Note: Descriptions are shown in the official language in which they were submitted.
Title of the Invention:
METHOD FOR MANUFACTURE OF ALUMINUM ALLOY CASTING
Abstract of the Disclosure:
A cast article of aluminum alloy is produced by
pouring into a mold a molten Al-Si-Mg type casting alloy having
an antimony (Sb) content in the range of about 0.03% - 1.0~ by
weight and, while the aolloy cast body is cooling following
complete solidification but before its temperature has fallen
below 450C, placing the solidified cast body into a heating
furance kept at temperatures in the range of from 500 to 550C
and retaining it at an intermediately high-temperature within
that temperature rang~ for not more than 30 minutes, su~se~uently
quenching said cast body in cold water or hot water and thereafter
subjecting the quenched cast body to a conventional artificial
aging treatment.
; The resulting cast articles are, in terms of strength,
toughtness and resistance to thermal shocks, comparable with or
superior to cast articles obtained by conventional methods but
can be manufactured in a reduced period of time with consequential
savir,gs in cost.
Background of the Invention:
Field of the Invention:
This invention relates to an improved method for the
.anufacture of cast aluminum articles from Al-Si-Mg type casting
alloys.
_ The term "Al-Si-Mg type casting alloys" as used herein
means the Al-Si-Mg alloys of the type corresponding to those
designated as AC4A and AC4(' by Japanese Industrial Standard for
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Aluminium Alloy Castings ~JIS H5202). Since these Al-Si-Mg
type casting alloys have good casting properties, possess
appropriate strength and toughness, and e~cel in weldability,
they are widely used for parts for engines in automobiles and
ships and other machine parts.
Description of the Prior Art:
_ _ _
Heretofore in the manufacture of cast articles of
these alloys, the alloys after melting and pouring into molds
have been subjected to a solid solution heat treatment and then
to quenching and an artificial aging heat treatment in order to
acquire the necessary strnegth and toughness. The solid solution
heat treatment has to be carried out at elevated temperatures
within the range of from 500 to 550C for long periods ranging
from several hours to ten or more hours. Further, the aging
step needs to continue at temperatures within the range of from
l~0 to 200C for similarly long periods ranging from several
hours to ten or more hours. These treatments have necessarily
affected the casting operation adversely notably from the
standpoints of production efficiency and heat economy.
With a view to avoiding these disadvantages involved
in castings of the type requiring thermal treatment, there has
been proposed a so-called "solutioning casting method" which,
as disclosed in Japanese Patent Publication No. lO901/1962, for
example, comprises quenching the casting body to room temperature
immediately after casting, thereby simultaneous~y e~fecting
quenching and formation of supersaturated solid solution, and
subsequently subjecting the shaped allo~ body to the artificial
aging treatment.
However, ~hen this "solutioning casting method" is
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39
applied to alloys having the composition contemplated by the
present invention, the ultimate cast articles obtained after the
aging treatment lack sufficient strength and toughness as
compared with the products of the so-called T6 material which
have undergone conventional aging subsequently to conventional
solution heat treatment.
Summar~ of the Invention:
The inventors have studied the various drawbacks
encountered in the manufacture of cast articles from alloys of the
aforementioned type and consequently have found that, by adding
a small amount of antimony to said alloy and, preparatory to the
quenching treatment, interrupting the normal, cooling stage
following casting while the cast articles are at an intermediate
high temperature and retaining said cast articles at that high
temperature for a limited time said cast articles at the end
of the treatment for artificial aging have acquired a degree of
strength and toughness comparable with or even superior to those
acquired by the castings produced by the conventional method,
even if the intermediate level treatment extends for only a short
period on the order of 5 to 30 minutes. Further, the intermediate
temperature treatment, when carried out as described above,
enables the cast products of alloys to avoid deformation or
uneven strength distribution otherwise often entailed by the
modified thermal treatment described above.
