13
 Open Access. © 2020 Zeka B., Markoli B., Mrvar P., Leskovar B., Petrič M., published by Sciendo.  This work is licensed 
under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. 
Received: Feb 28, 2020 
Accepted: Mar 20, 2020
 DOI: 10.2478/rmzmag-2020-0005 
Original scientific paper 
Abstract 
Lithium additions to Al offer the promise of sub-
stantially reducing the weight of alloys, since each 
1 wt. % Li added to Al reduces density by 3 % and in-
creases elastic modulus. In the present work, the ef-
fect of 1.46 wt. % Li addition to AlSi7Mg (containing 
7.05 wt. % Si and 0.35 wt. % Mg) was studied. The al-
loy showed reduced density and higher hardness after 
natural ageing. Experimental work showed that micro-
structural and mechanical properties changed with Li 
addition. It was observed that 0.80 wt. % Li addition 
resulted in formation of new phase AlLiSi which has 
a great effect to increase hardness of AlSi7Mg. Accord-
ing to Scanning Electron Microscope (SEM) and X-ray 
diffraction analysis it was confirmed that the addition 
of Li causes formation of different phases which are: 
α-Al, β-Si and AlLiSi.
Key words: aluminium, ageing, microstructural consti-
tuents, precipitation, mechanical properties.
Production and Investigation of New Cast Aluminium 
Alloy with Lithium Addition
Izdelava in preiskava nove livarske aluminijeve zlitine 
z dodatkom litija
Bastri Zeka, Boštjan Markoli, Primož Mrvar, Blaž Leskovar, Mitja Petrič*
University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Materials and Metallurgy, Aškerčeva 12, 
1000 Ljubljana, Slovenia
* mitja.petric@omm.ntf.uni-lj.si
Povzetek
Dodatki litija (Li) aluminijevim zlitinam prispevajo 
k bistvenemu zmanjšanju teže zlitin, saj vsak dodani 
odstotek litija zmanjša gostoto za 3 %. Litij tudi pov-
zroči povečanje elastičnega modula. V delu je preučen 
dodatek 1.46 mas. % litija livarski zlitini AlSi7Mg, ki 
vsebuje 7.05 mas. % Si in 0.35 mas.% Mg. Zlitina je po-
kazala zmanjšanje gostote in večjo trdoto po naravnem 
staranju. Rezultati so pokazali, da so se mikrostruk-
turne in mehanske lastnosti spreminjale z dodatkom 
Li. Izkazalo se je, da dodatek 0.80 mas. % Li povzroči 
pojav nove faze AlLiSi, ki močno vpliva na povečanje tr-
dote AlSi7Mg. Glede na rezultate vrstične elektronske 
mikroskopije (SEM) rentgensko difrakcijsko analizo 
(XRD) je bilo potrjeno, da dodatek Li povzroči nastanek 
različnih faz, ki so: α-Al, β-Si in AlLiSi.
Ključne besede: aluminij, staranje, mikrostrukturne 
sestavine, precipitacija, mehanske lastnosti.

