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Article Purification of Cast Melts through of Fe-Containing Compounds

Marina Gnatko *, Cong Li, Alexander Arnold and Bernd Friedrich IME Institute of Process and , RWTH Aachen University, 52056 Aachen, ; [email protected] (C.L.); [email protected] (A.A.); [email protected] (B.F.) * Correspondence: [email protected]; Tel.: +49-(0)241-80-95751

 Received: 19 August 2018; Accepted: 1 October 2018; Published: 4 October 2018 

Abstract: Aluminium secondary materials are often contaminated by such as . As the alloy properties are affected by impurities, it is necessary to refine aluminium melts. The formation of Fe in aluminium melts can be used to develop a purification technology based on the removal of intermetallic compounds. In this study, the range for effective separation of intermetallics was determined in an industrial-relevant Al–Si–Fe–Mn system with 6 to 10 Si wt. %, 0.5 to 2.0 Fe wt. %, and 0 to 2.0 Mn wt. %. Based on DTA (Differential Thermal Analysis) and SEM (scanning ) results and following the rules of boundary , isopleths were drawn. This method allows to derive the temperature ranges of intermetallic phase stability and can be applied for the assessment of melt-refining parameters.

Keywords: aluminium purification; iron removal; intermetallic formation; polythermal section

1. Introduction In order to achieve legal recycling rate requirements (e.g., regarding end-of-life vehicles, 95% of materials must be recycled), material cycles must be almost completely closed. The recovery of all metals in their pure form, however, is not possible. Secondary recovered materials are often contaminated. The complexity of such materials to difficulties in sorting, as as to pickup during the mechanical treatment processes. As property formation is affected by impurities, aluminium end-of-life is normally used for the production of cast alloys. Since impurities such as iron accumulate in aluminium secondary alloys at values of up to 2 wt. %, it is difficult to produce Al recycling alloys which conform to standards (Table1). Therefore, it is necessary to refine aluminium melts, as the current practice of diluting primary aluminium is becoming uneconomical. Among all the impurities that need to be removed, iron is a serious challenge.

Table 1. Composition of some Al cast alloys, data from [1,2].

Alloy Identification Alloy Composition Limits, wt. % Numerical Chemical Si Fe Cu Mn Mg Other cast alloys for pressure EN AC-44300 EN AC-AlSi12(Fe) 10.5–13.5 1.0 0.10 0.55 - 0.55 EN AC-46000 EN AC-AlSi9Cu3(Fe) 8.0–11.0 1.30 2.0–4.0 0.55 0.05–0.55 2.75 cast alloys for common application EN AC-44200 EN AC-AlSi12(a) 10.5–13.5 0.55 0.05 0.35 - 0.40 EN AC-46200 EN AC-AlSi8Cu3 7.5–9.5 0.8 2.0–3.5 0.15–0.65 0.05–0.55 2.45

While many efforts have been made for the removal of iron from primary aluminium and high-purity aluminium [3–6], only limited attention has been paid to that of secondary aluminium,

Metals 2018, 8, 796; doi:10.3390/met8100796 www.mdpi.com/journal/metals Metals 2018, 8, x FOR PEER REVIEW 2 of 12

Table 1. Composition of some Al cast alloys, data from [1,2].

Alloy Identification Alloy Composition Limits, wt. % Numerical Chemical Si Fe Cu Mn Mg Other cast alloys for pressure casting EN AC-44300 EN AC-AlSi12(Fe) 10.5–13.5 1.0 0.10 0.55 - 0.55 EN AC-46000 EN AC-AlSi9Cu3(Fe) 8.0–11.0 1.30 2.0–4.0 0.55 0.05–0.55 2.75 cast alloys for common application EN AC-44200 EN AC-AlSi12(a) 10.5–13.5 0.55 0.05 0.35 - 0.40 EN AC-46200 EN AC-AlSi8Cu3 7.5–9.5 0.8 2.0–3.5 0.15–0.65 0.05–0.55 2.45

While many efforts have been made for the removal of iron from primary aluminium and high- purity aluminium [3–6], only limited attention has been paid to that of secondary aluminium, which Metals 2018, 8, 796 2 of 12 contains usually more than 2 wt. % Fe. Conventional ways of iron removal from high iron-containing aluminium melts include filtration, centrifugal separation, and electromagnetic (EM) separation [7– 9]. Allwhich these contains methods usually are based more on than the 2 p wt.rinciple % Fe. of Conventional precipitation ways of Fe of-enriched iron removal phases. from It is high a well- knowniron-containing fact that in aluminiumthe Al–Si– meltsFe system include, a filtration,variety of centrifugal binary and separation, ternary and compounds electromagnetic with (EM)Al exist, separation [7–9]. All these methods are based on the principle of precipitation of Fe-enriched phases. including Al3Fe, Al5FeSi, Al8Fe2Si, Al3FeSi, and Al4FeSi2 [10,11]. On the one hand, the precipitation of It is a well-known fact that in the Al–Si–Fe system, a variety of binary and ternary compounds these phases impacts the quality of the end products. On the other hand, it can provide a basis for the with Al exist, including Al Fe, Al FeSi, Al Fe Si, Al FeSi, and Al FeSi [10,11]. On the one hand, development of a refining technology3 5 with 8the2 help 3of physical 4separation2 process, e.g., filtration. the precipitation of these phases impacts the quality of the end products. On the other hand, it can Thus,provide it was a the basis aim for of the a developmentsix-year project of a at refining IME ( technologyInstitute IME with Process the help Metallurgically of physical separation and Metal Recyclingprocess,) to e.g., find filtration. elements Thus, that it influence was the aim the of residue a six-year–melt project composition at IME (Institute in order IME to Process reduce the concentrationMetallurgically of impurities, and Metal Recycling) above all to iron. find elements Even if that intermetallic influence the compounds residue–melt are composition formed, the conditionsin order and to reduceseparation the concentration technique considered of impurities, are abovevery important all iron. Even for ifreaching intermetallic the highest compounds grade of purity.are The formed, aim the of conditions this work andwas separation to determine technique suitable considered temperature are very ranges important in the for Al reaching–Si–Fe–Mn systemthe in highest the industrially grade of purity. relevant The aimconcentration of this work areas was of to determine6 to 10 Si wt. suitable %, 0.5 temperature to 2.0 Fe wt. ranges %, and in 0 to 2.0 Mnthe wt. Al–Si–Fe–Mn %, in which system the separation in the industrially of intermetallics relevant concentration becomes effective. areas of 6 to 10 Si wt. %, 0.5 to 2.0The Fe eutectic wt. %, and iron 0 tocontent 2.0 Mn in wt. a pure %, in whichbinary the Al separation–Fe melt is of 1.8 intermetallics wt. % at 655 becomes °C [10]. effective. Therefore, in the The eutectic iron content in a pure binary Al–Fe melt is 1.8 wt. % at 655 ◦C[10]. Therefore, in the case of hypereutectic alloys (over 1.8 wt. % Fe), the iron content cannot be reduced by segregation case of hypereutectic alloys (over 1.8 wt. % Fe), the iron content cannot be reduced by segregation below this value. Iron precipitates in the form of the intermetallic compound Al3Fe, if the below this value. Iron precipitates in the form of the intermetallic compound Al3Fe, if the temperature temperaturefalls below falls the below liquidus the line liquidus (Figure line1). Since (Figure this 1). intermetallic Since this phaseintermetallic has a melting phase point has a of melting 1060 ◦C point of 1060and °C is insolubleand is insoluble in molten in aluminium, molten aluminium, it can be mechanically it can be mechanically removed from removed molten aluminium, from molten aluminium,e.g., by filtration. e.g., by filtration. Nevertheless, Nevertheless this system, hasthis nosystem industrial has significance.no industrial significance. IndustrialIndustrial cast cast alloy alloy compositions compositions are are based based on theon binary the binary system system Al–Si, where Al–Si, the where ternary eutecticthe ternary eutecticiron iron content content is reduced is reduced to 0.7 wt. to %0.7 at wt. 577 %◦C[ at10 577,11]. °C In [10 the,11]. Al corner In the of Al this corner system, of iron this is system, present iniron is presentthe phasesin the phases Al3Fe, Al Al8Fe3Fe,2Si, Al Al8Fe5FeSi,2Si, Al and5FeSi Al4FeSi, and2 (FigureAl4FeSi2).2 (Figure 2).

Metals 2018, 8, x FOR PEER REVIEW 3 of 12 FigureFigure 1. 1.AlAl–Fe–Fe phase diagram calculatedcalculated with with FactSage™. FactSage™.

FigureFigure 2.2. LiquidusLiquidus surface surface in in the the Al Al corner corner of the of Al–Si–Fethe Al–Si system–Fe system [10]. [10].

The addition of further alloying elements results in the formation of quaternary or higher alloy systems with complex phase relations. Ternary and quaternary intermetallic compounds with iron are formed in the Al–Si–Fe–Mn system, and iron solubility decreases to 0.29 wt. % at the eutectic point [12]. The current German standards regarding maximum Fe content in cast Al–Si–alloys range between 0.2 and 0.9 wt. % (depending on alloying class) [13]. For the current investigation, the Al– Si–Fe–Mn system was applied because numerous intermetallics are formed in this system, and the residue melt composition can be influenced depending on the Mn/Fe ratio [10–12,14,15]. Table 2 summarizes the phases to be expected in the Al–Si–Fe–Mn system.

Table 2. Published data on the expected phases in the Al corner of the Al–Si–Fe–Mn system, data from [10–12,14,15].