Specifically, this invention relates to a method for
the manufacture of cast articles of aluminum al~oy, characterized
by casting a molten Al-Si-Mg type alloy containing 0.03 to 1.0
percent of antimony into a mold, placing the completely solidified
cast bodies in a heating furnace kept at a temperature in the
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9~9
range of from 500 to 500C before it has cooled to a temperature
below 450C, thereby subjecting the solidified cast bodies to
an intermediate temperature treatment for a short time up to
about 30 minutes, then quenching said cast bodies in cold water
or warm water, and subjecting the quenched cast bodies to an
artificial aging treatment in the usual way.
srief Description of the Drawings:
. . _ .
I Figure 1 is a cQmparison of mod~l flow diagrams of
the manufacture of cast articles from an Al-Si-Mg type alloy
according to the method of the present invention and the con-
ventional method.
Detailed Description of the Invention:
According to this invention, when a aluminum alloy
cast bod~ is retained briefly at a specified high temperature,
it can be immediately subjected to the usual quenching and
artificial aging treatmen-ts. Since the alloy is no longer required
to undergo any time-consuming solid solution treatment, the total
manufacturing time for cast articles can be notably shortened and
all the treatments involved can be performed continuously. Thus,
the method of this invention not merely enhances production
efficiency but also proves highl~ advantageous from the stand-
point of heat economy.
Now, the present invention will be described in
comparison with the conventional method, with reference to the
model flow diagrams of Figure 1. In Figure 1, the solid line
indicates the process flow by the present invention and the __
broken line that b~v the conventional method.
In the diagram, the alphabetic symbols designating
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:~18~ 9
the various process steps involved are explained as follows~
(Conventional method) (Method of this invention)
A ~ B Completion of A ~ B (B') Completion of
solidification solidification
B -~ C ~pontaneous B (B') ~ E' Retention at
intermediate high
temperature
C ~ D Heating for E' ~ F' Quenching
temperature
elevation
D ~ E Treatment for F' ~ G' ~ H' Treatment for
. solid solution artificial aging
E ~ F Quenching
F ~ G H Treatment for
artifical
aging
sy the conventional method, the cast articles of an
Al-Si-Mg type alloy are manufactured by the steps of pouring
into the metal mount mold a molten alloy at a temperature in the
neighborhood of 720C and, after the molten alloy has completely
solidified, allowing the solid cast bodies to cool off sponta-
neously from its solidification temperature to room temperature
(A ~ B ~ C), then heating the cast bodies to a temperature within
the range of from 500 to 550~C, appropriate to the solid
solution heat treatment and retaining the cast bodies at this
elevated temperature for a period of from four to 16 hours
(C ~ D ~ E), subsequently quenching the cast bodies in cold water
or in hot water at a temperature in the range of from 60 to 100C
(E ~ F) and finally subjecting the cast bodies to aging at a
temperature in the range of from 140 to 200C for a period of
from four to 12 hours.
- By the conventional method, therefore, the series of
thermal treatments requires a fairly long time.
By contrast, in the case of this invention, cast
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articles possessing degrees of strength and toughness comparable
to those produced by the conventional method as described above,
can be obtained by similarly causing the molten alloy to solidify
iII the mold, then after solidification is completed, placing
the solid cast bodies in a heating furnace kept at a~ inter-
mediate level temperature in the range of from 500 to 550C,
while the cast bodies are still at a high temperature during
cooling retaining the cast bodies therein at the intermediate
temperature for 5 to 30 minutes (A ~ B ~ E'), then immediately
quenching the cast bodies in cold water or hot water (E' -~ FI),
and thereafter subjecting the quenched cast bodies to an ordinary
treatment for artificial aging. Thus, as a whole, the time
required for the manufacture of the cast articles are notably
decreased and the steps can be readily performed in a continuous
operation.
The antimoney which is used in the present invention
is an element frequently added to A1-Si type alloys for the
improvement of cast structure. When added to Al-Si-Mg type
alloys, it imparts unsightly spots in a brown to dark purple
color to the cast article obtained after the thermal treatment
steps and these spots seriously impair the market value of the
cast article. In the practice of this invention, the added
antimony does not impart such unsightly spots so that the cas~
product has a good appearance.
