Modification Of Eutectic Silicon Research Articles

Heterogenous Grain Nucleation in Al-Si Alloys: Types of Nucleant Inoculation

The objective of the current work is to establish, on the one hand, the conventional mechanisms of grain refining and, on the other hand, the effect of the refining-modification interaction in Sr-modified Al-Si alloys on the achieved grain refining and the modification of eutectic silicon. For this purpose, the hypereutectic alloy A390.1 (~17%Si) was used. Various grain refiners were used, namely, Al-10%Ti, Al-5%Ti-1%B, and Al-4%B. After the preparation of the liquid metal, several concentrations of these master alloys were added to the liquid bath according to the desired objective. The different melts prepared were heated at 750 °C and cast in a preheated graphite mold with a solidification rate of around 0.8 °C/s. The liquid metal was. The presence of strontium (added in the form of Al-10%Sr master alloy) and boron completely affects the microstructure of the alloy. An atom of Sr unites with 6 atoms of B to form a compound whose stoichiometric formula is of the SrB6 type, leading to a significant reduction in the modification. A strong relationship exists between the addition of B and the recovery level of Sr. The affinity between titanium and boron is stronger than the affinity between boron and strontium. Both B and TiB2 phase particles do not react with Si; it is only the Ti part of the Al-Ti-B master that forms (Al, Si)3Ti. Regardless of the amount of Si content in the alloy, the Al-4%B master alloy achieves the best grain refining compared to Ti-containing master alloys.

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.

Effects of antimony on eutectic silicon and fracture mode of A357 alloy at different cooling rates

AbstractThe effects of antimony on eutectic silicon and fracture mode of A357 alloy were investigated at slow and fast cooling rates by scanning electron microscopy, transmission electron microscopy, polarizing microscope, differential scanning calorimetry, optical microscope and tensile testing. The slow cooling rate is 0.16 °C/s, and the fast cooling rate is 3.20 °C/s. The results show that with antimony addition, the eutectic silicon of A357 alloy is modified. Antimony does not modify eutectic silicon of A357 alloy by increasing the number of twins. Under the same cooling rate condition, with antimony addition, the volume fraction of eutectic phases increases, and when studying the modification of eutectic silicon of some modifiers, we also need to study the eutectic phases including eutectic silicon and eutectic α‐aluminum. With antimony addition, tensile strength and elongation of A357 alloy increase, especially under fast cooling rate conditions. With the increase of elongation, the fracture mode of A357 alloy changes from I to I+II to I+II+III.

Microstructure and rheological properties of a semisolid A356 alloy with erbium addition

The effects of erbium addition on the rheological properties and microstructure of a semisolid A356 alloy were studied. The semisolid slurries were prepared through the serpentine channel technique before they were thixoformed using parallel-plate compression with cylindrical discs. The grain and globule size decreases as the Er content increases, resulting in an improved and uniform distribution of spherical primary α-Al phase within the semisolid slurry. The addition of the Er modifies the grain morphology and size of the α-Al grains, resulting in a better and more uniform distribution of spherical primary α-Al phase within the semisolid slurry. As a result, rheocast quality index increases with the addition of Er, which is suitable for the thixoforming process. The A356 alloy without Er has the highest viscosity herein. The viscosity decreases, and the flow characteristics of the semisolid feedstock are expected to improve when Er is added as a result of the refinement of primary α-Al and modification of eutectic silicon. Furthermore, the refined semisolid A356 alloys with Er show a slightly larger fraction of high-angle grain boundaries compared to that for the unrefined alloy.

Regresyon Analizi Kullanılarak A356 Alaşımında Stronsiyum İçeriği ve Soğutma Hızı Arasındaki İstatistiksel İlişki

Eutectic silicon modification is an important casting parameter on Al-Si alloys on the aspect of mechanical capability and energy absorption of the cast part. Chemical modifier element strontium has been used to obtain eutectic modification on Al-Si alloy commercially. On the other hand, high cooling rate on Al-Si alloys both refine dendrites and silicon phase which enhances mechanical characteristic. In order to find a statistical relationship between strontium amount and cooling rate, a special mold was designed in order to obtain different range of cooling rates in same cast part, then tensile test data of A356 alloy were analyzed in Minitab software. Therefore, after regression and analysis of variance tests have been proceeded, it was found that strontium amount is only dominant for lower cooling rates of < 0.9 oC.

