Mg2Si Alloy Research Articles

Influence of Asymmetric Rolling Process and Thickness Reduction on the Microstructure and Mechanical Properties of the Al–Mg-Si Alloy

Influence of Asymmetric Rolling Process and Thickness Reduction on the Microstructure and Mechanical Properties of the Al–Mg-Si Alloy

Tailoring microstructure and tensile properties of Mg-Si alloys varying solidification cooling rate and Si content

Mg-Si alloys were investigated in terms of their microstructural characteristics and tensile properties, by varying solidification cooling rate and Si content. This type of investigation becomes essential since these alloys are considered potentially base alloys for new biocompatible and biodegradable materials that might be used to produce a variety of temporary implants. This because Silicon (Si) has been recognized as a vital mineral in the human body, aiding both the healing process and the development of the immune system. Despite these characteristics provided by Si, Mg-Si alloys typically have low ductility and tensile strength due to the presence of coarse Mg2Si particles. Therefore, efforts to understand and improve these properties are most welcome. In order to deepen the knowledge of these alloys, the present research analyzed three Mg-Si alloys: Mg-0.6 wt% Si, Mg-1.3 wt% Si and Mg-1.7 wt% Si regarding their microstructures and phase's morphologies produced in a broad range of solidification rates' samples and their corresponding tensile properties. The predominance of dendritic arrangement with the interdendritic region composed of the (Mg + Mg2Si) eutectic was noted for the Mg-0.6 wt% Si and Mg-1.7 wt% Si alloys. Eutectic cells prevailed for the Mg-1.3 wt% Si alloy, with cells varying from squarer and hexagonal to a more rounded shape with the decrease in cooling rate. Experimental influences of the microstructural parameters on the tensile properties have been verified. Except for the Mg-1.3 wt% Si alloy, the tensile properties of the other alloys were found to be roughly independent of the dendritic length scales in the verified ranges. In general, increased Si content led to a reduction in strength and ductility, probably due to the increase in the fraction of Mg2Si particles, which is an effective phase in the stress concentration during loading, shortening the break.

Effect of Alloying Elements on the Stacking Fault Energy and Ductility in Mg2Si Intermetallic Compounds

Alloying elements can pronouncedly change the mechanical properties of intermetallic compounds. However, the effect mechanism of this in Mg2Si alloys is not clear yet. In this paper, systematic first-principles calculations were performed to investigate the effect of alloying elements on the ductility of Mg–Si alloys. It was found that some alloying elements such as In, Cu, Pd, etc. could improve the ductility of Mg2Si alloys. Moreover, the interatomic bonding mechanisms were analyzed through the electron localization functional. Simultaneously, the machine-learning method was employed to help identify the most important features associated with the toughening mechanisms. It shows that the ground state atomic volume (VGS) is strongly related to the stacking fault energy (γus) of Mg2Si alloys. Interestingly, the alloying elements with appropriate VGS and higher Allred–Rochow electronegativity (En) would reduce the γus in the Mg–Si–X system and yield a better ductility. This work demonstrates how a fundamental theoretical understanding at the atomic and electronic levels can rationalize the mechanical properties of Mg2Si alloys at a macroscopic scale.

Development of Aluminium Based Mango Seed Mangiferaindica Shell Ash (MSSA) Particulate Metal Matrix Composite