2S The continuous operation can integrate all of the steps
of pouring the molten alloy into the mold, retaining the
solidified cast bodies at the intermedia-te high temperature, and
immediately quenching the solid cast-bodies in water. Optionally
it may be extended to include the final step of artificial aging.
The equipment needed for carrying out these steps in a
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9~39
continuous operation includes tunnel furnaces for use as the
heating furnace at the various steps plus link conveyors for
advancing the cast articles between the adjacent steps. These
facilities are well known in the art.
Now, the present invention will be described with
reference to working examples.
Alloys of the different compositions indicated as
Examples (1) and (2) in Table 1 (which lists alloys of the types
designated as AC~A and AC4C in JIS-H5202) were each melted in a
smelting furnace and, after thorough fusion and treatment for
expulsion of entrapped gas and removal of slag, subsequently
poured at 720C into a boat-shaped testing mold of JIS H-5202
preheated to about 150C and, after complete solidification
therein, subjected to various after-treatments indicated below:
a) Conventional method (1), comprising the steps of allowing
the solidified alloy cast bodies to cool off sponta-
neously to room temperature, and then subjecting the
solid cast bodies for a solution heat treatment, quench-
ing and artificial aging.
b) Known alternative method described in the Japanese Patent
Publication No. 10901/1962 (2), comprising the steps of
immediately quenching the solidified cast alloy bodies
after the usual casting in cold water and subjecting
the quenched cast bodies to treatment fo artifical
aging.
c) Method of this invention, comprising the steps of
immediately placing the solidified cast bodies after
the usual casting in a hea~ing furnace, before it has
cooled substantially for retention therein at an
intermediate high temperature for a short time, and
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thereafter subjecting the cast bodies to quenching and
artificial aging.
The cast artic]es resulting from the several after-
treatments were visually inspected for surface condition and
tested for certain mechanical properties. The results are shown
in Table 1.
In the alloys of the type AC4C of Example (2), the
alloy identified d) in which sodium (an element usually employed
in alloys of this kind as an additive component for improvement
of alloy cast structure) was incorporated in lieu of antimony as
an alloy component~ was subjected to the procedure of the present
invention. The test results obtained of the casting of this
alloy are shown in the table for purpose of comparison.
The conditions of heat treatments given to the various
lS alloys of Table 1 are summarized in Table 2.
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~v~
From the test results seen in Table 1, it is evident
that in both of Examples tl) and (2), the sample cas-t bodies
obtained in Run c) corresponding to the method of this invention
wherein the thoroughly solidified cast bodies before being
subjected to quenching were retained about 8 to 10 minutes at an
intermediate high temperature and then given a treatment for
artificial agings ~ere, in terms of strength and toughness,
comparable with or even superior to the sample cast bodies
obtained in Run a) wherein the cast bodies were subjected to a
length solid solution heat treatment and far superior to the sample
cast bodies obtained in Run b) wherein the cast bodies were
subjected to quenching and artificial aging immediately after
solidification without going through any retention at an inter-
mediate high temperature or any solution heat treatment.
It is evident from the test results for Run d) in
Example (1) that the effect of the present invention reflected
in the notable decrease in the total time required for the
heat treatment cannot be obtained with an alloy using sodium
for an improvement of cast structure in the place of antimony.
Since the products obtained by the present invention
are free of dark spots on their surface, their commercial value
is unimpaired.
Heretofore, for cast articles of Al-Si-Mg type casting
alloys to acquire adequate toughness, it has been necessary for
them to undergo a prolonged period of thermal treatments. The
present invention, as described above, produces these cast
articles possessing more desirable strength properties by the
steps ~f casting the molten alloy into a mold, after complete
solidification of the cast bodies, retaining them at an
intermediate high-temperature briefly before they have cooled
39
below a specified level, then quenching the cast bodies, and
finally subjecting them to a treatment for artificial aging as
usual. Compared with the conven-tional method, the methoa of
this invention permits a drastic reduction in the overall time
required for heat treatment steps. Thus~ the method of this
invention proves advantageous for the manufacture of cast
articles of the aluminum alloys in question.
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