Effect of Ni on Microstructure and Creep Behavior of A356 Aluminum Alloy

The effect of 0.25, 0.5 and 1 wt% Ni addition on the impression creep behavior of the cast A356 alloy was investigated. Optical and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) were used for examination of the microstructure. The alloy’s creep properties were investigated using the impression creep technique under normalized stress of 0.022–0.03 (corresponding to 600–675 MPa) and temperature of 473–513 K. The results showed that the creep properties of A356 alloy were improved by the addition of Ni. The improved creep properties were attributed to the modification of eutectic silicon and the formation of Ni-rich intermetallics. Calculating the values of stress exponent (n) and creep activation energy (Q) indicated that the dominant mechanism was the lattice self-diffusion climb controlled and Ni had no effect on the creep mechanism.

Influence of Al-3Ti-0.15C and Ce on Microstructure and Tensile Properties of Al-Si-Cu 319 alloy

In the present research, an attempt has been made to evaluate the effects of addition of Al-3Ti-0.15C (0.05wt%) master alloy with different concentration (0.1, 0.3, 0.5, 0.8, 1wt%) of cerium (Ce), a rare earth element on microstructure and tensile properties of Al-Si-Cu 319 alloy. Optical microscopy (OM) and field emission scanning electron microscopy (FE-SEM) with EDS analysis was employed to study the microstructural modification and existence of intermetallic compounds. Experimental results show that addition of Ce with up to 0.3wt% increases the tensile properties up to 49.13% as compared to base alloy due to refinement of α-Al and modification of eutectic silicon. In contrast, tensile properties decline above 0.3wt% addition of Ce due to formation of needle like intermetallic compounds. These Ce rich needles like intermetallic compounds suppress the effect of modification, decreasing tensile properties of modified alloy.

T6 Solutionizing Heat Treatment Parameter of A356 Alloy by Investment Casting

The heat treatment process is important to conduct on A356 Aluminum Alloy that broadly used in an automotive application. Analysis of the effect grain refinement, eutectic silicon modification of T6 solutionizing heat treatment parameter on strength development of A356 Aluminum Alloy were performed to become an important prospect of controlling the behaviour of materials as well as duration and temperature. In this study, there are three parameters condition were conducted which is duration Time (Hour) and Temperature (°C) which is 465°C in 8 hours, 500°C in 7 hours and 535°C in 6 hours, respectively. The study generated three responses that are tensile, hardness test and microstructure analysis of the different temperature and duration time, respectively following by water-quenching. The result showed that the modification of duration time and high temperature of solutionizing heat treatment have superior mechanical properties while the microstructure analysis showed the clear formation of refinement α-Al dendrite and eutectic silicon particle.

Mechanical Properties and Conductivity of Low-Pressure Die-Cast 319 Aluminum Prepared with Hot Isostatic Pressing, Thermal Treatment, or Chemical Treatment

Low-pressure die-cast (LPDC) 319 Al alloy is commonly processed with hot isostatic pressing (HIP), heat treatment, and chemical eutectic silicon modification for advanced automotive applications. Yet, the microstructure can be similarly influenced by each of these processes, which may obscure their isolated benefits. Hence, this study aimed to differentiate their effects by processing step blocks of LPDC 319 alloy with either a HIP or ambient-pressure heat treatment, each for 2 h at 500 °C, or with strontium additions up to 150 ppm. Both chemical and thermal modifications of eutectic silicon were found to effectively improve alloy conductivity. However, the potential benefits of strontium to alloy strength and hardness were offset by the decreases in density associated with the addition. In contrast, the as-cast, unmodified samples featured relatively high densities, although this limited the ability of the HIP treatment to reduce porosity. With identical temperatures and heating times, both the HIP and heat treatment promoted comparable Al2Cu dissolution and silicon spheroidization. Accordingly, both treatments generally improved hardness and strength, and increased thermal and electrical conductivities by up to 12.5%. Thus, these processing parameters can each contribute to the development of enhanced engineering components individually, thereby reducing the need for their combined application.

