Aluminium Casting Alloys - Aleris

Microstructural formation in relation to
the content of phosphorous and sodium Al Si7Mg
Sodium Sand casting
[ppm]
140
cooling rate 0.1 K/s
120
100
80
60
40
20
0
Overmodifi ed
Granular
Modifi ed
Lamellar
can be omitted in the foundry. At low
cooling rates, strontium modifi cation is
less effective so that it is not advisable
to use this in sand casting processes.
To avoid the burn-off of strontium, any
cleaning and degassing of Sr-modifi ed
melts should be carried out with chlorine-
free preparations only, preferably using
argon or nitrogen. Strontium modifi cation
is not greatly impaired even when
remelting revert material. Larger losses
22
Aluminium Casting Alloys
Phosphorous [ppm]
Undermodifi ed
Figure 3
0 5 10 15 20 25 30 35 40 45 50 55 60
can be offset by adding Sr master alloy
wire in accordance with the respective
manufacturer‘s instructions. At the right
temperature, the addition of sodium to
the melt is best done by charging standard
portions. For easy handling, storage
and proportioning, the manufacturer‘s
recommendations and safety instructions
should be followed.
Since sodium burns off from the melt
relatively quickly, subsequent modifi -
Figure 4
Microstructural formation in relation to
the content of phosphorous and strontium Al Si7Mg
Strontium Gravity die casting
[ppm] gravity die cast test bar
cooling rate 2.5 K/s
450
400
350
300
250
200
150
100
50
0
0 10 20 30 40 50 60 70 80 90 100
Phosphorous [ppm]
Modifi ed Undermodifi ed Granular Lamellar
cation must take place in the foundry
at regular intervals. In melts modifi ed
with sodium, any requested cleaning
and degassing should be carried out
with chlorine-free compounds only
(argon or nitrogen). A certain amount
of sodium burn-off is to be reckoned
with, however, and needs to be taken
into account in the subsequent addition
of sodium. When absolutely necessary,
the melt can be treated with chlorine-
releasing compounds long before the