Hypoeutectic Al-Si Research Articles

Grain refiner fabricated by spark plasma sintering for hypoeutectic Al–Si alloy cast and its refining ability

Grain refiner fabricated by spark plasma sintering (SPS) for an as-cast hypoeutectic Al–Si alloy were proposed. The proposed grain refiner contains Al3Ti and Na flux particles in an Al-11 mass%Si alloy matrix. Through SPS, the grain refiner were obtained without any reaction between the Al3Ti particles, Na flux particles, and Al-11 mass%Si alloy matrix. Casting tests were conducted using the proposed grain refiners, and the refiners reduced the dendrite cell size and the dendrite arm spacing of the primary α-Al phase, as well as the lamellar spacing of the eutectic structure. The eutectic Si phase changed to a granular shape upon the refinement of the eutectic structure. Furthermore, the tensile strength and ductility of the as-cast Al-11 mass%Si alloy were drastically improved by adding the proposed grain refiner. This improvement was attributed to the refinement and granulation of the eutectic Si phase.

Synergetic Effect of La and Sb on the Eutectic Silicon and Mechanical Properties in Multi-elements Hypoeutectic Al–Si Alloy

Synergetic Effect of La and Sb on the Eutectic Silicon and Mechanical Properties in Multi-elements Hypoeutectic Al–Si Alloy

Effect of the addition of Ni and Cu on solidification microstructure evolution of Al-5Si-0.5Mg alloys

AbstractTo develop new high-performance hypoeutectic Al–Si–Mg alloys at elevated temperatures, it is often necessary to add alloying elements of Cu and Ni. The high-temperature strength of the most used Al–Si–Mg–Cu–Ni alloy depends on a load transfer from the α-Al matrix to the intermetallic compounds. However, there is still a lack of detailed investigation on the effects of the combined addition of Ni and Cu on the solidification microstructure evolution of Al–Si–Mg base alloys with a lower Si concentration. This investigation specifically addresses the effects of the addition of Cu or Cu and Ni on the solidification microstructure evolution of the Al–5Si–0.5Mg alloy. It was found that when Al–5Si–0.5Mg is alloyed with Cu or Cu and Ni, the solidus temperature decreases, while the freezing range of the Al–5Si–0.5Mg alloy increases. With the addition of Cu and even small amounts of Ni, the phases Al7Cu4Ni and Al5Cu2Mg8Si6 were predicted by TC simulations and also observed by SEM. With a higher Ni content, Al3Ni and Al3Ni2 also solidify. More importantly, the presence of Cu and Ni can partition into the α-AlSiFeMn phase and change the size and morphology of the α-AlSiFeMn phase. This investigation provides a helpful hint to the development of the high-performance Al–Si–Mg–Cu–Ni alloys with a simultaneous improvement of the thermal conductivity and mechanical properties.

Impact of Mg on the Feeding Ability of Cast Al–Si7–Mg(0_0.2_0.4_0.6) Alloys

The demand for high-performance Al–Si casting alloys is driven by their mechanical properties, making them popular in automotive, aerospace, and engineering industries. These alloys, especially hypoeutectic Al–Si–Mg, offer benefits like high fluidity, low thermal expansion, and good corrosion resistance. Silicon and magnesium primarily define their microstructure and mechanical properties. Silicon enhances fluidity, while magnesium improves strength and fatigue resistance. However, challenges like shrinkage porosity persist during solidification. Understanding solidification feeding regions is crucial, influenced by factors such as chemical composition, solidification characteristics, and casting design. This study investigates magnesium’s influence on feeding ability in hypoeutectic Al–Si7–Mg alloys through experimental tests. Increasing magnesium content from 0% to 0.6% affects the interdendritic and burst feeding regions. This could impact shrinkage porosity formation. The “Sand Hourglass” test results indicate a rise in porosity levels with higher magnesium content, which is linked to the narrowing of interdendritic channels and the formation of magnesium-rich intermetallic compounds. These changes hinder the liquid metal flow, worsening shrinkage porosity. Therefore, magnesium’s role in expanding the interdendritic region is a key factor in developing porosity in cast hypoeutectic Al–Si7–Mg alloys. This study highlights that porosity levels increase from 0% in magnesium-free Al–Si7 to 0.84% in Al–Si7–Mg0.6, underscoring magnesium’s significant impact on the occurrence of porosity in these alloys.

