Al Si Research Articles

Optimizing Tribological and Mechanical Properties of Hypereutectic Al–Si Alloys Through Advanced Grain Engineering and Graphene Reinforcement

Optimizing Tribological and Mechanical Properties of Hypereutectic Al–Si Alloys Through Advanced Grain Engineering and Graphene Reinforcement

Effect of boron nitride content on mechanical、dielectric and thermal shock resistance properties of Si3N4-BN-MAS composites

Achieving an optimal balance between mechanical properties, dielectric properties, and thermal shock resistance presents a significant challenge in the development of advanced ceramics. This study investigates Si3N4-BN composite materials, prepared by hot-press sintering with magnesium aluminum silicate (MAS) as the sintering additive, to assess the impact of varying hexagonal boron nitride (h-BN) content on their mechanical and dielectric properties, as well as their thermal shock resistance. At an h-BN content of 20 wt%, the BN layers act as a toughening phase through a pull-out mechanism, minimally impacting the composite's density. This composition results in superior fracture toughness (7.4 MPa m1/2), high strength (598 MPa), low dielectric constants (∼6.8), and dielectric loss (∼7.4 × 10−3). Notably, after a thermal shock at 1000 °C, the composite exhibits a peak residual strength of 621 MPa, surpassing its initial strength. This enhanced performance is attributed to the formation of a dense Mg–Al–Si–B–O oxide glass layer on the surface during thermal shock, which not only repairs surface defects but also induces compressive stress. The development of the Si3N4-BN-MAS composite, with its outstanding comprehensive performance, marks a significant advancement for materials used in high-temperature wave transmission applications.

Separation of silicon and germanium from the chlorination distillation residue based on co-precipitation of sodium-aluminum–silicon

Germanium (Ge) is known as a critical metal, and dust from coal burning is an important raw material for the extraction of Ge by the chlorination distillation process. Nevertheless, the residue produced by the chlorination distillation process (RCDP) also contains a considerable amount of Ge. The extraction of Ge from RCDP requires the conversion of Si and Ge into soluble compounds, and the efficient separation of large amounts of Si and Al from small amounts of Ge. In this study, Al, Si and Ge in RCDP were converted to soluble sodium slat by sodium roasting. Under the conditions of roasting temperature of 600 ℃, time of 120 min and the mass ratio of NaOH to RDCP of 3:1, 56.92 % of Al, 87.75 % of Si and 91.20 % of Ge are dissolved into solution. According to the formation mechanism of sodium aluminosilicate, the co–precipitation of Na–Al–Si can be promoted by adjusting the composition of the leaching solution to separate Si and Ge. Noteworthy, 73.97 % of Si have been removed by precipitation, while the precipitation ratio of Ge is only 8.77 %. Moreover, the Ge-containing solution is obtained with low Al–Si concentration (Al 0.37 g/L, Si 0.85 g/L and Ge 0.025 g/L). Overall, the obtained nano-microspherical non-dense cluster zeolite products have great potential for the removal of heavy metal ions from wastewater.

Experimental characterization and 3D sharp-interface model simulation of grain refinement during solidification of nano-TiCN/Al–7Si composites

Significant grain refinement was achieved in nano-TiCN/Al-7 wt.% Si composites through growth control induced by nano-TiCN particles (NPs). The microstructures displayed two types of NP distributions: within interdendritic eutectic Si phase and along grain boundaries. This refined microstructure contributed to enhancing mechanical properties. To elucidate the grain refinement mechanism in nano-TiCN/Al–7Si composites, a three-dimensional (3D) sharp interface model (SIM) was developed, integrating the cellular automaton (CA) technique with a transformation matrix comprising three Euler angles. This 3D SIM effectively replicated the dendritic morphology of α-Al. The exact impact of latent heat on grain refinement was clarified. The observed grain refinement induced by NPs could not be numerically reproduced without considering latent heat. The grain refinement in TiCN/Al–7Si composites is governed by multiple factors. As NPs layers inhibits solute diffusion along the solid-liquid interface, the dendrite growth rate reduces, leading to the reduced rate of latent-heat release. Consequently, constitutional undercooling in the surrounding liquid increases, activating more heterogeneous nuclei. The developed SIM model offers deeper insights into the grain refinement mechanism induced by TiCN NPs in Al–7Si alloy.