Components, wt. % Phases Al Mn Fe Si Al8Fe2Si 56.0–62.6 – 30.0 7.4–11.0 Al5FeSi 59.4–60.9 <0,8 25.5–26.5 12.8–13.3 Al16(FeMn)4Si3 53.0–64.6 14.6–19.7 10.4–15.3 10.4–12.0 Al15Mn3Si2 58.0–60.3 27.7–29.5 <1.8 10.2–10.7 Al4FeSi2 46.9–48.0 <0.8 25.9 25.3–26.4

Until now, no quaternary phase has been clearly identified in this system [10,12,15]. Initially, it was believed that an area of solutions existed between Al8Fe2Si and Al15Mn3Si2. Later, this assumption was rejected on the basis of the fact that these compounds had different crystal structures (hexagonal and cubic). The currently accepted version of the phase diagram illustrates a broad range of solid solutions based on the compound Al15Mn3Si2 extending towards the Al–Si–Fe surface [10]. In this variant, is replaced with iron to form the compound with the composition 31 wt. % Fe, 1.5 wt. % Mn, 8 wt. % Si. This broad range of homogeneity is considered as quaternary phase Al15(FeMn)3Si2 [10]. On the other hand, Zakharov A. et al. studied alloys containing 10–14 wt. % Si, 0– 3 wt. % Fe, 0–4 wt. % Mn, and proposed the existence of the quaternary compound Al16(FeMn)4Si3 [12]. The formation of this phase would allow a quasi-ternary section Al–Al16(FeMn)4Si3–Si and the formation of two secondary systems on both sides of this section: Al–Al16(FeMn)4Si3–Si–Al5FeSi and Al–Al16(FeMn)4Si3–Si–Al15Mn3Si2. According to reference [10], the solid solution of iron in the Al15Mn3Si2 phase has a cubic structure with a lattice parameter which decreases because of an increase of Fe content from 1.265 nm (0 wt. % Fe) to 1.25 nm (31.1 wt. % Fe). The quaternary phase found in reference [12] has a face- centered cubic structure with a lattice parameter of a = 1.252 ± 0.04 nm. The similar lattice parameters mean that it cannot be determined which version of the Al–Si–Fe–Mn phase diagram is correct. In references [11,15], it was proposed that non-equilibrium crystallization had a significant effect on phase composition, especially in Al–Si–Fe alloys. This is because of the inhibition of peritectic reactions, which take a long time to be completed. However, due to numerous intermetallics, this system shows a potential for removing iron and manganese from Al–Si melts. Phase diagrams are a useful for presenting the required relations in a metal system.

Metals 2018, 8, 796 3 of 12

The addition of further alloying elements results in the formation of quaternary or higher alloy systems with complex phase relations. Ternary and quaternary intermetallic compounds with iron are formed in the Al–Si–Fe–Mn system, and iron solubility decreases to 0.29 wt. % at the eutectic point [12]. The current German standards regarding maximum Fe content in cast Al–Si–alloys range between 0.2 and 0.9 wt. % (depending on alloying class) [13]. For the current investigation, the Al–Si–Fe–Mn system was applied because numerous intermetallics are formed in this system, and the residue melt composition can be influenced depending on the Mn/Fe ratio [10–12,14,15]. Table2 summarizes the phases to be expected in the Al–Si–Fe–Mn system.

Table 2. Published data on the expected phases in the Al corner of the Al–Si–Fe–Mn system, data from [10–12,14,15].

Components, wt. % Phases Al Mn Fe Si

Al8Fe2Si 56.0–62.6 – 30.0 7.4–11.0 Al5FeSi 59.4–60.9 <0,8 25.5–26.5 12.8–13.3 Al16(FeMn)4Si3 53.0–64.6 14.6–19.7 10.4–15.3 10.4–12.0 Al15Mn3Si2 58.0–60.3 27.7–29.5 <1.8 10.2–10.7 Al4FeSi2 46.9–48.0 <0.8 25.9 25.3–26.4

Until now, no quaternary phase has been clearly identified in this system [10,12,15]. Initially, it was believed that an area of solid solutions existed between Al8Fe2Si and Al15Mn3Si2. Later, this assumption was rejected on the basis of the fact that these compounds had different crystal structures (hexagonal and cubic). The currently accepted version of the phase diagram illustrates a broad range of solid solutions based on the compound Al15Mn3Si2 extending towards the Al–Si–Fe surface [10]. In this variant, manganese is replaced with iron to form the compound with the composition 31 wt. % Fe, 1.5 wt. % Mn, 8 wt. % Si. This broad range of homogeneity is considered as quaternary phase Al15(FeMn)3Si2 [10]. On the other hand, Zakharov A. et al. studied alloys containing 10–14 wt. % Si, 0–3 wt. % Fe, 0–4 wt. % Mn, and proposed the existence of the quaternary compound Al16(FeMn)4Si3 [12]. The formation of this phase would allow a quasi-ternary section Al–Al16(FeMn)4Si3–Si and the formation of two secondary systems on both sides of this section: Al–Al16(FeMn)4Si3–Si–Al5FeSi and Al–Al16(FeMn)4Si3–Si–Al15Mn3Si2. According to reference [10], the solid solution of iron in the Al15Mn3Si2 phase has a cubic structure with a lattice parameter which decreases because of an increase of Fe content from 1.265 nm (0 wt. % Fe) to 1.25 nm (31.1 wt. % Fe). The quaternary phase found in reference [12] has a face-centered cubic structure with a lattice parameter of a = 1.252 ± 0.04 nm. The similar lattice parameters mean that it cannot be determined which version of the Al–Si–Fe–Mn phase diagram is correct. In references [11,15], it was proposed that non-equilibrium crystallization had a significant effect on phase composition, especially in Al–Si–Fe alloys. This is because of the inhibition of peritectic reactions, which take a long time to be completed. However, due to numerous intermetallics, this system shows a potential for removing iron and manganese from Al–Si melts. Phase diagrams are a useful tool for presenting the required relations in a metal system. In comparison with binary systems (only two dimensions), ternary and multi-phase phase diagrams (here and after in this article, “Multi-” refers specially to more than three) are rather complicated. A ternary phase diagram is shown in Figure3a, where the composition forms the base triangle, and phase variations caused by temperature change are illustrated vertically (Figure3a). Vertical sections (Figure3b) of a ternary phase diagram—also known as isopleths—have been widely used because of their similarities to binary diagrams. Such sections are two-dimensional planes constructed by cutting the three-dimensional diagrams with a slice which is vertical to the base composition triangle. Once phase areas in an isopleth are clearly clarified, the liquidus and solidus for certain alloy compositions can be readily read from it. Metals 2018, 8, x FOR PEER REVIEW 4 of 12

In comparison with binary systems (only two dimensions), ternary and multi-phase phase diagrams (here and after in this article, “Multi-” refers specially to more than three) are rather complicated. A ternary phase diagram is shown in Figure 3a, where the composition plane forms the base triangle, and phase variations caused by temperature change are illustrated vertically (Figure 3a). Vertical sections (Figure 3b) of a ternary phase diagram—also known as isopleths—have been widely used because of their similarities to binary diagrams. Such sections are two-dimensional planes constructed by cutting the three-dimensional diagrams with a slice which is vertical to the Metalsbase composition2018, 8, 796 triangle. Once phase areas in an isopleth are clearly clarified, the liquidus4 andof 12 solidus temperatures for certain alloy compositions can be readily read from it.

Figure 3. ((aa)) Temperature Temperature–composition–composition space space diagram diagram of of a ternary system ( b) Isopleth through a ternary system [16].

From the metallurgical practice point of view, multi-phasemulti-phase alloy diagrams involving four or more elements are neededneeded more than binary or ternary diagrams. This is because most commercial alloys contain more than three alloying elements elements,, even without taking impurity into consideration. However, temperature–composition temperature–composition phase phase diagrams diagrams of multi of components multi components are extremely are inconvenient extremely andinconvenient highly complicated. and highly complicated. In order order to to determine determine the the phase phase variation variation caused caused by temperature by temperature changes, as change well ass, theas compositionwell as the differencecomposition in complex difference multi-components in complex multi system,-components a feasible system, way is ato feasible draw the way corresponding is to draw three- the orcorresponding two-dimensional three- sections, or two-dimensional in which temperature sections, in which and concentration temperature ofand certain concentration component(s) of certain are representedcomponent(s) as are variables. represented as variables. For the the construction construction of of a atwo two-dimensional-dimensional isopleth, isopleth, i.e., i.e., temperature temperature–composition–composition diagrams, diagrams, the thefollowing following information information is usually is usually needed: needed: (1) (1) the the general general di diagramagram including including the the number, number, disposition disposition,, and identity of the phases and the respective invariant reaction, and (2)(2) the temperature and compositions along all boundary lines (and surfaces). The most widely used method of constitutionalconstitutional investigation is DifferentialDifferential Thermal Analysis (DTA). It It is is capable capable of locating of locating the liquidus the liquidus lines and lines at and the same at the time same indicating time indicating the general the disposition general ofdisposition phases and of phases invariant and reactions invariant in reactions the system. in the Its principlesystem. Its is principle extremely is simple: extremely every simple: occurrence every ofoccurrence phase change of phase is accompanied change is accompanied by exothermic by exothermic and endothermic and endothermic effects such effects as heat such from as heat the from melt crystallization.the melt crystallization. The delay The and delay acceleration and acceleration of the cooling of the speedcooling compared speed compared to a reference to a reference material ismaterial monitored. is monitored.

