Eutectic Silicon Phase Research Articles

Effects of Strontium Modification on Corrosion Resistance of Al-Si Alloys in Various Corrosive Environments.

This study investigates the impact of strontium (Sr) additions on the corrosion resistance of an LM6 (A413) aluminium alloy. By incorporating varying concentrations of Sr (0.01 wt.% and 0.05 wt.%), the morphological and corrosion behaviours of the alloy were analysed under different corrosive environments, including sulphuric acid, sodium hydroxide, and sodium chloride solutions. The results demonstrate that Sr modifications significantly enhance the alloy's corrosion resistance, with the most substantial improvement observed at 0.05 wt.% Sr. The analysis revealed that the weight loss of the alloy in sulphuric acid decreased by 2.5% with 0.05 wt.% Sr after 10 days of immersion, due to the formation of a stable passive oxide layer. In sodium hydroxide, however, the weight loss was reduced by 5% with 0.05 wt.% Sr after 10 days, indicating aggressive uniform corrosion. In the 3.5% sodium chloride solution, the corrosion rates remain relatively low, and the 0.05 wt.% Sr alloy showed a decrease in corrosion product formation over time, suggesting enhanced resistance. Detailed surface analyses, including 3D profiling and morphology assessments, revealed that Sr additions refine the eutectic silicon phase, transforming it from a coarse to a more desirable fibrous or lamellar structure, thus improving the alloy's overall performance. The innovative findings underscore the potential of Sr as an effective microstructural modifier for enhancing the durability and longevity of Al-Si alloys in corrosive environments.

The Influence of the Combined Addition of La–Ce Mixed Rare Earths and Sr on the Microstructure and Mechanical Properties of AlSi10MnMg Alloy

This study investigated the effect of adding La–Ce mixed rare earths and Sr on the microstructure and mechanical properties of AlSi10MnMg alloy. The experiment utilized different combinations of modifiers, including single La–Ce rare earths, single Sr, and the combined addition of La–Ce mixed rare earths and Sr. This study compared their effects on grain refinement, the modification of the α-Al phase and eutectic silicon phase, and tensile properties and hardness. The results showed that the combined modification of Sr and mixed rare earth elements significantly refined the grains, optimized the morphology of the α-Al phase and eutectic silicon phase, and improved the overall mechanical properties of the aluminum alloy. Under the combined modification, the addition of 0.02 wt.% Sr and 0.1 wt.% RE (La–Ce mixed rare earths) exhibited the most pronounced refining effect. The secondary dendrite arm spacing (SDAS) was reduced by 59.18%. The eutectic silicon phase transformed from coarse needle-like shapes to fine fibrous or granular forms, with an aspect ratio reduction of 69.39%. Meanwhile, the alloy’s tensile strength and hardness were significantly improved. The tensile strength increased to 240 MPa, achieving an increase of 23.08%; the yield strength increased to 111 MPa, achieving an increase of 18.09%; and the elongation reached 7.3%, achieving an increase of 73.81%. This indicates that the proper addition of Sr and mixed rare earths can significantly optimize the microstructure and enhance the mechanical properties of AlSi10MnMg alloy, providing an effective method for the preparation of high-performance heat-treatment-free aluminum alloys.

Study on the Effect of Al-10Sr Intermediate Alloy on the Modification of A356 Aluminum Alloy after Different Purification Treatments

Abstract For three different purification treatment methods of aluminum melt: untreated (UT), conventional purification treatment (CPT), impurity removal flux purification treatment (IRF), and Al-10Sr intermediate alloy was applied for modification treatment. The results showed that due to the highest purity of aluminum liquid treated with IRF, the secondary dendrite spacing decreased by 31.32% after modification, and the eutectic silicon phase was in a granular and dispersed distribution. The tensile fracture exhibited ductile fracture characteristics, effectively improving the mechanical properties of the alloy. At the same time, it was found that reducing the Sr content did not decrease the modifying effect, indicating good purity of aluminum liquid can provide superior melt conditions for subsequent modification treatment.

Optimization of impurity removal and purification flux components and their application in the production of A356 aluminum alloy

Abstract Taking into account the thermodynamic and kinetic conditions of impurity removal and purification, three impurity removal and purification fluxes were designed for comparative experiments. It was found that the impurity and hydrogen removal rates of experimental flux II were the best, with a decrease of 28.1% in micro grain size 28.1 μ m. The spacing between secondary dendrites is significantly reduced. The eutectic silicon phase of the alloy treated with experimental flux II is granular, with small and dispersed inclusions. The fracture structure of the alloy exhibits ductile fracture characteristics, mainly in the form of transgranular microporous aggregation, which helps to improve the plasticity and fatigue resistance of the alloy. The flux purification method, which focuses on impurity removal, can provide a reference for the actual impurity removal in aluminum alloy smelting.

