Aluminium Casting Alloys - Aleris

Criteria for the selection of
aluminium casting alloys
In the following section, we provide an
insight into the chemical and physical
potentials of aluminium casting alloys by
describing their various properties. The
standardisation provided here helps to
establish whether a casting alloy is suitable
for the specifi c demands placed
on a casting.
Degree of purity
One important selection criteria is the de-
gree of purity of a casting alloy. With the
increasing purity of a casting alloy family,
the corrosion resistance and ductility of
the as-cast structure also increase; the
selection of pure feedstock for making
casting alloys, however, will necessarily
cause costs to rise.
The increasing importance of the closedcircuit
economy means that, for the producer
of aluminium casting alloys, the
transition between the previous quality
grades for aluminium casting alloys is
becoming ever more fl uid.
Due to their high purity, casting alloys
made from primary aluminium display the
best corrosion resistance as well as high
ductility. By way of example, Silumin-Beta
with max. 0.15 % Fe, max. 0.03 % Cu
and max. 0.07 % Zn can be mentioned.
In many countries, the Silumin trademark
has already become a synonym for aluminium-silicon
casting alloys.
14
Aluminium Casting Alloys
Classifi cation of casting alloys acc. to strength properties 1)
Table 1
Casting alloy Temper Tensile Elongation Brinell
strength hardness
Rm [MPa]
A5 [%] HB
Strong Al Cu4Ti T6 330 7 95
and ductile Silumin-Beta T6 290 4 90
Al Si10Mg(a) T6 260 1 90
Hard Al Si8Cu3 F 170 1 75
Al Si18CuNiMg F 180 1 90
Ductile Silumin F 170 7 45
Other Al Mg3 F 150 5 50
1) Typical values for permanent mould casting,
established on separately-cast test bars.
Casting alloys made from scrap are,
with regard to ductility and corrosion
resistance, inferior to other casting alloy
groups due to their lower purity. They are,
however, widely applicable and meet the
set performance requirements.
Strength properties
Strength properties should be discussed
as a further selection criterion (Table 1).
A rough subdivision into four groups is
practical:
“strong and ductile”
The most important age-hardenable
casting alloys belong to this group. By
means of different kinds of heat treatment,
their properties can be adjusted
either in favour of high tensile strength
or high elongation. In Table 1, the typical
combinations of R and A values for
m
different casting alloys are compared.
These casting alloys are used for highgrade
construction components, especially
for critical parts.
“hard”
The casting alloys of this group must
display a certain tensile strength and
hardness without particular requirements
being placed on the metal‘s elongation.
First of all, Al SiCu alloys belong to this
group. Due to their Cu, Mg and Zn content,
these casting alloys experience a
certain amount of self-hardening after
casting (approx. 1 week). These alloys
are particularly important for pressure
die casting since it is in pressure die
casting – except for special processes
such as vacuum die casting – that process-induced
structural defects occur,
preventing high elongation values. Due
to its particularly strong self-hardening
characteristics, the Autodur casting al-