Effect of Simultaneous Mg and Zn Addition on the Solidification and Microstructure of Multi-Element Hypoeutectic Al-Si Alloys

Effect of Simultaneous Mg and Zn Addition on the Solidification and Microstructure of Multi-Element Hypoeutectic Al-Si Alloys

A novel process for producing Al-Si alloy utilizing aluminum-silicon oxide extracted from coal fly ash

As a kind of solid waste rich in aluminum and silicon resources, the comprehensive utilization of coal fly ash (CFA) will be of great significance to reduce environmental pollution and improve economic benefits. This work proposed a facile and environmentally friendly cleaning process for producing Al-Si alloy by molten salt electrolysis from CFA extract, aluminum-silicon oxide (ASO). The dissolution behavior and dissolution reaction mechanism of ASO were studied by high temperature visual dissolution experiment, thermodynamics analysis and phase analysis. Due to the chemical reaction between ASO and cryolite-based melt, ASO powder dissolves rapidly in melt and the dissolution rate of ASO is not determined by the phase compositions but by the mass ratio of Al2O3/SiO2. For replenishing the oxide concentration in the electrolyte as quick as possible, the proper mass ratio of Al2O3/SiO2 is in the range of 0.75–7.5. The electrochemical co-reduction behavior of Si (IV) and Al (III) ions on the W electrode was performed by cyclic voltammetry and square wave voltammetry. The results indicated that the reduction of Si (IV) ion in the melt was a two-step irreversible process. Hypoeutectic Al-Si alloy and eutectic Al-Si alloy were prepared by galvanostatic electrolysis using ASO as raw material. This innovative technology can realize high-value recycling of CFA resources and low carbon emission, low energy consumption production of Al-Si alloy.

Breaking the strength-conductivity paradigm in hypoeutectic Al–Si alloy via annealing-induced Si nanoprecipitation

Hypoeutectic Al–Si alloys are increasingly recognized as promising materials for aluminum conductor cables owing to their remarkable combination of high strength and castability. However, the widespread industrial application of these alloys is limited by their moderate electrical conductivities (ECs). In this study, we explored the effects of direct annealing on the EC, mechanical properties, and microstructure of AA4043 rods fabricated via Properzi continuous casting. The AA4043 rods were annealed at different temperatures (200, 250, 300, and 350 °C) for 4 and 24 h. Direct annealing resulted in a significant improvement in the EC of the rods, with all samples exhibiting an EC improvement from 50 to 58% IACS. However, the mechanical strength of the rods was considerably reduced. The sample annealed at 250 °C for 4 h exhibited the best combination of EC (58.8% IACS), microhardness (43 HV), and ultimate tensile strength (141 MPa) among all the as-prepared samples. The sample annealed at 350 °C for 24 h showed the lowest microhardness (31.8 HV) and ultimate tensile strength (113 MPa), with EC of 58.05% IACS. Electron backscatter diffraction (EBSD) results revealed retained fibrous grains structure with partial recrystallization at a lower annealing temperature of 250 °C, whereas a higher annealing temperature of 350 °C resulted in complete recrystallization leading to coarse equiaxed grains. Transmission electron microscopy (TEM) analysis revealed the formation of nano-Si precipitates in the annealed samples. To understand the diverse contributions of the resistivity mechanisms and microstructural characteristics to EC improvement, a constitutive resistivity model was employed. These findings offer valuable insights into improving the EC and maintaining a delicate balance between the EC and strength of novel Al–Si conductor alloys.

Microstructure and mechanical properties of non-heat-treated Al–8Si-0.2Mg-0.5Mn alloy inoculated by Al–Nb–B refiner

Al–Nb–B refiner has been considered as an alternative to Al–Ti–B refiner for hypoeutectic Al–Si alloys due to Si-poisoning effect. In this paper, the effects of Al–Nb–B and Al–Ti–B refiner on the microstructure and mechanical properties in indirect squeeze casting Al–8Si-0.2Mg-0.5Mn alloy were compared. Results show that the grain sizes in the edge chilling layer, segregation band, and the center region of the Al–Nb–B refined alloys were refined by 13.9%, 12.5%, and 17.6% compared to Al–Ti–B refined alloys, respectively. The yield strength, tensile strength, and elongation of Al–Nb–B inoculated alloys were superior to those of the unrefined alloys and Al–Ti–B inoculated alloys. The coexistence of NbAl3 and NbB2 particles in the Al–Nb–B refiner exhibited excellent anti Si-poisoning capability. They significantly decreased the grain size and uniformly distributed the eutectic Si particles and Fe-rich phases, resulting in an increase in the yield strength of the alloy by 16.1% compared to the Al–Ti–B inoculated alloy. The distribution of iron-rich phases in the segregation band was affected by the inoculation. The size of α-Al15(Fe, Mn)3Si2 phase in Al–Ti–B inoculated alloys was refined, and the number significantly increased, resulting in a decrease in tensile strength of 12.82 MPa. In the Al–Nb–B inoculated alloys, the size and number of α-Al15(Fe, Mn)3Si2 phase decreased, and the δ-Al4FeSi2 phase increased, which effectively improved the fracture toughness and ductility. In addition, with the increase in grain refinement (from unrefined to Al–Ti–B to Al–Nb–B inoculated alloy), the fracture behavior changed from trans-granular fracture to intergranular fracture, improving the fracture toughness.

