Eutectic Al-Si Alloy Research Articles

Hypereutectic Al-Si Alloy with Completely Nodular Eutectic Silicon: Microstructure and Process

The achievement of hypereutectic Al-Si alloys with completely nodular eutectic Si has been studied. The procedure contained two steps: firstly, achieving hypereutectic direct electrolytic Al-Si alloys (HDEASA) with completely eutectic structure and secondly, spheroidizing eutectic Si upon soaking. HDEASAs with Si level in the range from 13.2 wt% to 17.6 wt% were made from direct electrolytic eutectic Al-Si alloy ingot and Al-50 wt% Si hardener. As cast microstructure of HDEASA was composed of primary-free quasi-eutectic cells. In comparison with commercial alloys, the lower heating temperature of 505°C -515°C for 4-8 hrs was required to fully spheroidize Si crystal, either fine fibrous or even flaky in casting. Most of the spheres ranged in size from 1.0μm to 4.0μm. Many measurements were focused on the variety of Si phase size in eutectic cells against the distance from the center of the cells. The origin of granulation of primary-free quasi-eutectic Si crystal is associated with its thermodynamic structural instability, accompanied by crystallographic defects, related to the electrolytic process.

What is the Process Window for Semi-solid Processing?

In semi-solid processing, the liquid fraction vs temperature is commonly used to define the process window. Conventionally, it is assumed that a freezing range is required for semi-solid processing but recently both high-purity aluminum and binary Al-Si eutectic alloy have been rheo-processed. Here, the kinetics during melting and solidification of pure metal are analyzed, and a comparison between the liquid fraction vs temperature and the liquid fraction vs time is presented. It is found that liquid fraction vs time is a significant criterion for semi-solid processing.

Solidification Simulation of Parts with Rotational Symmetry Using 2D Software in Cylindrical Coordinates

Solidification simulation software was developed, for parts having rotational symmetry cast of eutectic alloys or pure metals. The software uses a finite differences mathematical model described in cylindrical coordinates. Unlike software in Cartesian coordinates, it allows the solidification simulation for three dimensional parts with rotational symmetry using 2D simulation. As result the effective simulation time is much smaller (tens or even hundreds of times) in comparison with simulation in Cartesian coordinates. Cylindrical coordinates have the advantage of allowing a precise reproduction of the round contour parts. The paper presents the experimental verification of the results provided by the software. Experimental verification is performed by thermal analysis. A cylindrical sample with a diameter D = 60 mm and length L = 150mm was cast. The part was cast in Al-Si eutectic alloy (ATSi12). The temperature variation inside casting was recorded in three points: in the center, at the distance 1/2R and on the part surface. The experimental results were compared with those determined by computer solidification simulation. The values for liquid alloy initial temperature and for landing eutectic temperature used in simulation were chose accordingly to those experimentally determined for each point separately. The temperature variation curves during casting cooling and solidification obtained by simulation are close to those experimentally determined. The curves approaching in the first part (cooling in liquid state and solidification) can be appreciated as very good. Small differences appear in the final of the curves in the cooling area after the complete solidification of the alloy in that point. The experiment revealed that the tested software provide accurate data on castings solidification (solidification time and temperature distribution). As result, the software developed by the authors from Transilvania University, can be used with enough accuracy for fundamental and applied researches related to castings solidification.

Application of the Eyring Equation in the Evaluation of Semi-Solid Forming-Induced Si Particle Refinement in the Hypereutectic Al-Si Alloys

On the basis of Eyring’s theory of absolute reaction rate, an approach to modeling Si particle refinement acceleration in the semi-solid forming of a hypereutectic Al-Si alloy has been developed. The acceleration variable data used in the present analysis were obtained from a semi-solid compression test using Al-25 mass pct Si alloy cylindrical specimens with a diameter of 15 mm and a height of 15 mm; the test conditions comprised a combination of compression displacements ∆h = 5, 10, and 12 mm; compression rates v = 5, 25, and 125 mm/min; and test temperatures T = 853 K and 863 K (580 °C and 590 °C). The coarse primary Si particle refinement depends on a complex interaction among variables, such as compression displacement, compression rate, and test temperature. The performance of Si particle refinement degraded under higher temperature, slower strain rates, and slower shear rates. The results of the Si particle size are suitably summarized by the Eyring equation as a function of the temperature and the shear rate. The baseline Si particle size and the baseline temperature of Si particle refinement, i.e., the reference temperature, were GN = 0.27 mm and TN = 866.4 K (593.4 °C), respectively. The calculated results using this equation correlated well with the observed results. An acceleration factor of Si particle refinement was successfully derived on the basis of this equation and indicated that operating at a higher shear rate and a temperature just above the melting point of eutectic Al-Si alloy are the optimum conditions for refining Si particles.

