1
Original Scientific Article • DOI: 10.2478/rmzmag-2021-0006 Received: October 21, 2021
 Accepted: November 26, 2021
Determination of material quality by methods of  
thermal analysis
Ugotavljanje kakovosti materiala z metodami termične analize
Maja Vončina
1,
*, Gregor Hvala
1
, Jožef Medved
1
, Borut Žužek
2
,
 
Mitja Petrič
1
1
University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Materials and Metallurgy, Ljubljana, Slovenia
2
Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
*Corresponding author: E-mail: maja.voncina@ntf.uni-lj.si
Abstract in English
Cast aluminium alloys are commonly used in the 
 automotive industry for casting applications. There are 
both primary and secondary/recycled aluminium alloys 
in the market, which differ in price and quality. In this 
study, the effect of alloy quality on  solidification, micro-
structure and mechanical properties was  investigated. 
The comparison of properties was  carried out in the as-
cast condition and in the heat-treated condition. The in-
fluence of alloy quality on solidification was analysed by 
simple thermal analysis and  differential scanning calo-
rimetry, and thermodynamic simulations. The basic me-
chanical properties analysed were  tensile strength, yield 
strength, elongation, and hardness. The microstructural 
differences were  analysed using a light  microscope. The 
Mn:Fe ratio, which is strongly influenced by the alloy qual-
ity, was found to have a pronounced effect on the mechan-
ical properties, while magnesium together with silicon 
hardens the  aluminium matrix during heat treatment, 
which significantly increases the mechanical  properties.
This research proved that thermal analysis methods 
can give us a necessary and important indication of the 
quality of the alloys used.
Keywords: Alloy quality, casting alloys, thermal 
analysis, solidification, microstructure, mechanical 
 pr operties
Povzetek
Aluminijeve zlitine se pogosto uporabljajo v 
 avtomobilski industriji pri vlivanju. Na trgu obsta-
jajo primarne in sekundarne/reciklirane alumini-
jeve  zlitine, ki se razlikujejo po ceni in kakovosti. V 
tej  študiji je bil raziskan vpliv kakovosti zlitine na 
 strjevanje, mikrostrukturo in mehanske lastnosti. Pri-
merjava lastnosti je bila narejena v litem in v toplotno 
 obdelanem stanju. Vpliv kakovosti zlitine na strjevanje 
smo  analizirali z enostavno termično analizo in dife-
renčno vrstično kalorimetrijo ter termodinamičnimi 
simulacijami. Analizirane so bile osnovne mehanske 
lastnosti, kot so natezna trdnost, meja tečenja, razte-
zek in trdota. Mikrostrukturne razlike smo analizirali 
z optičnim mikroskopom. Dokazano je, da razmerje 
Mn:Fe, na  katerega močno vpliva kakovost zlitine, iz-
razito vpliva na mehanske lastnosti, medtem ko ma-
gnezij skupaj s silicijem med toplotno obdelavo utrjuje 
aluminijasto matrico, kar tudi bistveno poveča mehan-
ske lastnosti.
V tej raziskavi je bilo dokazano, da nam lahko metode 
termične analize dajo potreben in pomemben podatek 
o kakovosti uporabljenih zlitin.
Ključne besede: kakovost zlitin, livarske zlitine, ter-
mična analiza, strjevanje, mikrostruktura, mehanske 
lastnosti
Introduction
One of the few disadvantages of aluminium is 
its expensive and energy-intensive extraction. 
It is mainly extracted from bauxite ore by the 
Bayer process. This produces alumina (Al
2
O
3
), 
from which technically pure aluminium is later 
extracted by electrolysis. An alternative to this 
extraction method is secondary extraction, that 
is, recycling, which requires only about 10% of 
the energy needed to produce one tonne of pri-
mary aluminium. The disadvantage of recycling 

Vončina et al.
2
RMZ – M&G | 2022 | Vol. 68[2] | pp. 1–9
proportion and ratio of these phases depend 
on the ratio of manganese and iron in the  
alloy [5, 6, 7].
Strength properties increase significantly af-
ter heat treatment compared to as-cast condi-
tion. The elongation at yield strength decreases. 
Compared to alloys with different iron contents, 
the solidification rate has a great influence. The 
hardness is higher in the secondary alloy due to 
the higher iron content [3, 4, 8, 9].
