Si (x = 36, 50, 130) interface, the migration of Mg in thermoelectric material has been suppressed effectively. The results indicate that the contact performance and service stability of the Mg130Si15Ni50/Mg2Si interface has been improved by 50% compared to that of Mg36Si15Ni50/Mg2Si, which remains quite well after annealing at 400 ℃ for 480 h. TCP-IMC barrier with proper composition is a promising design for the manufacture of TEG interface to ensure its consistency in service especially under a large temperature difference. [ABSTRACT FROM AUTHOR]