Effect of thermal treatments on the surface electrical conductivity of AlSi7Mg produced by laser powder bed fusion

In the last years, the production of hypoeutectic Al-Si waveguide components by metal additive manufacturing has gained increasing attention in the telecommunications industry. The performances of waveguide components are influenced primarily by dimensional tolerances, surface electrical conductivity, surface roughness, and dimensional accuracy. Among these properties, electrical conductivity is known to be strongly influenced by the structural and microstructural characteristics of the alloys.In this work, microstructural and structural properties of an hypoeutectic Al-Si alloy, namely the AlSi7Mg alloy, were studied using FESEM, DSC, and XRD to understand how different thermal treatments (stress relieving, T5, and T6) affect the surface electrical conductivity. In the end, the most suitable thermal treatment to be applied to this alloy to maximize its electrical conductivity and, therefore, its appeal for microwave waveguide components is identified.

Analisa Komparasi Sifat Fisis dan Mekanis Piston Sepeda Motor dari Empat Pabrikan

The piston is an essential component in the internal combustion system. Unfortunately, most piston products on the market are of low quality, which is detrimental to consumers. Most pistons sold in spare parts shops in Medan City have varying prices and different quality. The study compares four manufacturers' chemical composition, microstructure and hardness of the pistons of 4-stroke motorcycles. The four types of pistons were purchased at an automotive component sales shop in Medan city. The pistons were cut by machine and then analyzed for chemical composition, microstructure and hardness. The research results show that the chemical composition of the four-piston manufacturers is almost similar, where the silicon content ranges from 2-3%, which is a hypoeutectic Al-Si aluminium alloy. Interestingly, the hardness values and microstructure of pistons are different. The hardness value for brand X is the highest compared to other products, at 41.16 VHN. Microstructural observations show that the microstructures of manufacturers W, X and Y are similar, where the Si particles are evenly distributed with almost uniform sizes. Meanwhile, the Z manufacturer shows a microstructure with fibrous Si particles with a coarse SDAS size.

Simulation of gas porosity formation and interaction with dendrite and eutectic structures during solidification of Al-Si alloys

A two-dimensional (2-D) multi-phase cellular automaton (CA)-finite difference (FD)-lattice Boltzmann (LB) coupled model is developed to simulate the hydrogen pore formation during dendritic and eutectic solidification of hypoeutectic Al-Si alloys. In this model, the dendrite and eutectic structures are simulated using a CA technique. The solute diffusion is solved by the FD method. The nucleation, growth, and motion behavior of gas pore, and hydrogen transport are simulated by a LB Shen-Chen scheme. It is found that the pores can grow fully but compete in the primary dendrite growth stage. Conversely, pores newly nucleated in residual inter-dendrite liquid during the eutectic solidification stage grow restrictedly and independently. Pore shape severely deformed by the compression of the surrounding solid structures. Moreover, the effects of the initial Si composition, initial hydrogen concentration and cooling rate on the pore formation are qualitatively and quantitatively studied. It is found that the initial Si composition significantly impacts on the pore size and distribution, but little effect on the porosity percentage which decreases markedly with the decreasing initial hydrogen concentration and increasing cooling rate. Comparison reveals that the simulated microstructure morphological characteristics and the predicted porosity percentage agree well with the experimental observation reported in the literature.

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.

Large supercooling of Al[sbnd]Si alloy in microcapsule composed of Al2O3 shell

Al–Si-based microencapsulated phase change materials (MEPCMs) with a eutectic temperature of 577 °C are promising thermal energy storage (TES) materials owing to their large latent heat. Various preparation methods for Al–Si-based MEPCMs with Al2O3 shells have been reported; interestingly, Al–Si-based MEPCMs have large supercooling that does not depend on the preparation method. Supercooling is an important property of MEPCMs in the engineering aspects of designing a TES system. However, limited studies have reported the mechanism of supercooling in MEPCM. Moreover, the large supercooling of AlSi alloys in microcapsules compared with bulk materials is an interesting phenomenon in the field of physical chemistry. This study investigates the supercooling phenomenon in eutectic, hypoeutectic, and hypereutectic AlSi alloy MEPCMs, that is, AlSi alloys in a microcapsule comprising an Al2O3 shell. For the MEPCM with a hypoeutectic composition, supercooling is not observed because the primary Al acts as a nucleation site. For MEPCMs of eutectic and hypereutectic compositions, supercooling is observed at 25–37 °C. When the MEPCMs are heated to 1000 °C and then cooled, the supercooling degree increases significantly. In MEPCMs with a hypoeutectic composition, the precipitation of primary Al crystals does not occur under these conditions. Such findings contribute to the optimization of the design and operation of TES systems.