Inferior alloys may contain up to twice as 
much iron. Two Fe-phases form in cast alumin-
ium alloys, namely, α-Al
15
(Fe,Mn)
3
Si
2
 and β-Al-
5
FeSi. The former is more desirable due to its 
rounded shape in the microstructure, as it does 
not adversely affect the mechanical properties 
like β-Al
5
FeSi. Therefore, manganese is add-
ed to the alloys to convert the needles of the 
β-Fe
5
FeSi phase to the α-Al
15
(Fe,Mn)
3
Si
2
 phase. 
The optimum Mn:Fe ratio in the alloys was 
found to be about 0.5 [10].
Materials and methods
Based on the chemical composition of the 
studied alloys, listed in Table 1, a simulation 
of Scheil’s thermodynamic non-equilibrium 
solidification was performed, using Thermo-
Calc software and the TCAL6 database. Alloy 
AlSi10Mg is marked as 239, with better and 
purer quality, and alloy AlSi10Mg(Fe) as 239D, 
of inferior quality.
To characterize the solidification path of 
two alloys under investigation, the samples 
were melted in an induction furnace in a steel 
crucible coated with BN-foundry coating. The 
experimental alloy was preheated to 700 °C. 
After completion of the melting process, the 
experimental samples were then cast at a tem-
perature of 700 °C in a Croning measuring cell, 
where the cooling rate was ~ 7 K/s and cool-
ing curves were recorded. To characterize the 
accurate solidification of the test alloys, cor-
responding initial derivatives were obtained 
from the cooling curves. At the same time, the 
melt was also poured into a square steel mould 
(Figure 1), from which four specimens were 
obtained for the tensile tests. 
Differential scanning calorimetry (DSC) 
analyses were also carried out to determine the 
is the slightly higher content of some elements, 
the removal of which is extremely difficult or 
inadvisable. One such element is iron, which is 
otherwise required in the die casting of alumin-
ium alloys because it prevents the castings from 
soldering to the tool. However , too much iron can 
deteriorate the alloy’s mechanical properties.
The addition of magnesium to Al-Si alloys is 
the basis for the group of alloys characterized 
by exceptional castability and excellent me-
chanical properties after heat treatment. They 
are corrosion resistant and thermal expansion 
is low. Magnesium is added to binary alloys to 
improve the properties after heat treatment 
T6, which is characteristic of this type of alloy, 
through the mechanism of precipitation hard-
ening. The heat treatment consists of solu-
tion annealing, quenching, and artificial ag-
ing, during which the hardening intermetallic 
phase Mg
2
Si precipitates. The mechanical prop-
erties can be further improved by the addition 
of manganese and beryllium, which affect the 
morphology of the iron-based phases, improv-
ing the strength properties and ductility [1, 2]. 
The best effect of magnesium addition is seen 
at a content between 0.2 and 0.6% by weight, 
very rarely exceeding 1% by weight. The lower 
limit is determined by a sufficient amount for 
precipitation of the Mg
2
Si phase, so that the ef-
fect on the mechanical properties is noticeable. 
The upper limit is determined by a still satis-
factory plasticity; there should not be too much 
Mg
2
Si phase in the microstructure. The mag-
nesium content has a great influence on aging, 
so that the permissible limits in the individual 
alloys are very narrow. They also depend very 
much on the other alloying elements and the 
expected aging regime of the alloy [3, 4].
Solidification of AlSi10Mg and AlSi10Mg(Fe) 
alloys depends largely on the cooling rate and 
alloying elements, and usually begins in the 
temperature range between 550 °C and 600 °C. 
Solidification of this type proceeds as  follows: 
First, the primary aluminium α-Al crystals 
solidify at T
L
. Further eutectic (α-Al + β-Si) 
is formed, meanwhile, the remaining melt is 
 enriched with the other elements, leading to 
the formation of different intermetallic phases.  