Aluminium-Silicon Lightweight Thermal Management Alloys with Controlled Thermal Expansion

With the ever-growing emphasis on global decarbonization and rapid increases in the power densities of electronics equipment in recent years, new methods and lightweight materials have been developed to manage heat load as well as interfacial stresses associated with coefficient of thermal expansion (CTE) mismatches between components. The Al–Si system provides an attractive combination of CTE performance and high thermal conductivity whilst being a very lightweight option. Such materials are of interest to industries where thermal management is a key design criterion, such as the aerospace, automotive, consumer electronics, defense, EV, and space sectors. This paper will describe the development and manufacture of a family of high-performance hypereutectic Al–Si alloys (AyontEX™) by a powder metallurgy method. These alloys are of particular interest for structural heat sink applications that require high reliability under thermal cycling (CTE of 17 μm/(m·°C)), as well as reflective optics and instrument assemblies that require good thermal and mechanical stability (CTE of 13 μm/(m·°C)). Critical performance relationships are presented, coupled with the microstructural, physical, and mechanical properties of these Al–Si alloys.

Study on microstructure and mechanical properties of 3003 aluminum alloy joints brazed with Al–Si–Cu–Ni paste brazing materials

Paste-type brazing materials have advantages such as adjusting the complexity of the parts to be soldered, easy storage and production in certain quantities. They can be used for brazing heat exchangers, liquid tanks and corrosion resistant parts. In this work, the microstructures and thermal behaviors of Al–Si–Cu–Ni brazing materials with different contents were investigated, and the effect of brazing process on the microstructural evolution and mechanical properties of brazed joints produced under nitrogen-filled environment was examined. It was found that the melting temperature of brazing material Al–5Si–20.5Cu–2Ni were ranged from 512.86 to 549.37 °C. The microstructure of Al–5Si–20.5Cu–2Ni consisted of α-Al solid solution, CuAl2 intermetallic compounds, the Al–Si–Cu phase, and some fine irregular Si particles in a homogenous manner. The microstructure of the brazed joints was uniformly formed during the brazing condition of 580 °C for 20 min, and the shear strength of the joints reached 41.76 MPa.

Effect of Si content on the phase transformation and pore structure evolution of porous Mo–Al–Si–B ceramics

Effect of Si content on the phase transformation and pore structure evolution of porous Mo–Al–Si–B ceramics

Phase transformation and microstructural evolution of coating layer of Al–Si coated 22MnB5 steel during thermal diffusion

Thermal diffusion experiments were conducted at 900 °C on Al–Si coated 22MnB5 steel to investigate phase composition and transformation. Results revealed that several compound phases, including Fe2Al7Si, FeAl3, (Al, Si)5Fe3 and Fe2Al5, observed beneath the eutectic structure in the Al–Si coating. At 900 °C, the eutectic structure is almost completely diffused over time. During thermal diffusion experiments, Fe element diffused into the coating, while Al and Si elements diffused within the coating and into the steel matrix. Electron backscatter diffraction analysis identified the phases of the Al–Si coating at different diffusion times at 900 °C, revealing a three-stage phase transition process, including diffusion of the Al–Si eutectic structure, formation of the Fe–Al (Si) phase, formation of the FeAl2 phase.

Effect of Two-Step Solution Treatments on the Microstructure and Mechanical Properties of B357 Aluminum Alloy