A composite material is a combination of two or more chemically distinct and insoluble phases; its properties and structural performance are superior to those of the constituents acting independently. MMCs are made by dispersing a reinforcing material into a metal matrix to improve their properties. They are prepared by powder metallurgy and casting, although several technical challenges exist with casting technology. Achieving a homogeneous distribution of reinforcement within the matrix is one such challenge, and this affects directly on the properties and quality of composite. In this work a composite is developed by adding Mango seed shell Ash (MSSA) particulate in Al- Si-Mg Alloy by mass ratio 5%, 10%, 15% and 20%. The composite was prepared by stir casting technique. It is proposed to use this material for production of motorcycle wheel hub which are subjected to continuous wear as the hubs are in direct contact with the brakes and rotating sprockets. The MSSA, was characterized using X- ray fluorescent (XRF). The result reveals SiO2, has the highest percentage composition followed by CaO, Al2O3, Fe2O3 and Mg2O as major phases. The presents of these hard constituent compounds suggests that the mango seed shell ash can be used as particulate reinforcement in various metal matrices since the chemical composition has similarity with the XRF analysis of Periwinkle shell ash, rice husk, fly ash, and bagasse ash currently used in metal matrix composite. Mechanical tests such as hardness test and impact test were conducted. The results revealed that increase in the percentage of MSSA progressively increased the hardness of the material from 5% wt to a maximum hardness of 43.2 HV at 15% addition of MSSA. This represents a 26.16% improvement over the unreinforced alloy. However, the impact energy progressively decreases of the material from 5%wt of MSSA and later increased to optimum energy at 15% addition of MSSA. From the results it is concluded that composite material such as Al- Si-Mg/ MSSA is one of the options as a material for production of motorcycle hub. The wear test of the composite was then carried out using Taguchi design to optimize the range of MSSA from 5% wt -15% wt., Sliding speed of 5cm/s -20cm/s, sliding distance from 50m to 200m, and the load of 2N, 4N, 6N, & 8N respectively. Analysis of the result of SN ratio for wear rate shows the optimum wear resistant value is in the combination of Load=4N, sliding speed = 10cm/s sliding distance=200m and MSSA=15 wt% These also correspond with the analysis of wear maps & wear rate presented in the diagrams of dynamic friction coefficient (COF) for Al-Si- Mg/ MSSA Composite.

Lifting the Optical and Thermoelectric Properties of Mg2Si as a Function of Sn Incorporation—Potential Thermoelectric Materials

By means of Density Functional Theory (DFT) study, we have performed the structural, electronic, optical and thermoelectric properties calculations of tin doped Mg2Si (Mg2Si1−xSnx, x = 0, 0.125, 0.25, 0.5, 0.75, 0.875, 1) using Full Potential Linearized Augmented Plane Wave (FP-LAPW) Method. The DFT study yields satisfactory results for electronic and thermoelectric properties of Sn doped Mg2Si compared with experimental values. With semiclassical Boltzmann transport theory, the transport properties of Mg2Si and Sn doped Mg2Si alloys has been investigated systematically. According to the calculated band structure, density of states and electron density, the parent Mg2Si/Sn materials having indirect energy gap (Γ−x) with ionic bonding; Sn doped ternary combinations Mg2Si1−xSnx, x = 0.125, 0.25, 0.5, 0.75, 0.875 having direct band gap (Γ−Γ) with a mixed covalent and ionic bonding nature. Band gap decreases linearly with the increase of Sn-concentration in each alloy system except for Mg2Si0.75Sn0.25 combination. The optical properties calculations have been performed for the energy range between 0–13.5 eV. The thermoelectric properties have been calculated for the temperature range 100 K to 800 K. Out of the five studied materials, Mg2Si0.75Sn0.25 found to be a better thermoelectric material with increased Power factor, Seebeck coefficient, electrical conductivity and corresponding thermal conductivity at high temperature range.

Kinetics of phase precipitation in Al–Mg–Si alloys subjected to equal-channel angular pressing during subsequent heating

Effects of equal-channel angular pressing (ECAP) with subsequent aging on the microstructure and phase transformation of Al–Mg2Si alloys with combined (Sc + Zr) and (Sc + Hf) additions were studied. The microstructure processed by ECAP and the precipitation of phases of Al–Mg2Si alloys were thoroughly examined by transmission electron microscopy (TEM). An analysis of the precipitation and determination of the temperatures of these precipitations in Al–Mg2Si alloys after ECAP was carried out by DSC. It has been revealed that transition metals added to Al–Mg2Si alloys do not change the character of decomposition of the solid solution but shift the precipitation temperatures of the β'', β' and β phases to lower temperatures compared to the quenched state. Recovery processes have been revealed in the temperature range 200–600 °C based on the changes in hardness and electrical resistivity of Al–Mg2Si alloys with additions of transition metals (Sc + Zr) and (Sc + Hf) and without them after ECAP.