Effects of the synergistic addition of AlCrNiTi and Ce on the microstructure and mechanical properties of hypoeutectic Al-7Si alloy

A new strategy is proposed in this study to modify the microstructure of the Al-7Si alloy, which is widely employed in the aerospace and transportation sectors due to its lightweight, high specific strength, and specific modulus. The primary challenge of the Al-7Si alloy is its coarse microstructure, which undermines its mechanical properties. This research focuses on the effects of adding the AlCrNiTi master alloy and Ce to the Al-7Si alloy. The impact on both the microstructure evolution and the mechanical properties is examined, including analysis and discussion of the underlying mechanisms for refinement and strengthening. When the alloy was modified by 0.9 wt% of the AlCrNiTi master alloy and 0.1 wt% of Ce, there was a notable refinement of the α-Al phase, transforming it from a coarse dendritic structure to fine equiaxed grains. The addition of 0.9 wt% of the AlCrNiTi master alloy and 0.1 wt% of Ce can also reduce the secondary dendrite arm spacing (SDAS) to 5.9 μm. The eutectic Si phase underwent a significant transformation, changing from coarse flakes to fine granularity with rounded edges. Furthermore, CeSi2Ni2, Al3Ni intermetallic compounds, and nanoscale Al45Cr7 particles were observed in the modified Al-7Si alloy. Tensile tests showed that the addition of the inoculant in the Al-7Si alloy enhanced the ultimate tensile strength (UTS) from 173 MPa to 211 MPa and increased the elongation (El) from 7.9% to 14.1%.

Morphological features of unmodified eutectic Si and morphological transformation after solution treatment

The morphological features of unmodified eutectic Si microstructure before and after solution treatment were revealed by the deep etching technique with a hypoeutectic Al-Si casting alloy as the study material. Before the solution treatment, the unmodified eutectic Si particles showed multi-faceted morphological features such as sheet-like, parallel hexahedral, truncated pyramidal, triangular platelet-like, octahedral, etc. After the six-hour solution treatment, the eutectic Si particles exhibit non-faceted morphological features such as spheroidal, cylindrical, and edge rounding. In addition, the edge rounding transformation of the octahedral Si particle during the holding process of solution treatment is visualised in combination with the molecular dynamics simulation.

The characterization of porosity and externally solidified crystals in a high pressure die casting hypoeutectic Al-Si alloy using a newly developed ceramic shot sleeve

The effective methods to regulating porosity and externally solidified crystals (ESCs) have been remained as a challenging task for high pressure die casting (HPDC) automobile parts. In this work, a newly designed ceramic shot sleeve is proposed for reducing porosity and optimizing ESCs. As a result, both porosity and ESCs achieve an effective reduction after applying the ceramic shot sleeve. This study provides insights into regulating porosity and coarse ESCs of die castings and it is expected to expand its application in industrial manufacture.

Upgrading recycling of Al–7 wt%Si alloys using electromagnetic force in directional solidification

The highly reactive chemical nature of aluminum makes it production energy-intensive or essentially impossible to extract alloying elements from Al-based liquids. Using molten salt fluxing and electrolysis processes can effectively refine coarse Al scraps. However, the generation of toxic gases and hazardous dross during these processes can cause significant environmental protection challenges and result in notable social concerns. Therefore, the primary recycling of post-consumer Al in industries currently proceeds mainly in a cascade manner, which is not sustainable when considering the Al cycle trends in the coming decades. Herein, we develop a novel process to separate primary Al from the crystallizing liquid when a constant electromagnetic force (EMF) is applied. Using this technique, we successfully upgraded Al–7mass%Si (hereafter, unless specified otherwise) alloy to approximately Al–3.6%Si in directional solidification. The separation mechanism was discussed in terms of the electrical properties of the respective phases during solidification. Fluid flow simulation results were applied to elucidate the separation behavior in the alloy. The upper and lower limits to separate the crystallizing alloy into an Al-rich and Si-rich areas were determined when the controlling factors were clarified, which made it possible to scale up the present laboratory-based setup to an industrial level. Moreover, the energy consumption of the process was slightly higher than that required for remelting only. Using the EMF technique to separate the crystallizing alloy into Al-rich and Si-rich regions did not produce hazardous dross or toxic gases. This energy-saving and eco-friendly process can provide a breakthrough to overcome the “dead metal” crisis and thus realize sustainability by upgrading recycling of post-consumer hypoeutectic Al–Si casting alloys.

