Note: Descriptions are shown in the official language in which they were submitted.
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ALUMINUM EXTRUSION ALLOY
CROSS-REFERENCE TO RELATED APPLICATION
[01] This application claims priority to, and the benefit of, U.S. Provisional
Application No.
62/774,661, filed December 3, 2018, which prior application is incorporated by
reference
herein in its entirety.
FIELD OF THE INVENTION
[02] This disclosure relates to aluminum alloys suitable for use in extrusion,
and more
specifically in one aspect to Al-Mg-Si-Cu-Mn-Cr extrusion alloys having high
strength and
ductility.
BACKGROUND
[03] Aluminum extrusion alloys are often used for automotive applications, and
higher
strength extrusion alloys having yield strengths of at least 350 MPa are
sometimes desired or
needed for this purpose. A number of existing commercial alloys are capable of
this strength
level, such as AA6066 and AA6056, but these alloys exhibit decreased
extrudability compared
to standard extrusion alloys. Ductility and crush performance can also be an
issue in such
higher strength alloys. Thus, there is a need for an aluminum extrusion alloy
capable of
consistently achieving a yield strength of 350 MPa or greater, with good
extrudability and
ductility. In order to ensure that an alloy in commercial production
consistently meets a
minimum yield strength, it is desirable that the average or typical yield
strength value should
significantly exceed the minimum target, such as by at least 20 MPa, to
account for variations
in strength from sample to sample. For example, to ensure that a targeted
minimum strength
of 350 MPa is consistently met, an average yield strength of 370 MPa or more
would be desired.
[04] The present disclosure is provided to address this need and other needs
in existing
aluminum extrusion alloys. A full discussion of the features and advantages of
the present
invention is deferred to the following detailed description, which proceeds
with reference to
the accompanying drawings.
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BRIEF SUMMARY
[05] Aspects of the disclosure relate to an aluminum extrusion alloy that
includes Si and Mg
in amounts within a quadrilateral defined by the following coordinates on an
Mg/Si plot, in
weight percent:
1.15 Si, 0.70 Mg
II 0.95 Si, 0.55 Mg
FIE 0.75 Si, 0.65 Mg
IV 0.95 Si, 0.85 Mg
wherein the alloy further comprises, in weight percent:
Mn 0.40 ¨ 0.80
Fe 0.25 max
Cr 0.05 ¨ 0.18
Cu 0.30 ¨ 0.90
Ti 0.05 max
Zr 0.03 max
Zn 0.03 max
0.01 max
with the remainder of the alloy being aluminum and unavoidable impurities in
amounts of up to 0.05 wt.% each and 0.15 wt.% total.
[06] According to one aspect, the Mg and Si are present in an Mg/Si ratio of
at least 0.69
and/or no more than 0.88.
1071 According to another aspect, the alloy includes excess Mg, and in one
embodiment, up
to 0.40 wt.% excess Mg as defined herein.
[08] According to a further aspect, the alloy, after homogenization,
extrusion, and artificial
ageing, has a predominantly non-recrystallized microstructure
[09] According to yet another aspect, after homogenization, extrusion, and
artificial ageing,
has a yield strength of at least 350 Ivfl'a and a tensile elongation of at
least 8%. The alloy may
have a yield strength of at least 370 IvfPa in one embodiment.
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1101 According to a still further aspect, the alloy includes Mg in an amount
of 0.60 - 0.80
wt.% and Si in an amount of 0.85 - 1.10 wt.%. In one embodiment, the Mg
content may be
0.70 - 0.80 wt.% and the Si content may be 0.85 - 0.95 wt.?/o.
1111 According to yet another aspect, the Si and Mg in amounts are within a
quadrilateral
defined by the following coordinates on the Mg/Si plot, in weight percent:
1.15 Si, 0.70 Mg
II 0.95 Si, 0.55 Mg
111 1': 0.80 Si, 0.65 Mg
IV': 0.95 Si, 0.80 Mg.