Towards a morphological control of Mg2Si and superior tensile properties of high-Zn Mg-0.6Si (-Zn) alloys

In this study it was found that Mg-0.6Si-Zn alloys with a high Zinc (Zn) content (>2 wt%) can generate fine fibrous Mg2Si particles, as long as the solidification cooling rates could be supervised. Due to the solubility of Zn in Mg and the morphology of Mg2Si fibers, improved tensile properties were obtained for samples having refined dendritic arrangements. These results open the perspective of development of Mg-Si alloys with higher Zn contents, with greater strength and ductility due to microstructural control. Although there is a considerable difference in Zn alloying between them, both the Mg-0.6wt.%Si-2.0wt.%Zn and Mg-0.6wt.%Si-3.0wt.%Zn alloys have reached quite close optimum levels of tensile properties of the order of 200 MPa and 9%.

Influence of neutron irradiation and ageing on behavior of SAV-1 reactor alloy

This study observed the effect of neutron irradiation and ageing on the microstructure, hardness, and corrosion resistance of SAV-1 (Al–Mg–Si) alloy. The investigated material was irradiated with neutrons to fluences of 1021–1026 n/m2 in the WWR-K research reactor and kept in dry storage. Long-term irradiation led to an increase in hardness of the alloy and a deterioration of pitting corrosion resistance. Post-irradiation ageing for 1 h at 100–300 °C resulted in a decrease in microhardness of the irradiated SAV-1. The effect of post-irradiation ageing on pitting corrosion was made clear through the formation of Guinier-Preston zones and secondary precipitates in the Al matrix. Ageing at 250 °C corresponded to the development of stable microstructure and the highest corrosion resistance for the irradiated samples. Mg2Si, Si, and needle-shaped β″ precipitates were formed in SAV-1 alloy that was irradiated with low fluences. β″ and clusters of rod-shaped B-type precipitates were observed in highly irradiated samples. The precipitates were similar to those seen in non-irradiated pseudo-binary Al–Mg2Si alloys with Si excess.

Effect of nano rare earth phase on microstructure and properties in rapidly solidifying Mg-Si-RE alloys

Mg-Si-RE reinforced by nano-precipitated phase were fabricated by rapid solidification process (RSP) and investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that nanosized (<500 nm) ternary phase CeMg2Si2, LaMg2Si2 and CeLaMg4Si4 were precipitated within the α-Mg grain and along the crystal boundary in Mg-Si-RE alloy samples with additions of Ce, La rare earth elements(RE). The CeLaMg4Si4 phases are formed by doping La atom in place of part Ce atom. The nanometer RE-contained ternary phases are the primary eutectic phase which precipitate prior to Mg2Si phase. These ternary phases with high Young's modulus and phase fraction can help to effectively enhance the mechanical properties of the Mg-Si alloy. Moreover, they can also serve as the heterogeneous nucleus of Mg2Si phase and greatly enhance the second-phase strengthening effect. This work provides new ideas for developing high performance magnesium alloys with low Si and high RE contents.