Extension of a phase-field KKS model to predict the microstructure evolution in LPBF AlSi10Mg alloy submitted to non isothermal processes

The out-of-equilibrium heterogeneous microstructure typical of AlSi10Mg processed by Laser Powder Bed Fusion (LPBF) is often modified by further heat treatment to improve its ductility. According to literature, extensive experimental investigations are generally required in order to optimize these heat treatments. In the present work, a phase-field approach is developed based on an extended Kim–Kim–Suzuki (KKS) model to guide and accelerate the post-treatment optimization. Combined with CALculation of PHAse Diagrams (CALPHAD) data, this extended KKS model predicts microstructural changes under anisothermal conditions. To ensure a more physical approach, it takes into account the enhanced diffusion by quenched-in excess vacancies as well as the elastic energy due to matrix/precipitate lattice mismatch. As the developed model includes the computation of the evolution of the thermo-physical properties, its results are validated through comparison with experimental DSC curves measured during the non-isothermal loading of as-built LPBF AlSi10Mg. The computed microstructure evolution reproduces the microstructural observation and successfully explains the peaks in the DSC heat flow curve. It thus elucidates the detailed microstructural evolution inside the eutectic silicon phase by considering the growth and coalescence of silicon precipitates and the matrix desaturation.

The Effect of Fe Content on the Microstructure and Tensile Properties of Friction-Stir-Welded Joints in Recycled Cast Aluminum Alloy.

The presence of the impurity element Fe significantly influences the overall performance of recycled aluminum alloy. This study aims to elucidate the impact of Fe content on the microstructure and tensile properties of friction-stir-welded (FSW) joints in recycled cast A356 aluminum alloy. Three samples with varying Fe content were prepared for FSW joints. The quality of the weld zone was meticulously assessed through macrostructure and microstructure analyses. The tensile strengths of the joints were carefully evaluated and correlated with the microhardness and microstructure of the weld zone. The research findings reveal that, among the three fabricated joints, the one with an Fe content of 0.3 wt.% demonstrates the most favorable tensile performance. This particular joint exhibits the highest tensile strength of 153 MPa, commendable yield strength of 90 MPa, and a favorable elongation of 5.7%. The mechanisms responsible for grain refinement in the weld nugget zone involve plastic deformation and dynamic recrystallization. Significantly, the disruptive effects of friction-stir action on eutectic silicon phases and rich iron phases emerge as crucial factors contributing to the enhanced performance of the weld nugget zone in the welded joint.

Exploring Microstructure, Wear Resistance, and Electrochemical Properties of AlSi10Mg Alloy Fabricated Using Spark Plasma Sintering

Al-Si-Mg alloy has excellent casting performance due to its high silicon content, but the coarse eutectic silicon phase can lead to a decrease in its mechanical properties. Samples of AlSi10Mg alloy were prepared by using a spark plasma sintering method, and it was found that sintering temperature has a significant impact on the grain size, eutectic silicon size and wear and corrosion properties after heat treatment. At a sintering temperature of 525 °C, the alloy exhibits the best wear performance with an average friction coefficient of 0.29. This is attributed to the uniform precipitation of fine eutectic silicon phases, significantly improving wear resistance and establishing adhesive wear as the wear mechanism of AlSi10Mg alloy at room temperature. The electrochemical performance of AlSi10Mg sintered at 500 °C is the best, with Icorr and Ecorr being 1.33 × 10−6 A·cm−2 and −0.57 V, respectively. This is attributed to the refinement of grain size and eutectic silicon size, as well as the appropriate Si volume fraction. Therefore, optimizing the sintering temperature can effectively improve the performance of AlSi10Mg alloy.

An investigation into the softening behavior of cast A356 alloy in the solid and semisolid deformation regimes

The current work deals with the hot deformation behavior of A356 aluminum alloy starting with the cast structure and an emphasize on the capability of flow softening. Toward this end, the hot compression tests were performed at temperatures of 150, 250, 350, 450, 500 and 550 °C in the solid range and 580 °C in the semisolid range under the typical strain rate of 0.01s−1. The materials represent high protentional for the occurrence of softening mechanism in solid state regime. During thermomechanical processing (above 250 °C), after reaching the peak stress, the dynamic recrystallization prevails over the deformation behavior and the stress level reaches a steady state regime. The α-dendritic arms are crushed and refined, and the silicon blades are mechanically fragmented and spread irregularly through the microstructure. Being in the semi-solid temperature range, the eutectic silicon phase is melted and causes a sharp decrease in the resistance against deformation. The penetration of the liquid phase along the developed sub-boundaries give rise to grain partitioning and resembles the occurrence of dynamic recrystallization. The presence of the liquid phase during semisolid forming, in addition to the lubricated flow mechanism, facilitates the deformation by providing proper condition for the occurrence of recrystallization. In the present case, a stable stress level as below as 1 MPa was recorded for the experiment cast structure.

