Al-12Si Alloy Research Articles

Achieving superior grain refinement efficiency for Al–Si casting alloys through a novel Al–La–B grain refiner

Conventional Al–Ti–B and Al–Ti–C refiners fail to refine Al–Si casting alloys with high Si content due to the well-known “Si-poisoning” effect. Developing a novel grain refiner with superior grain refinement efficiency for Al–Si casting alloys is the research focus in recent years. In this work, a superior anti Si-poisoning α-Al grain refiner Al–2La–1B alloy with fine LaB6 particles was successfully fabricated via the aluminum melt reaction method. The microstructural evolution, grain refinement performance and refinement mechanisms of the Al–2La–1B alloy were comprehensively investigated based on the experiment results and first-principles calculations. The currently designed Al–2La–1B refiner presents supreme grain refinement efficiency on Al–Si casting alloys. The average grain size of Al–7Si alloy inoculated with 0.5% Al–2La–1B alloy can be refined to 67 ± 5 μm. The superior grain refinement performance can be attributed to the presence of fine LaB6 particles in the refiner. These particles are highly stable in Al–Si alloy melt and can directly act as the potent nucleation sites for α-Al due to the small lattice misfit and low interfacial energy. Moreover, the nucleation potency of the LaB6 particles will not be influenced by the solute Si element. Our work provides an effective strategy for designing a superior α-Al grain refiner for Al–Si casting alloys.

Investigation of Grain Refinement and Mechanical Properties of Al-7Si Alloy with Al-5Nb-1B Master Alloy Addition Treated by Ultrasound Treatment

Investigation of Grain Refinement and Mechanical Properties of Al-7Si Alloy with Al-5Nb-1B Master Alloy Addition Treated by Ultrasound Treatment

Efficient modification eutectic Si of Al-10Si alloy with Mg-Gd master alloy addition

In this study, the modification of eutectic Si was carried out by adding Mg-Gd master alloy to Al-10Si aluminum alloy. The influence mechanism of Mg-Gd master alloy modification Si on the morphology, size and mechanical properties were studied. The results show that the Mg-Gd master alloy has a remarkable modification effect on eutectic Si, with the average length of eutectic silicon changing from 11.71 μm to 1.95 μm. A large number of twin bands appear in eutectic Si after modification, and the modification mechanism is mainly twin plane reentrant edges. After modification, the mechanical properties are improved significantly and the fracture mode is mainly quasi cleavage fracture.

New approach to achieve extremely high thermal conductivity of a powder extruded Al–50Si alloy

The Al–50Si alloy, designed for effective heat dissipation in electronic components, was subjected to a two-stage heat treatment process to optimize its microstructure and achieve high thermal conductivity (TC). Two distinct temperature stages were strategically chosen: 850 °C and 550 °C, respectively, with the former operating above and the latter below the eutectic point. The first stage at 850 °C led to the isolation of independent Si particles, each closely associated with individual Al crystal with grain size of approximately 1 mm. Subsequent heat treatment at 550 °C skillfully eliminated introduced eutectic Si through Ostwald ripening. Consequently, the impediments posed by grain boundaries to the movement of electrons and phonons were significantly reduced, yielding an exceptionally high TC of approximately 180 Wm−1K−1, closely approaching the theoretical TC value (∼193 Wm−1K−1) for the Al–50Si alloy. This work paved a new path for the design of outstanding thermal properties in Al–Si electronic packaging materials.

Combinatorial Experiment for Al-6061 and Al-12Si alloy Based on Directed Energy Deposition (DED) Process

Combinatorial Experiment for Al-6061 and Al-12Si alloy Based on Directed Energy Deposition (DED) Process

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.

