β-Al5FeSi Phase Research Articles

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.

Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy

Al-Mg-Si-Cu alloys with and without Zn addition were fabricated by conventional ingot metallurgy method. The microstructures and properties were investigated using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), tensile test, hardness test, and electrical conductivity measurement. It is found that the as-cast Al-Mg-Si-Cu-Zn alloy is composed of coarse dendritic grains, long needle-like β/δ-AlFeSi white intermetallics, and Chinese script-like α-AlFeSi compounds. During high temperature homogenization treatment, only harmful needle-like β-AlFeSi phase undergoes fragmentation and spheroidizing at its tips, and the destructive needle-like δ-phase does not show any morphological and size changes. Phase transitions from β-AlFeSi to α-AlFeSi and from δ-AlFeSi to β-AlFeSi are also not found. Zn addition improves the aging hardening response during the former aging stage and postpones the peak-aged hardness to a long aging time. In T4 condition, Zn addition does not obviously increase the yield strength and decrease the elongation, but it markedly improves paint-bake hardening response during paint-bake cycle. The addition of 0.5wt% Zn can lead to an increment of 99 MPa in yield strength compared with the value of 69 MPa for the alloy without Zn after paint-bake cycle.

Microstructure, hardness and tensile properties of A380 aluminum alloy with and without Li additions

In this work, the effects of lithium (Li) on the microstructure, hardness and mechanical properties of A380 aluminum alloy have been investigated. The alloy was produced by conventional casting. Microstructures of the samples were investigated using the optical and scanning electron microscopy. The results showed that with increase of Li content up to 0.1%, the morphology of β-Al5FeSi and eutectic Si phases changed from intersected and branched coarse platelets into fine and independent ones. Li decreased hardness values of the alloy. Also, it was revealed from tensile tests that with addition of 0.6% Li, the ultimate tensile strength (UTS) and elongation values increased from 274 to 300MPa and 3.8% to 6%, respectively. Fractographic examination of the fracture surfaces indicated that the alloys with Li addition had more ductile dimple and fewer brittle cleavage surfaces.

Effect of ultrasonic vibration on Fe-containing intermetallic compounds of hypereutectic Al–Si alloys with high Fe content

The Fe-containing intermetallic compounds with high melting point in hypereutectic Al-Si alloys can improve the heat resistance and wear resistance at elevated temperatures. However, the long needle-like Fe-containing compounds in the alloys produced by conventional casting process are detrimental to the strength of matrix. The effect of ultrasonic vibration (USV) on the morphology change of Fe-containing intermetallic compounds in the hypereutectic Al-17Si-xFe (x=2, 3, 4, 5) alloys was systematically studied. The results show that, the Fe-containing intermetallic compounds are mainly composed of long needle-like β-Al5FeSi phase with a small amount of plate-like δ-Al4FeSi2 phase in Al-17Si-2Fe alloy produced by conventional casting process. With the increase of Fe content from 2% to 5% in the alloys, the amount of plate-like or coarse needle-like δ-Al4FeSi2 phase increases while the amount of long needle-like β-Al5FeSi phases decreases. In Al-17Si-5Fe alloy, the Fe-containing intermetallic compounds exist mainly as coarse needle-like δ-Al4FeSi2 phase. After USV treatment, the Fe-containing compounds in the Al-17Si-xFe alloys are refined and exist mainly as δ-Al4FeSi2 particles, with average grain size ranging from 26 μm to 37 μm, and only a small amount of β-Al5FeSi phases remain. The mechanism of USV on the morphology of Fe-containing intermetallic compounds was also discussed.

Investigation of the Microstructure Evolution of 6016 Aluminum Alloy during Homogenization

The microstructure evolution of automotive sheet 6016 aluminum alloy has been studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC) analysis. The as-cast microstructure was the typical dendritical structure, consisting of four phases: α-Al, β-AlFeSi, Mg2Si and Si. The electron diffraction analysis indicated that the β-AlFeSi phase was Al5FeSi. After 545°C for 20h homogenization treatment, Mg2Si and Si have been dissolved into matrix completely, and the remaining phase was β-Al5FeSi intermetallic compound. The transformation of β-AlFeSi→α-AlFeSi was not found during the homogenization process.