2. Materials and Methods In this research work work,, approximately 60 allo alloyy compositions were prepared by induction melting within the following following concentration concentration ranges: ranges: 6 6to to 10 10 wt. wt. % %Si, Si,0 to 0 2 to wt. 2 wt.% Fe %, Fe,and and0 to 02 towt. 2 % wt. Mn. % ICP Mn. ICP(Spectro (Spectro ICP-OES ICP-OES Spectro Spectro Ciros Ciros Vision Vision,, Kleve Kleve,, Germany Germany)) analysis analysis was was applied applied to determine to determine the the composition of the samples. Differential Thermal Analysis (DTA) (IME, Aachen, Germany) and Scanning Electron Microscopy (SEM) (JEOL JSM-7000F, Tokyo, ) with integrated EDX (Energy Dispersive X-ray analysis) (Oxford Instruments, Oxford, UK) were applied to determine phase and the temperatures of phase transformations. In order to allow an evaluation in the form of isopleths, three of four element concentrations were kept constant. The groups of investigated alloys and isopleths are shown in Table3. The manganese content changed from 0 to 2 wt. % by representation on the isopleths in steps of 0.5 wt. %. Metals 2018, 8, x FOR PEER REVIEW 5 of 12 composition of the samples. Differential Thermal Analysis (DTA) (IME, Aachen, Germany) and Scanning Electron Microscopy (SEM) (JEOL JSM-7000F, Tokyo, Japan) with integrated EDX (Energy Dispersive X-ray analysis) (Oxford Instruments, Oxford, UK) were applied to determine phase precipitations and the temperatures of phase transformations. In order to allow an evaluation in the form of isopleths, three of four element concentrations were kept constant. The groups of investigated alloys and isopleths are shown in Table 3. The manganese content changed from 0 to 2 wt. % by representation on the isopleths in steps of 0.5 wt. %.

Metals 2018, 8, 796 Table 3. Groups of investigated alloys leading to the individual isopleth. 5 of 12

Iron/Manganese Content, wt. % GroupTable 3. Groups of investigated alloys leading to the individual isopleth. Fe/Mn Step 0.5 Fe/Mn Step 0.5 Fe/Mn Step 0.5 Fe/Mn Step 0.5 Iron/Manganese Content, wt. % AlSi6FeMnGroup 0.5/0–2 1.0/0–2 1.5/0–2 2.0/0–2 AlSi8FeMn Fe/Mn0.5 Step/0– 0.52 Fe/Mn Step1.0/0 0.5–2 Fe/Mn Step1.5/ 0.50–2 Fe/Mn Step2.0 0.5/0–2 AlSi10FeMnAlSi6FeMn 0.5/0–20.5/0–2 1.0/0–21.0/0–2 1.5/0–21.5/0–2 2.0/0–22.0/0–2 AlSi8FeMn 0.5/0–2 1.0/0–2 1.5/0–2 2.0/0–2 ExtendedAlSi10FeMn experimental 0.5/0–2 equipment for 1.0/0–2 the Differential 1.5/0–2 Thermal Analysis 2.0/0–2 (DTA) (IME, Aachen, Germany) was built, containing a resistance and a differential (Figure 4). The differentialExtended thermocouple experimental consists equipment of for two the connected Differential . Thermal Analysis The (DTA) first (IME, one, Aachen, the working Germany) was built, containing a resistance furnace and a differential thermocouple (Figure4). thermocouple, measured the temperature in the sample. The second one, the reference thermocouple, The differential thermocouple consists of two connected thermocouples. The first one, the working measured the temperature difference which existed during cooling between the samples and the thermocouple, measured the temperature in the sample. The second one, the reference thermocouple, referencemeasured substance. the temperature Two crucibles, difference one which with existed the reference during cooling substance between (Al2 theO3) samplesand the andother the with the sample, were placed in a to ensure the same external heat conditions for both crucibles reference substance. Two crucibles, one with the reference substance (Al2O3) and the other with the duringsample, cooling. were placed As steel in a has steel a blocklower to thermal ensure theconductivity same external than heat Al, conditions this block for protected both crucibles the crucibles fromduring temperature cooling. As changes steel has in a lower the furnace thermal space. conductivity Such changes than Al, thiscould block influence protected the the temperatur crucibles e data andfrom distort temperature the results. changes in the furnace space. Such changes could influence the temperature data andIn distort order the to results. determine an isopleth with sufficient accuracy, a minimum of five alloys must be investigated.In order Afterto determine melting an the isopleth alloy with, the sufficient differential accuracy, thermal a minimum analysis of commenced. five alloys must The be sample, weighinginvestigated. approximately After melting 20 g, the was alloy, placed the differential in the crucible thermal (Figure analysis 4) and commenced. heated to 750 The °C sample,–760 °C . This weighing approximately 20 g, was placed in the crucible (Figure4) and heated to 750 ◦C–760 ◦C. temperature value was chosen to allow a sufficient superheat. As according to literature data, the This temperature value was chosen to allow a sufficient superheat. As according to literature data, of the alloys studied was below or near 700 °C . Subsequently, the furnace was switched the melting point of the alloys studied was below or near 700 ◦C. Subsequently, the furnace was offswitched, and the off, cooling and the curve cooling with curve a rate with of a rateapprox. of approx. 4.5 °C 4.5/min◦C/min was recorded. was recorded.

Figure 4. Equipment for large scale Differential Thermal Analysis (DTA) at IME.

3. Results andFigure Discussions 4. Equipment for large scale Differential Thermal Analysis (DTA) at IME.

3.1. DTA Experimental Results

Figure5 illustrates a cooling curve example for the alloy AlSi8Fe2.0Mn1.0 from isopleth AlSi8Fe2.0–Mn. Two curves are indicated: one for the sample alloy and one for the reference (Al2O3). The curve of the sample demonstrates two significant effects, whereas the reference curve shows four. This is because of the special bonding of the thermocouples (Figure4), whereby the reference material Metals 2018, 8, x FOR PEER REVIEW 6 of 12

3. Results and Discussions

3.1. DTA Experimental Results Figure 5 illustrates a cooling curve example for the alloy AlSi8Fe2.0Mn1.0 from isopleth AlSi8Fe2.0–Mn. Two curves are indicated: one for the sample alloy and one for the reference (Al2O3). The curve of the sample demonstrates two significant effects, whereas the reference curve shows four. This isMetals because2018, 8of, 796 the special bonding of the thermocouples (Figure 4), whereby the reference material6 of 12 becomes very sensitive and can detect changes with lower evolutions of heat, e.g., at the liquidus temperature.becomes Therefore, very sensitive it was and presumed can detect that changes four phase with changes lower evolutions occurred in of this heat, alloy. e.g., Exemplary at the liquidus DTA temperature.results are shown Therefore, in Table it was4 for presumed the isopleths that AlSi8Fe0.5 four phase-Mn, changes AlSi8Fe1 occurred-Mn, AlSi8Fe1.5 in this alloy.-Mn Exemplary, and AlSi8Fe2.0DTA results-Mn; all are data shown are published in Table4 infor reference the isopleths [17]. After AlSi8Fe0.5-Mn, recording and AlSi8Fe1-Mn, evaluating AlSi8Fe1.5-Mn,all cooling curvesand, th AlSi8Fe2.0-Mn;e temperature– allcomposition data are published diagrams in were reference created [17 for]. After these recording isopleths. and evaluating all cooling curves, the temperature–composition diagrams were created for these isopleths.

FigureFigure 5. Cooling 5. Cooling curve curveof the ofalloy the AlSi8Fe2.0Mn1.0 alloy AlSi8Fe2.0Mn1.0 from isopleth from isopleth AlSi8Fe2 AlSi8Fe2–Mn.–Mn. Table 4. Results of the evaluation of the cooling curve effects of the alloys from isopleths AlSi8Fe0.5–Mn, Table 4. Results of the evaluation of the cooling curve effects of the alloys from isopleths AlSi8Fe0.5– AlSi8Fe1–Mn, AlSi8Fe1.5–Mn, and AlSi8Fe2.0–Mn. Mn, AlSi8Fe1–Mn, AlSi8Fe1.5–Mn, and AlSi8Fe2.0–Mn. Alloy Mn, Effect 1 Effect 2 Effect 3 Effect 4 Alloy Mn, Effect 1 Effect 2 Effect 3 Effect 4 (Target) wt. % T, ◦C T, ◦C T, ◦C T, ◦C (Target) wt. % T, °C T, °C T, °C T, °C AlSi8Fe0.5 0.00 602.3 586.4 - 574.4 AlSi8Fe0.5 AlSi8Fe0.5Mn0.50.00 0.54602.3 612.0 586.4 599.2 585.0- 573.7 574.4 AlSi8Fe0.5Mn0.5AlSi8Fe0.5Mn1.0 0.54 1.22612.0 649.9 599.2 601.2 597.0585.0 574.7 573.7 AlSi8Fe0.5Mn1.0AlSi8Fe0.5Mn2.0 1.22 1.94649.9 675.0 601.2 633.0 602.1597.0 574.9 574.7 AlSi8Fe0.5Mn2.0AlSi8Fe1.0 1.94 0.00675.0 613.0 633.0 598.1 -602.1 574.9 574.9 AlSi8Fe1.0Mn0.5 0.47 620.7 606.0 600.0 573.5 AlSi8Fe1.0 0.00 613.0 598.1 - 574.9 AlSi8Fe1.0Mn1.0 0.92 634.2 605.7 580.0 573.0 AlSi8Fe1.0Mn0.5 Al Si8 0.47 620.7 606.0 600.0 573.5 1.50 680.5 611.0 607.0 574.3 AlSi8Fe1.0Mn1.0Fe1.0Mn1.5 0.92 634.2 605.7 580.0 573.0 Al Si8 Al Si8 Fe1.0Mn1.5 1.50 1.98680.5 691.4 611.0 640.0 612.9607.0 574.8 574.3 Al Si8 Fe1.0Mn2.0Fe1.0Mn2.0 1.98 691.4 640.0 612.9 574.8 AlSi8Fe1.5 0.00 614.3 606.4 - 574.4 AlSi8Fe1.5 AlSi8Fe1.5Mn0.50.00 0.56614.3 645.0 606.4 638.0 609.9- 572.8 574.4 AlSi8Fe1.5Mn0.5 AlSi8 0.56 645.0 638.0 609.9 572.8 1.12 672.4 614.0 611.7 573.2 AlSi8 Fe1.5Mn1.0Fe1.5Mn1.0 1.12 672.4 614.0 611.7 573.2 AlSi8Fe1.5Mn1.5AlSi8Fe1.5Mn1.5 1.56 1.56681.3 681.3 612.6 612.6 576.0576.0 574.0 574.0 AlSi8Fe1.5Mn2.0 2.04 693.1 630.0 613.6 573.8 AlSi8Fe1.5Mn2.0 2.04 693.1 630.0 613.6 573.8 AlSi8Fe2.0 0.00 616.3 608.4 - 574.4 AlSi8Fe2.0 AlSi8Fe2.0Mn0.5 0.00 0.54616.3 657.1 608.4 609.2 589.1- 573.0 574.4 AlSi8Fe2.0Mn1.0 1.09 683.8 612.0 585.0 574.1 AlSi8Fe2.0Mn1.5 1.36 703.6 638.0 612.5 573.8 AlSi8Fe2.0Mn2.0 1.99 710.5 613.2 575.0 573.6