Refining Al–20Si Alloy by Appending Trace Sr–Sc–Ce Nanoparticles and Ultrasonic Vibration Processing

In this study, Al–20Si alloy is modified by appending trace Sr–Sc–Ce nanoparticles and ultrasonic vibration processing (UVP). The consequences indicate that its microstructure is significantly refined and its mechanical characteristics are improved. The effect of the favorable refinements is achieved by appending 0.2% Sr–0.15% Sc–0.3% Ce and performing UVP. The primary Si is the minimum, the grain roundness coefficient and the strength of extension are the maximum, and the spheroidizing effect of α‐Al is the best. The elongation and hardness are the highest when 0.4% Ce is appended. The research consequences afford a reasonable process scheme for manufacturing high‐quality wear‐resistant material of the automotive and aerospace industries.

A comprehensive analysis of cooling curves, fluidity, inclusions, porosity, and microstructure of NaCl-KCl-NaF flux treated Al-12Si alloy

In this study, we investigated the effects of treating Al-12 wt% silicon alloy with an equimolar composition mixture of NaCl, KCl, and NaF on various aspects of the alloy’s properties. Key findings of the research indicate that the flux treatment had significant effects on the alloy. It led to increased nucleation temperatures and reduced undercooling, thereby facilitating nucleation sites and grain refinement. Additionally, the inclusion of flux reduced the entrapment of inclusions in the melt, which can potentially enhance the mechanical properties of the alloy. However, it also led to a larger and more widely distributed gas porosity in the solidified samples, as gas evolved from the flux trapped during solidification. Moreover, the flux treatment had noticeable impacts on the morphology of eutectic silicon particles, reducing their aspect ratio. These findings offer valuable insights into the potential benefits and challenges of sodium-based flux melt treatment in optimizing the quality of Al-12Si alloy castings, particularly in die-casting applications.

Al-12Si Alaşımlarında Yüzey Oksit Uapısının Sr Varlığında Değişimi

Bifilm defects are the surface entrained double oxide films that are introduced into melts during turbulence and disturbance to the surface of the melt. These defects lead to porosity formation if they are not cleaned from the melt. Thus, the characterisation of the dross that is formed on the surface of the melt becomes a key parameter. In this work, Sr containing Al12Si alloy was used. For the modification process, 100, 200 and 300 ppm Sr was added to the alloy. The oxidation tests were carried out in liquid state at 700, 750 and 800 °C for holding durations of 12, 24, 36 and 48 hours. The structure was characterised by optical microscopy, Scanning Electron Microscopy, X-Ray Diffraction and X-ray photoelectron spectroscopy techniques. It was found that after 12 hours of holding, spinel oxides were formed on the surface mainly SrO.Al2O3 and MgO.Al2O3.

Effect of Annealing on Microstructure and Mechanical Properties of Al–18Si Alloy Cast by Melt Quenching

Effect of Annealing on Microstructure and Mechanical Properties of Al–18Si Alloy Cast by Melt Quenching

Silicon Poisoning and Effects of Tantalum on AlSi Alloys

Grain refinement in Al-Si alloys is crucial for enhancing material castability and mechanical properties. Industrial practice involves adding inoculants, composed of TiB2 particles coated with metastable Al3Ti via adsorption, to the melt. This introduces essential free titanium for metastable phase formation and subsequent growth restriction. The superstoichiometric grain refiner Al-5Ti-1B, with 2.2 wt.% free titanium, is applied for this purpose. A peritectic reaction forms α-aluminium from this layer. However, when silicon content exceeds 3.5 wt.%, grain coarsening occurs due to silicon’s detrimental effect. This study quantified silicon poisoning in an Al-10Si alloy using stoichiometric and superstoichiometric grain refiners through ASTM-standardized TP1 tests. Adding 0.02 wt.% tantalum acted as an antidote to the τ1 phase, resulting in a finer microstructure. This was attributed to the formation of a Ta-rich layer on TiB2 particles, which causes α-aluminium formation via a peritectic reaction without generating ternary phases with Ti or Si. Correlating to the increasing particle size curves from the TP1 tests, phases were collected in the filter cake with the help of a PoDFA apparatus. These could be examined more closely on the SEM and identified as needle- or plate-shaped. By using an EDS unit, the phases found were assigned to the poisoning phase and further investigated. After the addition of tantalum, a solubility of tantalum could be detected in former poisoning phases. In combination with the gradients of the grain size, it can thus be assumed that tantalum is both an antidote for silicon poisoning in the Al-Si-Ti system and can itself have a grain-refining effect in this system.