On the effect of hydrogen and Fe on reproducibility of tensile properties in cast Al–Si–Mg alloys

Gas porosities and Fe-rich phases and entrapped double oxide films (hereafter: oxides) are known to be the most detrimental defects in cast Al–Si–Mg alloys. The effects of H (gas porosities) and Fe (β-Al5FeSi phase) on reproducibility of tensile properties in Al–7Si–0.35Mg alloy have been investigated in this study. Four different casting conditions (Low H–Low Fe, Low H–High Fe, High H–Low Fe and High H–High Fe) were studied. In each case, 30 tensile test samples were prepared by casting in a metallic mold and machining (total of 120 tensile test samples). Results of tensile test were analyzed by Weibull three-parameter analyses. The microstructures of samples were studied by optical microscope. Total of 800 metallography images (200 images for each experiment) were taken and analyzed by image analysis software. Finally, the relationship between tensile properties and defects characteristics was discussed.According to the results, Fe (β-Al5FeSi phase) showed considerably larger negative impact on tensile properties of the alloy compared to H (pores). Results of Weibull analysis revealed that the scattering of tensile properties was mainly due to the presence of β phase within the microstructure. Results of image analysis showed that the pore area% and number of pores/cm2 were mainly controlled by H and Fe content of the melt, respectively. Also, it was shown that Weibull modules of UTS and El% increased linearly with increasing the shape factor of pores. Furthermore, tensile properties of the examined alloy showed strong dependence to the number of pores.

Hot Tear Susceptibility of Al-Mg-Si-Fe Alloys with Varying Iron Contents

Hot tear susceptibility in cast Al-0.52Si-0.34Mg-xFe 6060 aluminum alloys was investigated using a hot tearing test apparatus to simulate hot tearing in DC casting. The test apparatus has two cast bars, one that is used to measure the load response and one which is fixed at both ends to restrain thermal contraction so that hot tearing can be observed and rated where it occurred. The iron (Fe) content, ranging from 0.02 to 0.5 wt pct, was seen to have a major influence on the load response during solidification and the tear rating of these alloys. The findings are discussed in terms of Rappaz-Drezet-Gremaud (RDG) model sensitivity analysis and related to the effect of Fe content on the morphology and prevalence of the β-Al5FeSi and α-AlFeSi intermetallic phases and their influence on the coherency and coalescence of the microstructure.

Differential Thermal Analysis Assessment of Beta Phase Precipitation in Al-6.5Si-1Fe Alloy

Iron-bearing intermetallic phases formed during solidification of Al–Si casting alloys are known for having detrimental effect on their mechanical properties. This is particularly the case of the β-Al5FeSi phase which precipitates as thin and extended plates. Many researchers already studied the factors that could influence the formation of this phase and in most cases it has been concluded that low-level additives (e.g. manganese) may lead to the replacement of the beta phase with other intermetallics that are less harmful because of being more compact.In this preliminary work, differential thermal analysis (DTA) was used to study the effect of cooling rate (0.2–40 °C/min) on beta phase formation in Al-6.5Si-1Fe alloy. The effect of cooling rate on the characteristic temperature for phase changes was described and compared to literature information. The beta phase was then characterized using scanning electron microscopy and X-ray tomography. Metallographic analysis showed the phase morphology was heavily affected by the cooling rate, and parameters to quantify this have been selected and measured. Moreover, observation also revealed that some alpha phase precipitates at low cooling rate.

Fracture of thin cast slabs of Al–Sn alloys during cold rolling

Al 19%Sn 1%Cu (SAE 783) and Al 12%Sn 2.5%Si (SAE 788) alloys are ductile triboalloys which are produced by thin-slab casting followed by cold rolling. For SAE783, rolling defects are rare and generally associated to gross defects in the cast microstructure. SAE 788 forms the metastable β-AlFeSi phase, creating a brittle network within the microstructure. Heat treatment of the as-cast slabs allows reducing the effect of this phase by a reduction in its volume fraction and a change of composition, but this is a slow process. Instead, modification of the casting procedures, according to well-established rules for the production of sound aluminium castings, together with the use of base material of higher purity were shown to be equally efficient in the prevention of rolling defects. The heat treatment could then be omitted while rolling defects were eliminated.

