Improved Properties of Aluminium Cast Alloys due to a Boron Grain

Improved Properties of Aluminium
Cast Alloys due to a Boron Grain
Refinement
IMPROVED PROPERTIES OF ALUMINIUM CAST
ALLOYS DUE TO A BORON GRAIN REFINEMENT
alloys including the microstructure advantages, the mechanical properties and the possible applications.
Dr. Andreas Kleine, Dr. Macel Rosefort,
Christina Matthies, Dr. Hubert Koch
TRIMET ALUMINIUM AG, Aluminiumallee 1,
45356 Essen, Germany
Improving component properties is the main aspect of alloy development. The focus of this work is improving the
mechanical properties by influencing the grain size and
increasing the heat conductivity. This gives better material
performance for all applications with local heat maxima.
Due to better heat conductivity the maximal temperature
will be lower. This yields better local mechanical properties. As a result of these facts the fatigue behaviour should
be increased.
A. Pithan
Honsel AG, Germany
Keywords: Aluminium, cast alloys, grain refinement, boron
Abstract
The TRIMET-Group provides the aluminium processing industry with primary metal, alloys, semi-finished products,
castings and recycling. It produces and supplies the most
diverse forms and alloys of aluminium –customized to the
users’ special needs. The approach of a strategic link of
stock-related know-how combined with long-standing
experience with the material aluminium has a prolonged
effect. Research and development are a very specific challenge for TRIMET due to the pressure to innovate to which
the automobile industry in particular is subject worldwide.
For this reason the development of new materials with
improved properties and process-engineering advances
were the focus of this project.
The targets of this project are to improve properties of
aluminium cast alloys. The basic concepts for improving
the mechanical properties were to refine the grain size
and to increase the heat conductivity. The latter gives better material performance for all applications with local
heat maxima. Due to better heat conductivity the maximal temperature will be lower. This yields better local mechanical properties.
Introduction
Usually a boron melt treatment is used for increasing the
electrical and heat conductivity, [1]. This effect is caused
by the removal of elements like titanium, zirconium etc.
Additionally boron should work as a grain refiner instead
of TiB2, [1], [2]. Hence a better grain structure with improved mechanical properties was expected.
Results
All castings, which were carried out for this investigation,
are separately casted test bars with the following parameters:
-
AlloyAlSi7Mg
- Mould material:
gray iron
- Mould temperature
370°C
- Melt temperature
700-720°C
- Cooling conditions
air cooling
- Heat treatment
T6
Stated below the outstanding results of this investigation
can be seen. The grain refinement of the boron addition
can be seen in FIG. 1. In comparison to the TiB2 refined
alloy the boron refined alloy yields a much finer grain
structure.
Therefore a melt treatment with boron was tested, which
provides two main effects:
- The removal of elements like titanium, zirconium etc.
yields a higher electrical conductivity and heat conductivity.
- Furthermore the boron can be used as a grain refiner
instead of TiB2 to get a better grain structure for improved mechanical properties.
Figure 1. Examples for the grain structure of an GK-AlSi7Mg T6 a) with
TiB2 grain refinement; b) with boron. All specimens are separately casted test bars.
This paper describes the development process, the experiments and the results from the laboratory examinations.
It gives an outlook on the potential of such aluminium
The optimized microstructure results in significantly better
mechanical properties. While the yield strength is nearly
the same, the UTS is increased. But the greatest effect
2
I M P R O V E D P R O P E R T I E S O F A L U M I N I U M C A S T A L L OY S D U E T O A B O R O N G R A I N R E F I N E M E N T
could be observed for the ductility. The doubling of the
elongation in comparison to the TiB2 refined material is a
great benefit for multiple applications.
TAB. 1. Mechanical properties and grain sizes of the investigated specimen. All data are average values.
Grain refinement
Yield strength
UTS
Elongation
MPa
MPa
%
Grain size
µm
TiB2
252
292
4,0
500
AlB2
250
315
8,4
250
The second main aspect in this investigation was to improve the conductivity. The well-known advantages of the
boron melt treatment could be confirmed, [1]. As well as
the electrical conductivity, the heat conductivity could also
be increased significantly, FIG. 2. For example the heat
conductivity is increased at RT from 178W/Km to 203W/
Km. This means an overall increase of more than 14%.
Conclusions
As predicted, the boron melt treatment yields great improvements in the conductivity. Additionally the boron in
the melt is an excellent grain refiner for example for AlSi7Mg. This results in an optimized microstructure therefore in improved mechanical properties. Especially the remarkable improvement of the elongation in combination
with the higher heat conductivity shows great promise for
a higher thermal fatigue resistance. Hence many applications in combustions engines, brakes and many other
components in different areas could be optimized by this
new material.
Figure 2. Improvement of the heat and electrical conductivity of the boron grain refined AlSi7Mg in comparison to the AlSi7Mg with TiB2.
References
[1]: G.K.Sigworth, M.M.Guzowski, „Kornfeinung untereutektischer AlSi-Gußlegierungen“, Gießerei-Praxis, Nr.5/1987, Fachverlag Schiele &
Schön GmbH, Berlin, 1987
[2]: E.Nachtigall, “Kornfeinung bei Aluminiumguß”, ALUMINIUM,
42.Jahrg. 1966 . 11, Fachzeitschrift der deutschen Aluminiumindustrie.
Hrsg. von der Aluminium-Zentrale, Düsseldorf, 1966
I M P R O V E D P R O P E R T I E S O F A L U M I N I U M C A S T A L L OY S D U E T O A B O R O N G R A I N R E F I N E M E N T
3
TRIMET ALUMINIUM AG • Aluminiumallee 1 • 45356 Essen
Telefon 0201-3660 • www.trimet.de