Iron Intermetallic Phase Research Articles

Investigation of the effect of solidification rate on microstructure of Al-0.13Si-0.3Fe DC-cast alloy using EBSD and DSC techniques

Abstract Direct chill (DC) casting is used to cast aluminum alloy ingots. Casting speed influences the distribution and types of iron intermetallics in aluminum ingot microstructure. This study attempted to identify and quantify the iron intermetallic phases in the microstructure of laboratory scale DC Al- 0.13Si-0.3Fe samples using differential scanning calorimetry, scanning electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectroscopy. Both stable and non-stable iron intermetallic phases were observed but to different extents in all alloy samples’ microstructure. Two different types of iron-rich, AlFeSi globular particles were observed in the alloy samples’ microstructure. As a result, an attempt was made to understand the formation temperature and composition of these small, globular particles. DSC results confirmed that the enthalpy change of phase formation is dependent mainly on the volume fraction of the iron intermetallic phase in the microstructure. A good agreement was observed between the quantitative analysis results and the DSC analysis, which supports the reliability of the quantitative methods used in this study. The results obtained in this study bridge existing gaps in literature on the effect of cooling rate on the selection of iron intermetallic phases, in general, and in the AlSiFe globular particles, in particular.

Investigation of the effect of solidification rate on microstructure of Al-0.13Si-0.3Fe DC-cast alloy using EBSD and DSC techniques

Abstract Direct chill (DC) casting is used to cast aluminum alloy ingots. Casting speed influences the distribution and types of iron intermetallics in aluminum ingot microstructure. This study attempted to identify and quantify the iron intermetallic phases in the microstructure of laboratory scale DC Al- 0.13Si-0.3Fe samples using differential scanning calorimetry, scanning electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectroscopy. Both stable and non-stable iron intermetallic phases were observed but to different extents in all alloy samples’ microstructure. Two different types of iron-rich, AlFeSi globular particles were observed in the alloy samples’ microstructure. As a result, an attempt was made to understand the formation temperature and composition of these small, globular particles. DSC results confirmed that the enthalpy change of phase formation is dependent mainly on the volume fraction of the iron intermetallic phase in the microstructure. A good agreement was observed between the quantitative analysis results and the DSC analysis, which supports the reliability of the quantitative methods used in this study. The results obtained in this study bridge existing gaps in literature on the effect of cooling rate on the selection of iron intermetallic phases, in general, and in the AlSiFe globular particles, in particular.

Analysis of microstructure in AlSi7Mg0.3 cast alloy with different content of Fe.

Abstract The use of recycled alloys brings potential energy savings, and generates less CO2 emission compared to primary aluminum production, but it is necessary to take into account their specifics properties. The properties of the secondary aluminum alloys are comparable to primary alloys, but important attention must be paid due to the higher iron content. Iron with the presence of other elements in the alloy creates intermetallic compounds which have negative influence especially on the mechanical properties. It is impossible to remove iron from melt by standard operations. Some elements eliminates iron by changing iron intermetallic phase morphology, decreasing its extent and by improving alloy properties. Therefore, the effects of different content of Iron (Fe) on the microstructure and the morphology of the intermetallic iron phases of AlSi7Mg0.3 alloy casted in to the sand molds were investigated. For influencing their morphology formation the heat treatment T6 (according standards) and addition of Manganese (Mn) were used in some bars. 2D and 3D metallographic and image analysis have been performed to measure the microstructural changes occurring at different Fe, Mn levels and heat treatment conditions. The study confirms that T6 have influence on to size of Fe-rich phases (especially in needles form), but the increasing length of Fe-needles intermetallic phases with increasing content of Fe did not by confirmed.

Influence of Fe on the microstructure and mechanical properties of low Al-SI alloys

The present study investigates the influence of iron (precipitation of Fe-rich phases) on microstructure, ultimate tensile strength, elongation after fracture and hardness of the aluminium alloy A356, for which metallographic analysis and testing of mechanical properties were performed for iron weight percentages of 0.5, 0.8 y 1%. Phases identification was carried out by X-ray diffraction, which revealed the precipitation of β iron intermetallic phase of stoichiometry Al5FeSi and monoclinic crystal structure. Cooling rate (0.45°C/s) for sand mould was calculated through secondary dendrite arm spacing whose average length was 62.75 μm. Microhardness measurements showed the hard nature of the β phase, which produced a general increase on the alloy's hardness. The tensile strength reduced slightly (~11% for 1 wt. % Fe) unlike the fracture elongation (ductility) which suffered greatly reduces with iron increase (~54% for 1 wt. % Fe).