AbstractThis study investigates the effect of two-step solution treatments and aging times on the microstructure and mechanical properties of B357 Al–Si alloy, part of the most widely used cast aluminum alloy. Three sets of artificial aging heat treatments were conducted on the tensile samples prepared from B357 alloy produced by low-pressure die casting. Firstly, the conventional artificial aging heat treatment (T6) was carried out by solutionizing the tensile samples at 543 °C for 8.5 h, water quenching at 60 °C, and then artificially aging for 8.5 h at 160 °C. In the two-step solution treatment, the samples were solutionized at 400, 440, 480, and 520 °C for 4 h and then solutionized at 543 °C for 8.5 h and water quenched to 60 °C and then artificially aged for 8.5 h at 160 °C. Thirdly, the samples were solutionized at 480 °C for 4 h, solutionized at 543 °C for 8.5 h, water quenched to 60 °C, and artificially aged for 3–192 h. Despite different solutioning and aging processes, no significant differences were observed in the microstructures of the samples. Si particle coarsening was observed with increasing solution temperature (400–520 °C) and aging times (3–192 h). Si-containing dispersoids and dispersoid-free zones (DFZ) were observed in the primary-α matrix. While DFZ width increased with temperature and aging, dispersoid zones in primary-α dendrites significantly decreased. Differential Scanning Calorimetry (DSC) analysis shows that two-step solution treatment in B357 alloy increases β′ precipitates for Mg2Si precipitation strengthening. The two-step solutionized and aged sample showed the best combination of strength and ductility among all aged samples. B357 alloy exhibited the highest yield and tensile strength (309.7, 366.1 MPa) with 6% elongation for two-step solutionizing and 48 h aging. All aged B357 alloys showed ductile fracture as the primary fracture mode. However, brittle fractured Si particles were observed on the fracture surfaces.

Microstructure and mechanical properties of a hypereutectic Al–Si–Cu alloy manufactured by laser powder bed fusion

A novel Al–Si–Cu alloy was designed for additive manufacturing of automotive components, such as pistons and supercharger rotors, requiring a combination of elevated temperature properties and high cycle fatigue strength. The alloy was designed with an Al–Si hypereutectic chemistry to exploit the formation of primary Si nucleants to enable an equiaxed as-printed microstructure during laser powder bed fusion (LPBF). The alloy design space was assessed using a combined integrated computational materials engineering (ICME) approach with melt-spinning experiments to select a chemistry exhibiting primary Si nucleants acting as heterogeneous grain nucleation sites. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) of the LPBF as-printed samples revealed primary Si particles with a fully equiaxed grain structure and no apparent texturing as evaluated using electron backscatter diffraction (EBSD). High-resolution scanning transmission electron microscopy (STEM) revealed sub-micron Si particles and Al2Cu θ-phase precipitates which result in enhanced room and elevated temperature mechanical strength (room temperature: UTS: 449 ± 10 MPa, YS: 336 ± 12 MPa) as compared to commercial Al10SiMg (UTS: 417 ± 3 MPa, YS: 236 ± 6 MPa).

Effect of Ti microalloying and laser remelting on the microstructure and mechanical properties of laser powder bed fusion Al–12Si alloy

This study explores the impact of micron-Ti microalloying and laser remelting on the microstructure and mechanical properties of laser powder bed fusion (LPBF) Al–12Si alloy, analyzing the underlying reasons. The findings show that the tensile strength and elongation at 300 °C (184 ± 13 MPa and 7.4 ± 1.4 %) are on par with other LPBF heat-resistant Al alloys, such as near-eutectic Al–Ce and Al–Ni. Introducing micron Ti (1 wt%) to AlSi12 effectively eliminates the α-Al <100> texture and refines the grain structure, thanks to the strong nucleation effect from the formed D022-(Al, Si)3Ti, leading to enhanced tensile strength in both as-built and heat-treated (300 °C for 2 h) samples, while maintaining ductility within the typical range for LPBF near-eutectic Al–Si alloys. Laser remelting further decreases the presence of unmelted Ti powder in AlSi12Ti and encourages the formation of D022-(Al, Si)3Ti, offering insights into LPBF Al alloy composition design through promoting the melt of the modified powder and improving material homogeneity, especially for incorporating micron powders with high melting points. Additionally, the superior mid-high temperature properties (300 °C) of AlSi12+1 wt% micron-Ti contribute to expanding the database of LPBF Al alloys.

Influence of heat treatment on microstructure and thermo-physical properties of Al-50wt%Si alloy fabricated by selective laser melting