Characterisation of intermetallic particles formed during solution treatment of an Al–7Si–0.4Mg–0.12Fe alloy

When Fe-containing Al–7Si–xMg alloys are solution-treated, usually as the initial stage of a T6 heat treatment, some of the π-Al9Mg3FeSi5 phase present in the as-cast alloy transforms into fine needle-like intermetallic particles (as seen on a polished surface). These precipitated needles, speculated to be β-Al5FeSi phase, have not been definitively characterised to date. In this work, electron microscopy characterisation by various techniques was conducted to assess the nature (i.e. the composition, morphology and crystallography) of these particles to verify or otherwise the validity of the above hypothesis. It is found that the particles are indeed β phase platelets, of the same Al5FeSi or Al4.5FeSi stoichiometry as particles formed during solidification. Close observation of their crystallographic structure suggests fine-scale internal complexities in some of the particles.

The Sequence of Intermetallics Formation during the Solidification of an Al-Mg-Si Alloy Containing La

A mechanism by which La modifies the Fe-bearing intermetallics in a 6xxx series Al alloy is examined using calorimetry. Thermal events accompanying the formation of various phases are identified by establishing a correspondence between them and microstructures of as-cast alloys. It is concluded that a previously suggested surface adsorption mechanism is unlikely to be operative. During solidification, the addition of lanthanum results in the formation of the La(Al,Si)2 phase and the depletion of the remaining melt of Si. It is hypothesized that the decreased Si/Fe ratio in the melt caused by the presence of La favors the formation of the α-AlFeSi phase, which is less detrimental to the formability of the alloy than the β-AlFeSi phase.

Morphological Variation of Fe/Cr-Rich Intermetallic Phase in Recycled Al-Si Alloy as a Function of Solidification Rate: Time-Resolved Radiography

Effects of Cr addition on morphology of β-Al5FeSi phase formed in recycled aluminum alloy were studied as a function of cooling rate by technology of time-resolved radiography. The Cr addition to iron-contaminated recycled alloys modified the needle-like β-Al5FeSi into faceted dendritic α-AlFeCrSi phase in condition of conventional casting. Time-resolved radiography of the formation of α-AlFeCrSi revealed the transition of its morphology from polyhedron at about 10K/min of cooling rate to equiaxed dendrite of faceted arms at about 50K/min. of cooling rate.

Addition of iron for the removal of the β-AlFeSi intermetallic by refining of α-AlFeSi phase in an Al–7.5Si–3.6Cu alloy

Abstract Addition of iron into the molten metal for the removal of the β-AlFeSi intermetallic by refining of α-AlFeSi phase has been studied. Solidification conditions and composition determine the final microstructure and mechanical properties of a casting piece. It is known that increasing the iron content will produce an increasing of the α-AlFeSi and β-AlFeSi phases. This phenomenon was confirmed with calculations made by Thermo-Calc™ software and validated with experimental results, however, the technique of iron addition in this study plays an important role on the solidification kinetics of these iron phases because the refining of α-AlFeSi and removal of β-AlFeSi phases can be improved. Final results showed an improvement in mechanical properties by removal and refining of β-AlFeSi and α-AlFeSi phases, respectively. This study shows a new method of removal of β-AlFeSi that could be adopted in the aluminum smelting industry in aluminum alloys with a low cooling rate with a secondary dendritic spacing of about 37 μm.