Effects of Addition of Transition Metals on Intermetallic Precipitation in Al–2%Cu–1%Si-Based Alloys

Thermal analysis of various Al–2%Cu–1%Si alloy melts containing different transition metal additions was carried out to determine the sequence of reactions and phases formed during solidification under close-to-equilibrium cooling conditions. The main reactions observed in the base B0 alloy comprised (i) formation of the α-Al dendritic network at 640 °C, followed by precipitation of (ii) α-iron Al15(Fe,Mn)3Si2 phase at 620 °C and (iii) Al2Cu and Al5Mg8Si6Cu2 phases simultaneously as the final reaction at 495 °C. Two more reactions were observed with the addition of Zr, V and Ni to the base alloy, in addition to Mg2Si and AlSiTiZr, AlVTi, AlCuNi and AlCuNiFe phases. The addition of Mn (0.8%) resulted in reducing the detrimental effects of the platelet-like morphology of the β-Al5FeSi iron intermetallic phase by replacing it with the more compact and hence less harmful script-like α-Al15(Fe,Mn)3Si2 phase and sludge particles. Rare earth metals have an affinity to react with certain transition metals, in particular Cu. The results reported in this study were supported by EDS, WDS and DSC analysis.

Effect of Fe, Sr, P, Ti and Undercooling on the Precipitation of β-Al5FeSi in A319.2 Type Alloys

The present work was performed on an A319.2 alloy with different amounts of Fe. The melt was poured from two temperatures, i.e. 750 and 950 °C. The results show that increasing the melt superheat leads to an increase in the undercooling, e.g., 1.2 and 3 °C for melt temperatures of 750 and 950 °C, respectively. The presence of oxide films accelerates the precipitation of the β-Al5FeSi iron intermetallic phase platelets. The amount of oxide films increases with the increase in the melt temperature, coupled with the addition of Sr and P. Strontium has a strong tendency to break down the length of the β-platelets, e.g., 160 and 109 µm, for non-modified and Sr-modified alloys containing 1.2% Fe, respectively. In the absence of Sr and for a melt temperature of ~950 °C, P precipitates in the form of (Al, P)O2 oxide films. These films act as nucleation sites for the precipitation of β-platelets much finer (60 µm) than those obtained for samples poured at 750 °C. The addition of P to the 319 alloy modified with Sr results in the precipitation of (Al, P, Sr)2O5, which significantly reduces the beneficial effect of Sr. Titanium precipitates in the form of Ti(Al, Si)3 platelets at 740 °C. Relatively fine β-platelets (~130 µm) can precipitate along the long sides of the Ti–rich platelets. Iron has a harmful effect on the alloy strength due to the precipitation of dense β-platelets. The addition of Sr improves the alloy mechanical properties through fragmentation of β-platelets, especially at low content of Fe. Finally, phosphorus has an abnormal effect on the three tensile parameters, and the Sr–P interaction diminishes the beneficial effect of Sr.

Influence of Nickel Addition on Properties of Secondary AlSi7Mg0.3 Alloy

Abstract This paper deals with influence on segregation of iron based phases on the secondary alloy AlSi7Mg0.3 microstructure by nickel. Iron is the most common and harmful impurity in aluminum casting alloys and has long been associated with an increase of casting defects. In generally, iron is associated with the formation of Fe-rich intermetallic phases. It is impossible to remove iron from melt by standard operations. Some elements eliminates iron by changing iron intermetallic phase morphology, decreasing its extent and by improving alloy properties. Realization of experiments and results of analysis show new view on solubility of iron based phases during melt preparation with higher iron content and influence of nickel as iron corrector of iron based phases.

Vanadium and Chromium Impact to Microstructure of AlSi10MgMn Alloy with Elevated Iron Content

In Al-Si alloys iron as an impurity causes decreasing of mechanical and foundry properties of castings. Nowadays is paid attention to adding different elements into aluminium alloys to increase the properties of final castings. Some elements eliminates iron by changing iron intermetallic phase morphology, decreasing its extent and by improving alloy properties. Also there is a possibility of using lower amounts of more elements, what can lead to change of morphology and to improve casting properties at the same time. The contribution is devoted to vanadium and combined vanadium and chromium impact to AlSi10MgMn alloy with high iron level. This effect is evaluated through microstructural analysis using different etchants. Colour metallography is also used to find the better and faster identification of the intermetallic phases.