Hardness and Wear Behavior of Heat Treated Aluminium Silicon Alloy SiC Particle Reinforced Composite

The A356 Aluminium Silicon alloy is reinforced with Silica Carbide particles (SiCp) to form metal matrix composite by stir casting method to study the hardness and wear properties. The composites are prepared for weight fraction of 2, 4 and 6% of SiC with the base alloy and their characteristics are observed at post T6 full heat treated condition. The optical microscopic metallography observation shows the rosettes of uniform spheroidal grains of strain free eutectic silicon phase in proeutectic Aluminium matrix after heat treatment. The hardness and wear properties of the A356-SiC composites have increased with the increase in weight percentage of reinforcement particle in the base alloy. Maximum hardness and wear resistance is observed for 6% SiC which is the maximum percentage of inclusion of secondary element considered under this study. A comprehensive discussion is made on the strengthening of the A356 alloy on addition of hard SiC particles that has improved the hardness and wear characteristics of composites in heat treated conditions.

Eutectic Si Accumulation in Liquid Forged A356 Alloy Wheel and its Adverse Effect on Tensile Fracture Behavior

This investigation is aimed to study microstructural heterogeneities raised due to the inherent melt transport phenomenon and their effect on mechanical properties. Modified, Cleaned, and degassed A356 aluminum alloy melt was poured at 704°C in H13 tool steel die, while temperatures of lower die segment, side segment, and upper segment were 368°C, 375°C, and 290°C respectively. Then liquid melt was forged till its complete solidification under pressure using a hydraulic forging press. The liquid forged wheel was subjected to metallurgical investigation of microstructure, mechanical properties, and fractography of tensile test samples at different cross-sections along the protrusion of the wheel. Results conclude gradual variation in accumulation of eutectic Si phase from surface to the center of thickness and from flange to the outer rim region. The elastic properties are not affected by accumulation of the eutectic silicon however, plasticity have adversely affected with decrease in effective ductile cross-section. Also, refinement of primary α-aluminum and modification in the eutectic silicon phase in specific areas of the wheel is observed.

Optimisation of microstructure and mechanical properties of new low silicon cast aluminum alloy by Sr modification and B refinement

ABSTRACT In order to investigate the optimum refinement and modification scheme of the new low-silicon cast aluminum alloy, experiments were carried out on macroscopic grain size statistics, eutectic silicon phase morphology observation and tensile properties test for aluminum alloys with different contents of Al-3B refiner and Al-10Sr modifier. The results showed that when the amount of B added in the low-silicon cast aluminum alloy was 200 ppm, the AlB2 particle which can act as the ideal substrate for grain nucleation in the alloy can be saturated, and the alloy was distributed with fine uniform equiaxed grains while the grain size was minimised. Moreover, when the amount of Sr addition was 250 ppm, the eutectic silicon can exhibit a branched and dense coral branch because the Sr in free form was sufficiently adsorbed on the eutectic silicon. The effect of SrB6 formed by the interaction between Sr and B was the smallest. The alloy exhibited a uniform distribution of fine round grains after heat treatment, and obtained the optimum comprehensive mechanical properties. And the tensile strength reached 370.3 MPa, the yield strength was 307.3 MPa, and the elongation increased to 8.3%.

Effect of process parameters on microstructures and properties of Al–42Si alloy fabricated by selective laser melting

