I. KROUPOVÁ et al.: USE OF WATER-SOLUBLE PRECURSORS IN THE PRODUCTION OF CAST METAL FOAMS
125–127
USE OF WATER-SOLUBLE PRECURSORS IN THE PRODUCTION
OF CAST METAL FOAMS
UPORABA VODOTOPNIH DODATKOV V PROIZVODNJI LITIH
KOVINSKIH PEN
Ivana Kroupová
1*
, Petr Lichý
1
, Ivo Lána
2
1
VSB – Technical University of Ostrava, Faculty of Materials Science and Technology, Department of Metallurgy and Foundry, 17. listopadu
2172/15, 708 00 Ostrava – Poruba, Czech Republic
2
SaM Nové Ransko, s.r.o., Nové Ransko 234, 582 63 dírec nad Doubravou, Czech Republic
Prejem rokopisa – received: 2019-08-01; sprejem za objavo – accepted for publication: 2019-08-18
doi:10.17222/mit.2019.144
The paper is devoted to the field of manufacturing cast metallic foams – porous metal materials – with a stochastic arrangement
of the inner cavities. The mastering of inexpensive ways of manufacturing metallic foams is a prerequisite for a full utilization
of such a material. That is why the experimental part was devoted to the casting technologies for the production of metal foams
based on conventional foundry processes. In the experiment, the infiltration of molten metal into mould cavities filled with
precursors was tested. Particular attention was paid to the use of water-soluble precursor materials. It is assumed that a thorough
knowledge of the production parameters and conditions will contribute to the expansion of the foundry range, which can also
increase the competitiveness of this industry on a global scale.
Keywords: metallic foams, salt, water-soluble, casting
Pri~ujo~i ~lanek opisuje izdelavo litih kovinskih pen, to je poroznih kovinskih materialov s stohasti~no (naklju~no) poraz-
delitvijo notranjih praznin oz. por. Umetnost obvladovanja cenenih poti proizvodnje kovinskih pen je temelj za izkori{~anje
uporabnosti tega materiala. Avtorji ~lanka so se v eksperimentalnem delu tako posvetili tehnologijam litja v proizvodnji
kovinskih pen, ki temeljijo na konvencionalnih livarskih postopkih. S prakti~nim preizkusom so testirali potek infiltracije
raztaljene kovine v votlino modela, polnjeno s prekurzorji – izhodnimi dodatki. Posebno pozornost so posvetili vodotopnim
prekurzorjem. Zaklju~ujejo z ugotovitvijo, da poznavanje parametrov proizvodnje in pogojev te vrste proizvodnje, prispeva k
raz{iritvi livarskega programa, kar lahko tudi pove~a njihovo konkuren~nost na globalnem trgu.
Klju~ne besede: kovinske pene, sol, vodotopnost, livarstvo
1 INTRODUCTION
A metal foam is a material, which has attracted a
great deal of attention in many areas of human activities
in recent years. This porous metal material has unique
features that can be combined with each other. They are
characterized by, e. g., low density, high specific surface
area, acoustic or thermal insulation properties, etc.
1
Thanks to these properties, metal foams can be used in a
wide range of sectors of human activity from vehicle
construction, thermal engineering to medicine. However,
the application potential of these materials is limited by
the economic requirements of their production technol-
ogies. In most cases, these are costly methods based on
complicated procedures and the use of non-standard and
expensive input materials.
2–4
At the Faculty of Materials Science and Technology,
VSB-TUO, Department of Metallurgy and Foundry, the
possibilities of producing metal foams from the liquid
phase, namely using the foundry method, are studied.
One of the studied technologies is the infiltration of
liquid metal into a mould cavity filled with precursors.
The use of standard casting processes and standard ma-
terials makes it possible to identify affordable materials,
thereby making a full use of their application potentials.
The casting technology also offers the possibility of
producing very complex parts, both with a solid surface
layer and without it.
2 EXPERIMENTAL PART
Since the discovery of porous metallic materials,
numerous methods of production have been developed.
According to the state, in which a metal is processed, the
manufacturing processes can be divided into four groups
– metal foams can be made from a liquid metal, pow-
dered metal, metal vapours or metal ions.
1
In this research, we are interested in manufacturing
metal foams from a liquid metal, especially by way of
the foundry methods. There are several foundry methods
for the production of porous metals, such as the invest-
ment-casting technology (using an evaporative pattern),
which is considerably expensive.
5
Thanks to the foundry
technology we are able to control the porosity (%), pore
size and their distribution (regular/irregular). In our case,
the production of metal foams with an irregular structure
is carried out by pouring filling materials (precursors)
Materiali in tehnologije / Materials and technology 54 (2020) 1, 125–127 125
UDK 669.1:62-911-026.747 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(1)125(2020)
*Corresponding author's e-mail:
ivana.kroupova@vsb.cz (Ivana Kroupová)

into a mould cavity. These precursors are metal encap-
sulated and removed from the casting volume after the
solidification of the metal. The condition for their com-
plete removal is a mutual contact of all the precursors.
In all the experiments, the castings were made of an
Al-Si-type alloy (AlSi10MgMn) and the moulds were
made from a commonly used moulding mixture (green
sand).
