Hypoeutectic Al-Si Alloys 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 for hypoeutectic Al-Si alloy cast and its refining ability

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 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.

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.

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.

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.

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.

Effect of Alloying Elements Mg and Cu on the Modification of Eutectic Silicon in Hypoeutectic Al–Si Alloys

The modification of eutectic silicon plays a crucial role in enhancing the mechanical properties of hypoeutectic Al–Si alloys. However, there is still limited understanding regarding the factors that affect the modification of eutectic silicon in hypoeutectic Al–Si alloys, particularly in terms of the role played by alloying elements during the modification process. In order to address this gap, this study aimed to investigate the influence of two key alloying elements, Mg and Cu, on the modification effect of Sr. To achieve this, the morphology of eutectic silicon in the as-cast and heat-treated states of Al–7Si alloy, modified with Sr, was examined using scanning electron microscopy (SEM). Different levels of magnesium and copper content were used to analyze their impact on the modification effect of Sr. The results obtained from the analysis revealed that both Mg and Cu significantly weaken the modification effect of strontium on eutectic silicon. Furthermore, it was observed that the degree of deterioration in the modification effect increases progressively with higher alloying element content. Interestingly, increasing the strontium content and adjusting the cooling rate were found to be ineffective in eliminating this weakening effect caused by Mg and Cu. These findings highlight the complex interplay between alloying elements and the modification process of eutectic silicon in hypoeutectic Al–Si alloys. A deeper understanding of these factors is essential for the development of effective strategies to optimize the mechanical properties of such alloys.

Study on Preparation of Hypoeutectic Al–Si Alloy from Diamond Wire Saw Silicon Powder by Electromagnetic Method

Study on Preparation of Hypoeutectic Al–Si Alloy from Diamond Wire Saw Silicon Powder by Electromagnetic Method

Persistent Homology Analysis of the Microstructure of Laser-Powder-Bed-Fused Al-12Si Alloy.

The laser powder bed fusion (L-PBF) process provides the cellular microstructure (primary α phase surrounded by a eutectic Si network) inside hypo-eutectic Al-Si alloys. The microstructure changes to the particle-dispersed microstructure with heat treatments at around 500 °C. The microstructural change leads to a significant reduction in the tensile strength. However, the microstructural descriptors representing the cellular and particle-dispersed microstructures have not been established, resulting in difficulty in terms of discussion regarding the structure-property relationship. In this study, an attempt was made to analyze the microstructure in L-PBF-built and subsequently heat-treated Al-12Si (mass%) alloys using the persistent homology, which can analyze the spatial distributions and connections of secondary phases. The zero-dimensional persistent homology revealed that the spacing between adjacent Si particles was independent of Si particle size in the as-built alloy, whereas fewer Si particles existed near large Si particles in the heat-treated alloy. Furthermore, the first principal component of a one-dimensional persistent homology diagram would represent the microstructural characteristics from cellular to particle-dispersed morphology. These microstructural descriptors were strongly correlated with the tensile and yield strengths. This study provides a new insight into the microstructural indices describing unique microstructures in L-PBF-built alloys.

Thermomechanical Joining of Hypoeutectic Aluminium Cast Plates

Consistent lightweight construction in the area of vehicle manufacturing requires the increased use of multi-material combinations. This, in turn, requires an adaptation of standard joining techniques. In multi-material combinations, the importance of integral cast components, in particular, is increasing and poses additional technical challenges for the industry. One approach to solve these challenges is adaptable joining elements manufactured by a thermomechanical forming process. By applying an incremental and thermomechanical joining process, it is possible to react immediately and adapt the joining process inline to reduce the number of different joining elements. In the investigation described in this publication, cast plates made of the cast aluminium alloy EN AC-AlSi9 serve as joining partners, which are processed by sand casting. The joining process of hypoeutectic AlSi alloys is challenging as their brittle character leads to cracks in the joint during conventional mechanical joining. To solve this, the frictional heat of the novel joining process applied can provide a finer microstructure in the hypoeutectic AlSi9 cast alloy. In detail, its Si is finer-grained, resulting in higher ductility of the joint. This study reveals the thermomechanical joining suitability of a hypoeutectic cast aluminium alloy in combination with adaptively manufactured auxiliary joining elements.