Interactions Between Strontium and Sodium Fluorosilicate in the Combined Treatment of A319 Al Alloy

The mechanical properties of cast aluminum–silicon alloys are typically improved by eutectic silicon modification and melt degassing. First, trace strontium additions can modify the silicon phase and relieve stress concentrations at the naturally coarse, acicular particles. Second, chemical degasser additions, such as sodium fluorosilicate, can remove dissolved hydrogen gas from the aluminum melt to prevent the formation of deleterious gas porosity. However, combining both treatments is difficult, due to the tendency of the two chemicals to react and reduce their effectiveness. Nonetheless, there is limited research outlining specific procedures to enable their maximum potency, with both additions. In this work, the effects of strontium and sodium fluorosilicate on the eutectic silicon morphology and casting porosity in A319 aluminum alloy were investigated. This included a comprehensive study of the fading of their individual additions as well as the influence of separating the two chemical additions by various time intervals. The results of the melt treatments were characterized using optical microscopy, density measurements, and analysis of strontium contents using optical emission spectrometry. It was found that the maximum potency of both treatments was achieved by degassing prior to strontium additions, featuring both satisfactory silicon modification and porosity reductions.

Comparative study on the microstructures and hardness of the AlSi10.6CuMg alloy produced by sand casting and high pressure die casting

ABSTRACT This study compares the microstructures and hardness of an AlSi10.6CuMg alloy obtained by sand casting and high pressure die casting (HPDC). The results show that the morphology of HPDC dendrites was not uniformly distributed as in sand casting. HPDC refines the morphology of intermetallics and produces a modification of eutectic silicon. Chinese-script is the dominant iron intermetallic in sand casting, while primary polyhedral and secondary proeutectic particles are dominant in HPDC. The results of the X-ray diffraction show the presence of high residual stresses in the HPDC. Deep etching for HPDC samples reveals θ-Al2Cu phases in very thin compact dendrites. No evidence of twin plane re-entrant edge assistance was found in the growth of primary silicon. The primary silicon plate-like becomes unstable in HPDC, resulting in smooth and rounded outer surfaces. Hardness of HPDC alloy was about 11% higher than that of sand casting alloy.

Analysis of eutectic silicon modification during solidification of Al-6Si using in-situ neutron diffraction

Aluminum-silicon alloys contain coarse, acicular Si plates that are detrimental to material properties. However, trace additions of Sr have been found to modify the eutectic Si to have a fine, fibrous structure, which improves elongation, strength, and thermal conductivity. In this study, in-situ neutron diffraction was conducted during the solidification of unmodified and Sr-modified binary Al-6 wt.% Si to obtain a novel view of the modification mechanism. Neutron diffraction intensity data was collected at temperatures ranging from 660 °C to 200 °C and was integrated to create fraction solid curves for the individual Al and Si phases in each alloy. Scanning electron microscopy revealed that the Sr-modified alloy microstructure contained many micro-sized Al-Si-Sr intermetallics scattered about the eutectic regions at the Al-Si interfaces, and a few Si flakes close to some β-(Al,Si,Fe) intermetallics, suggesting important interactions between both the Fe-bearing phases and Sr in the solidification of eutectic Si. Comparing the isolated phase evolution temperatures for each alloy revealed in-situ for the first time that Sr suppresses the nucleation temperatures of both the eutectic Al and eutectic Si phases by several degrees. Accordingly, the eutectic reaction was observed to evolve at a higher primary Al solid fraction with Sr modification.

Effect of Sr Additive Amount and Holding Time on Microstructure of A390 Aluminum Alloy

The microstructure of A390 alloy under different Sr additive amounts and holding times was studied by means of direct reading spectrum analysis, energy spectrum analysis, optical microscope and electron microscope. The results show that Sr has a good modification to eutectic Si, while it has a negative effect on primary silicon. The Sr addition will increase the size of primary silicon. When the addition amount of Al-10Sr alloy is 0.6%, the modification of eutectic silicon is the optimum. The Sr has a short incubation period and a fine modification at 10min, but it is more serious burning rate in small furnace smelting, and the modification effect disappears basically after 100min.