A Study on Quantification of Homogenizing Treatment for Al-Mg-Si Alloy AA 6063

Abstract Homogenization of aluminum extrusion billets facilitates extrusion and improves product quality. In this work, a parameter has been developed that defines the homogenization level of AA6063 extrusion billets. The insoluble α-AlFeSi and β-AlFeSi phases have been experimentally determined by evaluating the length/width ratio of the AlFeSi intermetallic in the microstructure. Using this identification, the area fraction of each phase has been measured. The area fraction of the β-AlFeSi phase in the cast structure is over 65%. In the well-homogenized sample, the β-AlFeSi area fraction decreases to values lower than 20%, while the α-AlFeSi phase ratio increases to over 80%. As the α-AlFeSi percentage in the structure increases, the elongation of the samples steadily increases, from 1% to 24%. Based on the ratio of α-AlFeSi to the entire intermetallic phase, we propose six different homogenization levels. The proposed indexing can be used to define the homogenization state of the billet, regardless of the homogenization temperature and time. The index numbers exhibit a good correlation with the deformation potential of the samples.

Effects of Mg Content on Microstructure and Mechanical Properties of Al-14.5Si-4.5Cu Alloy

This study elucidates how Mg content affects the microstructure and mechanical properties of Al-14.5Si-4.5Cu alloy by adding 0.45 and 0.90 wt pct Mg. Primary silicon, eutectic silicon, acicular β-Al5FeSi, Al2Cu, and Al5Cu2Mg8Si6 phases were observed under the as-cast condition in low-Mg alloy. In high-Mg alloy, a large proportion of the acicular β-Al5FeSi phase was converted to Chinese script Al8Mg3FeSi6 phase. Neither the acicular β-Al5FeSi phase nor the Chinese script Al8Mg3FeSi6 phase dissolved in the Al matrix during solution heat treatment. Tensile testing indicates that T6-treated high-Mg alloy containing the Chinese script Al8Mg3FeSi6 phase is better than the T6-treated low-Mg alloy that contains the acicular β-Al5FeSi phase. The morphologies of Chinese script Al8Mg3FeSi6 and acicular β-Al5FeSi phases affect the tensile properties of Mg-containing Al-14.5Si-4.5Cu alloys. Additionally, high-Mg alloy contains a higher concentration of Mg solute atoms in the Al matrix than low-Mg alloy, and so the former contains more λ′ precipitates (Al5Cu2Mg8Si6) after T6-tempering treatment. The large amount of λ′ that precipitates in T6-treated high-Mg alloy may also enhance its tensile strength. The ultimate tensile strength (UTS) and elongation of the high-Mg alloy are superior to those of the low-Mg alloy.

Microstructural evolution of Al-20Si-5Fe alloy during rapid solidification and hot consolidation

Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43−1.2 cm/s and 15–28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 105 K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 107 K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural refinement and modification. The size of the primary silicon decreased from approximately 1 μm to 30 nm while the formation of iron-containing intermetallic compounds was suppressed. Supersaturation of the aluminum matrix in an amount of ∼7 at.% Si was noticed from the XRD patterns. During the hot consolidation process, coarsening of the primary silicon particles and precipitation of β-Al5FeSi phase were observed. Evaluation of the compressive strength and hardness of the alloy indicated an improvement in mechanical properties due to the microstructural modification.

Effects of ultrasonic vibration on the iron-containing intermetallic compounds of high silicon aluminum alloy with 2% Fe

Abstract The effects of ultrasonic vibration (USV), the combined effects of USV and the addition of Mn on the morphology of iron-containing intermetallic compounds of Al–20Si–2.0Fe–2.0Cu–0.4Mg–1.0Ni alloy have been studied respectively. The mechanism of shape-transformation of Fe-containing phases is also investigated. A large amount of long needle-like β-Al5FeSi phases accompanied with a few δ-Al4FeSi2 phases existed in the matrix of high silicon aluminum alloy with 2% Fe in traditional casting process. The effects of acoustic cavitation and acoustic streaming generated by USV which was applied near the liquidus temperature of this alloy, homogenized the solute distribution field and temperature field of the melt, lowered the concentration level of Fe atoms in solidification front, and decreased the start-freezing temperature of β phase. That the formation of acicular β phase was suppressed, contribute to enlarge the forming temperature range of δ phase of the alloy with certain time of USV imposed near the liquidus temperature. The finest δ particles and only a small amount of β phase were obtained in the matrix of the Fe-containing alloy with USV for 120 s. With the complex effects of USV and addition of 0.5% Mn, the forming of acicular β phase was almost repressed and the Fe-containing phases were in forms of fine Al4(Fe,Mn)Si2 and Al5(Fe,Mn)Si particles in the size of 20–30 μm.