Zeka B., Markoli B., Mrvar P ., Leskovar B., Petrič M. RMZ – M&G | 2020 | Vol. 67 | pp. 013–020
14
Introduction
Al-Li base alloys have low density, high elastic 
modulus and high strength properties which 
make these alloys attractive for aerospace ap-
plications. The high strength is produced by the 
process of precipitation hardening. The addi-
tion of elements can form incoherent disper-
soid or semicoherent precipitates and change 
the microstructure and mechanical properties 
of alloys [1–5]. Al-Li alloys use in aircraft appli-
cations, where the weight savings effected by 
using these low-density alloys greatly reduce 
the vehicle fuel costs and increase performance 
of parts such as: Aircraft parts such as leading 
and trailing edges, access covers, seat tracks; 
military and space applications such as main 
wing box, centre fuselage, control surfaces are 
made by Al-Li alloys. Al-Li alloys are used as 
substitute for conventional aluminium alloys in 
helicopters, rockets and satellite systems [5–8].
The precipitates of Al-Li alloys are in sever-
al metastable and stable phases which can be 
present in Al-Li alloys, depending on the alloy-
ing elements. The metastable precipitates in 
this section are δ’ (Al
3
Li), while the stable phase 
discussed is δ (AlLi) [8]. The precipitation, in 
turn, depends upon chemistry, grain structure, 
and total thermomechanical history. In Al-Li al-
loys, the strengthening from Li additions is due 
to both solid solution strengthening and pre-
cipitation hardening [1–20]. The precipitation 
hardening is primarily due to the metastable 
strengthening phase, δ’ (Al
3
Li), which forms 
spherical, coherent, and ordered precipitate 
particles having a cube-on-cube orientation re-
lationship with the aluminium matrix [20–25]. 
At equilibrium, and at its simplest in binary 
Al-Li alloys, the only phases present are the 
aluminium-rich solid solution and the δ (AlLi) 
phase [25–30]. 
New aluminium cast alloy was produced and 
analysed with Li additions based on AlSi7Mg 
alloy with improved mechanical properties 
where characterisation of solidification path 
was determined with all microstructural con-
stituents. In order to develop new alloys with 
Li addition was used an optic microscope and 
Scanning electron microscopy (SEM) Thermal 
analysis and differential scanning calorimetry 
in accordance with thermodynamic equilib-
rium calculations were used to determine the 
solidification course. Also, XRD analyses and 
mechanical testing (hardness testing,) were 
performed. 
Experimental Work
New aluminium cast alloy AlSi7MgLi was in-
vestigated experimentally. The thermodynamic 
calculations were performed with ThermoCalc 
software and the chemical compositions of al-
loys given in Table 1 were used in order to cal-
culate phase diagrams of alloys. Samples were 
melted in an induction furnace in a graphite 
crucible and cast in a steel mould where sim-
ple thermal analysis was performed. After data 
acquisition their numerical data, cooling curves 
and their derivatives were plotted and charac-
teristic temperatures determined. Differential 
scanning calorimetry was performed, and sam-
ple prepared for microstructural investigation 
with optic microscope and scanning electron 
microscope with EDS in order to determine the 
phases present in alloy AlSi7Mg. Vickers Hard-
ness test was used to determine mechanical 
properties in period of 30 days after casting.
Results and Discussion
Thermodynamic description of system Al-
Si7MgLi cast alloys was constructed using 
ThermoCalc software. From the chemical 
composition in Table 1 the solidification and 
equilibrium phases were calculated for exper-
imental alloy. According to the thermodynamic 
equilibrium calculation we have predicted so-
lidification of the primary α-Al, β-Si, new phases 
(AlLiSi), Mg
2
Si, iron bearing phase π- AlMgFeSi 
and β-AlFeSi.
Table 1: Chemical composition of alloy in wt. %.
Alloy Al Si Fe Cu Mg Zn Ti Li
AlSi7Mg Rest 6.7 0.44 0.01 0.35 0.01 0.01 -
AlSi7MgLi Rest 7.05 0.10 0.05 0.36 0.02 0.09 0.80

Production and Investigation of New Cast Aluminium Alloy with Lithium Addition
15
Thermal Analysis
Solidification process was analysed by thermal 
analysis on the samples cast in the steel mould 
and croning cell, each sample subjected to the 
solidification by cooling in the air. After the 
data acquisition their numerical and graphical 
processing with the marked temperatures of 
the phase transformations was performed. The 
cooling and differentiated curves of AlSi7Mg al-
loy with Li addition from casting temperature 
730 °C in steel mould are shown in Figure 2. Di-
agram with cooling curves in the Figure 2 indi-
cates interactive significant deviation in values 
of the characteristic temperatures of the solid-
ification, acording to calculation and diargram 
of cooling curves at 730 °C with solidification 
start phases at 658 °C. Solidification interval 
ended at 570 °C.
The heating curve indicates melting start at 
572 °C and the curve changes after 582.6 °C and 
continued with evaluation of phase at 644.1 °C, 
furthermore small peaks at 212 
o
C indicates 
precipitation process. Simultaneous thermal 
analysis was performed on the sample part 
from the sample poured in the steel mould, dif-
ferential scanning calorimetry (DSC) resulted 
in diagrams of the heating and cooling curves 
shown in the figure 3-a and 3-b. Diagrams in the 
Figure 3 resulted in values of significant tem-
peratures of the phase transformations. The 
temperature of the solidification start (liquidus 
temperature) at 659.8 °C with AlLiSi phase at 
620.6 °C, the α-Al+AlLiSi should solidify accord-
ing to thermocalc at 607.8 °C, followed by iron 
Figure 1: a) phase diagram of experimental alloy AlSi7MgLi 
and b) amount of phases of alloy during solidification.
Figure 2: The cooling curve and differentiated curves of 
AlSi7MgLi alloy.
Figure 3: Heating DSC curve (a) and cooling DSC curve (b) of 
AlSi7MgLi alloy.

