M. VON^INA et al.: INFLUENCE OF TEMPERATURE ON THE INTERACTION KINETICS BETWEEN MOLTEN ALUMINIUM ...
401–405
INFLUENCE OF TEMPERATURE ON THE INTERACTION
KINETICS BETWEEN MOLTEN ALUMINIUM ALLOY AL99.7
AND TOOL STEEL H11
VPLIV TEMPERATURE NA KINETIKO INTERAKCIJ MED
STALJENO ALUMINIJEVO ZLITINO AL99.7 IN ORODNIM
JEKLOM H11
Maja Von~ina
*
, Ale{ Nagode, Jo`ef Medved, Tilen Bala{ko
Department for Materials and Metallurgy, Faculty of Natural Sciences and Engineering, University of Ljubljana, A{ker~eva 12, 1000
Ljubljana, Slovenia
Prejem rokopisa – received: 2023-03-09; sprejem za objavo – accepted for publication: 2023-06-29
doi:10.17222/mit.2023.825
Hot-work tool steels are used in casting and hot-forming processes and are subjected to thermal, mechanical and chemical
stresses that can cause damage to various parts of the tool. Therefore, knowledge of the interaction between tool steel and mol-
ten aluminium alloy is necessary to extend the life of the tool. The present work was carried out to predict the influence of tem-
perature on the interaction kinetics between tool steel and molten aluminium. To investigate the effect of temperature on the dis-
solution rate of tool steel in molten aluminium and the rate of formation of interaction layers, DSC analysis was performed at
two different temperatures, 670 °C and 700 °C, for 12 h. The results were corroborated and supported by a detailed
microstructure analysis.
It was found that very small temperature changes, in this case 30 °C, significantly affect the kinetics of the interaction layer’s
formation between the tool steel H11 and molten aluminium Al99.7. All test methods show a pronounced influence of the test
temperature. A significantly faster dissolution was observed in the DSC curve, with the slope of the curve being larger for the
specimen tested at 700 °C, which was also confirmed by measurements of the thicknesses of the interaction layers. The thick-
ness of the composite layer was almost the same in both cases, and the temperature has no effect on this layer. The types of in-
teraction layers do not differ from each other.
Keywords: interaction between tool steel and molten aluminium, reaction kinetics, temperature, differential scanning calorime-
try
Orodna jekla za delo v vro~em se uporabljajo v postopkih litja in vro~ega oblikovanja in so izpostavljena toplotnim, mehanskim
in kemi~nim obremenitvam, ki lahko povzro~ijo po{kodbe razli~nih delov orodja. Zato je za podalj{anje `ivljenjske dobe orodja
potrebno poznavanje interakcije med orodnim jeklom in staljeno aluminijevo zlitino. Raziskava je bila izvedena z namenom
napovedovanja vpliva temperature na kinetiko interakcije med orodnim jeklom in staljenim aluminijem. Za prou~evanje vpliva
temperature na hitrost raztapljanja orodnega jekla v staljenem aluminiju in hitrost tvorbe interakcijskih plasti je bila izvedena
analiza DSC pri dveh razli~nih temperaturah, 670 °C oziroma 700 °C, 12 h. Rezultati so bili utemeljeni in podprti s podrobno
analizo mikrostrukture.
Ugotovljeno je bilo, da zelo majhne spremembe temperature, v tem primeru 30 °C, pomembno vplivajo na kinetiko nastajanja
interakcijskih plasti med orodnim jeklom H11 in staljenim aluminijem Al99.7. Vse raziskovalne metode ka`ejo izrazit vpliv
preskusne temperature. Bistveno hitrej{e raztapljanje smo opazili na DSC krivulji, kjer je naklon krivulje ve~ji pri vzorcu
testiranem pri 700 °C, kar so potrdile tudi meritve debelin interakcijskih plasti. Debelina kompozitne plasti je bila v obeh
primerih pribli`no enaka, na to plast temperatura nima vpliva. Vrste interakcijskih slojev se med seboj ne razlikujejo.
Klju~ne besede: interakcija orodnega jekla in staljenega aluminija, kinetika reakcije, temperatura, diferen~na vrsti~na
kalorimetrija
1 INTRODUCTION
Hot-work tool steels are used in casting and hot-
forming processes and are subjected to thermal, mechan-
ical and chemical stresses that can cause damage to vari-
ous parts of the tool. Therefore, knowledge of the inter-
action between the tool steel and the molten aluminium
alloy is necessary to extend the life span. Applying pro-
tective coatings to the functional surfaces of tools im-
proves the wear resistance.
1,2
The interaction between the
molten aluminium and the tool steel can lead to material
adhering to the tool, mainly through chemical reactions,
diffusion and dissolution, which occur more rapidly at
higher temperatures.
3–5
The Al-Fe system consists of a solid solution based
on iron and six intermetallic compounds with different
iron and aluminium contents, which affect the wear re-
sistance and durability of the tool. Studies show that the
interaction layer between molten aluminium and tool
steel contains Al
5
Fe
2
and Al
3
Fe phases, with Al
3
Fe grow-
ing faster in the later reaction phases and partially dis-
solving in molten aluminium.