Modification of Eutectic Si in Hypoeutectic Al-Si Alloys with Erbium Addition

Effect of erbium (Er) on the eutectic Si morphologies in hypoeutectic Al-Si based alloys was investigated using thermal analysis and microstructure examination. The microstructural observations show that the addition of Er causes significant modification of the eutectic silicon morphology from a coarse plate-like to a fine fibrous one. Furthermore, the results of thermal analysis reveal that the addition of Er decreased the temperatures of eutectic nucleation and growth, and increased the eutectic undercooling. The eutectic undercooling caused by the presence of Er plays an important role in the modification of eutectic silicon.

New Method of Eutectic Silicon Modification in Cast Al–Si Alloys

The aim of the present work was to investigate various means of obtaining a fine eutectic silicon structure in A356.2 alloy and therefore improve the alloy mechanical properties. The effects of solidification rate, Sr modification and melt thermal treatment (MTT) on the silicon particle characteristics of A356.2 (Al–7 %Si–0.4 %Mg) alloy were studied. The particle characteristics measured were the average particle area, average particle length, average particle roundness and average particle aspect ratio, using image analysis and optical microscopy. The results showed that Sr modification-, superheat- and Sr modification-MTT (SrMTT)-processed castings provide fine eutectic Si particles, the SrMTT process giving the best modification results. Both size and morphology of the eutectic silicon particles are affected by the modification process used. The Sr-grain-refined, Sr-melt superheat and SrMTT castings show well-modified fibrous Si particles, whereas the MTT casting exhibits Si particles that, although refined to a certain extent, still retain their acicular morphology. Solidification rate affects the eutectic Si particle size in that a higher solidification rate produces finer Si particles. However, within the range of solidification rates provided by the end-chill mold used in this work, the solidification rate does not affect the morphology of the Si particles.

The Effect of Boron and Sequence on Refining Efficiency and Eutectic Silicon Modification in Al-Si-Mg Cast Alloy

วตถประสงคงานวจยนเปนการศกษาอทธพลของโบรอน (0.04, 0.08 และ 0.12 wt.%) และลำดบขนทแตกตางกนตอประสทธภาพในการปรบสภาพเกรนละเอยดและเฟสยเทคตกซลคอนในโลหะผสมหลออะลมเนยม-ซลคอน-แมกนเซยม โลหะแม Al-4%B, Al-4%B-2%Sr และ Al-10%Sr ใชสำหรบการสภาพเกรนละเอยดและเฟสยเทคตกซลคอนในแตละสภาวะการหลอวเคราะหขนาดเกรนเฉลยโดยใชวธลากเสนตดผาน ผลการทดลองพบวาขนาดเกรนจะมขนาดเลกลงเมอปรมาณโบรอนสงขน ในขณะทเฟสยเทคตกซลคอนปรบสภาพจากรปรางไมแนนอนกลายเปนรปรางกลมมนแคบางสวนโลหะผสมทไมไดผานการปรบสภาพเกรนละเอยดมขนาดเกรน α-Al เฉลยเทากบ 3377 ไมครอน และลดลงเทากบ 1159, 439 และ 428 ไมครอนเมอเตมโบรอน 0.04, 0.08 และ 0.12 wt.% ตามลำดบการเตมโลหะแมชนด Al-4%B-2%Sr ปรมาณ 2 wt.% มประสทธภาพในการปรบสภาพเกรนทนอยกวาเมอเปรยบเทยบกบปรมาณการเตมโบรอน 0.08 wt.% ผสมกบธาตสตรอนเทยม 0.02 wt.% ในขณะทเฟสยเทคตกซลคอนปรบสภาพเปนรปรางกลมมนการศกษาลำดบขนทแตกตางกนพบวามอทธพลตอขนาดเกรน α-Al อยางมนยสำคญ เมอเปรยบเทยบกบการเตมแบบผสม คำสำคญ: โลหะผสม Al-Si-Mg การปรบสภาพ การปรบสภาพเกรนละเอยด งานหลอ The objective of this research was to study the influence of boron content (0.04, 0.08 and 0.12 wt.%B) and different sequences on refining efficiency and eutectic modification in Al-Si-Mg Cast Alloy. The Al-4%B, Al-4%B-2%Sr and Al-10%Sr master alloys were used for grain refiner and modifier of each casting condition. Grain size analysis was measured using the linear intercept method. The experimental results showed that the Grain size decreased with increasing B content, while eutectic silicon partially modified the acicular silicon into fibrous morphology. The Grain size of α-Al in the as-cast alloy is 3377 and decreases to 1159, 439 and 428 micron in 0.04, 0.08 and 0.12 wt.% B added, respectively. The addition in terms of 2 wt.% of Al-4B-2Sr revealed less refining efficiency than 0.08 wt.%B + 0.04Sr added, while the eutectic Si was fully modified into the fibrous morphology. The different sequence of addition showed significant influence on the grain size of α-Al when compared to their combined addition.

