Note: Descriptions are shown in the official language in which they were submitted.
11338(~5 l
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--~ ~ BACKGROUND OF TI~E INVENTION
.
6201 Aluminum Alloy is a high strength aluminum maq- !
nesium silicon alloy which in wire form and in the heat treated
condition has a tensile strength of over 46,000 PSI, elongation
greater than 3 percent, and an electrical conductivity greater
. than 52.5 percent IACS. In the past, 6201 Aluminum Alloy redraw I
~ rod and similar aluminum alloy redraw rods have been manufactured
-` for commercial use ~y a plurality of separate steps .which include
~ DC casting an aluminum in~ot reheating thc in~ot to about 700
L0 ~: to 850F, hot rolling the cast ingot to redraw rod and solution-
izing the rod at a temperature of approximately 1000F and water
quenching the rod. The rod is cold drawn to form wire, and the
wire is artificially aged ~t tR~p~AtUres ~QtwQen 25~ a~d
450F. This proccdure is capable of producing wire having
..... ...tensile.strength and electrical conductivity characteristics
which are sim~lar to or in excess of those for 6201 Aluminum. ?
While the foregoing procedure produces an acceptable
product, such a ~atch process or non-continuous casting process,
is ~apable of producing only a limite-3 amount of rod; that is,
~ the given size billet will produce on1y a corresponding mass of
rod, and the lengths of separately produced rod must be welded
together to form longer lengths of rod. When the billet is
reheated and rolled to form rod, it is customary to crop tne
leadtng end of the rod since it is of an inferior quality. Tl~us
a su~stantial amount of waste is experienced in the formcr
procedure. An e~ongated rod which comprises several lengths of
batch produce~ products welded together will include poor g~ain
,, . _ . .. .. . .
~i33805
structure at the places where it is welded together, which
affects tensile strength and conductivity. Furthermore, it is
virt~ally impossible to create identical conditions in the
reheating and rolling of different billets, and the lengths of
rod welded together will usually have different grain
characteristics.
In order to reheat the rod in this batch system, the rod
must be carefully handled in order to achieve uniform heating
and in order to produce a uniform product. For instance, the
oven in which the rod is placed for solutionizing must ~reate
relatively e~en heat distribution in order that the rod be
uniformly heated. ~urthermore, the rod usually must be
arranged so that there is enough circulation of air or gases
n the oven between the coils to insure proper heat
distribution. It is customary to place individual coils of
ro~ on porta~le racks which space the coils from cach other
for this purpose; however, the racks occupy space in the oven
and reduce the volume of rod which can be heated. Whilo the
purpose of reheating the rod is to solutionize the rod, it is
desirable to keep the rod from reaching a temperature
substantially higher than its solutionizing temperature since
the overlapping portions of the rod in the coils in the rod
tend to hecome tacked or welded together. This tacking
together of the portions of the rod creates surface ~lemishes
on the rod when pulled apart, and frequently the coils remain
tacked together so that several coils of rod tend to pay out
together. Thus even heat distribution within the
solutionizing oven is a practical necessity so that the rod
can be rapidly and uni~ormly solutionized to hold the hazard
of rod tacking to a minimum.
The prior art batch process provides a substantial
amount of time in which the aluminum can oxidize, as when the
cast ingot cools or is being reheated, when the rod fron the
roll~ng mill cools or is being reheated ~or solutionizing, and
when the solutionized rod from the reheating oven cools. I'h~
resu~t is that the rod becomes substantially oxidized, "hich
mak~s it relatively hard for redrawing purposes, and which
causes a rod to ha~e a relati~ely dull finish. ~rther, a
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highly oxidized and hard rod is more difficult to draw and the
dies used for drawing deteriorate rapidly. Thus, the separate
steps require~ in the prior art batch process for forming 6201
Aluminum Alloy rod are expensive in that separate handling of
the rod is required between and during each step, the product
must be handled in a careful manner, and extra equipment must
be available and maintained to handle this product.
An improved method for continuously casting and rolling
h201 Aluminum Alloy was described in U.S. Patent No.
3,613,767. Briefly described, the invention of U.S. Patent
~o. 3,613,767 comprised a method of continuously manuacturing
aluminum base alloy rod, such as 6201 Aluminum Alloy rod,
without the necessity or reheating the ingot or the rod during
the process. The bar emerging from a continuous castin(3
machine was passed through a rolling mill, a quench tubc, and
then cooled in a continuous process. The heat of the cast bar
emerging from the continuous casting machine was not
dissipated and bar temperature was maintained in the
solutionizing temperature range of the metal as a rod was
passed to the rolling mill. The rod was hot worked in the
rolling mill and quenched immediately as it emerged fro-n the
rolling mill so that the time lapse from the point where the
bar entered the rolling mill to where the rod was ~uenched to
a temperature level below the crystallization temperature of
the alloy metals was less than the time required for the alloy
metals to precipitate to the grain houndarics of the metal.