The first to solidify are the Fe-phases 
α-Al
15
(Fe,Mn)
3
Si
2
 and β-Al
5
FeSi, and among 
the latter, the Mg-phase Mg
2
Si solidifies. The 

Determination of material quality by methods of thermal analysis
3
temperature changes and thermal effects occurring 
during heating / melting and cooling /  solidification 
of the alloys studied. The experiments were car-
ried out using a STA Jupiter 449C instrument from 
Netzsch by placing two identical corundum cruci-
bles on the platinum sensor. The sample under 
investigation was placed in one crucible and an 
(inert) reference sample in the other. The sys-
tem was heated to 720 °C in a furnace accord-
ing to the preprogrammed temperature pro-
gramme. It was kept at this temperature for 10 
minutes. The heating and cooling phases were 
performed at a constant rate of 10 K / min. The 
test was performed in a protective atmosphere 
of Ar 6.0. During the measurement, the instru-
ment recorded the temperature, the tempera-
ture difference between the tested sample and 
the reference sample, and the time. DSC analy-
sis was performed on cast samples taken from 
the centre of the casting from Croning mea-
surement cell [11]. The samples were turned to 
Table 1: Chemical composition of the alloys investigated in % by weight.
Sample Si Fe Cu Mn Mg Ni
239 10.398 0.3548 0.005 0.2654 0.5513 0.0038
239D 10.439 0.8788 0.0229 0.3092 0.4459 0.0062
Sample Zn Pb Sn Ti Sr Al Mn:Fe
239 0.0039 0.001 0.0003 0.0983 0.0369 rest 0.748
239D 0.0167 0.001 0.0004 0.0253 0.0015 rest 0.352
a diameter of 4.5 mm and a height of 4 mm and 
inserted into the instrument where the analysis 
was performed. After the measurements, the 
heating and cooling curves of the DSC were re-
corded, while the characteristic temperatures 
were determined from the heating and cooling 
curves of the DSC.
Specimens for microstructure investigations 
were prepared metallographically from the 
center of the casting from the Croning mea-
suring cell [11] and photographed with a BX61 
light microscope to analyze the effect of alloy 
quality on the formation and distribution of mi-
crostructural constituents. 
Specimens of B 6 x 30 mm type were used 
for the tensile test, prepared according to DIN 
50125: 2016-12. Four specimens of each test 
alloy were prepared in as-cast and T6 heat- 
treated condition. Tensile tests were carried 
out on INSTRON 8802 apparatus in accordance 
with SIST EN ISO 6892-1:2020 A224 standard. 
Figure 1: (a) Steel mould with a square profile; (b) Casting obtained from the steel mould for tensile specimens.

Vončina et al.
4
RMZ – M&G | 2022 | Vol. 68[2] | pp. 1–9
To analyse the hardness of two grades of al-
loy in the as-cast and heat-treated condition, the 
instrument NEXUS 7500 was used and the mea-
surements were made in accordance with the 
standard SIST EN ISO 6506 - 1: 2014. A tungsten 
carbide ball with an HBW of 2.5 / 62.5 was used. 
Hardness measurements were carried out on 
specimens from a square-profile steel mould.
Results and discussion
Figure 1a shows the calculated cooling curve 
of sample 239 and Figure 2b shows the calcu-
lated cooling curve of sample 239D, where the 
dashed line indicates the equilibrium solidifica-
tion. The results show that in sample 239 both 
Fe-phases solidify after the primary α-Al crystals 
and eutectic (α-Al + β-Si). It does not end with 
the Fe-phase β-Al
5
FeSi; the phases π-Al
8
Si
6
Mg
3
Fe 
and Mg
2
Si also solidify from the melt. The main 
difference between the investigated alloys is 
that at the alloy 239D the solidification of both 
Fe-phases occurs before the solidification of 
eutectic (α-Al + β-Si), whereas also the amount 
of those phases is much higher, respectively. The 
solidus temperature T
S
 is 554.7 °C for sample 
239 and 555.1 °C for sample 239D.
The main difference between the sam-
ples / alloys in solidification, calculated with 
the Thermo-Calc program, is seen in the 
sonification path and proportions of each phase 
(Table 2). The calculated amount of Fe-phase 
α-Al
15
(Fe,Mn)
3
Si
2
 in sample 239D is about twice 
that in sample 239, and an even greater differ-
ence occurs for the β-Al
5
FeSi phase; it is up to 
150% higher than in sample 239.
