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National Advisory Committee for Aeronautics, Technical Notes - An Exploration of the Longitudinal Tensile Compressive Properties Throughout an Extruded Shape of 24ST Aluminum Alloy

The thicker extruded shapes of 24S—T aluminum alloy
are usually- composed of an inner unrecrystallized portion
in which there is a high degree of preferred orientation'”
and an outer portion in which coarse grains have formed
as a result of'the greater equivalent cold work during exe
trusion and recrystallization during solution heat treat—
ment.

At the present time there is no practi-cal method
for producing shapes that consist either entirely of re- ' f"
crystallized or entirely of unrecrystallized metal.' The
proportions of these areas vary along the length of such _}
an extrusion: the recrystallized area is larger at the _
back end than along the remainder of the length. Because
.of the high degree of preferred orientation in the unre—
crystallized part, this part exhibits higher longitudinaI
strength than the recrystallized part. The over—all '
strength of an extruded shape iS, therefore. governed to
some extent by the proportional amounts of each kind of
structure of which the cross section is composed. Sinc_e_
the proportions vary along the length, the over-all
strength of the crosS'section also.varies along the length:
this_over-all strength is greatest at the front end and
least at the back end of the extruSion.- '

Although some data are available on the variations in
properties throughout extruded shapes, there is little ev-
idence as to how these properties vary along the_length of
the extruded shape or how the over—all strength of a shape
is affected by the different—areas and properties of the
recrystallized and unrecrystallized portions. In order tn
obtain some specific data on this question. the plant se~
lected an extruded shape in which the recrystallized and
unrecrystallized portions were sufficiently extensive to
permit test specimens to be cut entirely from each differ-
ent portion. The properties of this extrusion were deter-
mined at a number of different sections.

The object of-this investigation was to determine the
tensile and compressive properties at various locations in
a Zés-T extruded shape. In addition to tests of specimens
representing localized areas in the shape, forrcomparison
tensile tests were made of specimens representing practi~
cally~the full cross section of the shape.