After the rod was quenched it was at a temperature helow the
temperature where immediate and substantial precipitation
occurs. When the rod was subse~uently cold drawn into wire it
3~ had an unus~ally high tensile strength and a relatively high
electrical conductivity, and an unusually bright appearance.
~hus, the major problems of separate han~lng betwccn cclch o
the steps in the prior art process were e1l?ninate~ by the
practice of the invention disclosed in U.S. Patent ~o.
3,613,7~7. ~owever, the solution to the pro~lems inherent in
the prior art batch process ~or preparing ~01 Aluminum Alloy
resulted in an aluminum alloy t-od, which due to the heat loss
betwee~ the casting wheel of the continuous casting machinc
11338~S
and the point at which the bar entered the rolling mill, had
large precipitates on the order of 20,000 angstrom units in
size formed therein because of the relatively high temperature
at which precipitation was occuring. Also the solution to the
problems caused by batch preparation of 6201 Aluminum Alloy by
the method of U.S. Patent No. 3,613,767 created an entirely
new problem. In Column 5 beginning at line 3~ of Patent No.
3,613,767 the following statement is found:
"It has been found that the temperature and other
conditions in the process can be varied within
reasonable limits without detriment to the
characteristics of the product. ~or instance, the
temp~rature of the molt~!n metal in the pouring pot.and
the metal bar extracted from the casting wheel appear to
have no effect on the quality of the 6201 alloy rod as
long as the temperature is not lowered below the
solutionizing temperature."
While this statement may be true with respect to the
alloy properties of 6201 it is incorrect with respect to the
properties of the cast bar and the rod rolled from the cast
~ar. U,S. Patent No. 3,616,7h7 describes a method of
continuously casting 6201 which requires that the cast bar
exit the casting wheel at a temperature above the
solutionizing temperature and remain above this tempercture
until the cast bar enters the rolling mill where hot wc,rking
and quenching subsequently occur. In order to meet this
requirement the cast bar o~ U.S. Patent ~o. 3,613,767 m~st
exit the casting wheel at a temperature substantially above
the solutioizing temperature of the a~loy. To remove the cast
bar from the casting wheel at the temperatures taught ~,y U.S.
Patent No. 6,613,767 the bar must ~e cooled in such a way that
the bar does not become totally solid until it reaches a point
on the casting wheel that molten metal cannot flow into, and
fill, voids created in the bar by the shrin~age of the metal
in the casting mold during so:lidification. If such voids are
created on the exterior portions of the cast bar oxidat,ion
will occur within the void and when the har is rolled o,cide
inclusions will be trapped within the resul,tant rod caosinc~
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-- 6
the rod to b~come brittle an~ the points where the oxid~
inclusions occur thereby significantly decreasing the
drawability of the rod. If solidification shrinkage voids
occur in the interior of the rod where oxidation cannot occur
such voids will caus internal microcracking which
significantly affects the elongation of the rod thereby
directly affecting the post cold working characteristics of
the rod.
It has also been found that the solutionizing
temperature of 6201 alloy varies according to the
concentration of alloying elements present within the alloy in
that the higher the concentration of alloying elements present
the low~r the solutionizing temperature range of the alloy.
There~ore given the range of concentrations acceptable within
6201 alloy the solutionizing temperature may vary from about
850~F to a~70ut 114~ . Accordingly U.S. Patent No. 3,616,767
does not provide an acceptable method for continuously
producing 6201 alloy rod having alloying element
concentrations in the range which cause the alloy to
solutionize at temperatures in the upper portion of the 620L
alloy solutionizing temperature range. Accordingly, there
still remains significant improvements to he made in a process
for continuously casting heat treatable aluminum alloy rod
from alu~inum alloys such as 6201.
For the purpose of clarity, heat treatable aluminum
alloys as used in this specification shall mean those a]uminum
alloys which contain alloying ~lements which have a high solid
solut7ility in aluminum at high temperatures and low s013d
solubility in aluminum when cooled to room temperature. These
3~ alloys harden be precipitation of a second phase during heat
treatment and the alloying ele~ents are kept ~n solution by
rapid quenching from hiyh temporatures,
For the purpose of clarity, wrought a:Luminum allo-~s as
used in this specification shaLl mean those aluminum alLoys
which contain alLoying eLements which have low solid
solubility in aluminum at high temperatures as well as low
temperatures. These alloys normally harden by work har<ienin~
which is a hardening mechanism which operates during cold
~133805
working of the alloy.
SUMMARY OF THE INVENTIO~
Thus, it is an object of this invention to provide an
improved method for producing aluminum alloy products from
heat treatable aluminum alloys.