Precipitation of β-Al5FeSi Phase Platelets in Al-Si Based Casting Alloys

The aim of the present work has been to investigate the factors affecting the precipitation of the β-Al5FeSi iron intermetallic phase of directionally solidified A356- and 319-type alloys as a function of the iron content, a Sr addition of ~250 ppm, and superheating or cooling rates. The iron levels selected varied from 0.12 to 0.8 wt pct and cover the range of Fe levels in commercial casting alloys. The use of an end-chill mold provided different cooling rates along the height of the same casting, with dendritic arm spacing values that varied from ~15 to 85 μm, corresponding to levels of 5, 10, 30, 50, and 100 mm above the chill end. The microstructure and phase identification were monitored using optical microscopy, scanning electron microscopy (SEM), thermal analysis, and electron probe microanalysis (EPMA) techniques. An image analyzer was used in conjunction with the optical microscope for quantification purposes. The results showed that, for the range of cooling rates covered in the present study, the highest cooling rate (at a 5-mm distance from the chill) is the more significant parameter in controlling the size and distribution of theβ-Al2FeSi intermetallic phase in the nonmodified 319 and 356 alloys. The addition of strontium leads to fragmentation of coeutectic or posteutectic β platelets. This effect diminishes with an increase in the iron concentration, and further strontium addition leads to the precipitation of Al2Si2Sr phase particles, instead.

Parameters controlling the microstructure of Al–11Si–2.5Cu–Mg alloys

This study investigated the effects of cooling rate during solidification, heat treatment, and the addition of Mn and Sr on the formation of intermetallic phases in Al–11Si–2.5Cu–Mg alloys. Microstructures were monitored using optical microscopy and EPMA techniques. The results reveal that the volume fractions of intermetallic phases are generally much lower in the furnace-cooled samples than in the air-cooled ones due to the dissolution of the β-AlFeSi and Al 2Cu phases during slow cooling at critical dissolution temperatures. Strontium additions increased the volume fraction of the Al 2Cu phase in the as-cast conditions at low and high cooling rates, as well as at varying ranges of Mn levels. Platelets of the β-AlFeSi phase were to be observed in the microstructure of the as-cast air-cooled samples with a DAS of 40 μm at both Mn levels, while none of these particles were to be found in the furnace-cooled samples with a DAS of 120 μm. Sludge particles were observed in almost all of the air-cooled alloys with sludge factors of between 1.4 and 1.9. These particles, however, were not observed in the furnace-cooled alloys with similar sludge factors. Solution heat treatment coarsens the Si particles in the non-modified alloys under both sets of cooling conditions studied. In the Sr-modified alloys, solution treatment has varied effects depending on the cooling rate and the level of Mn present.

Effect of Cooling Rate and Fe/Mn Weight Ratio on Volume Fractions of α-AlFeSi and β-AlFeSi Phases in Al–7.3Si–3.5Cu Alloy

The crystallization behavior of iron intermetallic compounds in Al−7.3Si−3.5Cu alloy was investigated using thermal analysis, metallography, and a thermodynamic simulation performed with the Scheil module of ThermoCalc®. We observed that β-AlFeSi disappeared when both high (>3.5°C/s) and low cooling rates (<0.1°C/s) were used. The elimination of β-AlFeSi at low cooling rates may be attributable to a decrease in the magnitude of microsegregation associated with low cooling rates. The disappearance of β-AlFeSi at high cooling rates may be related to growth difficulties when this phase precipitates during solidification of eutectic Al−Si: β-AlFeSi precipitation approaches the solidification onset of eutectic Al−Si when the cooling rate is increased. Moreover, the cooling rate at which the β-AlFeSi phase is suppressed should depend on the chemical composition of the alloy. According to thermodynamic simulations, the alloy composition determines the precipitation onset temperature of both β-AlFeSi (Tβ) and eutectic Al−Si (Teut). The cooling rate at which the β-AlFeSi phase disappears may be even higher as the difference betweenTβ andTeut increases.