6–8
However, the reaction
kinetics at the interface can cause the formation of
Al
5
Fe
2
as the main component.
This article discusses how a chemical reaction occurs
between aluminium and iron due to their solubility, lead-
Materiali in tehnologije / Materials and technology 57 (2023) 4, 401–405 401
UDK 669.715:691.714:52-335.7 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(4)401(2023)
*Corresponding author's e-mail:
maja.voncina@ntf.uni-lj.si

ing to the formation of intermetallic phases in certain
stoichiometric ratios based on the binary phase diagram
for Al-Fe.
5
The most frequently formed phases are
Al
5
Fe
2
and Al
13
Fe
4
, which form a reaction layer.
3
Opti-
mal wetting and diffusion are required for the formation
of these phases, which result from the difference in
chemical potentials between the solid tool steel and the
molten aluminium.
9
However, to achieve the desired me-
chanical and physical properties of the tools, the forma-
tion of these phases must be limited or prevented.
When tool steels dissolve in molten aluminium, the
dissolution is initially intense but slows down after about
250 s due to the difficult diffusion of aluminium and iron
atoms through the resulting interaction layer.
3,8,10
The
interlayer between the tool steel and the aluminium alloy
consists of an intermetallic and a composite layer, and
the thickness of the interaction layer is influenced by the
alloying elements in the molten aluminium and the tool
steel. Tool-steel alloying elements such as chromium,
manganese, silicon, molybdenum, and vanadium are
present in the reaction layer and reduce or prevent the
formation of an intermetallic layer.
7
The iron content in
the aluminium alloy also affects the lower layer thick-
ness, but should not be too high to avoid deterioration of
the mechanical properties. The temperature of the alu-
minium melt also influences the thickness of the interac-
tion layer, with higher temperatures leading to a thicker
layer.
7,11,12
The present work was carried out to predict the influ-
ence of temperature on the interaction kinetics between
tool steel and molten aluminium. To investigate the ef-
fect of temperature on the dissolution rate of tool steel in
molten aluminium and the rate of formation of the inter-
action layers, a DSC analysis was performed at two dif-
ferent temperatures, 670 °C and 700 °C, for 12 h. The re-
sults were substantiated and supported by a detailed
SEM analysis.
2 MATERIALS AND METHODS
The reaction kinetics between molten aluminium and
tool steel were analysed using differential scanning calo-
rimetry (STA Jupiter 449c, NETZSCH Holding, Selb,
Germany), which provides information on the dissolu-
tion rate of tool steel in molten aluminium at constant
temperatures of 670 °C and 700 °C. The samples for
DSC analysis were machined in the shape of a cylinder
with a diameter of 4.5 mm and a height of 3 mm for the
aluminium alloy and a diameter of 4.5 mm and a height
of 1 mm for the tool steel. The crucibles used for DSC
analysis were made of corundum. An empty crucible
served as the reference material. In the instrument, the
heating rate of the samples was set to 20 K·min
–1
, they
were heated to 670 °C and 700 °C and kept there for
12 h. They were then cooled at the same rate of
20 K·min
–1
. The experiments were performed under a
protective atmosphere. After completion of the analyses,
two DSC curves were plotted as a function of time, from
which the effect of temperature on the reaction kinetics
between the molten aluminium alloy Al99.7 and the tool
steel H11 was predicted.
After completion of the DSC testing, the specimens
were examined metallographically, and the thicknesses
and types of interaction layers were analysed by light
and scanning electron microscopy. For the micro-
structural characterization of the interaction layer, the
specimens were carefully removed from the crucibles af-
ter the DSC analysis and placed in a horizontal position
in the specimen-preparation models for the microstruc-
tural analysis to obtain an overview of the cross-section
of the interaction layer between aluminium and tool
steel. This was followed by metallographic specimen
preparation. The specimens were then examined using an
Olympus BX61 light microscope. Micrographs were
produced and the thicknesses of the interaction layers
were measured.
A detailed analysis of the interaction layers and the
phases occurring in the interaction layer was performed
using a Thermo Fisher Scientific Quattro S FEG SEM
(ThermoFisher Scientific, Waltham, MA, USA) micro-
scope with an Oxford Ultim® Max 65 mm
2
EDS SDD
EDS analyzer (Ultim®Max, Oxford Instruments,
Abingdon, UK). For imaging and EDS analyses the ac-
celerating voltage was 15 kV . For secondary electron im-
aging (SEI) an Everhart–Thornley detector was used,
while for the backscatter electron imaging an angular
backscatter (ABS) detector was used.