Another object of this invention is to provide a method
of continuously manufacturing a heat treatable aluminum alloy
rod without the necessity of reheating an ingot or rod to
produce a product having a hiqh tensile strength and high
10 conductivity characteristics.
Another object of this lnvention is to provide ar
improved 6201 aluminum product and a method for forming such a
product without the formation of large precipitated
intermetallic particles in the grain structure.
Another object of this invention is to provide ar,
ecomomical and expedient method ~or manufacturing 6201
al~lminum alloy rod.
Still another object of this invention is to provide a
method for continuously manufacturing a heat treatable 6201
20 aluminum alloy rod from 6201 aluminum alloys having
solutioniæing temperatures within the range of from about
8~0F to about 10B0F.
Yet another o~ject of this invention is to provi<~e a
method for continuously casting and rolling a heat treata~le
6201 aluminum alloy rod wherein the cast bar is not sut,ject to
solidification shrinkage.
Another object of this invention is to provide an
improved 6201 heat treatable aluminum alloy product with a
more uniform heat treatment along its entire length. ~ther
3~ obiects, features and advantages of the present invention will
hecome apparent upon reading the following specifications when
ta3~en in coniunction with ~he accompanying drawings.
~RIEF DFSCRIPTIO~ OF ~F _ AWI~GS
Fig. 1 is a schematic side elevationcll view of a casting
machine, rolling mill, quenching tube, ancl coiler utilized in
~,
1133805
-- 8
the procedure herein set forth.
Fig. 2 is a ternary diagram which graphically represents
the solubility of magnesium, silicon and the intermetallic
compound magnesium silicide in aluminum at various
temperatures.
Fig. 3 is a graphical representation of the effec~ of
heat treating 6201 aluminum alloy by the present invention
compared to prior art methods of preparing 6201 aluminum
alloy.
DESC~IPTION OF THE PR~FE~RED EM~ODIMENT
Referring now in particular to the drawings, in which
like numerals indicate li~e parts throughout the several
vi~-~ws, Fig 1 shows a casting machine 10, a heater 11, a
rolling mill 12, a quench tube assembly 13, and coiler 14. In
summary, the process of the prescnt invention comprises
pouring moltem metal from a furnace (not shown) into a casting
wheel 10a of casting machine 1~. The molten metal is cooled
and solidified in casting wheel 10a and extracted as a solid
bar 15 at a temperature below 940~ and guided toward and
through heater 11 wherein the solid bar 15 is continuously
heated until the temperature O the bar is within the range of
from about 850~F to about 1080F. The heated bar 15 is then
guided toward and through rolling mill 12. The product is
lengthened and reduced in its cross-sectional area within
rolling mill 12, and emerges as a wrouyht rod 17. Pod 17 is
passed through quench tube assembly 13 which includes first
stage quench tube 18, pinch rollers 1~, second stage quench
tu~e 20, pinch rollers 21, and rod conduit 22. The rod
emerges from rod conduit 22 and is formed into coils b~ coiler
3~ 14. Pump 23 receives the quenching liquid from sump 24 and
pressurizes first stage quench tube 18. ~he yuenching ~iquid
is passed through quench tube 1~ in a direcrion of ~low which
Is along the path of travel of rod 17 and is passed through a
conduit system to cooling tower 26, where it is cooled ~nd
recirculated back to sump 24. Pump 27 receives quenchi~g
liquid from sump 2~ and pressurizes second ~stage ~uench tuhe
20. The ~uenching liquid of the second stage ~uench tuhe is
1133805
passed through q~sench tube 20 in a counterflow relationship
with the respect of the movement of the rod 17, and is ~assed
through a conduit system to cooling tower 31 where it i~
cooled and recirculated back to sump 28. Thus, the quenching
liquids are maintained at controlled temperatures during the
quenching process.
In more detail, the molten metal process throu~sh the
apparatus is a heat treatable aluminum alloy. If the product
to be formed is to be 62~1 aluminum alloy, the ranges of
silicon and magnesium contents are from about 0.50 to ahout
0.90 percent, and from about 0.60 to about 0.90 percent,
respectively. The range of silicon and magnesium alloys can
vary in this metal beyond the range for 6201 alloy to ~.3 to
about 1.2 percent and to 0.3 to about 1.2 percent
respectively, if desired. The metal in its ~olten state is
poured through a fiberglass screen into a holding pot
maintained at a temperature al:,ove 12~0F, usually at as~,out
1270DF. From a holding pot, the metal is poured into casting
wheel lOa where it is cooled and solidified into a cast bar 15
at a rate at which inverse se~regation will be substantially
minimized, for example at a rate of from about 24~F per second
when casting a 3.3 square inch bar at a rate of 30 feet per
minute to about 321? per second when casting a bar of equal
cross-section at a casting rat:e of 40 feet per minute and
approximately 50F per second when casting a bar of equal
cross-section at a castiny rat:e of 50 feet per minute. The
cast bar is stripped from casting wheel lOa at a temperature
of from about 70~F to about 940F and passed to and through
heater 11 wherein the temperal:ure of cast bar is incre,lsed to
a point at which the alloying elements are solutionize(l.
