As an example of the production of syntactic metallic foams, we can mention the method called Stir Casting, where a high
shear impeller is used to mix and homogenize solid particles in a molten alloy [4]. Another of these techniques is called
Pressure Infiltration, where the molten metal is forced into a mold with the assistance of a high pressure and/or vacuum, whose
interior is formed by a preform or bed of hollow and free particles [5]. These foams can also be produced via Powder
Metallurgy, with hollow particles and metallic powder mixed, compacted and sintered [6].
The method of manufacturing metallic matrix composite materials, known as squeeze casting, is derived from the joining
of forging methods in mold and casting and consists of the compression of a metallic alloy in the liquid state contained in a
mold. This technique has been used for the manufacture of metallic composites reinforced by particles. Therefore, through the
pressure imposed by a mobile mold, the molten alloy is impelled to infiltrate in a preform of reinforcements. Therefore, several
advantages can be mentioned, such as low operating cost, low level of gaseous porosity defects, excellent surface finish,
refined product structure and short processing cycles [7].
The technique thixoinfiltration, which was used in the current work, came from another called “squeeze casting
infiltration”. However, at this methodology, the temperature of work is between the solidus and liquidus temperature of the
alloy, therefore, at the semisolid state.
During combustion, minerals in coal become fluid at elevated temperatures. In pulverized coal boilers, the furnace typically
operates at temperatures above 1400
C, and at those temperatures the mineral content in the coal can oxidize, decompose,
melt, disintegrate or agglomerate. Consequently, the rapid cooling in the post-combustion zone results in the formation of
particles with ceramic/amorphous structures, known as Fly Ash balloons [8]. Particles which, in an aluminum matrix
composite, when in contact with the molten metal perform the function of grain refiners [9].
4.2 Materials and Methods
In this study, an AMSF composed of AlSiMg0.5Mn matrix reinforced with Fly Ash balloons was produced by
thixoinfiltration process. The alloy’s nominal composition is presented at Table 4.1.
Before producing the material, a wide study had been done concerning the aluminum alloy and the Fly Ash balloons. First
of all, the thixotropic behavior of alloy was studied through differential exploratory calorimetry (DSC), followed by an
investigation of the morphology of Fly Ash balloons.
For the thermal analysis by DSC a rate of 5
C/min was used and samples with 100 g of mass. For this purpose, a NETZCH
brand model STA 409 with a controller model TASH 414/x coupled to a digital analog plate model IEEE 488 was used. Thus,
since during cooling stage the reading is more accurate due to the greater contact of the liquid alloy with the equipment’s
crucible, the Energy versus Temperature curve, referring to that moment of the experiment was chosen to be investigated with
the aid of the Proteus
® -NETZSCH software.
Through the second differential of DSC curves were found the inflection points of the Tsolidus (555
C) and Tliquidus
(655
C), and the integral curve describing the behavior of the alloy phase transformation were possible the synthesis of
precursor experiments, and the work window has been defined from 644
C (75% of liquid phase) to 646
C (85% of liquid
phase).
Composed most of S i O 2 (60 wt%) and Al 3 O 2 (40%), because of the irregular format of Fly Ash balloons showed in
Fig. 4.1, measures were taking aiming the diameter (ø), length (A) and wall thickness of 40 balloons and the averages were
noted to be ø ¼ 231.24 Æ 39.55 μm, wall thickness of 2.35 Æ 0.21 μm and A ¼ 340.16 Æ 79.28 μm.
For the production by thixoinfiltration of Fly Ash balloons, the following experiment was carried out: in a steel matrix
SAE1020 with a diameter of 45 mm, coated with a ceramic paste based on alumina, two AA6351 aluminum alloy discs were
positioned and 5 wt% of Fly Ash balloons between them.