3.2. Precipitated Phases Figure6 shows exemplary SEM examination patterns of the alloys AlSi8Fe2Mn0.5(a) and AlSi8Fe2Mn1.0(b) performed by GfE (Gemeinschaftslabor für Electronenmikroskopie) RWTH Metals 2018, 8, x FOR PEER REVIEW 7 of 12

AlSi8Fe2.0Mn0.5 0.54 657.1 609.2 589.1 573.0 AlSi8Fe2.0Mn1.0 1.09 683.8 612.0 585.0 574.1 AlSi8Fe2.0Mn1.5 1.36 703.6 638.0 612.5 573.8 MetalsAlSi8 2018Fe2.0, 8, x Mn2.0FOR PEER REVIEW 1.99 710.5 613.2 575.0 7573.6 of 12 AlSi8Fe2.0Mn0.5 0.54 657.1 609.2 589.1 573.0 3.2. PrecipitatedAlSi8Fe2.0 PhasesMn1.0 1.09 683.8 612.0 585.0 574.1 FigureAlSi8 6Fe2.0 showsMn1.5 exe mplary1.36 SEM examination703.6 patterns638.0 of the alloys612.5 AlSi8Fe2Mn0573.8 .5(a) and AlSi8Fe2Mn1.AlSi8Fe2.00(b)Mn2.0 performed by1.99 GfE (Gemeinschaftslabor710.5 613.2 für Electronenmikroskopie575.0 573.6 ) RWTH (Rheinisch-Westfälische Technische Hochschule) Aachen University. The dark grey crystals are 3.2. Precipitated Phases eutecticMetals silicon2018, 8, precipitations. 796 White needle-like precipitations indicate the ternary phase Al57FeSi. of 12 The groups Figure of white 6 shows net-forming exemplary precipitations SEM examination (also patterns known ofas the Chinese alloys script) AlSi8Fe2Mn0 are clusters.5(a) and of the quaternaryAlSi8Fe2Mn1. phase0( b)Al(FeMn)Si. performed These by GfE descriptions (Gemeinschaftslabor of phase shapes für Electronenmikroskopie were previously accepted) RWTH, as in (Rheinisch(Rheinisch-Westfälische-Westfälische Technische Hochschule) Hochschule Aachen) Aachen University. University. The The dark dark grey crystals grey crystals are eutectic are references [18,19]. The composition of the precipitations was determined by EDX analysis. eutecticsilicon precipitations. precipitations. White needle-likeWhite needle precipitations-like precipitations indicate indicate the ternary the ternary phase Alphase5FeSi. Al The5FeSi. groups The groupsof white of net-forming white net- precipitationsforming precipitations (also known (also as Chinese known script) as Chinese are clusters script) of arethe quaternary clusters of phase the quaternaryAl(FeMn)Si. phase These Al(FeMn)Si. descriptions These of phase descriptions shapes wereof phase previously shapes were accepted, previously as in references accepted, [as18 ,in19 ]. referencesThe composition [18,19]. ofThe the composition precipitations of the was precipitations determined bywas EDX determined analysis. by EDX analysis.

Figure 6. SEM pattern of the .

According to the EDX microanalysisFigureFigure 6. 6. SEMSEM of pattern patternthe investigated of of the the microstructure. microstructure. alloys, the compositions of the phases precipitated were determined and are shown in Table 5. The appearance of the above-mentioned According to the EDX microanalysis of the investigated alloys, the compositions of the phases According to the EDX microanalysis of the investigated alloys, the compositions of the phases phasesprecipitated depended were on determined their composition, and are shown and in Tablethe extent5. The appearance varied with of the the above-mentioned Mn content of phases the alloy, precipitated were determined and are shown in Table 5. The appearance of the above-mentioned especiallydepended for onthe their precipitation composition, of and the the Al(FeMn)Si extent varied phase.with the Mn Mn content content of in the the alloy, quaternary especially for phase phases depended on their composition, and the extent varied with the Mn content of the alloy, increasedthe precipitation from 8.42 of the to Al(FeMn)Si 15.68 wt. phase. %, and Mn Fe content content in the decreased quaternary phase from increased 18.64 to from 12.57 8.42 wt. to %, especially for the precipitation of the Al(FeMn)Si phase. Mn content in the quaternary phase correspondingly15.68 wt. %, and (Figure Fe content 7). decreased from 18.64 to 12.57 wt. %, correspondingly (Figure7). increased from 8.42 to 15.68 wt. %, and Fe content decreased from 18.64 to 12.57 wt. %, correspondingly (Figure 7).

Figure 7. Composition change in the Al(FeMn)Si phase with increasing Mn content in the alloy

AlSi8Fe1.5–Mn.

The ternary Al5FeSi disappeared after a specific Mn content was reached in the alloy, and the formation of Al16(FeMn)4Si3 was not as clearly determined as reported by A. Zakharov [12]. This was caused by the fact that the Mn content of our Al(FeMn)Si phases changed with the Mn content of the alloys. On the other hand, the diagram version proposed by L. Mondolfo [17] cannot be accepted Metals 2018, 8, 796 8 of 12

as fundamental information for drawing the isopleths because of Al5FeSi disappearance (see above). Since phase compositions are significantly influenced by the crystallization conditions, the deviations in the Mn content of the Al(FeMn)Si phases, in comparison to A. Zakharov’s study, must be considered in consequence of different crystallization conditions. Metals 2018, 8, x FOR PEER REVIEW 8 of 12 MetalsMetalsMetals 2018 2018 2018, ,8 ,8, 8,x ,x FORx FOR FOR PEER PEER PEER REVIEW REVIEW REVIEW 88 of8 of of 12 12 12