Achieving high thermal conductivity of Al–50Si alloy through heat treatment and its microstructural evolution

Al–50Si alloys were prepared by powder extrusion and characterized for electronic packaging. The optimization of powder size, extrusion temperature, and heat treatment parameters was performed to enhance the microstructure and thermo-physical properties. The alloy exhibits a high relative density >99 %, a low coefficient of thermal expansion (CTE) < 10 × 10−6/K, and a good thermal conductivity (TC) ∼117 Wm−1K−1 achieved by employing a large size powder and high extrusion temperature during the extrusion process. Subsequent heat treatment of the optimized alloy at 550 °C for various time reveals a fluctuating increasing trend in TC during the heat treatment process. The TC values exhibit periodic fluctuations as they alternate between increments and decrements, primarily resulting from the recrystallization and secondary recrystallization of Al grains during heat treatment process. Notably, the maximum TC value (∼159.1 Wm−1K−1) at room temperature is obtained after heating the alloy to 550 °C for 26 h. Compared to the as-extruded alloy, the TC of heat-treated alloy increases by approximately 36 %, which can be attributed to the elimination of eutectic Si and growth of Si and Al grains within the alloy. The study may shed light on the mechanism underlying the improvement in thermal conductivity of Al–50Si alloy by microstructural evolution.

Wear performance of composite dual-layer coated Al-12Si alloy: Effect of Al2Ce reinforcement and micro-arc oxidation

An attempt has been made to enhance the wear resistance of Al-12Si alloy by forming a dual-layer coating consisting of an Al-12Si matrix composite layer (Al-12Si + ∼40 vol % Al2Ce) and an external composite oxide layer. While the hardness of monolithic Al-12Si alloy was ∼110 HV, the Al-12Si matrix composite layer has got hardness of ∼140 HV and exhibited ∼6 times higher sliding wear resistance due to the suppression of the plasticity-induced adhesive wear by Al2Ce particles. Applying micro-arc oxidation (MAO) as a post-treatment favoured an oxide layer (Al2O3) on the Al-12Si alloy and a composite oxide layer (CeO2 + Al2O3) on the Al-12Si matrix composite layer. The MAO coatings fabricated on the Al-12Si alloy and Al-12Si matrix composite layer, with hardness of ∼11 GPa and ∼13 GPa, respectively, provided more than two orders of magnitude increase in the wear resistance by shifting the wear mode to elasticity-dominated wear. However, the critical load imposing the complete detachment of the MAO coating by intense cracking and spallation during testing was determined as 3 N for the MAO'ed Al-12Si alloy and 5 N for the MAO'ed Al-12Si matrix composite layer. The wear resistance of the MAO coating of the Al-12Si matrix composite layer was ∼2 times higher than that of the MAO coating of the Al-12Si alloy below the critical test loads, where the coatings remain intact with the substrate.

Synergistic Effect of Strontium and Melt Quenching on the Solidification Microstructure of Hypereutectic Al-Si Alloys.

The synergistic effect between strontium (Sr) and melt quenching on the solidified microstructure of hypereutectic Al-Si alloys was investigated by optical and scanning electron microscopy. The results indicate that melt quenching can suppress the growth of primary Si particles in the solidified structure of the hypereutectic Al-Si alloy, resulting in a significant decrease of in the average size of primary Si particles in Al-(18~22)Si alloys from 30.35~66.31 μm to 15.13~34.63 μm. The synergistic effect between Sr and melt quenching can further inhibit the precipitation of primary Si particles in the Al-18Si alloy. After the addition of Sr to Al-18Si alloy and undergoing melt quenching, the area fraction of primary Si clearly decreases. When the added amount of Sr increases from 0.1 wt.% to 0.5 wt.%, the area fraction of primary Si decreases from 1.13% to 0.16%. With 0.5 wt.% Sr in the tested alloy, the inhibiting effect on primary Si precipitation was significantly improved. Research has shown that the cooling rate has a significant impact on the solidified structure of the melt-quenched Al-18Si-0.5Sr alloy. There exists no primary Si in solidified structures on the area of 1/8R and 1/4R from the surface of the round bar sample, but the area fraction of primary Si increases, respectively, to 1.97% and 12.48% on the area of 1/2R and R from the surface. The higher the cooling rate, the higher the inhibitory effect on the primary Si precipitation in the Al-18Si-0.5Sr alloy.