Evolutions of Electromagnetic Fields and Forced Flow Driven by the Pulse Length of a Pulsed Magnetic Field and Their Relevance to the Grain Refinement of a Solidified Al–Si Hypoeutectic Alloy

Evolutions of Electromagnetic Fields and Forced Flow Driven by the Pulse Length of a Pulsed Magnetic Field and Their Relevance to the Grain Refinement of a Solidified Al–Si Hypoeutectic Alloy

Slurry preparation for semi-solid metal direct writing by a novel approach of mixed powder remelting

Extrusion-based metal direct writing is a promising metal additive manufacturing technology due to its high efficiency and low cost. However, fabricating parts with high integrity and complex geometry remains challenging. The most critical factor is the unavailable of semi-solid slurries with uniform and nearly spherical solid particles, resulting in uncontrollable extrusion and printing. Currently, mixed powder remelting (MPR) is reported to preset the features of the solid phases, including volume fraction, morphology, and size distribution. Specifically, the semi-solid slurries of hypoeutectic AlSi alloys were obtained by preheating and shearing the mixed powder composed of eutectic AlSi alloy powder and pure aluminum powder. Their microstructural characteristics and rheological behavior were investigated, demonstrating the microstructure tailoring (controllable solid fraction and size distribution, high shape factor of about 0.9) and the reduced viscosity fluctuation by a factor of 7 compared with traditional processes. MPR shows unparalleled advantages for further engineering applications of metal direct writing.

High temperature effect on short crack behaviour in hypoeutectic Al-Si alloys and its modelling

Hypoeutectic Al-Si alloys used for components facing the combustion chamber of automotive engines necessitate excellent high-temperature mechanical properties. In this study, the effect of high temperature on short crack behaviour of hypoeutectic Al-Si alloys is investigated experimentally. The results show that the short crack growth rate is affected by thermal softening and precipitate coarsening. At 200 °C, the slight thermal softening and the positive effect of short-term precipitate coarsening causes the crack growth rates remain unchanged compared to room temperature (RT). At 250 °C, the crack growth rate remains essentially constant during the early stage, while with increasing testing time, the crack growth rate increases rapidly due to the precipitate coarsening. At 300 °C, the crack growth rate is significantly enhanced due to thermal softening and precipitate coarsening. Due to thermal softening, the elastic modulus and yield stress (σys) decrease with increasing temperature. Due to time and temperature dependent precipitate coarsening, the σys drops sharply with the testing time at 250 °C and 300 °C. At 200 °C, the σys increases first and then decreases with the increase of testing time. The transgranular mode dominates the short crack growth at both RT and high temperatures. The grain boundaries have an apparent suppression effect on crack growth. Finally, the relationships between σys and temperature are established for crack tip opening displacement range (ΔCTOD) calculation. The short crack growth rates can be well characterized and predicted by ΔCTOD.

Enhancement of the strength-ductility synergy of Al-Si-Mg alloys via C-doped TiB2 particles

• Novel C-doped TiB 2 particles are introduced into an Al-Si-Mg alloy. • The average grain size of α-Al can be reduced by 70% via C-doped TiB 2 particles. • The C-doped TiB 2 particles enhance the strength-ductility synergy of A357 alloy. We report novel C-doped TiB 2 particles introduced into an Al-Si-Mg alloy. The impact of C-doped TiB 2 particles on the α-Al grain and associated mechanical properties were systematically investigated. These particles were introduced via a master alloy (Al-TBC master alloy, or Al-TBC for short). The results show that the C-doped TiB 2 particles have a dramatical nucleation capability for the α-Al grain, thus eliminating the grain refinement problem of Si “poisoning” in the A357 alloy (one typical category in Al-Si-Mg alloy). As a result, the average grain size of α-Al can be refined to 140 μm from 490 μm by adding 0.5 wt.% Al-TBC. The C-doped TiB 2 particles can also enhance the strength-ductility synergy of A357 alloy at room temperature. At 0.5 wt.% Al-TBC, the ultimate tensile strength, yield strength, and elongation of T6-treated A357 alloy are 370.1 ± 1.2 MPa, 302.5 ± 7.5 MPa, 12.38 ± 1.2 %, respectively. This work provides a novel prospect for resolving the problem of Si “poisoning” in grain refinement and strength-ductility trade-off in hypoeutectic Al-Si alloys via C-doped TiB 2 particles.