HANDBUCH DER GUSSWERKSTOFFE - Honsel

out. The process also contributes to an increase in the
electrical conductivity.
Stabilization:
Age hardening and precipitation processes can still con -
tinue at high operating temperatures and lead to small
changes in volume which can for example cause distortion.
These processes are impeded by stabilization
annealing above the working temperature for several
hours, followed by cooling in air.
Stress relief annealing:
This is used for the elimination of internal stresses, which
for example occur with rapid cooling or after mechanical
machining. It is necessary to ensure a low cooling rate,
which is well achieved by cooling in the furnace.
Homogenisation:
This is used for the elimination of segregations and pre -
cipitations in castings. In accordance with their solubility
the phases occurring at the cell boundaries are either
dissolved in the crystal lattice or spheroidi zed. Al alloys
with a high Mg content are subjected to homogenisation
annealing and quenching in air.
MAGNESIUM
As with Al castings, heat treatment of Mg castings is
also used for increasing the mechanical properties,
reduction of internal stresses and stabilisation. How ever,
an increase in the mechanical properties is not always
based on classical solution annealing with quenching.
It sometimes involves precipitation treatments from
the as cast condition, which simultaneously produce a
reduction in the internal stresses.
Age hardening of the EN-MC 95320 alloy is produced
by solution treatment, quenching and artificially aging.
With the MgAlZn alloys preliminary annealing serves for
G-AlSi10Mg
Relationship between solution annealing period
and hardness
Brinell hardness HB
120
110
100
90
80
70
10 mm
50 mm
100 mm
sand casting
permanent mold casting
60
0 4 8 12 16 20
Solution annealing period in h
Reference: Aluminium Taschenbuch
G-AlSi10Mg
Age hardening behaviour
Brinell hardness HB
110
100
90
80
70
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the solution and spheroidization of specific intermetallic
phases and is equivalent to homogenization. Heat
treatment of the EN-MC 65110 alloy in creases the yield
strength, although it is only carried out for stress relieval
purposes.
For safety reasons, with treatments above 350°C pro -
tec tive gas (inert gas) is fed into the furnace in order to
prevent a fire hazard. This can for example be achieved
by the addition of pyrites to the furnace.
170∞C
60
225∞C
2 4 6 8 10 12
Artificially aging period in h
180∞C
200∞C
150∞C
Reference: Aluminium Taschenbuch
31