Effect of High-Frequency Electric Pulse on the Solidification Microstructure and Properties of Hypoeutectic Al-Si Alloy.

The effects of different pulse frequencies on the microstructure grain size and solid solubility of Al-9Si alloy were systematically investigated using OM, SEM, and EDS. The impact on the mechanical properties of the alloy was analyzed using a micro-Vickers hardness tester and multifunctional friction tester. During solidification, the Al-9Si alloy is exposed to high-frequency electric current pulses with a current density of 300 A/cm2 and frequencies of 0 Hz, 500 Hz, 1000 Hz, and 2000 Hz. The experimental results show that the Lorentz force also increases as the high-frequency pulse frequency increases. Intense electromagnetic stirring leads to grain refinement. However, as the pulse frequency continues to grow, the combined effect of Joule heating and Lorentz force results in an enlargement of the melt zone and an increase in grain size. At a pulse frequency of 1000 Hz, the eutectic structure size of the Al-9Si alloy is optimal, with the average size being reduced to 13.87 μm and a dense distribution, effectively eliminating primary Si. The EDS results revealed that the high-frequency pulse led to a more uniform distribution of Si elements within the matrix, and the solid solubility of Si in the α-Al matrix increased to a maximum value of 1.99%, representing a 39.2% increase. At a pulse frequency of 1000 Hz, the sample demonstrates the most favorable mechanical properties, with the friction coefficient reaching a minimum value of 0.302, representing a 37.7% decrease in the average friction coefficient. The results demonstrate that high-frequency pulsing is an effective method for enhancing the mechanical properties of Al-9Si alloy.

Insights into the dual effects of Ti on the grain refinement and mechanical properties of hypoeutectic Al–Si alloys

Hypoeutectic Al–Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance, and grain refinement is regarded as an important way to improve casting and mechanical properties. Titanium (Ti) is a basic element for grain refinement; thus, a certain amount of Ti is often included in Al–Si alloys. In the present work, the changes in the grain refinement, mechanical, and casting properties of Al–Si alloys with different Ti concentration levels under various grain refinement conditions were systematically investigated. The specific roles of Ti in the heterogeneous nucleation of α-Al grains were summarized, and the formation mechanism of Ti-rich zones in Al–Si alloys was revealed. Excess Ti concentration could not efficiently reduce the grain size of Al–Si alloys and eventually resulted in inferior mechanical and casting qualities; hence, the recommended Ti concentration level for the aluminum alloy grades of A356 and A357 is ≤ 0.1 wt%. Furthermore, an optimized technique for the grain refinement of hypoeutectic Al–Si alloys was presented. A small amount of an Al–TCB master alloy was introduced to achieve the best grain refinement and mechanical properties in a trace Ti environment. The addition of 0.5 wt% of the Al–TCB master alloy at the Ti concentration level of 0.06 wt% increased the ultimate tensile strength, elongation, and quality index of the Al–7Si–0.45Mg alloy to 328.8 ± 5.0 MPa, 14.4 % ± 0.6 %, and 970.7 ± 33.1 MPa, respectively.

Mechanical properties of hypoeutectic, eutectic, and hypereutectic Al-Si automotive alloys under ageing treatment

The role of different levels of silicon on mechanical properties has been investigated through tensile and impact tests along with fractography of Al-Si automotive alloys. Cast alloys are given precipitation strengthening through T6 heat treatment. It has been experimentally determined that ageing these alloys leads to the enhancement of tensile properties, which is mainly caused by the precipitation of the intermetallics such as Al2Cu, Mg2Si, and Al2CuMg within the Al-matrix. The ductility of these alloys primarily exhibit a diminishing trend as the ageing temperature increased. This diminishing trend can be attributed to the formation of fine precipitates like GP zones and metastable phases. However, after reaching a certain temperature, the ductility started to increase again. This is caused by the coarsening of the precipitates. At higher strain rates, the tensile strength is found to be identical for higher Si-added alloys due to their brittleness. The microstructures of the alloys reveal that as Si content increases, eutectic phases become more apparent. Fractography of the base alloy exhibits a small dimple structure, and higher Si-added alloys initiate the crack propagation. Beyond eutectic composition, the mechanical properties of the alloys became distorted due to block-like primary Si into the Al-matrix.