The set was taken to the oven at room temperature and heated to 550
C at a rate of 5
C/min, which was kept constant for
1.5 h to homogenize the temperature throughout the set. After that time, with a heating rate of 5
C/min the temperature was
Table 4.1 Alloy AlSiMg0.5Mn chemical composition
Component
Si
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
Al
Nominal content—wt%
1.354
0.358
0.063
0.466
0.446
0.032
0.008
0.042
0.024
Balance
20
J. P. Paschoal et al.
shear impeller is used to mix and homogenize solid particles in a molten alloy [4]. Another of these techniques is called
Pressure Infiltration, where the molten metal is forced into a mold with the assistance of a high pressure and/or vacuum, whose
interior is formed by a preform or bed of hollow and free particles [5]. These foams can also be produced via Powder
Metallurgy, with hollow particles and metallic powder mixed, compacted and sintered [6].
The method of manufacturing metallic matrix composite materials, known as squeeze casting, is derived from the joining
of forging methods in mold and casting and consists of the compression of a metallic alloy in the liquid state contained in a
mold. This technique has been used for the manufacture of metallic composites reinforced by particles. Therefore, through the
pressure imposed by a mobile mold, the molten alloy is impelled to infiltrate in a preform of reinforcements. Therefore, several
advantages can be mentioned, such as low operating cost, low level of gaseous porosity defects, excellent surface finish,
refined product structure and short processing cycles [7].
The technique thixoinfiltration, which was used in the current work, came from another called “squeeze casting
infiltration”. However, at this methodology, the temperature of work is between the solidus and liquidus temperature of the
alloy, therefore, at the semisolid state.
During combustion, minerals in coal become fluid at elevated temperatures. In pulverized coal boilers, the furnace typically
operates at temperatures above 1400
C, and at those temperatures the mineral content in the coal can oxidize, decompose,
melt, disintegrate or agglomerate. Consequently, the rapid cooling in the post-combustion zone results in the formation of
particles with ceramic/amorphous structures, known as Fly Ash balloons [8]. Particles which, in an aluminum matrix
composite, when in contact with the molten metal perform the function of grain refiners [9].
4.2 Materials and Methods
In this study, an AMSF composed of AlSiMg0.5Mn matrix reinforced with Fly Ash balloons was produced by
thixoinfiltration process. The alloy’s nominal composition is presented at Table 4.1.
Before producing the material, a wide study had been done concerning the aluminum alloy and the Fly Ash balloons. First
of all, the thixotropic behavior of alloy was studied through differential exploratory calorimetry (DSC), followed by an
investigation of the morphology of Fly Ash balloons.
For the thermal analysis by DSC a rate of 5
C/min was used and samples with 100 g of mass. For this purpose, a NETZCH
brand model STA 409 with a controller model TASH 414/x coupled to a digital analog plate model IEEE 488 was used. Thus,
since during cooling stage the reading is more accurate due to the greater contact of the liquid alloy with the equipment’s
crucible, the Energy versus Temperature curve, referring to that moment of the experiment was chosen to be investigated with
the aid of the Proteus
® -NETZSCH software.
Through the second differential of DSC curves were found the inflection points of the Tsolidus (555
C) and Tliquidus
(655
C), and the integral curve describing the behavior of the alloy phase transformation were possible the synthesis of
precursor experiments, and the work window has been defined from 644
C (75% of liquid phase) to 646
C (85% of liquid
phase).
Composed most of S i O 2 (60 wt%) and Al 3 O 2 (40%), because of the irregular format of Fly Ash balloons showed in
Fig. 4.1, measures were taking aiming the diameter (ø), length (A) and wall thickness of 40 balloons and the averages were
noted to be ø ¼ 231.24 Æ 39.55 μm, wall thickness of 2.35 Æ 0.21 μm and A ¼ 340.16 Æ 79.28 μm.
For the production by thixoinfiltration of Fly Ash balloons, the following experiment was carried out: in a steel matrix
SAE1020 with a diameter of 45 mm, coated with a ceramic paste based on alumina, two AA6351 aluminum alloy discs were
positioned and 5 wt% of Fly Ash balloons between them.
The set was taken to the oven at room temperature and heated to 550
C at a rate of 5
C/min, which was kept constant for
1.5 h to homogenize the temperature throughout the set. After that time, with a heating rate of 5
C/min the temperature was
Table 4.1 Alloy AlSiMg0.5Mn chemical composition
Component
Si
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
Al
Nominal content—wt%
1.354
0.358
0.063
0.466
0.446
0.032
0.008
0.042
0.024
Balance
20
J. P. Paschoal et al.