Optimizing the effect of tramp elements on intermetallic phases in HPDC Al alloys – A thermodynamic approach
Publicerad
Författare
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The growing interest in increasing the recycled content of aluminium for highpressure
die casting (HPDC) is driven by a demand for greater sustainability, as
recycled content offers a ∼nearly 95% reduction in energy compared to primary aluminium.
However, elevated levels of elemental contamination from recycled content,
mainly tramp elements such as iron (Fe) and manganese (Mn), pose significant challenges.
This thesis focuses on the thermodynamic analysis of the Al-Si-Fe-Mn system
with additions of magnesium (Mg) by using Thermo-Calc through CALPHAD-based
Scheil simulations at a high rate of 100 K/s, in conjunction with validation using
complementary microstructure analysis.
The simulations, comprising over 300 compositions, demonstrated a strong linear
correlation between increasing Fe content and the fraction of the β-Al5FeSi phase.
In contrast, increasing Mn content suppresses β phase formation by promoting the
more benign α-Al15(MnFe)3Si2 phase. Si notably altered the solidification range and
eutectic transitions within the system. Higher Mg levels led to phase competition
between π-AlFeMgSi and β phases. The potential evaporation of Mg was also found
to shift phase equilibria, increasing the fraction of β phase, emphasising the need
for accuracy control of alloy compositions.
Microstructure analysis, employing SEM and EDS on the cast alloys, shows that Fe
influences β-intermetallics, as it is composed of Fe instead of Mn. The analysis also
reveals compositional variations that influence kinetic effects, such as the formation
of the δ-AlFeSi phase and localised solute depletion zones around α-phase particles.
These findings clarify the effects of Fe, Mn, Si, and Mg on intermetallic phase formation
and emphasise the importance of integrating kinetic effects to contribute to
a more comprehensive understanding of optimising recycled aluminium alloys.
Beskrivning
Ämne/nyckelord
recycled aluminium, Scheil simulation, HPDC, Thermo-Calc, intermetallic phases, CALPHAD