Near zero thermal performance loss of Al-Si microcapsules with fibers network embedded Al2O3/AlN shell

Al-Si alloy, a high temperature phase change material, has great potential in thermal management due to its advantages of high heat storage density and thermal conductivity. Microencapsulation of Al-Si alloy is one of the effective techniques to solve high temperature leakage and corrosion. In this paper, commercial Al-10Si alloy micro powders were encapsulated with flexible ceramic shells whose total thickness is below 1 µm by hydrothermal treatment and heat treatment in N2 atmosphere. The compositions and microstructures were characterized by XRD, SEM and TEM. The shell was composed of AlN fibers network structure embedded with α-Al2O3/AlN which prevented the alloy from leaking and oxidizing, as well as had excellent thermal stability. The latent heat of microcapsules was 351.8 J g–1 for absorption and 372.7 J g–1 for exothermic. The microcapsules showed near zero thermal performance loss with latent heat storage (LHS)/ release (LHR) was 353.2/ 403.7 J g–1 after 3000 cycles. Compared with the published Al-Si alloy microcapsules, both high heat storage density and super thermal cycle stability were achieved, showing promising development prospects in high temperature thermal management.

Effect of rare earth Ce on the microstructure and mechanical properties of cast Al–7Si alloys

Casting experiments were carried out on Al–7Si using different additions of rare earth Ce at a reaction temperature of 1200 K. Based on the ternary phase diagram of Al–Si–Ce, the effects of rare earth Ce on the α-Al grain refinement, the mechanism of the eutectic Si phase modification, as well as on the mechanical properties and fracture morphology of the alloy were investigated. The results show that the addition of rare earth Ce generates a Ce-containing phase inside the alloy, which becomes a heterogeneous core of eutectic Si and changes the nucleation conditions of eutectic Si. The mechanical properties of the alloy were optimal when the Ce addition was 0.2 wt.%, and the defect porosity and average pore area were minimized. Ce-containing phases were found at fracture cracks, and these Ce-containing phases were deviated and aggregated at grain boundaries, which induced defects to be generated, and microcracks were easily produced during plastic deformation, which ultimately led to the fracture of the alloy. According to the growth kinetic relationship, due to the difference of different atomic radii, the inter-atomic forces lead to different nucleation densities of grains. With the generation of Ce-containing phases at the interfaces, the eutectic Si changes its growth direction and grows towards a 70° angle to the original direction with a tighter atomic ordering sequence of the stacking, and more twinned Si is generated and gradually stacked up at the interfaces, which directly alters the morphology of the eutectic Si.

Characterization of Al-12Si Thin-Wall Properties Fabricated with Laser Direct Energy Deposition

Additive manufacturing is an emerging process that is used to manufacture industrial parts layer by layer and can produce a wide range of geometries for various applications. AM parts are adopted for aerospace, automobiles, antennas, gyroscopes, and waveguides in electronics. However, there are several challenges existing in manufacturing Al components using the AM process, and their mechanical and microstructural properties are not yet fully validated. In the present study, a gas-atomised powder of a eutectic Al-12Si alloy was used as feedstock for the Laser Direct Energy Deposition (LDED) process. A SEM analysis of Al-12Si powder used for processing illustrated that particles possess appropriate morphology for LDED. A numerical control system was used to actuate the deposition head towards printing positions. The deposited samples revealed the presence of Al-rich and Al-Si eutectic regions. The porosity content in the samples was found to be around 2.6%. Surface profile roughness measurements and a microstructural analysis of the samples were also performed to assess the fabricated sample in terms of the roughness, porosity, and distribution of Al and Al/Si eutectic phases. The tensile properties of fabricated thin walls were better compared to casted Al alloys due to the uniform distribution of Si in each layer. Micro-hardness tests on the deposited samples showed a hardness of 95 HV, which is equivalent to casted and powder bed fusion melting samples. The gas atomised Al-12Si powders are highly reflective to a laser and also quick oxidation takes place, which causes defects, porosity, and the balling effect during fabrication. The results can be used as a base guide for the further fabrication of aerospace component design with high structural integrity.

