BBBBflt] «BlJIUrIrlr - Clpdigital.org

346 Forging- Stamping - Heat Treating
October, 1925
H e a t T r e a t m e n t o f C a s t A l - C u - F e - M g A l l o y
The Author Discusses the Heat Treatment of Sand-Cast Al-Cu-
Fe-Mg Piston Alloy—Principles of Heat Treatment Are
A M O N G the light materials commonly used for
pistons and other parts operating at elevated
temperatures is the 88.5 aluminum — 10 copper
- 1.25 iron — 0.25 magnesium alio}-. Ordinarily this
has been employed in permanent mold casting, which
affords pistons which arc- closer to size and weight tolerances
than those which are produced by sand-casting,
a much slower and less economical though satisfactory
method of manufacture. Then, too, the chillcast
metal, with its usually finer grain size, develops
in the cast condition better tensile and hardness properties
than the less rapidly cooled sand-cast metal.
The possibilities in the heat treatment of this alloy
have not been widely appreciated. While sonic manufacturers
have actually been quenching and artificially
aging (reheating) pistons or annealing them before
The strength and hardness of the sand-cast 88.5
aluminum 10 copper 1.25 iron - 0.25 magnesium alloy
may be strongly increased to about 35,000 lb. per sq.
in. and 120, respectively, by a heat treatment which involves
heating at 925 deg. F. for 5 hr., quenching in
boiling water, and aging at 300 deg. F. for 16 hi. or
at 400 deg. F. for 2 hr. Quenching from temperatures
much less than 925 deg. F. results in inferior strength
but not necessarily lower hardness. Very little is to
be gained by soaking the alloy at 925 deg. F. for more
than 5 hr. At much in excess of 975 deg. F. the alloy
starts to melt The presence of this condition cannot
be detected from the hardness and the quenched alloy,
but it can be deduced from the inferior strength of test
specimens which should always be heat treated with
castings. Air-quenching produces less uniformity and
lower ultimate strength than does quenching in boiling
water. The percentage of elongation of the alloy in any
machining condition of to treatment stimulate is the practically growth nil. and The distortion metal­
which lography otherwise of the alloy might is of occur much during value as their a method operation of
in control the engine, to proper it has heat often treatment. been the practice to place
pistons in service in the cast condition.
The present paper describes a portion of the research
on the properties of piston alloys undertaken
by the .Metals Branch of the Material Section. Engineering
Division, Air Service, I". S. A., at McCook
Field, Dayton, Ohio. The principles of the heat treatment
are applicable both to the sand and the chillcast
alloy, with greater intensification of the resultant
tensile and hardness properties in the case of the
latter.
Material.
The parent ingot (Melt 3427) for this investigation,
whose calculated composition was 10 Cu, 1.25 Fe,
0.2.1 Mg, in accordance with the requirements of Air
Service Specification 11.024. was made in a 300-lb.
batch by melting down the proper quantities of aluminum
ingot, aluminum-copper-iron hardener, and alum­
•Chief, Metals Branch. Material Section, Engineering Divi
in. Air Service. IT S. A.. McCook Field. Dayton, Ohio.
Applicable Both to Sand and Chill Cast Alloy
By SAMUEL DANIELS, A.B., Met.E.*
inum-copper hardener together and the magnesium
metal just before pouring. The analysis of these materials
follows:
Metal
Al ingot . .
Al-Cu-Fe
Al-Cu
Mg slab
Melt
Copper
. . 324(1 0.02
3095 25.11
. . . 328(1 40.78
2013
-Per ih ire i lomposlt on
Iron Silicon M
0.52 0.54
13.38
0.38
6.24
agnoBium
99.5 +
The maximum furnace temperature during melting
was 1370 deg. F and the pouring temperature 1300
deg. F.. the measurements being taken with a bare
chromel-alumel couple and a Leeds & Northrup potentiometer.
The metal was pigged into 5-lb. ingots.
The actual analysis of Melt 3427 was as follows:
Copper 9.66%
Iron . , 1.38
Magnesium , 0.28
Silicon 0.40
The properties of one standard TBI sand-cast mold
of this melt were, five days, after casting:
Ultimate strength, Ib./sq. in 25,210
Elongation in 2 in., per cent 1.0
Brinell, 500 kg 80
Procedure — Foundry.
Thirty molds (three specimens to the mold, as in
Fig. 1) ot standard TBI specimens, were sand cast
for this experimentation in two lots, molds 1 to 11,
FIG. 1—Standard (TBI) Air Service mold of sand-cast
tension test specimens.
inclusive, being cast as Melt 3925 and molds 14 to 30,
inclusive, as Melt 3712. Equal parts of ingot and of
gates made up the metal charge.
With the use of oil as fuel, Melt 3712 was ready
for pouring in 45 and Melt 3925 in 35 minutes. The
pouring temperature was 1300 deg. F. in each case and
the maximum furnace temperature was but slighlv
higher. The molding sand was a coarse grade of
Sanduskv.