The Study of Iron Intermetallic Phases Morphology with Applying Deep Etching in Secondary Al-Si Alloys

The morphology control of intermetallic phases is very important in secondary aluminium cast alloy, because these alloys contain more of additional elements, which forms various intermetallic phases in the structure. Improvement of the mechanical properties is strongly depending upon the morphology, type and distribution of the second phases, which are in turn a function of the alloy composition and cooling rate. The iron intermetallic phase has the greatest influence on mechanical properties. It is necessary to study microstructure of Al-Si alloys, because the metallographic evaluation of aluminium alloys is not simple and these alloys are used for production many mechanical components, especially for cars, aerospace and rail vehicles. The study of iron intermetallic phases was performed using light microscope Neophot 32 and SEM observation with EDX analysis. For study the morphology of these phases were samples deep-etched for 30 s in HCl solution, in order to reveal the three-dimensional morphology of the iron phases.

Kinetic–Statistical Approach in a Detailed Study of the Mechanism of Thermal Decomposition of Zinc–Iron-Intermetallic Phase

Kinetic–statistical approach was applied to investigate the mechanism of thermal decomposition of Zinc–Iron-intermetallic phase, as by product from neutral leach residues. In present paper, in order to characterize the tested material, the following experimental techniques were used: Rietveld analysis, scanning electron micrograph and tube furnace sample heating procedure. Based on dependence of Avrami constant in function of effective activation energy, it was found that at T > 950 °C, the process of crystal growth takes place in autocatalytic stage, under the conditions, where rate of nucleation rapidly increases. It was established that high nucleation rate can be attributed to formation of both Zn and Fe rich regions which provide a high number of heterogeneous nucleation sites. It has been proposed that emergence of line defects under ZnO branched crystals can serve as pin-points for secondary nucleation to occur. It was confirmed that increase in temperature in Zn vapor did not result in a decrease of existing in Zn constitutional vacancies.

Role of decomposition of AlMgFeSi phase in mechanical properties and fracture behaviour of 357 alloys

The π-AlFeMgSi iron intermetallic phase in Al–Si–Mg alloys is known for its detrimental effect on ductility and strength. An attempt was made to correlate the impact and tensile properties of heat treated Al–7Si–0·55Mg–0·1Fe alloy samples with the changes that occur in the microconstituents such as the eutectic Si and π phase with prolonged solution treatment. Impact and tensile tests showed that the first 20 h of solution treatment is more sensitive to the changes occurring in the Si particle morphology than that in the π phase. Decomposition of the π phase significantly reduces the impact properties after prolonged solution times. Fracture behaviour is controlled mainly by the eutectic silicon morphology. The π phase particles act as crack initiation sites and facilitate crack propagation in as cast and heat treated alloys. Quality index values show that optimum solution time for Sr modified alloys is 12 h. Impact properties are more sensitive to changes in the π phase during solution treatment than tensile properties.

Effects of Mg, Fe, Be additions and solution heat treatment on the π-AlMgFeSi iron intermetallic phase in Al–7Si–Mg alloys

The presence of magnesium in Be-free Al–7Si–Mg alloys results in the formation of an undesirable iron-intermetallic known as the π-AlMgFeSi phase. The effect of Mg, Fe, and Be on the formation of this phase in both unmodified and Sr-modified Al–7Si–xMg–yFe alloys containing 0.4–0.8-wt% Mg and 0.1–0.8-wt% Fe has been investigated at a dendrite arm spacing of 65 μm. A qualitative microstructural examination was carried out to study the effect of solution heat treatment (540 °C/8 h) on the decomposition of the π-AlMgFeSi phase (“π-phase”) in Al–7Si–xMg–0.1Fe alloys containing 0.4–1.0-wt% Mg. The results indicate that increasing the Mg and Fe content increases the amount of the π-AlMgFeSi phase formed. Quantitative measurements revealed a reduction in the surface fraction of the π-phase after solution heat treatment. Different levels of decomposition of the π-phase into needles of β-Al5FeSi iron intermetallic phase (“β-phase”) were observed at 0.4-, 0.6-, and 0.8-wt% Mg, after solution heat treatment.

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.

Effect of beryllium and non-equilibrium heat treatment on mechanical properties of B319.0 alloy with 1.0%Fe