In this paper, high-silicon Al–42Si alloy was prepared by selective laser melting (SLM) with different process parameters. Microstructures evolution and defects formation were studied and process parameters were optimized. The results shown that the density of SLM-fabricated Al–42Si alloy increases as input energy density increases. The highest and lowest density of SLM-fabricated Al–42Si alloy are obtained, when input energy density is 42.9J/mm3 and 33.8J/mm3 respectively. The microstructures of Al–42Si alloy fabricated by selective laser melting is mainly composed of primary silicon phase and eutectic silicon phase, which is distinct from casting alloy because of diffient grains size and shapes of the primary silicon. With higher energy density, larger size of the primary silicon observed during process due to higher heat released by powder. The size of primary silicon phase particles is in the range of 2.9–9.4μm, and the size of molten pool during SLM process is in the range of 125 ± 10μm–140 ± 10μm in this study. Also the hardness of SLM-fabricated Al–42Si alloy increases as input energy density increases between 40.0J/mm3 and 42.9J/mm3. After heat treatment, the residual stress is eliminated, microstructure stability and homogeneous of SLM-fabricated Al–42Si alloy are improved. The silicon distribution is more uniform and sizes increases about 1∼2μm, and the hardness decreases after heat treatment. The optimal SLM parameters for Al–42Si alloy are laser power of 320W, scanning speed of 1355 mm/s, layer thickness of 50μm and scanning space of 110μm.

Refining and reinforcing effects of TiC-Al2O3/Al ribbons inoculant on Al–Si–Mg–Ti alloy

In this study, TiC-Al2O3/Al ribbons inoculant were prepared by mechanical alloying, spark plasma sintering (SPS) and melt spinning. Adding 5vol.% TiC-Al2O3/Al ribbons to an Al–Si–Mg–Ti (ASMT) alloy melt significantly refined the α-Al grains from 28.5 μm to 14.9 μm. In addition, the morphology of the eutectic silicon were modified and optimized, changing from needle-like silicon to spherical silicon. Adding the TiC-Al2O3/Al ribbons significantly improved the mechanical properties of TiC-Al2O3/Al–Si–Mg–Ti (TAASMT) alloy, including its elastic modulus (EM), yield strength (YS), ultimate tensile strength (UTS) hardness, and elongation which were increased by 5.4%, 18.4%, 32.7%, 8.3%, and 62.3%, respectively. These increases in the mechanical properties could be attributed to the intracrystalline reinforcement of the Al2O3 and TiC nanoparticles, well-bonded particle/matrix interface, modification of the eutectic silicon phases, and synergistic effects of the Orowan strengthening, Coefficient of thermal expansion (CTE) mismatch strengthening, load transfer, grain refining strengthening, and geometrically necessary dislocations (GND) strengthening.

Influence of Alloying Element Mg on Na and Sr Modifying Al-7Si Hypoeutectic Alloy.

The influence of alloying element Mg on Na and Sr modifying Al-7Si hypoeutectic alloys was investigated. The residual content of Na and the morphology of modified eutectic silicon were characterized. It was found that the alloying element Mg had an enhanced effect on the uptake of sodium in the Al-7Si hypoeutectic alloy modified by the Na-contained modifier. Moreover, the morphology of eutectic silicon of the modified Al-7Si alloys was significantly different from that of Al-7Si-0.4Mg alloys in the present research. When the addition of the modifier is enough, both modifiers could entirely modify the eutectic silicon phase of Al-7Si alloys, while incompletely modified eutectic silicon was observed in both Na-modified and Sr-modified Al-7Si-0.4Mg alloy. It was observed that there was an adhering relationship between the partially modified eutectic silicon with Mg-rich phases. According to the results, it can be proposed that the addition of Mg will affect the solidification behavior of alloys, thereby, leading to the incomplete modification of eutectic silicon phases.

The influence of Ni and Zr additions on the hot compression properties of Al-SiCp composites

The present work investigates different additions of nickel and zirconium to the matrix alloy of Al-SiC metal matrix composites to enhance their high-temperature performance. These composites are promising for the demand for lightweight solutions for automotive components like brake discs. In such components, the compression behaviour at elevated temperatures is crucial. The resulting properties were combined with microstructural analysis. Ni additions led to a continuous improvement of the mechanical response, but the same result did not hold for the Zr additions. The interaction of SiC particles, eutectic silicon, and eutectic Ni-based phases led to a 44 % increment of the activation energy.

Microstructure evolution, thermal conductivity and mechanical properties of hot-rolling Al–Si–Fe–Mg alloy under different reductions

To further improve the properties of the Al–11.5Si–0.4Fe–0.35Mg, the effects of different reductions of hot-rolling (HR) Al–Si–Fe–Mg alloy on microstructure, thermal conductivity (TC), and mechanical properties were investigated in this paper. The results show that the eutectic silicon phases are broken and moved during the HR process. The average size of eutectic silicon phase decreases. Meanwhile, the aspect ratio of eutectic silicon phase closer to 1 and the distribution of that are more uniform with the increase of HR reduction. In addition, the ternary Al–Fe–Si phases are also broken after HR. It indicates that the action of shear force induced by the HR process is beneficial to promote refinement and spheroidization of the eutectic silicon phase, hence further improves the properties of the alloy. Apparently, the fine and dispersed distribution of spherical silicon particles can minimize the splitting of the [Formula: see text]-Al matrix, decrease the scattering effect on free electrons, and increase the number of free-electron transport channel. Therefore, the overall performance of HR Al–Si–Fe–Mg alloy with a reduction of 71.25% is the best with the TC of 170.24 W/m[Formula: see text]K, the tensile strength of 241.98 MPa and elongation of 8.73%, respectively.