Figure 7. Composition change in the Al(FeMn)Si phase with increasing Mn content in the alloy group Table 5. CompositionFigureFigureFigure 7. 7. 7. Composition Composition Composition of detected change change change in in in precipitatedthe the the Al(FeMn)Si Al(FeMn)Si Al(FeMn)Si phase phase phasesphase with with with increasing inincreasing increasing all investigated Mn Mn Mn content content content in in in the the alloys.the alloy alloy alloy group group group AlSi8Fe1.5–Mn. Metals 20182018,, 88,, xx FORFOR PEERPEERMetalsAlSi8Fe1 AlSi8Fe1 REVIEWREVIEWAlSi8Fe1 20182018,, .5 88.5 ,.5,– x–xMn.– Mn. FORFORMn. PEERPEER REVIEWREVIEW 88 ofof 1212 88 ofof 1212 Components, wt. % FigureFigure 7.7. CompositionTable 5. CompositionFigureFigure change 7.7. in Composition theof detected Al(FeMn)Si changeprecipitated phase in the with phases Al(FeMn)Si increasing in all investigatedphase Mn contentcontent with increasing ininalloys. thethe alloyalloy Mn groupgroup contentcontent inin thethe alloyalloy groupgroup Phase TableTableTable 5. 5. 5. Composition Composition Composition of of of detected detected detected precipitated precipitated precipitated phases phases phases in in in all all all investigated investigated investigated alloys. alloys. alloys. AlSi8Fe1.5.5––Mn. AlSi8Fe1.5.5––Mn. AlComponents, Mn wt. % Fe Si Phase Components,Components,Components, wt. wt. wt. % % % PhasePhasePhaseAl Mn Fe Si Al matrixTable 5.5. Composition 98.37–99.66 Tableof detected 5.5. CompositionAl AlprecipitatedAl 0.0–0.45 of phasesdetected inMnMn precipitatedMn all investigated 0.0–0.50 phases alloys. inFe FeallFe investigated 0.73–2.55 alloys.SiSi Si Al matrix 98.37–99.66 0.0–0.45 0.0–0.50 0.73–2.55 Al5FeSiAlAlAl matrix matrix matrix 55.02–56.03 98.3798.3798.37––99.66–99.6699.66 1.92–2.590.00.00.0––0.45–0.450.45 23.73–26.210.00.00.0––0.50–0.500.50 16.86–17.650.730.730.73––2.55–2.552.55 Al5FeSi 55.02–56.03 1.92–Components,2.59 wt.23.73 %–Components, 26.21 wt.16.86 %– 17.65 αPhase AlAlAl5FeSi5PhaseFeSi5FeSi 55.0255.0255.02––56.03–56.0356.03 1.921.921.92––2.59–2.592.59 23.7323.7323.73––26.21–26.2126.21 16.8616.8616.86––17.65–17.6517.65 α-Al(FeMn)Si-Al(FeMn)Si 57.77Al–61.46 57.77–61.46 8.07MnAl–17.39 8.07–17.39 12.62MnFe–19.85 12.62–19.85 10.06FeFeSi–13.70 10.06–13.70Si αα-α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si 57.7757.7757.77––61.46–61.4661.46 8.078.078.07––17.39–17.3917.39 12.6212.6212.62––19.85–19.8519.85 10.0610.0610.06––13.70–13.7013.70 β-βAlAl(FeMn)Si-Al(FeMn)Si matrix 98.3756.4798.37Al matrix––99.6662.5899.66 56.47–62.58 98.3798.3712.630.00.0–––0.450.4599.6699.6617.93 12.63–17.93 11.250.00.00.0––––0.450.450.500.5013.44 11.25–13.44 10.840.730.730.00.0––––0.500.502.5511.342.55 10.84–11.340.730.73––2.552.55 ββ-β-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si 56.4756.4756.47––62.58–62.5862.58 12.6312.6312.63––17.93–17.9317.93 11.2511.2511.25––13.44–13.4413.44 10.8410.8410.84––11.34–11.3411.34 Al55SiFeSi Si 55.0255.020.30Al––5556.03FeSi3.5056.03FeSi 0.30–3.50 55.0255.021.921.92–––-56.03 56.032.592.59 -23.7323.731.921.92–––-2.59 2.5926.2126.21 -23.7323.7316.8696.5016.86–––26.2126.2117.6599.7717.65 96.50–99.7716.8616.86––17.6517.65 SiSiSi 0.300.300.30––3.50–3.503.50 ------96.5096.5096.50––99.77–99.7799.77 α--Al(FeMn)Si α57.7757.77--Al(FeMn)Si––61.4661.46 57.7757.778.078.07–––17.3917.3961.4661.46 12.6212.628.078.07––––17.3917.3919.8519.85 12.6212.6210.0610.06–––19.8519.8513.7013.70 10.0610.06––13.7013.70