3 RESULTS AND DISCUSSION
Figure 1 shows the DSC curves for both samples
tested at 670 °C and 700 °C. The slopes of the curves are
different, with the DSC curve of the specimen tested at
700 °C rising faster and the slope being larger, indicating
the faster dissolution of the tool steel in the aluminium
alloy and greater diffusion of the atoms of some ele-
M. VON^INA et al.: INFLUENCE OF TEMPERATURE ON THE INTERACTION KINETICS BETWEEN MOLTEN ALUMINIUM ...
402 Materiali in tehnologije / Materials and technology 57 (2023) 4, 401–405
Figure 1: DSC curves of the dissolution of H11 in molten aluminium
alloy Al99.7

ments through the protective layer. Based on these re-
sults, a thicker interaction layer is expected in the sample
tested at 700 °C. The temperature difference of 30 °C
plays an important role.
The microstructure analysis presented in Figure 2
confirmed that an interaction layer was formed at the
contact between the tool steel H11 and the molten alu-
minium Al99.7, which was divided into two parts: a
layer consisting of an intermetallic phase based on
Al
5
Fe
2
closer to the tool steel and composite layers based
on the intermetallic phase Al
3
Fe formed closer to the alu-
minium alloy.
11,12
As a result of the reaction between the
tool steel and the liquid aluminium alloy, an Al
3
Fe inter-
metallic phase is formed, which slows down the inter-
phase reaction because it acts as a diffusion barrier. This
is reflected in a drop in the slope of the DSC curve. The
thicknesses of the layers are different. The layer closer to
the tool steel has an average thickness of about 420 μm
for the sample tested at 670 °C and 540 μm for the sam-
ple tested at 700 °C. The reason for the change in the
thickness of the interaction layer is the faster diffusion of
atoms at a higher temperature. The layer closer to the
aluminium alloy is much thinner, about 130 μm in both
cases.
SEM and EDS analyses confirmed that the layer
closer to the tool steel consists of an intermetallic phase
M. VON^INA et al.: INFLUENCE OF TEMPERATURE ON THE INTERACTION KINETICS BETWEEN MOLTEN ALUMINIUM ...
Materiali in tehnologije / Materials and technology 57 (2023) 4, 401–405 403
Figure 2: Micropraphs of the interaction layers of samples tested at: a) 670 °C and b) 700 °C
Figure 3: SEM (BEI) micrographs of the interaction layer of samples tested at: a) 670 °C and b) 700 °C. The corresponding EDS results are
g i v e ni na t% .

based on Al
5
Fe
2
(Figure 3a, site 3 and 4). This also con-
tains a greater proportion of certain alloying elements
such as cobalt, molybdenum and vanadium (Figure 4),
which are present in the microstructure due to the steel.
These elements form carbides, e.g., based on Mo of the
M
6
C type, based on Cr of the M
23
C
6
type, and based on
V of the MC type. These carbides can further inhibit the
formation of a reaction layer and the diffusion of ele-
ments through this layer.
11
The silicon content in this
layer increases from the aluminium alloy towards the
tool steel, while the iron content increases and the alu-
minium content decreases (Figures 3a and 5a). This is
followed by the so-called composite layer, which is
formed by an intermetallic phase based on Al
3
Fe (site 5)
and is much thicker. The analysis sites 1 and 2 in Fig-
ure 3a confirm the composition of the tool steel H11.
M. VON^INA et al.: INFLUENCE OF TEMPERATURE ON THE INTERACTION KINETICS BETWEEN MOLTEN ALUMINIUM ...
404 Materiali in tehnologije / Materials and technology 57 (2023) 4, 401–405
Figure 4: SEM (SEI) micrographs of the transitions between the intermetallic layer and the tool steel of samples tested at: a) 670 °C and b)
700 °C. The corresponding EDS results are given in at. %.
Figure 5: EDS line-scan analyses across the interface between tool-steel H11 and Al99.7 aluminium alloy tested at: a) 670 °C and b) 700 °C

Sites marked 6 and 8 represent the region of primary
 -Al in the presence of iron phases (Al
3
Fe), which dis-
solve in the molten aluminium. A similar phenomenon is
observed in the sample tested at 700 °C (Figure 3b): tool
steel (sites 1 and 2), intermetallic layer Al
5
Fe
2
(sites 3-5),
composite layer Al
3
Fe (sometimes written as Al
13
Fe
4
)
(site 6), and aluminium alloy in which iron dissolves in
the form of the Al
13
Fe
4
phase (sites 8 and 9).
4 CONCLUSIONS
Even very small temperature changes, in this case
30 °C, significantly affect the kinetics of the formation
of interaction layers between the tool-steel H11 and mol-
ten aluminium Al99.7. All the test methods show a pro-
nounced influence of the test temperature. From the DSC
curve, a significantly faster dissolution can be seen, with
the slope of the curve being larger for the sample tested
at 700 °C, which was also confirmed by measurements
of the thicknesses of the interaction layers. The thickness
of the intermetallic layer is 520 μm for the sample tested
at 700 °C and 420 μm for the sample tested at 670 °C.
The thickness of the composite layer is about 130 μm in
both cases, which is not affected by the temperature. The
types of interaction layers do not differ from each other.
An intermetallic layer based on the Al
5
Fe
2
phase, which
is thicker, always forms next to the tool steel H11, and a
composite layer based on the Al
3
Fe phase always forms
next to the aluminium alloy.
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