2.1 Principle of the technology
The irregular distribution of pores that we deal with
can be achieved with the use of various types of pre-
cursors, filling in a mould cavity (Figure 1). A precursor
must be made of a material that preserves its shape at the
impact of molten metal (having sufficient strength, low
abrasion, refractoriness) and it must also allow a good
disintegration after the casting.
6
The key step in this technology is a perfect removal
of all the precursors from the casting volume, which is
problematic due to the complex cavity of a casting. This
is why our experiment focused on water-soluble mater-
ials for the precursors.
2.2 Salt precursors
The tested filler materials were precursors with a
salt-based core composition. These materials were
included in the experiment because of the ease of their
removal from the casting volume after the casting. The
composition of the moulding mixture for the precursors
included crystalline sodium chloride NaCl (foundry
sand) and water glass, M = 2.38 (the binder). The
hardening was done in a microwave oven (3 × 2 min) at
1000 W.
From the prepared moulding mixture, beams were
made, which were cured and subsequently cut into
cubes. These semi-finished products were placed on a
rotating screen where they were tumbled. The proposed
technology ensures the production of the precursors of
the same size, shape and properties. The mould cavity
with dimensions of 30 × 60 × 120 mm was filled with
precursors (Figure 2) and after the mould was manufac-
tured, the melt – the AlSi10MgMn aluminum alloy with
a casting temperature of 730 °C – was infiltrated. Four
minutes after the casting process, the casting was
immersed into water to flush the precursors out. An
example of the resulting casting is shown in Figure 3.
3 RESULTS
Special materials and technologies for manufacturing
precursors were tested. The porosity of the produced
castings amounted to 60 %. The use of salt precursors
seems to be very suitable in view of their removal from
the casting volume. After casting, these can be removed
immediately after the solidification of the cast by
flushing them out of all internal cavities (assuming the
precursors touch each other to form interconnected cavi-
ties). Thus, the complicated process of mechanical remo-
val of the filler material, which used to be a common
disadvantage of all the processes using precursors made
of standard moulding mixtures, is now eliminated.
7
This
way, the manufacturing of precursors allows the for-
mation of the same size, shape and the resulting charac-
teristics of precursors.
I. KROUPOVÁ et al.: USE OF WATER-SOLUBLE PRECURSORS IN THE PRODUCTION OF CAST METAL FOAMS
126 Materiali in tehnologije / Materials and technology 54 (2020) 1, 125–127
Figure 3: Casting after the salt precursors have been removed by
flushing
Figure 1: Principle of the liquid-metal infiltration into a mould cavity
filled with precursors; from the left: the mould, the mould cavity filled
with precursors, a metal-foam casting and its detail after the removal
of the precursors
Figure 2: Mould cavity filled with salt precursors

4 DISCUSSION
During the experiment, the use of special water-sol-
uble moulding mixtures for the manufacture of pre-
cursors was confirmed. In view of the possibility of
removing the precursors from the complex structure of a
casting, it is particularly advantageous to use salt
precursors. This process of manufacturing metallic
foams fully complies with the original requirements – it
is a low-cost technology based on the commonly used
foundry operations.
5 CONCLUSIONS
With the method of infiltrating molten metal into a
mould cavity filled with precursors, foams with irregular
internal structures can be prepared from the materials
that are normally processed in the foundry operations. It
is necessary to know the technological and metallurgical
parameters of the production for a successful casting. It
is assumed that a thorough knowledge of the production
parameters and conditions will contribute to the expan-
sion of the foundry range, which can also increase the
competitiveness on a global scale.
Acknowledgment
This contribution was carried out with the support of
the Technology Agency of the Czech Republic –
TH02020668 and TA02011333, and the support of the
projects within “the Student Grant Competition”, with
numbers SP2020/39 and SP2020/64.
6 REFERENCES
1
J. Banhart, Manufacture, characterisation and application of cellular
metals and metal foams, Progress in Materials Science, 46 (2001)6 ,
559–632, doi:10.1016/S0079-6425(00)00002-5
2
F. García-Moreno, Commercial Applications of Metal Foams: Their
Properties and Production, Materials, 85 (2016) 9, doi:10.3390/
ma9020085
3
L. Drenchev, J. Sobczak, S. Malinov, W. Sha, Gasars: A class of me-
tallic materials with ordered porosity, Materials Science and Tech-
nology, 22 (2006) 10, 1135–1147, doi:10.1179/174328406X118302
4
L. J. Gibson, Biomechanics of cellular solids, Journal of Biomecha-
nics, 38 (2005), 377–399, doi:10.1016/j.jbiomech.2004.09.027
5
I. Kroupová, P. Lichý, F. Radkovský, J. Beòo, V . Bednáøová, I. Lána,
Optimization of the annealing of plaster moulds for the manufacture
of metallic foams with an irregular cell structure, Mater. Tehnol., 49
(2015) 4, 527–530, doi:10.17222/mit.2014.132
6
I. Kroupová, F. Radkovský, P. Lichý, V . Bednáøová, Manufacturing
of cast metal foams with irregular cell structure, Archives of Foundry
Engineering, 15 (2015) 2, 55–58, doi:10.1515/afe-2015-0038
7
I. Kroupová, P. Lichý, V . Merta, I. Lána, Use of Precursors for the
Production of Cast Metallic Foams, Mater. Tehnol., 53 (2019)2 ,
189–191, ISSN 1580-2949, doi: 10.17222/mit.2018.141
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