β-The-Al(FeMn)Si ternary Al5FeSiβ56.4756.47-- Al(FeMn)Sidisappeared––62.5862.58 after56.4756.4712.6312.63 a specific–––62.5862.5817.9317.93 Mn content12.6312.6311.2511.25 was–––17.9317.9313.4413.44 reached in the11.2511.2510.8410.84 alloy–––13.4413.4411.3411.34, and the 10.8410.84––11.3411.34 TheTheThe ternary ternaryternary Al AlAl5FeSi5FeSi5FeSi disappeared disappeareddisappeared after afterafter a a a specific specificspecific Mn MnMn content contentcontent was waswas reached reachedreached in inin the thethe alloy alloyalloy, , and, andand the thethe 3.3. Developingformation IsoplethsSi of Al16(FeMn) from0.3040.30Si DTA3 was––SiSi3.503.50 not and as clearly Phase0.300.30 determined Analysis––--3.50 3.50 as Results reported--- by A. Zakharov96.5096.50 [12].-–-– 99.7799.77 This was 96.5096.50––99.7799.77 formationformationformation of of of Al Al Al1616(FeMn)16(FeMn)(FeMn)4Si4Si4Si3 3was 3was was not not not as as as clearly clearly clearly determined determined determined as as as reported reported reported by by by A. A. A. Zakharov Zakharov Zakharov [12]. [12]. [12]. This This This was was was caused by the fact that the Mn content of our Al(FeMn)Si phases changed with the Mn content of the causedcausedcaused by by by the the the fact fact fact that that that the the the Mn Mn Mn content content content of of of our our our Al(FeMn)Si Al(FeMn)Si Al(FeMn)Si phases phases phases changed changed changed with with with the the the Mn Mn Mn content content content of of of the the the alloys.The On ternary the other Al5 5FeSihand,The disappeared the ternary diagram Al after 5version5FeSiFeSi a disappeareddisappearedspecific proposed Mn bycontentaftercontentafter L. Mondaa specific specific waswasolfo reachedreached MnMn[17] content contentcannot inin thethe bewasalloywasalloy accepted reachedreached,, andand thethe as inin thethe alloyalloy,, andand thethe Based on the DTAalloys.alloys.alloys. and On On On SEM the the the other other other results, hand, hand, hand, the 12the the diagram diagram isoplethsdiagram version version version were proposed proposed proposed drawn by by by L. L. L. (accordingMond Mond Mondolfoolfoolfo [17] [17] [17] tocannotcannot cannot Table be be be accepted accepted4 accepted). All as as isoplethsas formationfundamentalformation of Alinformation1616(FeMn)(FeMn)formationformation44Si for33 was ofdrawingof not AlAl1616 as(FeMn)(FeMn) clearlythe isopleths44SiSi determined33 was not because as asclearly reported of Al determined5FeSi by disappearanceA. Zakharov as reported [12]. (see by This A.above). Zakharovwas [12]. This was fundamentalfundamentalfundamental information informationinformation for forfor drawing drawingdrawing the thethe isopleths isoplethsisopleths because becausebecause of ofof Al AlAl5FeSi5FeSi5FeSi disappearance disappearancedisappearance (see (see(see above). above).above). are publishedcausedSincecaused phase in byby reference thethe compositions factfact thatthatcausedcaused thethe [17 are Mn Mn byby]. significantly the thecontentcontent As factfact examples, that thatofof ourour influencedthethe Al(FeMn)SiAl(FeMn)Si MnMn contentcontent four by the phases isoplethsphases ofof crystallization ourour changedAl(FeMn)SichangedAl(FeMn)Si AlSi8Fe–Mn withwith conditions, phasesphases thethe MnMn changedchanged the contentcontent aredeviations withwith of shownof thethe thethe MnMn in contentcontent Figure ofof thethe8a–d. SinceSinceSince phase phase phase compositions compositions compositions are are are significantly significantly significantly influenced influenced influenced by by by the the the crystallization crystallization crystallization conditions, conditions, conditions, the the the deviations deviations deviations alloys.inalloys. the OnOn Mn the the content otherother alloys. alloys. hand, ofhand, the theOn theOnAl(FeMn)Si thediagramdiagramthe otherother version versionhand,hand, phases, thethe proposedproposed in diagramdiagram comparison byby versionversion L.L. MondMond to proposed proposed A.olfo Zakharov’s [17] byby cannot L.L. Mond Mond study, be acceptedolfoolfo must [17][17] becannotascannot bebe acceptedaccepted asas The constructionininin of the the the isopleths Mn Mn Mn content content content was of of of the the thebased Al(FeMn)Si Al(FeMn)SiAl(FeMn)Si on phases,the phases, phases, following in in in comparison comparison comparison theory to to to A. A. A. Zakharov’sas Zakharov’s Zakharov’s well as study, study, study, on must rules must must be be be of phase fundamentalconsideredfundamental in informationinformationconsequencefundamentalfundamental forfor of differentdrawingdrawing informationinformation crystallizationthethe isoplethsisopleths forfor drawingdrawing because conditions. thethe of isoplethsisopleths Al 55FeSi disappearancebecausebecause ofof Al55 FeSiFeSi(see disappearancedisappearanceabove). (see(see above).above). boundary drawing: consideredconsideredconsidered in in in consequence consequence consequence of of of different different different crystallization crystallization crystallization conditions. conditions. conditions. Since phase compositionsSinceSince phase phaseare significantly compositionscompositions influenced areare significantlysignificantly by thethe crystallizationcrystallization influencedinfluenced byby conditions,conditions, thethe crystallizationcrystallization thethe deviationsdeviations conditions,conditions, thethe deviationsdeviations in3.3.in the theDeveloping Mn Mn content content Isopleths inin of of the the thefrom the Mn MnAl(FeMn)Si DTA content content and Phase of ofphases, the theAnalysis Al(FeMn)Si in comparisonResults phases, to A. in Zakharov’scomparison study, to A. Zakharov’smust be study, must be 3.3.3.3.3.3. Developing Developing Developing Isopleths Isopleths Isopleths from from from DTA DTA DTA and and and Phase Phase Phase Analysis Analysis Analysis Results Results Results (1) The quaternaryconsideredconsidered inin consequenceconsequence Al(FeMn)Siconsideredconsidered ofof differentdifferent inin are consequenceconsequence differentiated crystallizationcrystallization ofof differentdifferent conditions.conditions. by crystallizationcrystallization the Mn/Fe conditions.conditions. ratio into α-Al(FeMn)Si if Mn/Fe ≤ 1.1 Based on the DTA and SEM results, 12 isopleths were drawn (according to Table 4). All isopleths BasedBasedBased on on on the the the DTA DTA DTA and and and SEM SEM SEM results, results, results, 12 12 12 isopleths isopleths isopleths were were were drawn drawn drawn (ac (ac (accordingcordingcording to to to Table Table Table 4). 4). 4). All All All isopleths isopleths isopleths and βare-Al(FeMn)Si published in reference if Mn/Fe [17]. As > examples, 1.1. These four isopleths three systems AlSi8Fe–Mn are are formed shown in Figure depending 8a–d. on the Mn/Fe ratio 3.3.3.3. DevelopingDeveloping IsoplethsIsoplethsareareare 3.3.3.3.published published published fromDevelopingfromDeveloping DTADTA in in in reference andand reference IsoplethsreferenceIsopleths Phase [17].from fromAnalysis[17]. [17]. AsDTA DTAAs As examples, examples,Results examples, andand Phase four four Analysisfour isopleths isopleths isopleths Results AlSi8Fe AlSi8Fe AlSi8Fe ––Mn–MnMn are are are shown shown shown in in in Figure Figure Figure 8a 8a 8a––d.–d.d. The construction of isopleths was based on the following theory as well as on rules of phase of the alloy: if Mn/FeTheTheThe < construction construction1.1,construction after of crystallization, ofof isopleths isoplethsisopleths was waswas based basedbased the on onon alloys the thethe following followingfollowing consist theory theorytheory of as Al–asas well wellwellα -Al(FeMn)Si–Si–Al as asas on onon rules rulesrules of ofof phase phasephase 5FeSi; boundaryBased drawing: on the DTA andBased SEM on results, the DTA 12 andisopleths SEM results,were drawn 12 isopleths (accordingcording were toto drawn TableTable 4).(ac4). AllcordingAllcording isoplethsisopleths toto TableTable 4).4). AllAll isoplethsisopleths boundaryboundaryboundary drawing: drawing: drawing: if Mn/Feareare publishedpublished > 1.1, inin referencereference theareare publishedpublished alloys [17].[17]. AsAs inin examples,examples, consist referencereference fourfour [17].[17]. of isoplethsisopleths AsAs Al– examples,examples,α-Al(FeMn)Si–Si– AlSi8FeAlSi8Fe fourfour––Mn isoplethsisopleths are shown AlSi8FeAlSi8Feβ in-Al(FeMn)Si; Figure––Mn are 8a ––shownd. in ifFigure Mn/Fe 8a––d. = 1.1, (1) The quaternary Al(FeMn)Si are differentiated by the Mn/Fe ratio into α-Al(FeMn)Si if Mn/Fe ≤ The construction(1)(1)(1) The TheofTheThe isoplethsquaterna quaterna quaterna construction rywasryry Al(FeMn)Si Al(FeMn)Si Al(FeMn)Si based of isopleths on are theare are differentiated followingdifferentiated wasdifferentiated based theory on by by bythe the asthe the following wellMn/Fe Mn/Fe Mn/Fe as ratio onratio ratiotheory rulesrules into into into as ofofα α -α well-Al(FeMn)Siphasephase-Al(FeMn)SiAl(FeMn)Si as onon rules rulesif if ifMn/Fe Mn/Fe Mn/Fe ofof phasephase ≤ ≤ ≤ only Al–1.1α-Al(FeMn)Si–Si and β-Al(FeMn)Si if Mn/Fe coexist > 1.1. [12 These]. three systems are formed depending on the Mn/Fe boundary drawing: boundary boundary1.11.11.1 and and and β drawing:β drawing:-β-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si if if ifMn/Fe Mn/Fe Mn/Fe > > >1.1. 1.1. 1.1. These These These three three three systems systems systems are are are formed formed formed depending depending depending on on on the the the Mn/Fe Mn/Fe Mn/Fe ratio of the alloy: if Mn/Fe < 1.1, after crystallization, the alloys consist of Al–α-Al(FeMn)Si–Si– (2) Crossing the tilted phaseratioratioratio of of of the boundarythe the alloy: alloy: alloy: if if ifMn/Fe Mn/Fe Mn/Fe line < < <1.1, leads1.1, 1.1, after after after tocrystalli crystalli crystalli exhaustzzationzationation, , orthe ,the the precipitationalloys alloys alloys consist consist consist of of of Al Al Al of––α–α-α-Al(FeMn)Si one-Al(FeMn)SiAl(FeMn)Si phase,––Si–SiSi––– whereas (1)(1) TheAl5FeSi quaterna; if Mn/Feryry(1)(1) Al(FeMn)SiAl(FeMn)Si > The1.1, thequaterna alloys areare differentiateddifferentiatedryry consist Al(FeMn)SiAl(FeMn)Si of Al byby– areαare the-theAl(FeMn)Si differentiateddifferentiated Mn/FeMn/Fe ratioratio–Si– intoβbyintoby-Al(FeMn)Si thethe αα-- Al(FeMn)SiMn/FeMn/Fe ; ratio ratioif Mn/Fe if intointo Mn/Fe α=α --1.1Al(FeMn)Si ≤≤, if Mn/Fe ≤≤ AlAlAl5FeSi5FeSi5FeSi; ;if ;if ifMn/Fe Mn/Fe Mn/Fe > > >1.1 1.1 1.1, ,the ,the the alloys alloys alloys consist consist consist of of of Al Al Al––α–α-α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si––Si–SiSi––β–β-β-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si; ;if ;if ifMn/Fe Mn/Fe Mn/Fe = = =1.1 1.1 1.1, , , passing1.1only1.1 through andand Al –ββα--Al(FeMn)Si-Al(FeMn)Si the horizontal1.11.1 if – andandSi Mn/Fe coexist ββ--Al(FeMn)Si >> [12].1.1. phase1.1. TheseThese if boundary threeMn/Fethree systemssystems >> 1.1.1.1. TheseThese line, areare formedformed threethree where systems systems depending eutectic areare onformedformed the or Mn/Fe depending peritetic on reactions the Mn/Fe occur, onlyonlyonly Al Al Al––α–α-α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si––Si–SiSi coexist coexist coexist [12]. [12]. [12]. (2) ratioCrossingratio ofof thethe the alloy:alloy: tilted ifif phase ratioMn/Feratio of ofboundary < > Al1.11.1 horizontal55,,FeSiFeSi thethe ; ; alloys alloysifif Mn/FeMn/Fe phase consistconsist >>boundary 1.11.1 ofof,, thethe AlAl ––alloysalloys αline--Al(FeMn)Si, where consistconsist eutectic ofof––Si AlAl––β––--α Al(FeMn)Sior--Al(FeMn)Si peritetic ;reaction; ifif–– SiSiMn/Fe––β--Al(FeMn)Sis occur = 1.1,,, ;; ifif Mn/Fe = 1.1,, boundary results inpassingpassingpassing either t through throughhrough exhaust the the the horizontal horizontal horizontal (precipitation) phase phase phase boundary boundary boundary of line twolineline, ,where ,where where phases eutectic eutectic eutectic or or or or exhaustperitetic peritetic peritetic reaction reaction reaction of oness soccur occur occur phase, , , and onlycauses Al exhaust––α--Al(FeMn)Si of oneonlyonly phase––Si AlAl coexist–– αand--Al(FeMn)Si precipitation [12]. ––SiSi coexistcoexistof one phase [12].