Tribological behavior of Al–6.5%, –12%, –18.5% Si alloys during machining using CVD diamond and DLC coated tools

Abstract Tribological behavior of cast Al–Si alloys was studied by considering samples from hypo-eutectic (Al–6.5% Si), eutectic (Al–12% Si) and hyper-eutectic (Al–18.5% Si) compositions that were subjected to dry drilling experiments. Tool materials tested consisted of hydrogenated diamond-like carbon (H-DLC), CVD diamond coated and uncoated WC–Co drills. Tool failure mechanisms were identified and correlated with the drilling torques. The drilling torque vs. number of holes curves typically exhibited three stages, each identified with a characteristic slope (m). A failure criterion was established, such that when m ≥ 1.0 × 10− 2 N m the onset of tool failure in dry drilling of Al–Si alloys could be predicted. For hypo-eutectic and eutectic Al–Si alloys drilled using uncoated WC–Co the failure criterion was satisfied rapidly (

Effect of Grain Size of Calcium Carbonate Foaming Agent on Physical Properties of Eutectic Al–Si Alloy Closed Cell Foam

Aluminium foams have become popular because of their properties such as high stiffness combined with very low density. The aluminium foams are being used in many applications like automobiles, railways, aerospace, ship building, household applications etc. The development of foam with consistent quality and study of foam structure–property relation is important for both scientific and industrial applications. Metallic foams are commonly produced using hydride and carbonates foaming agents. However carbonate foaming agents are safer to handle than hydrides and produce aluminum foam with a fine, homogenous cell structure, low cost and easily available. The number of pores per inch and relative density of the foam play an important role on their physical and mechanical properties. Hence it is very important to investigate effect of grain size of calcium carbonate foaming agent on pores per inch and relative density. The present work deals with the effect of grain size of the calcium carbonate forming agent on the physical properties of an eutectic Al–Si alloy closed cell foam. The foam was produced with different grain size of calcium carbonate (150, 106, 75, 53 µm) as a foaming agent. The pores per inch and density of the foam produced with different grain size of calcium carbonates as foaming agent are determined. Relative density is in the range of 0.21–0.34, pores per inch is in the range of 11–20 for the produced eutectic Al–Si alloy closed cell foam. It is observed that as grain size of calcium carbonate used for production of aluminium foam increases, the number of pores per inch decreases, relative density decreases and porosity increases.

Study on the Effects of Squeeze Pressure on Mechanical Properties and Wear Characteristics of Near Eutectic Al–Si–Cu–Mg–Ni Piston Alloy with Variable Mg Content

In the present work, the effects of pressure on the wear resistance characteristics, mechanical properties and the microstructures of Al–Si piston alloys that have variable Magnesium (Mg) content are studied. The paper begins with an explanation of the desirable properties of eutectic Al–Si alloys and why these chemical and mechanical properties are desirable in the fabrication of light weight machine components. The methods for further strengthening the alloys using alloying elements such as Ni, Cu and Mg, and applying heat treatment are also discussed. The paper also emphasises on the addition of Magnesium, and compares the traditional gravity die casting with a novel hybrid technology known as squeeze casting. In the results and discussion section, the microstructure properties of the Al–Si both as-cast and after heat treatment conditions are discussed. The mechanical and wear properties as well as the implications of pressure on the alloys are also discussed in details. SEM analyses of wear surface and fracture behavior on the as cast Al–Si alloys and after heat treatment, reveal that squeeze pressure increases fracture ductility as well as resistance to wear; more so upon heat treatment. It is also determined that the hardness and UTS values increases with increase in Magnesium content and reaches the maximum values when Mg content is at 1 % of the alloy’s composition.