The cooling curves in Figure 3 show that the 
T
L 
in sample 239 is higher and the solidification 
interval is wider , which is consistent with Scheil’s 
non-equilibrium solidification curve. This is fol-
lowed by the solidification of the Fe-phases, the 
onset of which is indicated by T
1
. This was de-
termined from the derivative where the cooling 
rate is high, followed by a drop in the cooling rate 
due to the release of latent heat. This is followed 
by solidification of the eutectic with Fe-phases, 
namely α-Al
15
(Fe,Mn)
3
Si
2
 and / or β-Al
5
FeSi. 
Undercooling after the onset of eutectic solidifi-
cation is illustrated by the temperature T
E/min
, la-
tent heat is released by the solidification and the 
temperature increases to T
E/max
. The solidifica-
tion proceeds in the same way until the tempera-
ture T
2
, which was observed only for sample 239. 
Using calculations with Thermo-Calc, the eutectic 
solidification of the π-Al
8
Si
6
Mg
3
Fe phase can be 
predicted. The point T
3
 represents the beginning 
of the solidification of the Mg
2
Si eutectic phase. 
The final solidification temperatures ( solidus 
temperatures) are much lower than those theo-
retically determined by the Scheil  simulation of 
non-equilibrium solidification.
Figure 2: The Scheil cooling curve of the non-equilibrium solidification of (a) sample 239 and (b) sample 239D.

Determination of material quality by methods of thermal analysis
5
0.0229 wt%). The second inflexion point rep-
resents T
S
 (239: 552.2 °C; 239D: 551.2 °C) and illus -
trates the onset of eutectic melting (α-Al + β-Si) with 
the Mg
2
Si phase present. According to Thermo-Calc 
calculations, the next characteristic point (239: 
565.5 °C; 239D: 563.7 °C) defines the melting of the 
eutectic (α-Al + β-Si) and the last characteristic tem -
perature (239: 608.1 °C; 239D: 605.0 °C) represents 
the melting of the primary α-Al dendrites. On the 
cooling curves (blue), the first characteristic point 
is T
L
 (239: 575.5 °C; 239D: 569.4 °C), where the 
solidification of the primary α-Al dendrites begin. 
According to Thermo-Calc calculations, the next 
inflexion point is the solidification temperature of 
the eutectic (α-Al + β-Si) and the last one is the 
solidification of the eutectic (α-Al + β-Si + Mg
2
Si) 
(239: 522.1 °C; 239D: 521.8 °C). In sample 239D, 
another inflexion point occurs at 544.3 °C, which 
most likely represents the eutectic solidification 
of the Fe-phases.
Table 2: The proportions of phase formed during the 
solidification.
Phase / Sample
239 239D
α-Al 87.00 85.20
β-Si (eutectic) 9.91 9.74
α-Al
15
(Fe,Mn)
3
Si
2
0.89 1.03
β-Al
5
FeSi 1.31 3.26
Mg
2
Si 0.86 0.65
Q-Al
5
Cu
2
Mg
8
Si
6
0.02 0.11
Figure 3: The cooling curve and corresponding derivative of (a) sample 239 and (b) sample 239D.
Figure 4: Heating (green) and cooling (blue) DSC curve of the sample (a) 239 and (b) 239D.
The results of the DSC analysis are shown in 
Figure 4 and show both the heating (green) and 
cooling (blue) curves for both samples tested. In 
both figures, the first inflexion point is at about 
220 °C and can be associated with the precipita-
tion of the Q-Al
5
Cu
2
Mg
8
Si
6
 or Mg
2
Si phase; a later 
point is not possible due to the very low copper 
content in the samples (239: 0.005 wt%; 239D: 

Vončina et al.
6
RMZ – M&G | 2022 | Vol. 68[2] | pp. 1–9
Figure 5: Micrographs of (a and b) sample 239 and (c and d) sample 239D.