B319.0 hypoeutectic alloy is a heat treatable Al-Si-Cu-Mg system with nominal composition Al-6Si-3.5Cu-0.3Mg and about 0.1-1.2Fe. The purpose of this study was to determine the influence of Be and non-equilibrium heat treatment on the microstructure and mechanical properties of B319.0 alloys with a higher Fe (1.0 wt-%) content. Results indicate that Be additions can reduce the amount and average length of iron bearing phases, can transform some platelet like shapes (β-Al5FeSi) of iron intermetallic phase to comparatively harmless Chinese-script shapes (α-Al8Fe2Si), and can also refine the eutectic silicon. High temperature solution heat treatment(≥ 510°C) may not only completely dissolve the Al2Cu intermetallics, but may also cause dissolution and fragmentation behaviour in β-phase platelets and consequently reduce their volume fraction. Because the β-phase platelets are smaller in the Be-containing alloy under identical conditions, their dissolution behavior is more obvious than that in Be-free alloy. However, if deterioration of the mechanical properties is to be avoided, the solution temperature should be lower than the interdendritic melting temperature which resulted in an ultrafine eutectic phase on quenching. DSC and electrical conductivity analysis showed that the combined effect of Be additive and non-equilibrium heat treatment caused significant increase in the precipitation kinetics of B319.0 alloy. Fractographic analysis of tensile specimens revealed that fracture processes were mainly initiated by nucleation at β-Al5FeSi platelets as a result of their cracking and decohesion from the matrix. Therefore, adding Be to B319.0 alloy and optimising the solution heat treatment could result in fewer fracture initiating sites and greater precipitation of strengthening phases, with a consequent improvement in tensile properties.

Metallographic observations on phase precipitation in strontium-modified Al-11.7% Si alloys: Role of alloying elements

The effects of alloying elements such as Mg, Cu, Ag, Ni, and Zn-added individually, or in combination, on the microstructure and phase precipitation in fourteen Al-11.7% Si alloys have been studied. Strontium (0.02–0.04 wt%) was used to produce well-modified structures. Beryllium (∼ 0.02%) was added to some alloys containing ∼ 0.4 wt% Mg to prevent oxidation, as well as to study its effect on fluidity and microstructure. Optical microscopy and electron probe microanalysis (EPMA), including energy dispersive X-ray (EDX) and wavelength dispersion spectroscopic (WDS) facilities were used to allow for a complete assessment of the microstructural changes and intermetallic phase precipitation occurring during solidification. Image analysis was used for quantification purposes. Thermal analysis was used to determine the precipitation reactions and temperatures of the various intermetallic phases formed. By measuring the size, shape, and density of the Si particles, the modifying effect of Sr and various other alloying elements was monitored.The modifying effect of Sr diminishes as the amount of added Cu and Mg is increased. In the Al-11.7% Si alloy containing ∼2.6% Cu and ∼ 0.4% Mg, additions of Ag, Ni, and Zn are found to improve the modification effect, with the Ag addition producing a Si particle density much higher than that achieved with Ni or Zn additions. Copper and Ni do not dissolve in the β-Al5FeSi iron intermetallic phase, but dissolve in measurable amounts in the α-iron Al15(Fe, Mn)3Si2 phase, and produce various Al- Ni-Cu intermetallics with different Al:Ni:Cu ratios, in addition to Al2(Ni, Cu).Also, the Al8MgCuSi phase is seen to precipitate separately, in the form of Chinese script, rather than growing out of the Al2Cu phase as is observed in the Ni-free alloys. Zinc is found to segregate at the boundaries of the α-Al dendrites, without forming any specific intermetallic.

Observations on the formation of ?-Al5FeSi phase in 319 type Al-Si alloys

In Al-Si alloys, the properties are influenced by the shape and distribution of the eutectic silicon particles in the matrix, as also by the iron intermetallics and copper phases that occur upon solidification. The β-Al5FeSi iron intermetallic phase, in particular, is known for its detrimental effect on the properties, and is controlled variously by the iron content and the melt/solidification conditions of the alloy. The formation of the iron intermetallics has been observed in commercial 319 alloy end-chilled castings, obtained from non-treated and treated melts, where the effects of cooling rate, strontium modification and grain refinement have been studied. The volume fraction of β-phase formed was seen to increase with the decrease in cooling rate (i.e. with increasing distance from the chill) in the untreated alloy. Sympathetic (preferential) nucleation of the β-iron needles was also observed, in which the branching of β-needles from a parent needle resulted in the formation of large β-needle entities that can cover distances of ∼ 1200 μm across the matrix surface. The beneficial effect of modification, i.e. strontium addition to the melt, was manifested through its influence on the fragmentation and dissolution of the β-needles. The strontium “poisons” the sites where sympathetic nucleation takes place. Dissolution was accelerated with increasing strontium content, the optimum level being ∼ 300 p.p.m. Grain refining, on the other hand, negated the beneficial effect of modification, in that the β-needles underwent thickening and the sympathetic nucleation/branching also occurred. The modified alloy was found to possess the lowest volume fraction of β-Al5FeSi phase among the unmodified, modified, grainrefined, and modified/grain-refined alloys.