~eater 1~ continuously supplies energy to t:he rod t~ler~s~y
increasing the temperature of rod 15 to rom as`~out 5350F to
about 108~F, usually to from about 95~. to about 1020DF and
depending upon the alloy conposition to from as~out 1020F to
about 1080~F. As the cast bar exits heater 15 it is ~3;sided
toward and through rolling mill 12, the bar is ho~ ~orsned and
coated with a soluble oil concentration maintained at 3bout 40
percent and at a temperature below 200~, usuA11~ at a~out
1~338~S
-- 1() --
160F. ~olling mill 12 includes a plurality of roll stands
which compress the cast bar alternatively from top to bottom
and side to side, which functions to lengthen the cast bar and
reduce the cross-sectional area of the cast bar, so that the
cast bar is progressively fromed into redraw rod 17. The
volume of the soluble oil concentration in rolling mill 12 is
maintained at a level of about two-thirds the volume in a
typical continuous casting system for EC rod. The temperature
and volume of the coolant applied to the rod in the rolling
mill are adjustable so that when the rod ~7 emerges from
rolling mill 12, the temperature of the rod is at a level so
that the rod is still within its hot forming temperature
range, which is usually abovc 6~0F, so that the alloy metals
have not precipitated from the aluminum. The low volume of
coolant applied to the rod in the rolling mill requires a
higher concentration of lubricant, approximately 40 per-cent
solution as compared to approximately 10 percent for an EC rod
system, and the flow is adjusted so that approximately equal
flow of coolant is maintained at each rsll stand.
Fig. 2 is a Ternary dia~ram which graphically re~resents
the solubility o~ magnesium, silicon and magnesium silicide in
aluminum at various temperatures ranging from 440C or 852F
to 535~ or 995F.
Straight line 40 represfnts the increase in solut)ility
of maynesium silicon and magnesium silicide in the 62~1 alloy
system as temperature increases to approximately g95F. Point
42 on straight line 40 represents the amount of magnesium,
solicon and magnesium silicide which is in solution in a
continuously cast rod of 6201 aluminum alloy when the rod has
been treated by the prior art method of heat treating
continuously cast 6201 alloy. Point 43 represents the amount
of magnesium, magnesium silicide and silicon which is retained
~n the 6201 alloy system in solution when a continuously cast
rod of 62nl aluminum alloy is heat treated hy the presfnt
invention. As can ~e seen from the diagram of Fig. 2, there
is a ~2 percent increase in the amount o~ magnesium sllicide
in solution in the 6201 alloy system when the alloy is
continuously cast and rolled into a rod and is hf~at treatd
- 11338~5
according to the present invent:ion during the continuouc
casting and rollin~ operation.
~ n example of the improvc-d properties result from the
increased amount of magnesium silicide in solution in the
alloy matrix prior to aging and prcipitation follows. I~ cast
bar was continuously cast usin~3 the prior art method for heat
treating continuously cast 6201 aluminum alloy and the
following results were obtained. ~ltimate tensile strength of
the final wire was 45 700 PSI with an elongation of ~.3
percent and a conductivity of 52.5 percent IACS. After
establishing the above properties as a base line, the bar
temperature at a point between the casting machine and t:he
entry of the bar into the rolling mill was raised from 900F
to 1020F by the method of the present invention. The ~)ar was
then rolled into a rod and made into wire and the physical
properties of the wire made from the bar treated according to
the present invention were as follows:
~ltimate tensile strength - 50,800 PSI
Elongation - 7.9~
Conductivity - 52.5%
Fig. 3 is a graphical representation of propertie;
resulting from prior art heat treatment of continuously cast
6201 aluminum alloy rod and 62()1 alloy rod continuously cast
and heat treated according to the present invention wherein
curve 50 depicts the relationship between the conductivity and
ultimate tencile strength of wire fabricated from 6201
aluminum alloy rod processed by prior art techni~ues an(~ c~rve
52 depicts the relationship between the conducti~ity an(3
ultimate tensile strength of wire fabricated from 62~1
aluminum alloy rod processed by the method of the present
invention.
While this invention has bcen described in detail wit~,
particular reference to preferfed embodiments thereof, it will
be understood that variations and modifications can be
effective within the spirit and scope of the invention as
descrihed hereinbefore and as defined in the appended claims
,