1121 Additional aspects of the disclosure relate to an aluminum extrusion
alloy that includes,
in weight percent:
Mg 0.60 - 0.80
Si 0.85 - 1.10
Mn 0.40 - 0.80
Fe 0.25 max
Cr 0.05 - 0.18
Cu 0.30 - 0.90
Ti 0.05 max
Zr 0.03 max
Zn 0.03 max
0.01 max
with the remainder of the alloy being aluminum and unavoidable impurities in
amounts of up to 0.05 each and 0.15 total. The alloy may include any other
aspects discussed
above herein.
1131 Further aspects of the disclosure relate to an extruded product that
is at least partially
formed of an aluminum alloy as described herein.
1141 Still further aspects of the disclosure relate to a method that
includes casting or
otherwise forming a billet of an aluminum alloy as described herein, e.g.,
using direct chill
casting or other continuous casting technique, then homogenizing the billet
and extruding the
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homogenized billet to form an extruded product. The homogenization may be
conducted by
heating the billet at a temperature of 540-580 C for 2-10 hours, and then
cooling the billets at
a cooling rate of 300 C/hour or more after homogenization.
[15] Other features and advantages of the disclosure will be apparent from the
following
description taken in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[16] To allow for a more full understanding of the present disclosure, it will
now be
described by way of example, with reference to the accompanying drawings in
which:
[17] FIG. 1 illustrates magnesium and silicon content of embodiments of an
aluminum alloy
according to aspects of the disclosure;
[18] FIG. 2 illustrates a plot of crush rating and fracture strain vs. yield
strength for several
alloys tested in Examples 1 and 2 herein;
[19] FIG. 3 illustrates a plot of mean crush force vs. yield strength for
several alloys tested
in Examples 1 and 2 herein:
[20] FIG. 4 illustrates a plot of ram pressure vs. yield strength for
several alloys tested in
Example 2 herein; and
[21] FIG. 5 illustrates magnesium and silicon content of embodiments of an
aluminum alloy
according to aspects of the disclosure, as well as example compositions tested
in Example 5
herein.
DETAILED DESCRIPTION
[22] While this invention is susceptible of embodiments in many different
forms, there are
shown in the drawings and will herein be described in detail example
embodiments of the
invention with the understanding that the present disclosure is to be
considered as an
exemplification of the principles of the invention and is not intended to
limit the broad aspect
of the invention to the embodiments illustrated. It is to be understood that
other specific
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arrangements features may be utilized and modifications may be made without
departing from
the scope of the present invention.
[23] Aspects of the disclosure relate to an aluminum alloy that is useful for
extrusion
applications, having various alloying elements including Mg, Si, Fe, Mn, Cu,
and Cr. An alloy
as described herein may also be useful in forging applications, and may
produce beneficial
properties in such an application. All composition percentages listed herein
are in weight
percent unless otherwise indicated.
[24] In one embodiment, the alloy may include magnesium in an amount of 0.60 ¨
0.80
wt.%, or 0.6 ¨ 0.8 wt.%, and silicon in an amount of 0.85 ¨ 1.10 wt.%. The Mg
and Si in this
composition may also be present in an Mg/Si ratio (wt.%) of at least 0.69 in
one embodiment.
The Mg/Si ratio may additionally or alternately have an upper limit of 0.88 in
one embodiment
or 0.85 in another embodiment. Alloys with Mg/Si ratios that are too high can
be detrimental
to extrudability in amounts, and alloys with Mg/Si ratios above these amounts
may exhibit
unsatisfactory extrudability. In another embodiment, the alloy may include
magnesium in a
range of 0.70 ¨0.80 wt.% and silicon in a range of 0.85 ¨ 0.95 wt.%.
1251 In another embodiment, the alloy may include magnesium and silicon in
amounts
defined within a quadrilateral defined by the following coordinates on a Mg/Si
plot, as shown
in FIG. 1:
1.15 Si, 0.70 Mg
0.95 Si, 0.55 Mg
III: 0.75 Si, 0.65 Mg
IV: 0.95 Si, 0.85 Mg
1261 The alloy in a further embodiment may include magnesium and silicon in
amounts
defined within a quadrilateral defined by the following coordinates on an
Mg/Si plot, as shown
in FIG. 1:
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1.15 Si, 0.70 Mg
II: 0.95 Si, 0.55 Mg
1111': 0.80 Si, 0.65 Mg
IV': 0.95 Si, 0.80 Mg
[27] In any of the embodiments herein, the alloy may include at least some
excess
magnesium (i.e., excess Mg > 0) as defined by the equation below:
Excess Mg = Mg ¨ (Si ¨ (Mn+Fe+Cr)/3)/1.16 (all values in wt%)
[28] The alloy may include up to 0.40 wt.% excess magnesium in one embodiment,
and up
to 0.35 wt.% excess magnesium in another embodiment. Excess Mg can be
detrimental to
extrudability in amounts that are too high, and alloys with excess Mg above
these amounts may
exhibit unsatisfactory extrudability.