Effect of Scandium and Other Transition Metals on the Recrystallization of Al–Mg2Si Alloys after Equal-Channel Angular Pressing

Effect of Scandium and Other Transition Metals on the Recrystallization of Al–Mg2Si Alloys after Equal-Channel Angular Pressing

Investigation on the Stability, Elastic Properties, and Electronic Structure of Mg2Si Doped with Different Concentrations of Cu: A First‐Principles Calculation

Herein, the effects of Cu doping with different concentrations on the stability, elastic properties, and electronic structure of Mg2Si are investigated by first‐principles calculations based on density functional theory. The research results show that Mg2Si and Mg8−xSi4−yCux+y (x, y) = {(0.125, 0), (0, 0.125), (0.25, 0), (0, 0.25), (0.5, 0), (0, 0.5), (1, 0), (0, 1)} are stable in the system. The Cu atoms tend to preoccupy Mg sites in Mg2Si lattices, and the alloying ability is stronger than that of Mg8Si4−yCuy (y = 0.125, 0.25, 0.5, 1). Although all dopants are brittle phases, the doping behavior of Cu atoms improves the elastic and plastic properties of the Mg2Si alloy system. The bonding modes of the crystal are also changed. The SiCu covalent bond formed by Mg8−xSi4Cux (x = 0.125, 0.25, 0.5, 1) further increases the structure stability. Meanwhile, Mg7Si4Cu and Mg8Si3Cu are changed from semiconducting to metallic state by energy band structure analysis. It not only increases the carrier concentration, but also reduces the free electron transition energy, which improves the conductivity of the intrinsic Mg2Si. These investigations will provide some theoretical basis for the application of Mg2Si intermetallic compounds in structural materials and thermoelectric materials.

Improvement of Microstructure and Mechanical Properties of Near‐Eutectic Al–Mg2Si Alloys by Eu Addition

To modify the microstructure and improve the tensile properties of Al–Mg2Si alloys, different contents of Eu are added into near‐eutectic Al–Mg2Si alloys by melting. Results show that the near‐eutectic Al–Mg2Si alloys consist of primary α‐Al, the first eutectic and second eutectic (Al + Mg2Si) phases, and a few Fe‐containing phase. When the addition of Eu reaches 0.05%, the first eutectic structure is refined, and the first eutectic Mg2Si phase transforms from platelet into fiber. Meanwhile, the second eutectic phase increases, even that the alloy is almost the second eutectic phase when the Eu content is 0.3%. These changes are induced by the modification of Eu. Tensile testing shows that the ductility and the strength are improved to 8.6% and 178 MPa from 1% and 145 MPa when the Eu content is 0.05%, and fracture mode is also changed. This improvement is caused by the modification of the eutectic structure. The tensile properties are decreased or even deteriorated with further increasing the Eu content, which is induced by over‐modification of Eu addition. It is concluded that the modification of eutectic Mg2Si phase by Eu addition contributes to the enhancement of mechanical properties of the near‐eutectic Al–Mg2Si alloys.

Green and facile fabrication of nanoporous silicon@carbon from commercial alloy with high graphitization degree for high-energy lithium-ion batteries

Silicon (Si) is considered as one of the most promising anodes for lithium-ion batteries (LIBs). However, rapid capacity decay caused by huge volume change and low electrical conductivity limit its further development. Herein, uniform porous Si@C (pSi@C) from commercial Mg2Si alloy and pitch is synthesized by green vacuum distillation method. During this process, the low boiling-point Mg is evaporated and cycled to form porous Si. Besides, the high-graphitization C layer is obtained because the metallic Mg favors the graphitization degree of C. As a result, the carbon coating layer and unique porous structure can improve electrical conductivity and accommodate volume change of Si anode without destroying solid electrolyte interface. The optimal pSi@C shows improved lithium storage with stable cyclability and superior rate capability.

Перспективні ливарні сплави з підвищеною міцністю на основі потрійних систем Al―Mg―Ge(Si)