Zeka B., Markoli B., Mrvar P ., Leskovar B., Petrič M. RMZ – M&G | 2020 | Vol. 67 | pp. 013–020
16
bearing phase β-AlFeSi at 565.2 °C, β-Si and 
Mg
2
Si at 547.7 °C.
Microstructure Analysis
After analysis of solidification by thermal anal-
ysis technique samples were prepared for me-
tallographic investigation. According to mi-
crographs the microstructure consists of α-Al 
phase, AlLiSi phase, π- AlMgFeSi phase, Mg
2
Si 
which they are confirmed by EDS and XRD anal-
ysis and they presented in Figure 4b, 4d, 4f and 
Figure 5. With SEM we observed phases which 
Figure 4: Optical (a, c, e) and SEM micrographs (b, d, f) of AlSi7MgLi.

Production and Investigation of New Cast Aluminium Alloy with Lithium Addition
17
they are formed with Li addition. From Figure 4 
it can be concluded that new phase AlLiSi ap-
pears. According to thermocalc calcalucaltion 
the elemental composition of phase present as-
cast state alloy the percentage of each element 
in the phase of AlLiSi is 33 wt %, after analy-
sis by SEM- EDS it was proved that AlSi contain 
lithium according to the thermodynamic calcu-
lation. Furthermore, microstructure in the alloy 
with Li addition consists from α-Al, β-AlFeSi, 
π- AlMgFeSi and Mg
2
Si. With XRD analysis we 
observed phases which they are formed with Li 
addition. From Figure 5 we confirm the forma-
tions of alpha α-Al, AlLiSi phases and β-Si. 
Mechanical Properties
The samples were age-hardened for 30 days 
where 8 micro hardness measurements were 
performed at room temperature and average 
values were calculated. 
Hardness test analysis for sample AlSi7Mg for 
first measurement was 66 HV. During 2–4 mea-
surements, values showed a linear increase of 
hardness from 66 HV-73 HV. It can be concluded 
that peak hardness was achieved after 7 days. 
Hardness test analysis for sample AlSi7MgLi 
showed the hardness for first day was 89 HV 
as cast state. After 24 hours of ageing, the hard-
ness of sample dropped until 87 HV. After 2 to 
7 days hardness of AlSi7MgLi alloy increased 
gradually from 87 HV to 96 HV where plateau 
is reached at 96 HV. It can be concluded that 
peak of hardness was achieved after 30 days 
at 102 HV. Our research showed that value of 
Figure 5: XRD pattern of AlSi7MgLi alloy.
Figure 6: presents graph of hardness for natural ageing of 
AlSi7Mg and AlSi7MgLi.

Zeka B., Markoli B., Mrvar P ., Leskovar B., Petrič M. RMZ – M&G | 2020 | Vol. 67 | pp. 013–020
18
hardness increased during 30 days of age-
ing time from 65–73 at AlSi7Mg whereas at 
AlSi7Mg with Li addition from 89–102 HV. Ac-
cording to results of both alloys, the Li addition 
to AlSi7Mg has great influence on increasing of 
hardness compared to AlSi7Mg.
Conclusion
New alloy with Li addition to AlSi7Mg alloy 
was studied. For this purpose 1.46 wt. % Li was 
added to designed AlSi7MgLi alloy containing 
0.36 wt. % Mg and 7.05 wt. % Si. It was found 
that Li combination with AlSi7Mg resulted on 
different solidification, development of new mi-
crostructure and creation of new phase AlLiSi. 
Li has influence to increase the mechanical 
properties in as cast state to AlSi7Mg. SEM/ EDS 
and XRD analysis revealed that the addition of 
Li promotes the formation of new phase α-Al, 
β-Si and AlLiSi.
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