Fabrication of Ingot with Lotus Type Through-Holes in Semisolid Condition

In this paper, an easy casting method of an ingot with through holes is shown. The Core-Bar-Pulling Method is proposed to improve the disadvantages of lotus type porous metal. The through holes were formed by pulling core-bars from a semisolid ingot. Holes with diameters ranging from 0.5 mm to 5 mm and length 50 mm were made in Al-Si alloy ingots. The relationship between temperature and formability of the holes was investigated by using eutectic Al-Si alloys. The pulling of core-bars and the forming of holes were easy, under the condition that the Si content was less than 6 mass%. This means that the forming of holes in Al-Si alloys is easy under the condition that flow ability at semisolid condition decreases.

Effects of Sr and pressure on microstructure, mechanical and wear properties of near eutectic Al–Si piston alloys

Near eutectic Al–Si alloys exhibit smaller coefficients of thermal expansion than those of hypoeutectic and hypereutectic alloys and are thus used preferentially to fabricate automotive pistons. The mechanical properties of near eutectic Al–Si alloys depend on the alloying elements used and the micro structural changes induced by the rate of cooling and the heat treatment to which they are subjected. In this study, Sr is added as a modifier in an Al–Si–Cu–Ni–Mg alloy and subjected the alloy to a pressure and a heat treatment in order to carry out a systematic inquiry to discover and examine the effects of Sr on and wear characteristics of the alloy. The addition of Sr, the application of a pressure, and the heat treatment produced a finer microstructure and resulted better properties. The fracture and wear mechanisms of alloy specimens subjected to tensile and wear tests were investigated using scanning electron microscopy.

Effect of Cr content and heat-treatment on the high temperature strength of eutectic Al–Si alloys

In this work, the effects of Cr content (0–0.67 wt%) and heat treatment on the microstructure evolution and high temperature (HT) tensile strength (350 °C) of the Fe-containing eutectic Al–Si alloy were studied. The results show the main intermetallics are similar in tested specimens at both different heat treatment states, including γ-Al3CuNi, δ-Al7Cu4Ni, Al4Cu2Mg8Si7, and AlFeSi. The addition of Cr leads to the transformation from needle-like β-AlFeSi phases to fishbone-like α-Al(Fe,Cr)Si phases. For the HT strengths (350 °C), the UTSs of Al–Si alloys at T5 state are higher than T6 state correspondingly, both of which are progressively decreased with the Cr contents. For the elongation, the Al–Si alloys at T6 state have better plasticity than T5 state correspondingly. Comparably, the elongations remain stable at T5 state, and keep increasing at T6 state with the addition of Cr. The variations of HT strengths and elongations dependent on the Cr content and heat treatment are accounted on the microstructural evolutions, including AlFeSi phase transformation and the Si spheroidization.

Influence of surface etching pretreatment on PEO process of eutectic Al–Si alloy

To solve the problems generally encountered during the plasma electrolytic oxidation (PEO) of Al alloys with high Si content, a pretreatment of chemical etching was applied before the process. The influence of such pretreatment was studied by SEM, EDS and XRD. The pretreatment presents a significant effect on positive voltage at the beginning stage of PEO, leading to higher voltage over the whole process. The difference between the positive voltages of non-etched and etched specimens decreases gradually with the increase of processing time. The pretreatment exhibits much less influence on the negative voltage. For the sample with surface pretreatment, the average growth rate of PEO coating is increased from 0.50 to 0.84μm·min−1 and the energy consumption is decreased from 6.30 to 4.36kW·h·μm−1·m−2. At the same time, both mullite and amorphous SiO2 contents are decreased in the coating.