The relative analysis of phase equilibria in the Al-corner of the ternary phase diagrams of Al―Mg―Ge(Si) systems is carried out. Both systems are characterized by the presence of a quasi-binary cross-section of the eutectic type, which is shifted towards Mg-enriched alloys, and sufficiently width range existence of the univariant eutectic transformation L-Al + Mg2Ge(Si). The melting point of quasi-binary eutectic (-Al + Mg2Ge) in the Al―Mg–Ge system and (-Al + Mg2Si) in the Al―Mg―Si is 629 °С and 597 °С, respectively, and the content of the strengthening phase ((Mg2Ge or Mg2Si) in eutectics is 7% (vol.) и 13% (vol.). The properties of non-alloyed alloys with different volume content of eutectic are investigated and the basic compositions of alloys with the optimal strength/ductility ratio for subsequent doping are selected as well. Taking into account the coordinates of the corresponding eutectic transformations, the doping system with the participation of Zn, Cu and other elements is determined. The heat treatment regimes for multicomponent eutectic alloys were selected, to ensure precipitation of Zn(Cu)-nanoparticles that strengthen matrix solid solution. It was shown that according to the level of mechanical properties, these alloys belong to high-strength alloys with property ranges: -Al + Mg2Ge) ― В = 470―590 МPа, 0,2 = 350―520 МPа, = 8,0―15,5%; -Al + Mg2Si) ― В = 400―560 МPа, 0,2 = = 430―520 МPа, = 2,3–-4,5%. Using a complex U-like Nechenji―Kuptsov test, casting properties were determined and it was shown that the fluidity of (-Al + Mg2Si) alloy was 1,3 times higher than that of the AK7ch cast alloy. In terms of the combination of mechanical and casting properties, the new multicomponent eutectic alloys based on the Al―Mg―Ge(Si) ternary systems are superior to the best modern industrial casting aluminum alloys. Keywords: casting aluminum alloys, ternary Al―Mg―Ge(Si) systems, eutectic alloys, alloying, microstructure, mechanical properties, fluidity.

Characterization and Tribological Properties of Novel AlCu4.5SiMg Alloy–(B4C/TiO2/nGr) Quaternary Hybrid Composites Sintered via Microwave

In the future, hybrid aluminum matrix composites, which are the second generation composites, will be replaced by solid reinforced third-generation quaternary hybrid composites in which nano- and micro-scale reinforcement particles are used together. In this study, microwave sinterability of B4C, TiO2 (nm + µm), and nGr reinforced quaternary hybrid composites that had AlCu4.5SiMg alloyed Matrix, and their microstructural and tribological properties after sintering were examined. The proportion of nGr in the composite sample was taken as 0.5 wt%, while B4C and TiO2 were used in three different proportions (3, 9, 12 wt%). After being compressed under 600 MPa pressure, the composite samples were sintered for 60 min at 550 °C by a microwave oven with a power of 2.9 kW and a frequency of 2.45 GHz. It was determined that due to its high microwave absorbency, B4C reinforcement improved the microwave sinterability more compared to TiO2. In XRD analyses, whereas Al4C3 and Al3BC reaction products were not seen as harmful, the intermetallic phase of Al2Cu was detected. It was determined that both friction coefficient and wear resistance increased as the proportion of B4C increased in composite samples. In AlCu4.5SiMg–(12 wt% B4C/3 wt% TiO2/0.5 wt% nGr) quaternary hybrid composites with the highest hardness (97.6 HV), the lowest specific wear rate (0.118 mm3 Nm × 10−3) was detected.

Effect of Cu addition on precipitation and age-hardening response of an Al-15%Mg2Si alloy

Microalloying of an Al-15%Mg2Si alloy (wt%) with 1%Cu produced an enhanced age-hardening response, increasing peak hardness and ultimate tensile strength due to a modified precipitation process. The solid solubility of Cu in Al-15%Mg2Si alloy effectively promotes the formation of the high number density of Guinier-Preston-Bagaryasky (GPB) zones combined with S precipitates. It suppresses β′ and β″ formation during ageing at 200 °C. Consequently, Al-15%Mg2Si-1%Cu alloy with the high density of GPB zones and S phase exhibited high peak hardness (121 HVN) and ultimate tensile strength (284 MPa), 42.4% and 49.5% higher than that of the Al-15%Mg2Si alloy, respectively.

Microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys

Abstract The microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys were studied by TEM and EBSD. The results showed that an increase in the tool rotation speed (300−700 r/min) led to a decrease in the defect area (from 10.5 mm2 to zero), whereas the defect area demonstrated the opposite trend (increased to 1.5 mm2 from zero) upon further increasing the rotation speed (700−1200 r/min). The types of defects were transformed from tunnel defects to fusion defects as the rotational speed increased. The coarse Mg2Si dendrites were broken and fine particles (smaller than 10 μm) formed in the weld nugget (WN). The amount of low-angle grain boundaries increased significantly from 57.7% to 83.6%, which was caused by an increase in the content of the deformed structure (from 1.7% to 13.6%). The hardness, ultimate tensile strength (UTS) and elongation were all greatly improved for the weld nugget. The hardness values of the WNs had the following order: R300

Corrosion behavior of Al-15%Mg2Si alloy with 1% Ni addition

Corrosion behaviors of Al-15%Mg2Si-1%Ni alloy in 3.5% NaCl solution were studied by characterizing the corrosion morphologies of Al3Ni, Mg2Si, and Al phases. The results show that there are two galvanic coupling systems (Al/Al3Ni and Al/Mg2Si) in Al-15%Mg2Si-1%Ni alloy. In the Al/Al3Ni coupling system, the intermetallic Al3Ni phase (nobler than the Al matrix) acts as the cathode throughout the corrosion process. For the Al/Mg2Si coupling system, electrochemical polarity conversion occurs between the Al matrix and the Mg2Si phase. The corrosion pits around the Al3Ni and Mg2Si are connected to form long corrosion channels, which accelerate corrosion of the Al-Mg2Si-Ni alloys.

Effect of Sb modification on microstructure and mechanical properties of hypoeutectic Al–11Mg2Si alloy

Effects of Sb modification on the eutectic microstructure and tensile properties of hypoeutectic Al–11Mg2Si alloy were systematically investigated in this work. Eutectic Mg2Si phase in hypoeutectic Al–11Mg2Si alloy was successfully refined from the long rod-like structure into fine spherical morphology when introducing 0.2 wt% Sb, whereas 1.0 wt% Sb reversely led to the formation of coarse eutectic Mg2Si phase. Specifically, the elongation to failure in the 0.2 wt% Sb modified alloy was significantly improved to 9.7% as compared to the unmodified counterpart (1.5%), and the ultimate tensile strength increased from 183 MPa to 208 MPa. This result can be attributed to the spheroidization of eutectic Mg2Si phase with Sb modification, which greatly relieved the stress concentration and restrained the crack source from initiating and propagating. The achieved results could shed new light on a more efficient and economical way to obtain high-performance hypoeutectic Al–Mg2Si alloys.

Purification of Metallurgical Grade Silicon Via the Mg-Si Alloy Refining and Acid Leaching Process

A novel process by combining Mg-Si alloy refining and acid leaching was suggested to purify metallurgical grade Si (MG-Si) in this paper. The proposed process was mainly composed of three steps, such as electromagnetic solidification, evaporation, and acid leaching. The results show that the precipitated Mg2Si crystals in the Mg-Si melt were successfully separated and enriched at the bottom of the sample because of the electromagnetic stirring and temperature gradient. Then, a porous structure Si with pore sizes ranging from nanometer- to micrometer-scale was obtained by evaporating Mg from the Mg2Si crystals. Finally, the high-purity Si powders with a purity of 99.995% were prepared by employing a successive acid leaching process. Most of the impurities (B, P, Fe, Ca, Ti, Ni, V, Cu) can be removed to less than 1 ppmw after the leaching process, indicating that an efficient elimination of impurities can be achieved with the help of the porous structure. Although bits of Mg was contained in the purified Si, it is expected to be eliminated by using a vacuum directional solidification. During the process, most of the magnesium can be recycled for cyclic utilization, which should be beneficial for the cost reduction. Therefore, it could be proposed that an efficient method of Si purification was obtained, which may be a valuable idea for the fabrication of solar grade silicon (SoG-Si).