[12]. , respectively. Crossing a point-phase causescausescauses exhaust exhaust exhaust of of of one one one phase phase phase and and and precipitation precipitation precipitation of of of one one one phase phase phase, ,respectively ,respectively respectively. .Crossing .Crossing Crossing a a apoint point point--phase-phasephase precipitation(2)(2) Crossingboundary of thethe results the tiltedtilted(2)(2) other in phaseCrossing either [ boundary20 exhaust ].thethe tiltedtilted line(precipitation) phase leads boundary to exhaust of two line or phases precipitationleads toor exhaust exh austof one or of precipitation phase,one phase whereas and of one phase, whereas boundaryboundaryboundary results resultsresults in inin either eithereither exhaust exhaustexhaust (precipitation) (precipitation)(precipitation) of ofof two twotwo phases phasesphases or oror exh exhexhaustaustaust of ofof one oneone phase phasephase and andand passingprecipitation through of the thethe passingother horizontal [20]. through phase thethe boundary horizontal line phase,, where boundary eutectic lineor peritetic,, where eutecticreaction sors occur peritetic,, reactionss occuroccur,, precipitationprecipitationprecipitation of of of the the the other other other [20]. [20]. [20]. causescauses exhaustexhaust ofof oneonecausescauses phasephase exhaustexhaust andand precipitationprecipitation ofof oneone phasephase ofof and andoneone precipitation precipitationphasephase,, respectivelyrespectively ofof oneone. . phase phaseCrossingCrossing,, respectivelyrespectively aa pointpoint--phase.. CrossingCrossing aa pointpoint--phase In the caseIn the of case AlSi8Fe1–Mn, of AlSi8Fe1–Mn, α-Alα -Alor α-Al(FeMn)Si or α-Al(FeMn)Si precipitated primarily precipitated, and the liquidus primarily, line and the liquidus boundary resultsInIn Inin the boundaryboundarythe theeither case case case exhaustof of of resultsAlSi8Fe1results AlSi8Fe1 AlSi8Fe1 (precipitation) inin– –Mn,eithereither–Mn,Mn, α α -α exhaust-Alexhaust-AlAl ororof or α αtwo -α -Al(FeMn)Si(precipitation)(precipitation)-Al(FeMn)SiAl(FeMn)Si phases or precipitated precipitatedexhprecipitated ofofaust aust twotwo ofofphasesphases primarily oneoneprimarily primarily phase phase oror exhexh, , and ,andand austandaust the the theofof liquidus liquidus oneoneliquidus phasephase line line line andand (marked by ① in Figure8(b)) was drawn by fitting the data of the primary precipitation temperature. line (markedprecipitation by in(marked(marked (markedof Figurethethe precipitationotherother by by by ① ① ① 8[20].[20]. inb) in in Fig Fig Fig was ureofureure the8(b)the8(b)8(b) drawn otherother)) was) was was [20].[20].drawn drawn drawn by by by by fittingfitting fitting fitting the the the thedata data data of of dataof the the the primary primary primary of the precipitation precipitation precipitation primary temperature. temperature. temperature. precipitation At the AlSi8Fe1 side, ②, ③, ④ phase boundaries were extended from corresponding points, which temperature. At the AlSi8Fe1AtAtAt the the the AlSi8Fe1 AlSi8Fe1 AlSi8Fe1 side, side, side, side, ②, ②, ②,, ③, ③, ③, ,④ ④ ④ phase phase phasephase boundaries boundaries boundaries boundaries were were were extended extended extended were from from from extended corresponding corresponding corresponding from point point point correspondingss,s ,which ,which which indicatesInIn thethe, respectively casecase ofof AlSi8Fe1AlSi8Fe1, precipitationInIn thethe––Mn, casecase α-- Alofof of AlSi8Fe1orAlSi8Fe1 Al α5FeSi,--Al(FeMn)Si– –SiMn,, and α-- Al exhaustprecipitated or α--Al(FeMn)Si of the primarily melt. precipitatedFor,, andandMn thecontentthe liquidus liquidusprimarily from lineline 0.5,, andand thethe liquidusliquidus lineline indicatesindicatesindicates, ,respectively ,respectively respectively, ,precipitation ,precipitation precipitation of of of Al Al Al5FeSi,5FeSi,5FeSi, Si Si Si, ,and ,and and exhaust exhaust exhaust of of of the the the melt. melt. melt. For For For Mn Mn Mn content content content from from from 0.5 0.5 0.5 (markedto(marked 2 wt. %, byby the ① exhaust inin Fig(marked(markedure of8(b)8(b) melts) ) by by was ①were drawn inin causedFigFig ure by 8(b)fitting8(b) by )two) was thethe four drawn datadata-phase ofof byby thethe fittingeutecticfitting primary thethe reaction precipitationdatadata ofofs :thethe primary temperature. precipitation temperature. points, which indicates,tototo 2 2 2wt. respectively,wt. wt. %, %, %, the the the exhaust exhaust exhaust of of precipitationof melts melts melts were were were caused caused caused of by by by Al5FeSi,two two two four four four--phase-phasephase Si, eutectic eutectic andeutectic exhaustreaction reaction reactionss:s : : of the melt. For Mn ②, ③, ④ ②, ③, ④ content fromAt the 0.5 AlSi8Fe1 to 2 wt.side,At %, the the AlSi8Fe1 exhaustphase side, boundaries of melts werephase wereextendedextended boundaries caused fromfrom were correspondingcorresponding byextendedextended two four-phase fromfrom pointpoint correspondingcorrespondingss,, which eutectic pointpointss reactions:,, which indicates(1)indicates L + α,, -respectivelyrespectivelyAl + α-Al(FeMn)Siindicatesindicates,, precipitation,, respectively+respectively Al5FeSi of Al= α5,5, FeSi,- precipitationAl + Siα-,,Al(FeMn)Si andand exhaustexhaust of Al55 FeSi,+FeSi, ofofSi the+the Si SiAl, , melt. 5andandFeSi exhaustexhaust Forand Mn of ofcontentcontent thethe melt. fromfrom For 0.50.5 Mn contentcontent fromfrom 0.50.5 (1)(1)(1) LL L+ + +α α -α-Al-AlAl + + +α α -α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si + + +Al Al Al5FeSi5FeSi5FeSi = = =α α -α-Al-AlAl + + +α α -α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si + + +Si Si Si + + +Al Al Al5FeSi5FeSi5FeSi and and and to(2)to 2 2 wt.wt.L + %, %,α- Althethe + exhaust exhaustα-Al(FeMn)Sitoto 22 ofof wt.wt. meltsmelts %,%, + the the βwerewere-Al(FeMn)Si exhaustexhaust causedcaused ofof by by meltsmelts= αtwotwo-Al were were fourfour+ α- - Al(FeMn)Si-causedcausedphase eutectic byby twotwo + Si fourreactionfour + β---Al(FeMn)Siphasess:: eutectic reactionss:: (2)(2)(2) LL L+ + +α α -α-Al-AlAl + + +α α -α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si + + +β β -β-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si = = =α α -α-Al-AlAl + + +α α -α-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si + + +Si Si Si + + +β β -β-Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si (1) L + α-Al + α-Al(FeMn)Si + Al5FeSi = α-Al + α-Al(FeMn)Si + Si + Al5FeSi and Depending on these reactions, ⑤, ⑥ phase boundaries were drawn. At nearly 610 °C , ⑦, ⑧ (1)(1) L + α--Al + α--Al(FeMn)Si(1)(1)DependingDepending DependingL + α -+-Al Al on+5on 5 FeSionα -these -these Al(FeMn)Sithese = α reactions, --reactions, Alreactions, + α -+-Al(FeMn)Si Al ⑤ ⑤55⑤FeSiFeSi, ,⑥ ,⑥ ⑥ == phase phaseα phase -+-Al Si + +boundaries + boundaries α boundariesAlAl--Al(FeMn)Si55FeSi and were were were + Sidrawn. drawn. drawn. ++ AlAl55FeSiFeSi At At At nearly andand nearlynearly 610 610 610 °C °C °C, ,⑦ ,⑦ ⑦, ,⑧ ,⑧ ⑧ (2) L + αphase-Al +boundariesα-Al(FeMn)Si were drawn + becauseβ-Al(FeMn)Si of not only the = DTAα-Al results + α,-Al(FeMn)Si but also of the fact + that Si +a threeβ-Al(FeMn)Si- (2)(2) L + α--Al + αphase--phaseAl(FeMn)Siphase(2)(2) boundaries boundaries Lboundaries + α -+-Al β- -+Al(FeMn)Si were αwere were--Al(FeMn)Si drawn drawn drawn = αbecause because -- because+Al β -+-Al(FeMn)Si α --of Al(FeMn)Siof of not not not only only only = α the-+-the Althe Si DTA +DTA +DTA αβ---Al(FeMn)SiAl(FeMn)Si results results results, ,but ,but but + als alsSi als o+o o ofβof of-- Al(FeMn)Sithe the the fact fact fact that that that a a athree three three--- phase area should occur between of a two-phase area and a four-phase area. For Mn content of 1.0, it phasephasephase area area area should should should occur occur occur between between between of of of a a atwo two two--phase-phasephase area area area and and and a a afour four four--phase-phasephase area. area. area. For For For Mn Mn Mn content content content◦ of of of 1.0, 1.0, 1.0, it it it was assumedDepending that on the these precipitationDepending reactions, of ⑤on α, , -these ⑥Al(FeMn)Si phase reactions, boundaries would ⑤,, ⑥ were phase to a drawn. decrease boundaries At of nearly Mn were concentration 610 drawn. °C ,, ⑦ At,, ⑧ nearlyin 610 °C°C,, ⑦,, ⑧ Depending on thesewaswaswas assumed assumed reactions,assumed that that that the the the precipitation ,precipitation precipitationphase of of boundariesof α α α--Al(FeMn)Si-Al(FeMn)SiAl(FeMn)Si would werewouldwould lead lead drawn.lead to to to a a adecrease decrease decrease At nearly of of of Mn Mn Mn concentration concentration concentration 610 C, in in ,in phase phasethe melt boundaries, and therefore werephase αdrawn- Alboundaries was because assumed were of not todrawn precipitate only becausebecausethethe DTA prior ofof results notto that only,, but of thethe Alals DTA5oFeSi, of the resultsaccording fact, , thatthatbutbut to alsaalsa whichthreethreeoo ofof -the-the factfact thatthat aa threethree-- thethethe melt melt melt, ,and ,and and therefore therefore therefore α α α--Al-AlAl was was was assumed assumed assumed to to to precipitate precipitate precipitate prior prior prior to to to that that that of of of Al Al Al5FeSi,5FeSi,5FeSi, according according according to to to which which which boundariesphase were area should drawn occurphase because between area should of of a nottwooccuroccur--phase only betweenbetween area the of ofand aa DTA two twoa four--phase- results,-phase area area. and but For a four Mn also- -contentphasecontent of area. the of 1.0, For fact it Mn that contentcontent a of three-phaseof 1.0,1.0, itit area shouldwas occur assumed between thatthat thethewas precipitationprecipitation assumed of a two-phase thatthat ofof αtheαthe--Al(FeMn)Si precipitationprecipitation area would and ofof αα --leadleadAl(FeMn)Si afour-phase toto aa decrease would of leadlead area.Mn toconcentrationto aa Fordecrease Mn of in contentMn concentration of 1.0, in it was