Herein, we investigate the influence of heat treatment on microstructure and thermo-physical properties of Al-50wt%Si alloy fabricated by selective laser melting (SLM). Microstructure characterizations reveal that SLM and heat-treated Al-50wt%Si alloys are all characterized by the primary Si and eutectic structure consisting of dominant Al matrix and tiny eutectic Si. However, the size of primary Si monotonously increases with increasing the heat treatment holding time at 550 °C. In addition, the SLM Al-50wt%Si alloy displays a highest coefficient of thermal expansion (CTE) among all examined alloys. As the heat treatment holding time increases, the Si precipitates from the Al(Si)-supersaturated solid solution, leading to the formation of a skeleton-like Si phase, which effectively alleviates the thermal expansion. Furthermore, the SLM Al-50wt%Si alloy exhibits a lowest coefficient of thermal conductivity (CTC), since the significantly increased size of primary Si with increasing the heat treatment holding time leads to a substantial reduction in the number of grain boundaries, which severely restricts the scattering of heat transfer phonons. Moreover, theoretical models are employed to calculate the CTE and CTC. Results indicate that the Schapery lower model provides a better prediction of CTE, and the actual CTC values of Al-50wt%Si alloys after heat treatment are closer to theoretical values. These findings can provide new insights into designing Al matrix composites with low CTE and high CTC through microstructural optimization.

Formation and Evolution of Interfacial Structure in Al–Si–Mg/Stainless Steel Bimetals during Hot-Dipping Process

Understanding trends in the formation of the intermetallic compound (IMC) layer in Al/Fe bimetallic composites can aid in significantly improving their mechanical properties. However, it is currently challenging to predict IMC layer formation during hot-dip aluminizing. Furthermore, the results from previous studies are difficult to compare owing to the variation in the process parameters used. Therefore, to understand how temperatures and holding times affect the thickness and hardness properties of IMC layers, we investigated the interfacial properties of aluminized stainless steel in molten Al-Si-Mg. AISI 420 stainless steel was hot-dip aluminized in an Al–Si–Mg alloy melt for 10–120 min at four different temperatures: 700, 750, 800, and 850 °C. Morphology, type, and element distribution of the phases formed in the reaction layer and the reduction rate of the aluminizing process were studied. Notably, while the reaction layer thickness increased with increasing aluminizing temperature when the holding time was low, long-term reaction caused the reaction layer to become thicker at lower temperatures. The mechanism of this morphological transformation is discussed. The results demonstrated effective trends in controlling the morphology of the intermetallic compound layer with respect to various hot-dip Al plating process parameters.

Mechanical and Tribological Properties of Hybrid and Monolithic Reinforced Hypoeutectic Al–Si Matrix Composites

This study investigates the combined influence of Si element and reinforcing particles on the hardness and wear performance of aluminum matrix composites. The composites in focus include Fe‐based metallic glass (FMG) monolithic reinforced and FMG/SiC hybrid reinforced Al‐5 wt% Si matrix composites, fabricated through spark plasma sintering (SPS). A comprehensive investigation is carried out, encompassing the analysis of microstructural attributes and the examination of worn surfaces through field emission scanning electron microscopy (FESEM). Additionally, the study scrutinized two pivotal factors—hardness and density—recognizing their pivotal roles in determining the tribological performance of these composites. The experimental findings demonstrated the presence of an oxide protective layer on the worn surfaces of all specimens. Although, FMG/SiC hybrid reinforced Al‐5 wt% Si matrix composite possessed the highest hardness value, the best tribological performance is observed in Si‐bearing monolithic reinforced composite. The addition of Si to the matrix of monolithic reinforced composite facilitates improved densification behavior and enhances the distribution of reinforcing particles, resulting in a more stable and protective oxide layer in this specific sample. Furthermore, the study identifies a transition in the operative wear mechanisms from delamination to mild abrasion and adhesion with the inclusion of Si element.

Impact of intermetallic phases on the localised pitting corrosion and high-temperature tensile strength of Al–Si[sbnd]Mg[sbnd]Cu[sbnd]Ni alloys

The influence of Ni-rich intermetallic particles (IMPs) on the microstructure, high-temperature mechanical properties, and corrosion behaviour of Al–Si–Mg–Cu–Ni alloys was investigated. The presence of coarse block-like γ-Al7Cu4Ni and thin needle-like δ-Al3NiCu IMPs contributed to low-temperature alloy strengthening during tensile tests. However, void nucleation and coalescence within the IMPs facilitated ductile fracture and alloy rupture, resulting in a lower tensile strength at high temperatures. Although both IMP phases had a cathodic electrochemical nature, resulting in strong galvanic corrosion, the γ-Al7Cu4Ni phase acted as the primary cathode, amplifying localised pitting while reducing the overall alloy corrosion resistance.

