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AA 19 Document Information:
Title
Special Report on the Mechanical Properties of Sand Cast Aluminum Alloy Test Castings
The Aluminum Association Inc.
Publication Date:
Scope:
Many variables affect the mechanical properties in aluminum alloy
castings. The most important of
these are:
1. Alloy and the variation of the chemical composition within the
specified limits for that alloy.
2. Metal soundness. This can be affected by gas porosity, shrinkage
porosity and non-metallic
inclusions.
3. Metallurgical characteristics. Examples are macro grain size and
constituent distribution.
4. Solidification rate. This will likely vary throughout the casting.
It is affected by section
thickness, location with respect to gates and risers, metal flow in
the mold cavity, special
chilling techniques. Solidification rates can be directly related to
dendrite arm spacing with
smaller cell sizes indicating more rapid cooling and higher mechanical
properties. (Footnote *)See
Note 1
5. Heat treatment - optimum time and solution heat treat temperature
to insure solution of the
soluble constituents, proper quenching to retain those constituents in
solution, and artificial
aging to the desired temper.
Foundrymen can and do control alloy, chemistry and heat treatments
rigidly. It is possible to
control grain size and constituent distribution. Good melting and
degassing practices will control
oxide inclusions and hydrogen gas porosity. The major variations in
mechanical properties then come
from the ability to control shrinkage and the solidification rates
attainable in a casting.
This report is an attempt to show the relationship of mechanical
properties to some of the
variations in solidification rate which might be expected in a
casting. To do this, a test casting
as shown in Figure 1 was designed by the Aluminum Association's
Technical Committee on Castings.
Patterns were made and distributed to at least six Jobbing Foundry
Division member foundries. The
foundries made test castings from several melts. The test castings
from all foundries, along with
separately cast test bars from each melt, were heat treated at one
facility. Test bars (0.250"
diameter with a 1" gauge length) were then machined from sections 1
through 6 in each test casting.
The test results for each alloy are presented in tabular form to show
the relationship of
properties to gating, section thickness, and chills; and also to show
in a graphical form the
relationship of the properties to solidification rate as represented
by dendrite arm spacing.
The test values shown relate only to the test casting. They represent
good foundry practice and
favorable casting design. The values are intended as a guideline for
commercial design purposes,
but they are neither the maximum nor the minimum properties
obtainable. The ability to apply
increased chill rates could improve the properties, while casting
design limitations which restrict
the foundry's ability to produce sound sections will reduce the
properties. The design
considerations and casting techniques for each particular casting will
therefore affect the
properties in that casting.
Footnote * - Note 1: Dendrite Cell Size, G. R. Gardner, R. E. Spear,
Modem Castings, May 1963
Cast Aluminum Structures Technology (CAST), Technical Bulletin No. 7,
June 1978, The Boeing Company
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