The role of elevated temperature exposure on structural evolution and fatigue strength of eutectic AlSi12 alloys

Pistons of internal combustion (IC) engines are typically subjected during operation to high cycle fatigue loading at elevated temperatures (up to 350°C). The materials typically used for piston production are eutectic Al–Si alloys for their excellent fluidity and suitable mechanical properties. Results of a fatigue testing program of eutectic Al–Si alloys at room temperature and at elevated temperatures (250°C, 300°C and 350°C) performed with the aim to support piston design and material optimization are reported in this paper. Specimens were extracted from piston crowns and tested in a rotating bending test machine. The fatigue strength at 107cycles was quantified by a staircase approach.To investigate the strengthening mechanism based on the formation of precipitates (Guinier–Preston (GP) zones) during decomposition of a metastable supersaturated solid solution, a structural investigation of one of the alloys before and after fatigue testing at elevated temperatures was conducted. Metallography, color etching, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to elucidate the following aspects: (1) the structural features of the alloy (dendrites of α-phase, primary Si particle size and distribution, morphology and distribution of intermetallic phases); (2) the changes of the strengthening mechanism (GP zones) with elevated temperature exposure.

A selective laser melting and solution heat treatment refined Al–12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

This study shows that a eutectic Al–12Si alloy with controllable ultrafine microstructure and excellent mechanical properties can be achieved by using selective laser melting and subsequent solution heat treatment. This provides a novel and promising approach to the refinement of eutectic Al–Si alloys. Unlike Al–12Si alloys fabricated and refined by traditional methods, the as-fabricated Al–12Si in this study contains nano-sized spherical Si particles surrounding a supersaturated Al matrix. During solution heat treatment, precipitation and coalescence of the Si particles occur, which decreases the Si concentration in the matrix and sub-micron to micron-sized spherical particles embedded in an Al matrix form. The as-fabricated Al–12Si exhibits significantly better tensile properties than the traditionally produced counterparts; while the solution treated Al–12Si has an extremely high ductility of approximately 25%. Importantly, the mechanical properties of the Al–12Si can be tailored through controlling the precipitation and coalescence of the Si particles by varying the solution heat treatment time. A detailed transmission electron microscopy study was conducted to investigate this Al–12Si alloy with ultrafine eutectic microstructure. The excellent tensile properties have been attributed to the refined eutectic microstructure containing spherical Si particles. The formation of this unique microstructure is due to the super heating and an extremely high cooling rate during selective laser melting and the subsequent solution heat treatment, which enables Si to grow along its most stable plane {111}Si.

J0330105 半凝固状態における通孔材の作製

In this paper, easy casting method of the ingot with through holes is shown. Core-bar-pulling method is proposed to improve the disadvantages of the lotus type porous metal. The through holes were formed by pulling core-bars from the semisolid ingot. The holes with diameters ranging from 0.5 mm to 5 mm and 50 mm length was made in the Al-Si alloy ingots. Relationship between temperature and formability of holes were investigated using the eutectic Al-Si alloys. The pulling of core-bars and the forming of the holes were easy, in the condition that the Si content was less than 6 mass%. This means that the forming of the holes in the Al-Si alloys was easy at Si content with which the flow ability at semisolid condition becomes worse.

Effect of combined grain refinement and modification on microstructure and mechanical properties of hypoeutectic, eutectic and hypereutectic Al-Si alloys

The effect of melt treatment owing to the combined addition of grain refiner and modifier on the microstructure and mechanical properties of Al-Si alloys having 7% (hypoeutectic), 12% (eutectic) and 15% silicon (hypereutectic) is studied. 1 wt. % of Al-1Ti-3B Master alloy was used as grain refiner. For modification of eutectic Si, 0.2 wt. % of Al-10Sr Master alloy was added to hypoeutectic alloy and 0.4 wt. % is added to eutectic alloy as well as hypereutectic alloy. Furthermore, refinement of primary Si in hypereutectic alloy was achieved by addition of 0.04 wt. % of phosphorus. The goal of this investigation is to determine the influence of combined addition of grain refiner and modifier on mechanical properties and qualitatively correlate with the microstructural changes.