The effect of B and Sb on the corrosion behavior of T6-treated Al–Si–Mg alloys

The influence of B and Sb on the microstructure and corrosion behavior of T6-treated Al–Si–Mg alloys has been specifically studied. It is found that the addition of 0.03 wt% B to Al–Si–Mg alloys results in the lowest corrosion rate (0.02451 mm/y) when immersed in 3.5 wt% NaCl solution for 3 days. This improvement can be attributed to the transformation of coarse dendritic α-Al grains into refined equiaxed grains, which is beneficial for the formation of uniform and compact passive film. In contrast, the Al–Si–Mg alloy with addition of 0.2 wt% Sb shows the highest corrosion rate (0.05795 mm/y), which can be attributed to two reasons. First, the addition of Sb contributes to the transformation of rod-like eutectic Si particles into a spherical morphology, increasing the number of micro-galvanic corrosion sites and thus accelerating the corrosion process. Second, the generated Mg3Sb2 phase, being more noble than the eutectic Si phase, strengthens the micro-galvanic corrosion.

A marine incursion during the onset of T-OAE in Sichuan Basin, China: Evidence from green clay minerals and carbonate concretions

A high-amplitude global sea level rose rapidly during the early Toarcian (Early Jurassic), making the transgression deposits potential stratigraphic correlation markers of marine and terrestrial successions. Green clay minerals (i.e., glauconite and chamosite), carbonate concretions, and geochemical database associated with the early Toarcian global transgression are archived in the Lower Jurassic Da'anzhai Member (the Early Toarcian age) in the Sichuan Basin of China, a mega lake along the Tethys Ocean. The fine-grained glauconites with high Al and low Si contents suggested that they were transported from offshore to the lake by marine incursion and were oxidized during the transport processes. The green authigenic chamosite cement and redeposited chamosite grains with high Mg/Fe and low Al/Si ratios were diagenetically transformed from berthierine formed in the brackish water caused by marine incursion. The chemically impure siderite concretions with low 87Sr/86Sr ratios and high δ13C values suggested that the lake water and sediment pore waters were mixed with seawater. Coeval calcareous concretions have low 87Sr/86Sr ratios and high δ13C values, indicating the mixing of lake water with seawater. Combining the stratigraphic low 87Sr/86Sr values, we suggested that there was a marine incursion into the Sichuan Basin. According to the organic carbon isotopic stratigraphy correlation, the marine incursion occurred during the onset of T-OAE. The rapid and high-amplitude global sea-level rise may have caused this marine incursion.

Tensile properties and fracture behavior of Al–8Si alloy sheets with different Mg under natural aging

Tensile properties and fracture behavior of Al–8Si alloy sheets with different Mg under natural aging

Localized corrosion characteristics of Al-Mg-Si aluminum alloy with aging time and pre-delayed aging condition

The effects of single aging, delayed aging and pre-delayed aging treatment on the corrosion resistance of Al-Mg-Si alloy were studied by scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), three-dimensional X-ray tomography (3D-XRT), confocal laser scanning microscopy (CLSM) and electrochemical measurements. The surface potentials of Al(MnFe)Si, Mg2Si, and Si-rich remnant phases are determined, identifying Al(MnFe)Si phase as the crucial cathodic site for corrosion initiation, and the increase in surface potential implies an accelerated corrosion rate after immersion. The intergranular corrosion susceptibility of the alloy is predominantly influenced by the microstructure caused by aging conditions. The factors affecting corrosion resistance are summarized as (i) adjustment of electrochemical reaction activity by controlling the area fraction of Al(MnFe)Si phase, (ii) the spacing of grain boundary precipitates (GBPs), and (iii) the width of the precipitation-free zone (PFZ). The delayed aging (DA) sample exhibits inferior corrosion resistance due to the continuous GBPs and extended sub-grain boundaries corrosion propagation paths. The pre-delayed aging treatment successfully mitigates the corrosion degree of DA by widening the GBPs spacing and narrowing the PFZ width. This suggests that pre-aging treatment is a potent strategy for enhancing corrosion resistance without compromising the alloy's strength.

Improvement of impact properties of Al–Si–Mg alloy via solution treatment and joint modification with Sr and La

Improvement of impact properties of Al–Si–Mg alloy via solution treatment and joint modification with Sr and La