assumed thatthethe melt the,, andand precipitation thereforetherefore thethe meltαα--Al,, wasandand of assumedthereforethereforeα-Al(FeMn)Si toαα- -Alprecipitate was assumed would prior to leadthatprecipitate of toAl55 aFeSi, prior decrease according to that of of toAl which5 Mn5FeSi,FeSi, concentrationaccordingaccording toto whichwhich in the Metals 2018, 8, x FOR PEER REVIEW 9 of 12 Metals 20182018,, melt, 88,, xx FORFOR PEERPEER and REVIEWREVIEW therefore α-Al was assumed to precipitate prior to99 ofof that 1212 of Al5FeSi, according to which the

the phase composition area ⑨ was determined. Lastly, according to rules of phase boundary thethe phase phasephase composition composition composition area area ⑨ was area determined.was Lastly, determined. according to rulesLastly, of phase according boundary to rules of phase boundary drawing, drawing, ⑩–⑮ phase boundaries were added in the diagram for a complete isopleth. drawing, ⑩––⑮ phasephase boundaries boundaries were added were in the added diagram in for the a complete diagram isopleth. for a complete isopleth. It is worth noting that in the case of Al Si8Fe1.5–Mn isopleth, ternary phase Al5FeSi or quaternary ItIt isis worthworth notingnoting thatthat inin thethe casecase ofof AlAl Si8Fe1.5Si8Fe1.5––Mn isopleth, ternary phase Al55FeSiFeSi oror quaternaryquaternary α-Al(FeMn)Si precipitated primarily, whereas in the case of AlSi8Fe2-Mn isopleth, ternary phase α--Al(FeMn)Si precipitatedIt is worth primarily noting,, whereas that in the the case case of AlSi8Fe2 of Al Si8Fe1.5–Mn--Mn isopleth, ternary isopleth, phase ternary phase Al5FeSi or quaternary Al8Fe2Si or quaternary α-Al(FeMn)Si precipitated primarily. Al88FeFe22SiSi ororα quaternaryquaternary-Al(FeMn)Si αα--Al(FeMn)Si precipitated precipitated primarily,primarily. whereas in the case of AlSi8Fe2-Mn isopleth, ternary phase In AlSi8Fe2-Mn isopleth, one more phase change occurred before the eutectic equilibrium: L + InIn AlSi8Fe2AlSi8Fe2--Mn isopleth, one more phase change occurred before the eutectic equilibrium: L + Al8Feα-Al2Si + Al or8Fe quaternary2Si + α-Al(FeMn)Siα-Al(FeMn)Si = L + α-Al + Al5FeSi precipitated + α-Al(FeMn)Si primarily. (shown as a dotted horizontal α--Al + Al88FeFe22SiSi ++ αα--Al(FeMn)Si = L + α--Al + Al55FeSiFeSi ++ αα--Al(FeMn)Si (shown as a dotted horizontal line at 591 °C in Figure 8d). Therefore, the ternary Al8Fe2Si was absent in the microstructure of solid lineline atat 591591 °C°C inin FigureFigure 8d).8d). ThereforeTherefore,, thethe ternaryternary AlAl88FeFe22SiSi waswas absentabsent inin ththee microstructuremicrostructure ofof solidsolid alloys. alloys.alloys.

(a) ((aa))

(b) ((b))

Metals 2018, 8, x FOR PEER REVIEW 9 of 12 the phase composition area ⑨ was determined. Lastly, according to rules of phase boundary drawing, ⑩–⑮ phase boundaries were added in the diagram for a complete isopleth. MetalsIt2018 is worth, 8, 796 noting that in the case of Al Si8Fe1.5–Mn isopleth, ternary phase Al5FeSi or quaternary9 of 12 α-Al(FeMn)Si precipitated primarily, whereas in the case of AlSi8Fe2-Mn isopleth, ternary phase Al8Fe2Si or quaternary α-Al(FeMn)Si precipitated primarily. InIn AlSi8Fe2 AlSi8Fe2-Mn-Mn isopleth, isopleth, one one more more phase phase change change occurred occurred before before the theeutectic eutectic equilibrium: equilibrium: L + L + α-Al + Al Fe Si + α-Al(FeMn)Si = L + α-Al + Al FeSi + α-Al(FeMn)Si (shown as a dotted α-Al + Al8Fe2Si 8+ α2-Al(FeMn)Si = L + α-Al + Al5FeSi + α-5Al(FeMn)Si (shown as a dotted horizontal horizontal line at 591 ◦C in Figure8d). Therefore, the ternary Al Fe Si was absent in the microstructure line at 591 °C in Figure 8d). Therefore, the ternary Al8Fe2Si was8 absent2 in the microstructure of solid alloys.of solid alloys.

(a)

(b)

Figure 8. Cont.

Metals 2018, 8, 796 10 of 12 Metals 2018, 8, x FOR PEER REVIEW 10 of 12

(c)

(d)

FigureFigure 8. 8. (a()a Isopleth) Isopleth AlSi8Fe0.5 AlSi8Fe0.5–Mn.–Mn. At At 0, 0,0.5, 0.5, 1, 1,1.5 1.5,, and and 2.0 2.0 wt. wt. % % Mn Mn concentrations, concentrations, three three points points werewere set set vertically vertically,, according according to to the the DTA DTA results results shown shown in in Table Table 4.4.( (bb) )Isopleth Isopleth AlSi8F AlSi8Fe1–Mn.e1–Mn. At At 0, 0, 0.5,0.5, 1, 1,1.5 1.5,, and and 2.0 2.0 wt. wt. % % Mn Mn concentrations, concentrations, three three points points were were set set vertically vertically according according to tothe the DTA DTA resultsresults shown shown in in Table Table 44. .((c)c Isopleth) Isopleth AlSi8Fe1.5 AlSi8Fe1.5–Mn.–Mn. At At 0, 0,0.5, 0.5, 1, 1,1.5 1.5,, and and 2.0 2.0 wt. wt. % %Mn Mn concentrations, concentrations, threethree points points were were set set vertically vertically acco accordingrding to the DTA resultsresults shown shown in in Table Table4.( 4.d ()d Isopleth) Isopleth AlSi8Fe2–Mn. AlSi8Fe2– Mn.At 0,At 0.5, 0, 0.5, 1, 1.5, 1, 1.5 and, and 2.0 2.0 wt. wt. %Mn % Mn concentrations, concentrations, four four points points were were set verticallyset vertically according according to the to the DTA DTAresults results shown shown in Table in Table4. 4.

Metals 2018, 8, 796 11 of 12

Serving as a reliable reference for deriving temperature ranges of intermetallic stability in a small continuous range, these isopleths can open part of a process for the removal of iron from the melt through separation of Fe-enriched intermetallic compounds. For instance, in a melt with 2 wt. % Fe and 1 wt. % Mn (Figure8d, isopleth AlSi8Fe2.0–Mn), the precipitation of α-Al(FeMn)Si can be controlled by defining the temperature in an interval of 684 ◦C–643 ◦C, which could be employed for Fe removal. If the melt is treated in the temperature range of 643 ◦C–610 ◦C, the precipitation and ◦ segregation of two iron-containing phases, Al8Fe2Si and α-Al(FeMn)Si, can be expected. Below 610 C, α-Al, α-Al(FeMn)Si, Al8Fe2Si, and Al5FeSi will, respectively, crystallize from the melt. However, with a decreasing temperature, the viscosity of the melt increases rapidly because of a more abundant solid/liquid fraction, which makes phases separation difficult.

4. Conclusions Alloys of the system Al–Si–Fe–Mn were investigated in the concentration range of 6 to 10 Si wt. %, 0.5 to 2.0 Fe wt. %, and 0 to 2.0 Mn wt. % by DTA and SEM analyses. Intermetallics precipitated during solidification in the form of the ternary Al8Fe2Si, Al5FeSi, quaternary Al(FeMn)Si, and Si. With a decreasing temperature, a series of peritectic reactions took place in the melt. Crystallization of the alloys resulted in two four-phase eutectic reactions:

(1) L + α-Al + α-Al(FeMn)Si + Al5FeSi = α-Al + α-Al(FeMn)Si + Si + Al5FeSi; (2) L + α-Al + α-Al(FeMn)Si + β-Al(FeMn)Si = α-Al + α-Al(FeMn)Si + Si + β-Al(FeMn)Si.

In the range of the investigated alloys, solid alloy consisted of α-Al–α-Al(FeMn)Si–Si–Al5FeSi after crystallization if Mn/Fe < 1.1, of α-Al–α-Al(FeMn)Si–Si–β-Al(FeMn)Si if Mn/Fe > 1.1, and of α-Al–α-Al(FeMn)Si–Si if Mn/Fe = 1.1. Based on the results and following the rules of phase boundary drawing, isopleths were constructed. It can be inferred from these isopleths that at low Mn content, the melt precipitates primarily the low Fe-containing intermetallics Al5FeSi or Al8Fe2Si. With the rise of Mn content in the melt, quaternary α-Al(FeMn)Si phase becomes the primary phase, thus a better refining effect can be expected. The isopleths can serve as an informative reference for the purification of secondary recycling aluminium through the precipitation route from an industrial point of view. An initial idea concerning the process design includes: (1) Composition setting by addition of Mn in the melt, (2) Fe-enriched phase precipitation controlling by holding the melt at a specified temperature, and (3) Precipitated phase physical separation by filtration. The real quantity of precipitated α-Al(FeMn)Si or β-Al(FeMn)Si and Al5FeSi in the melt at different temperatures is a matter of experimental investigation, which will be presented in future publications.

Author Contributions: A.A. conceptualized the work. B.F. was the principal investigator and supervisor. M.G. performed the experiments. A.A. and M.G. analyzed the data. M.G. wrote and edited the manuscript. C.L. revised the manuscript. Funding: This research was funded by The DFG (Deutsche Forschungsgemeinschaft)–German Research Society project “Refining of Al–Si melts” FR 1713/5-1. Acknowledgments: The DFG–German Research Society is greatly appreciated for the support of the project “Refining of Al–Si melts” FR 1713/5-1. Conflicts of Interest: The authors declare no conflict of interest.

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