A light microscope was used to image the mi-
crostructure of all samples at various magnifica-
tions. Figures 5a and b show the microstructure of 
sample 239, while Figures 5c and d show sample 
239D. According to the literature, the following 
microstructural components are observed in the 
microstructures in the figure: primary α-Al den-
drites, binary eutectic (α-Al + β-Si), Fe-eutectic 
phase α-Al
15
(Fe,Mn)
3
Si
2
 (‘Chinese script’), needle 
shape β-Al
5
FeSi phase, and the eutectic phase of 
Mg
2
Si (black) [5]. Due to the presence of magne -
sium, the formation of the π-Al
8
FeMg
3
Si
6
 phase is 
also possible [12]. Given the presence of stron-
tium in the chemical composition of sample 239, 
the formation of the Al
2
SrSi
2
 phase can also be 
inferred [13]. The black arrows in Figures 5a 
and c indicate the deleterious β-Al
5
FeSi phases, 
which are hardly observed in the microstructure 
of sample 239, while they are common in the mi-
crostructure of sample 239D. In sample 239, the 
eutectic (α-Al + β-Si) is much finer and rounder, 
which is due to the presence of strontium acting 
as a modifier of the eutectic β-Si.
Figures 6a and b show the microstructures 
of the as-cast and heat-treated sample 239 
(239 and 239T). Figures 6c and d show the 
microstructures of the cast and heat-treated 
sample 239D (239D and 239DT). It can be 
observed that there is a visible decrease in 
the primary α-Al, according to the litera -
ture. A decrease in the eutectic (α-Al + β-Si) 
is observed especially for sample 239DT . As 
in the as-cast condition, the density of the  
β-Al
5
FeSi phases in the heat-treated condi-
tion is much higher in the secondary alloy 
(239DT). After heat treatment, the thicker 
needles are rounded.
Figure 7 shows a comparison of the average 
hardness values between the qualities of alloys 
in the as-cast samples and after heat treatment. 
It can be seen that the hardness of sample 239 
increases by ~ 28% and that of 239D alloy in-
creases by ~ 42% after heat treatment. In gen-
eral, the hardness of the as-cast sample 239D is 
~ 6% higher than that of the purer alloy, and af-
ter heat treatment it is ~ 24% higher than that 
of the purer 239 sample.
Figure 8 shows a comparison of tensile test 
results between qualities of alloy and between 
the as-cast and heat-treated states. For better 
quality alloy, tensile strength and yield strength 
are increased by heat treatment, while elonga-
tion is greatly reduced by heat treatment. The 
alloy produced from secondary raw materials 

Determination of material quality by methods of thermal analysis
7
Figure 6: Micrographs of sample 239 in (a) as-cast state and (b) T6 heat-treated state and of sample 239D (c) in as-cast state and 
(d) T6 heat-treated state.
Figure 7: Hardness of AlSi10Mg alloy and AlSi10Mg(Fe) alloy in as-cast state and after heat treatment.

Vončina et al.
8
RMZ – M&G | 2022 | Vol. 68[2] | pp. 1–9
has significantly lower mechanical property 
values in the as-cast condition, and after heat 
treatment the material was so brittle that the 
mechanical properties could not be measured.
Conclusion
Thermal analysis methods can give us an 
important and necessary indication of the qual-
ity of the alloys used.
Recycling aluminium is the future from an 
energy point of view. Therefore, it is important 
to produce high quality alloys from secondary 
raw materials that can replace those produced 
from primary aluminium.
The deleterious β-Al
5
FeSi phases were hard-
ly observed in the microstructure of the purer 
sample, while they are common in the micro-
structure of inferior quality sample. A visible 
decrease in the primary α-Al and in the eutectic 
(α-Al + β-Si) was observed, especially for sam-
ples of inferior quality after heat treatment. 
As in the as-cast condition, the density of the  
β-Al
5
FeSi phases in the heat-treated condition is 
much higher in the alloy of inferior quality. After 
heat treatment, the thicker needles are rounded. 
In general, the hardness of the as-cast sample 
of inferior quality was ~ 6% higher than that of 
the purer alloy and after heat treatment was ~ 
24% higher than that of the purer sample. For 
better quality alloy, tensile strength and yield 
strength are increased by heat treatment, while 
elongation is greatly reduced by heat treatment. 
The alloy produced from secondary raw materi-
als has significantly lower mechanical property 
values in the as-cast condition.
The analysis of the effects of alloy quality 
of primary and secondary produced AlSi10Mg 
 alloys on solidification, microstructure and 
 mechanical properties revealed significant dif-
ferences in the results of the analysed proper-
ties. Based on the results, we can predict when it 
is appropriate to use a primary produced  alloy 
with higher purity and when to use a  secondary 
produced alloy with more and  higher concen-
tration of alloying elements. 