Al–9.00 %Si–0.25 %Mg alloys modified by ytterbium

The effects of ytterbium (Yb) on microstructure and solidification behavior of Al–9.00 %Si–0.25 %Mg alloys were investigated. By optical microscope (OM) and scanning electron microscopy (SEM), it is found that the morphology of eutectic silicon changes from coarse plates to fine fibers by the addition of 0.7 %wt Yb. In addition, the grains of α-Al matrix are refined by Yb addition. Phase constitution of the alloy was analyzed by X-ray diffractometer (XRD) and energy dispersive spectroscopy (EDS) attached with SEM and mechanical properties were measured by hardness test. It is concluded that the Yb atoms are incorporated into the silicon by the adsorption at the solid–liquid growth front to cause the modification of eutectic silicon. Furthermore, the results of XRD and EDS analysis reveal that the Yb-containing phase forming in the alloys is Al3Yb.

Effect of chilling and cerium addition on microstructure and cooling curve parameters of Al–14%Si alloy

Al–14%Si alloys, with and without cerium, were cast at varying cooling rates by solidifying them in a crucible and against chills. The effect of melt treatment and chilling on microstructure and cooling curve parameters of the alloy was assessed. Ce treated alloys solidified in clay graphite crucible at a slow cooling rate showed refinement of primary silicon and the formation of Al–Si–Ce ternary intermetallic compound. The addition of Ce to the alloy solidified against chills resulted in simultaneous refinement and modification of primary and eutectic silicon. Nucleation temperatures of both primary and eutectic silicon decreased on addition of cerium. The formation of the intermetallic compound decreased with increase in cooling rate, leading to the modification of the eutectic silicon. The increase in the degree of modification of the eutectic Si was associated with the decrease in the volume fraction of the intermetallic compound formed.

Modification of eutectic silicon and β-Al5FeSi phases in as-cast ADC12 alloys by using samarium addition

The effects of Sm additions (0, 0.5 wt.%, 1.0 wt.% and 1.5 wt.%) on the eutectic Si and β-Al5FeSi phases of ADC12 as-cast alloys were studied by optical microscopy (OM), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The experimental results showed that Sm was an effective modifying agent for the eutectic Si of ADC12 alloy, when 1.0 wt.%–1.5 wt.% Sm was added to the alloy, the coarse acicular eutectic Si was modified into fine particle or short rod structure. Moreover, the appropriate addition of Sm (about 1.0 wt.%) had marked effects on shortening the length of needle-like β-Al5FeSi phase. Whereas, Sm was less effective on modifying the needle-like β-iron to the Chinese script or spherical α-iron phase. The modification mechanism was also discussed.

Thermal analysis study on the simultaneous grain refinement and modification of 380.3 aluminum alloy

In this research, effect of integrated Al–10Sr–1Ti–2B master alloy has been studied on the microstructure and solidification characteristics of 380.3 aluminum alloy. Thermal Analysis has been used as a technique to study the cooling curves and first derivative curves during solidification of the alloy. Effect of integrated grain refiner and modifier on solidification parameters such as α-Al dendrite growth temperature (T G,α), α-Al dendrite recalescence undercooling (∆T R,α), aluminum–silicon eutectic growth temperature (T G,E), and eutectic recalescence undercooling (∆T R,E) has been determined. By increasing master alloy content, T G,α and ∆T R,E have been increased, but, ∆T R,E has been decreased, and T G,E increases first and then decreases. Aluminum–silicon eutectic depression temperature ( $$ \Updelta T_{\text{G,E}}^{{{\text{Al}} - {\text{Si}}}} $$ ) can be used as a parameter to control the modification of eutectic silicon. The results of this research indicate that the optimum level of Al–10Sr–1Ti–2B master alloy for the simultaneous grain refinement and modification of 380.3 alloy is about 0.5 mass%.