Grain-refining mechanism in hypereutectic Al-20Si alloy with minor Sr - Sc - La and ultrasonic vibration treatment

The grain-refining mechanism with minor Sr - Sc - La and ultrasonic vibration treatment (UVT) in the hypereutectic Al-20Si alloy were studied. The results demonstrated that the microstructure of the hypereutectic Al-20Si alloy could be refined significantly, further improve its mechanical properties. The desirable refinement of the microstructure was achieved using 0.2% Sr, 0.15% Sc, and 0.3% La under UVT, achieving the highest grain circularity coefficient, hardness, elongation, and area reduction. The tensile strength was the largest with the addition of 0.2% La. The findings of this study provide theoretical and experimental guidelines for the fabrication of structural materials for application in automotive, aerospace, and deep-sea equipment.

Solidification of Al12Si Melt Pool in Laser Powder Bed Fusion

An understanding of the solidification characteristics of the melt pool during laser powder bed fusion, L-PBF, metal printing is essential to ensure the manufacture of sound parts. This is the main theme of this article where it is attempted to unlock the solidification black box through calculation/measurement of the main solidification parameters of cooling rate, growth rate, temperature gradient, and undercooling. The very small melt pool size and its rapid cooling hinder the application of conventional tools to extract such information. A knowledge of these parameters and their effect on the microstructure and morphology of constituent phases could help to better control the L-PBF process and indeed all the fusion-based additive manufacturing routes, to fabricate high-quality parts. Al12Si alloy solidification during the L-PBF fabrication route is examined to highlight the extreme changes in solidification parameters and their effect on the morphology and size of eutectic Si. This is because the morphology of Si controls the mechanical properties of the finished part. The Al–Si eutectic has a divorced architecture attributed to the difficulty associated with Si growth resulted from rapid solidification. The generation of a temperature gradient of about 7700 °C/mm resulted in cooling rates in the range of 1.1 × 106 °C/s and a growth rate of 140 mm/s. Such values were then used to predict the morphology of eutectic Si based on the traditional approach.

Processing defect, microstructure evolution and mechanical properties of laser powder bed fusion Al-12Si alloys

The laser power and scan speed are significant processing parameters influencing the defects and microstructures due to affecting the thermal state within the melt pool during laser powder bed fusion (LPBF). To this end, these process parameter combinations under a constant laser energy density are correlated with defects (balling phenomenon and pores) and microstructures (melt pool arrangement and cell morphology). Setting the parameter combination (laser power and scan speed are 200 W and 910 mm/s, respectively) yields large balling droplets (average size of 150 μm) due to the relatively high melt viscosity resulting from the low melt pool temperature. In this case, a limited surface tension difference acting on a liquid surface cannot provide sufficient driving forces against viscous drags to promote the efficient spreading of the molten alloy. Cavity regions are formed between the large balling droplets and the previous layer, forming lack-of -fusion pores. By increasing the laser power and scan speed gradually, samples with relative densities greater than 99.5% are produced. This phenomenon can be attributed to the increases in laser power and scan speed, which improves the spreading ability of the molten alloy. With increasing laser power and scan speed, the cell size decreases (from 0.51 μm to 0.42 μm) because of the increase in the cooling rate. The sample (laser power and scan speed are 350 W and 1590 mm/s, respectively) has the highest performance (310 MPa yield strength, 470 MPa ultimate tensile strength, and 6.6% fracture strain) due to its highest relative density (greater than 99.5%) and fine microstructure (average cell size of 0.45 μm). All four samples exhibit anisotropic mechanical properties resulting from the combination of the melt pool boundary and lack-of-fusion pores.