Acknowledgement
The work was co-financed by the Republic of 
Slovenia, the Ministry of Education, Science 
and Sport, and the European Regional 
Figure 8: Tensile test results for 239 alloys and 239D alloys in the as-cast state and after heat treatment.

Determination of material quality by methods of thermal analysis
9
Development Fund. The work was carried 
out in the framework of the project Modelling 
of Thermomechanical Processing of the 
Aluminium Alloys for High Quality Products 
(MARTIN, Grant No.: C3330-18-952012).
References
 [1] Yildirim, M., Özyürek, D. (2013): The effects of Mg 
amount on the microstructure and mechanical prop-
erties of Al-Si-Mg alloys. Materials & Design, 51,  
pp. 767-774, DOI:10.1016/j.matdes.2013.04.089.
 [2] Kaufman, J.G., Rooy, E.L. (2004): Aluminium alloy 
castings: Properties, processes, and aplications.  
ASM International, 340 p. 
 [3] SS-EN 1676:2010. Aluminium and aluminium alloys 
- Alloyed ingots for remelting – Specifications [cited 
20/10/2020]. Available on: https://www.stenaalu-
minium.com/siteassets/document/product-sheets/
eng-en-ab-43400.pdf.
 [4] Raffmetal the Aluminium Evolution. Continuous 
casting alloys: EN AB 43000 AlSi10Mg(Fe) alloy [cited 
11/7/2020]. Available on: https://www.raffmetal.com/
web_eng/prodotti.asp?q=1.
 [5] Vončina, M., Medved, J., Mrvar, P . (2005): 
Thermodynamic analysis of MgSi10Mg alloy. RMZ – 
Materials and Geoenvironment, 52(3), pp. 621–633.
 [6] Que, Z., Wang, Y., Fan, Z. (2018): Formation of the 
Fe-containing intermetallic compounds during solid-
ification of Al5Mg2Si0.7Mn1.1 Alloy. Metallurgical 
and Materials Transactions A, 49, pp. 2173–2181, 
DOI: 10.1007/s11661-018-4591-6.
 [7] Ravi, M., Mech, K., Sasidharan, V., et al. (2014): 
Influence of alloying elements and casting process 
on the mechanical properties of al-si piston alloy. 
National conference on advances in materials and 
advances in bioprocess engineering. At: Mohandas 
College of Engineering and technology.
 [8] Girelli, L., Tocci, M., Gelfi, M., Pola, A. (2019): Study of 
heat treatment parameters for additively manufac-
tured AlSi10Mg in comparison with corresponding 
cast alloy. Materials Science & Engineering A, 739, 
 pp. 317–328, DOI: 10.1016/j.msea.2018.10.026.
 [9] Zyguła, K., Nosek, B., Pasowiec, H., Szysiak, N. 
(2018): Mechanical properties and microstructure 
of AlSi10Mg alloy obtained by casting and SLM tech-
nique. World Scientific News, 104, pp. 462–472,  
DOI: 10.1007/s12633-021-01340-9.
 [10] Bäckerud, L., Chai, G., Tamminen, J. (1990): 
Solidification characteristics of aluminium alloys. 
Volume 2, foundry alloys. AFS/SKANALUMINIUM: 
Stockholm, 266 p.
 [11] Medved, J., Kores, S., Balaško, T ., Vončina, M. (2019): 
Influence of minor alloying element addition on alumin-
ium casting alloys, Livarski vestnik, 66(3), pp. 191-202.
 [12] Vončina, M., Medved, J., Kores, S., Xie, P ., Schumacher, 
P ., Li, J. (2013): Precipitation microstructure in 
Al-Si-Mg-Mn alloy with Zr additions. Materials 
characterization, 155, 8 p., DOI: 10.1016/j.
matchar.2019.109820.
 [13] Petrič, M. (2013): Sprememba dimenzij in električne 
upornosti med strjevanjem litin iz sistema Al-Si. Ph. D. 
Thesis. University of Ljubljana, Faculty of Natural 
Sciences and Engineering, Department of Materials 
and Metallurgy: Ljubljana, 138 p.