Determination Of The Effect Of Cooling Rate And Strontium Amount On Eutectic Si Modification Performance Of A356 Alloy Via Casting Simulation

It is well-known that strontium addition into molten metal as a eutectic modifier increases the elongation and toughness values of the cast parts by refining the eutectic phases. However, when over-modification occurs, porosity increases due to some unwanted physical and chemical reactions that develop within the structure. On the other hand, it has been seen that high cooling rates tend to reduce the porosity of the alloy, decrease grain size and secondary dendrite arm spacing and refine eutectic silicon phase on Al-Si casting alloys. Within the scope of this project, it is aimed to investigate the effects of the cooling rate of cast part and the addition amount of strontium on the silicon modification behavior of Al A356 (AlSi7Mg) alloy parts using casting simulation environment. In order to examine the effect of strontium addition, 150, 250, 350 and 450 parts per million of strontium additions were chosen based on thermodynamic calculations. After the casting session of each Al A356 composition with different strontium amount by using special designed 5-spoke mold on casting simulation, thermal analysis was done by obtained thermocouple data from casting part’s each spoke. Obtained thermal analysis data was interpreted with the casting simulation outputs. Within all aspects, the 150 parts per million strontium addition on Al A356 alloy has been identified as the most useful simulation model in terms of casting performance.

Modeling Ablation Casting

Research published in open literature on ablation casting has been mainly experimental. Modeling of this innovative technology is scarce. This article describes an initial attempt in modeling ablation casting process. Material properties and boundary conditions were defined for calculating cooling curves and microstructural length scales in A356 alloy castings made using sand casting and ablation casting processes. Model predictions were compared with published data on cooling curves and solidification times in an A356 alloy casting. The validated model was then used to predict unique solidification features associated with the ablation casting process, including the eutectic solidification time, shrinkage porosity formation, eutectic front morphology, the advancing rates of the eutectic front and the associated eutectic silicon morphology. Simulation results indicate that the progressive advancing ablation cooling is capable of reducing secondary dendrite arm spacing, modifying the eutectic silicon phase owing to the water quench effect, and eliminating shrinkage porosity using much smaller risers than usual if the ablation is correctly driven towards the risers.

Effect of erbium on the rheocast quality index of A356 semisolid feedstock

The effects of erbium on the microstructure of a semisolid A356 alloy for thixoforming were investigated. Semisolid A356 alloys were prepared using the serpentine channel technique. The results demonstrated that a semisolid A356 alloy could be successfully produced. The addition of erbium refined the size of primary α-Al globules; moreover, the eutectic silicon phase was modified. The thermal analysis results showed that the addition of erbium decreased the amount of nucleation sites for eutectic phases, leading to increased undercooling of the melts. Therefore, erbium delays the nucleation of eutectic phases, resulting in refinement of the eutectic silicon phases. Moreover, the addition of erbium increased the rheocast quality index value of the semisolid A356 alloy, which is beneficial for thixoforming.

Effect of Sr Addition to a Modified AA3003 on Microstructural and Corrosion Properties

Sr is known to transform the morphology of the eutectic silicon phase as well as the Fe-rich β phase in Al-Si alloys, improving their mechanical properties. However, little is known about the effect Sr has on the (local) corrosion properties of aluminium alloys. This study investigates the effect of Sr addition to a modified AA3003 heat exchanger material on the morphology of the different phases present, especially the Fe-rich phases, as well as on the (local) corrosion properties of this material. This work reports the formation of a Sr-rich phase, which slightly increases the macrohardness of the material. The Fe-rich phases are not shown to be refined/influenced by the addition of Sr Potentiodynamic polarization experiments showed an increase in pitting potential by increasing the amount of Sr in the material up to 0.4 wt.%. Nevertheless, the analysis of the corrosion morphology revealed that the Sr-containing particles did not contribute to the corrosion process despite their cathodic behaviour compared to the Al matrix as measured by Scanning Kelvin Probe Force Microscopy. This behaviour was attributed to the thicker oxide layer found on the Sr-rich particles.