Effect of the Near-Net Shape Forming on Silicon Morphology in an Al–Si Functionally Graded Material Generated by the Centrifugal Method

A work toward practical usage of hypereutectic Al–25 mass% Si alloy, which exhibits superior properties, as a functionally graded material (FGM) was done. The Al–Si FGM, which is based on the concept of overcoming the limitations imposed by the presence of a hard silicon phase in an aluminum matrix, was generated by a vacuum centrifugal method as a thick-walled tube. Grain coarsening, which is the primary disadvantage of the centrifugal method, was observed. The fraction of silicon phase in the tube unexpectedly varied from greater than 60 mass% at the outer surface to 15 mass% at the inner surface because of the greater density of molten silicon compared to that of the eutectic melt. Thus, the outer region of the tube was lighter than the inner region after solidification. FGM billets for near-net shape forming were machined from the thick-walled tube and were formed into an Al–Si FGM cup using a backward extruding. The products of the FGM cup were successfully manufactured in the temperature range from 853 K (580 oC) to 863 K (590 oC) through visco-plastic deformation. The fraction of silicon phase in the FGM cup varied from greater than 70 mass% Si at the formed cup bottom region to less than 15 mass% Si at the cup wall region. Coarse silicon particles were refined irrespective of the pre-existence of elongated spindle-shaped particles under some experimental conditions. The optimum operating conditions were inferred to be high-speed operation at approximately 853 K (580 °C), which was just above the melting point of the eutectic Al–Si alloy.

Modeling Cavitation in ICE Pistons Made with Isothermal Forging

Possible causes for cavitations in parts made with an Al-Si eutectic alloy AK12D (AlSi12) were explored with mathematical and physical modeling with involved acoustic emission. Pores were formed from micro-cracks, which appear during the early stages of a deformation process, with the help of micro-stresses appearing at phase boundaries (Al/Si interface) due to thermal expansion. At the design stage of isothermal forgings of such products it is recommended to provide a scheme of the deformed shape, which is under uniform compression, to compensate for the inter-phase stresses.

Experimental characterization of the mechanical behavior of two solder alloys for high temperature power electronics applications

An experimental investigation of two potential candidate materials for the diamond die attachment is presented in this framework. These efforts are motivated by the need of developing a power electronic packaging for the diamond chip. The performance of the designed packaging relies particularly on the specific choice of the solder alloys for the die/substrate junction. To implement a high temperature junction, AuGe and AlSi eutectic alloys were chosen as die attachment and characterized experimentally. The choice of the AlSi alloy is motivated by its high melting temperature Tm (577°C), its practical elaboration process and the restrictions of hazardous substances (RoHS) inter alia. The AuGe eutectic solder alloy has a melting temperature (356°C) and it is investigated here for comparison purposes with AlSi. The paper presents experimental results such as SEM observations of failure facies which are obtained from mechanical shear as well as cyclic nano-indentation results for the mechanical hardening/softening evaluation under cyclic loading paths.

Role of bismuth on solidification, microstructure and mechanical properties of a near eutectic Al-Si alloys

Computer aided thermal analysis and microstructural observation showed that addition of bismuth (Bi) within the range of 0.25 and 2 wt% produced a greater effect on the Al-Si eutectic phase than on primary aluminium and Al2Cu phases. Results showed that with addition of 1 wt% Bi the eutectic silicon structure was refined from flake-like morphology into lamellar. Bi refines rather than modifies the Si structure and increases the Al-Si eutectic fraction solid and more significantly there was no fading even up to 180 min of melt holding. Transmission electron microscopy study showed that the Si twin spacing decreased from 160 to 75 nm which is likely attributed to the refining effect of Bi. It was also found that addition of 1 wt% Bi increased the tensile strength, elongation and the absorbed energy for fracture due to the refined eutectic silicon structure.

Study of parametric optimization of burr formation in step drilling of eutectic Al–Si alloy–Gr composites

In this study, the effect of the step drill's geometries such as step angle, step size and cutting parameters such as feed and spindle speed on the exit burr height was investigated for burr minimization in drilling of Al–Gr composites which are fabricated through squeeze casting method. The experimental study was conducted as per the L27 orthogonal array of Taguchi method to find the optimum drilling parameters, and analysis of variance (ANOVA) was performed to investigate the influence of parameters on the burr height of composites during drilling. Confirmation tests were conducted to validate the test results. Results revealed that feed, step angle, step size and spindle speed were the significant parameters in the formation of exit burr.