1291 The alloy may further contain the following elements, in wt.%:
Mn 0.40 ¨ 0.80
Fe 0.25 max
Cr 0.05 ¨ 0.18
Cu 0.30 ¨ 0.90
Ti 0.05 max
Zr 0.03 max
Zn 0.03 max
with the remainder of the alloy being aluminum and unavoidable impurities,
which may be
present in amounts of up to 0.05 wt.% each and 0.15 wt.% total. In one
embodiment, the alloy
may include additional elements not listed.
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1301 Silicon can combine with iron, manganese, and/or chromium in
intermetallic phases in
the alloy. Additionally, manganese and chromium in sufficient amounts can form
dispersoid
particles that inhibit grain recrystallization after extrusion. The iron
content of the alloy in one
embodiment is 0.25 wt% max. In another embodiment, the iron content of the
alloy may be
0.15 - 0.25 wt.%. The chromium content of the alloy in one embodiment is 0.05 -
0.18 wt.%.
In another embodiment, the chromium content of the alloy may be 0.05 - 0.15
wt.%. The
manganese content of the alloy in one embodiment is 0.40 - 0.80 wt.%, but may
alternately be
0.4 - 0.8 wt.%. In another embodiment, the manganese content of the alloy may
be 0.40 - 0.55
wt.%.
1311 Copper can increase strength of the alloy. The copper content of the
alloy in the
embodiment listed above is 0.30 - 0.90 wt%, but may alternately be 0.3 - 0.9
wt.%. In other
embodiments, the copper content of the alloy may be 0.30 - 0.80 wt.%, 0.60 -
0.80 wt.%, or
0.60 - 0.90 wt.%.
1321 Titanium is added as a grain refiner in one embodiment, and may be added
along with
boron in the form of TiB rod (e.g., 5% Ti, 1% B). Accordingly, the alloy may
also include up
to 0.01% or up to 0.005% boron in one embodiment.
1331 Alloys according to aspects and embodiments herein may be prepared by
forming into
billets through direct chill casting or other continuous casting method in one
embodiment, and
then homogenizing the billets. Homogenization may be performed, for example,
at 540-580 C
for 2-10 hours, and then cooling the billets at 300 C/hour or more, e.g., 300-
600 C/hour, after
homogenization. It is understood that these cooling rates may be measured over
a portion of
the cooling range, and not throughout the entire cooling of the billet (i.e.,
homogenization
temperature to ambient temperature). For example, in one embodiment, the
relevant cooling
rate may be measured between the temperatures of 500 C and 200 C during
cooling. The
billets may then be extruded into an extrusion profile or extruded product,
which may include
at least one concave surface, at least one convex surface, at least one angled
corner, and/or at
least one internal cavity in some uses. Extrusion may be performed in one
embodiment by
preheating to 470-520 C prior to extrusion and water quenching at the press
exit, e.g., by water
sprays or a standing wave water box, which may achieve cooling at about 50-
1000 C/sec. The
extruded product may be subjected to artificial ageing after extrusion, such
as heating for 5-16
hours at 160-185 C. It is understood that other processing may be used in
other embodiments,
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including post-extrusion processing to the extruded product to achieve desired
properties,
geometry, etc.
1341 The extruded product produced using the alloys and processing techniques
described
herein may have a post-extrusion grain structure that is predominantly fibrous
or non-
recrystallized in one embodiment. This predominantly fibrous microstructure
may have a
microstructure that is at least 50% unrecrystallized in one embodiment, or at
least 75%
unrecrystallized in another embodiment, which may be over a majority of the
length of the
extruded profile or over the entire length. A non-recrystallized grain
structure may improve
the yield strength of the alloy after extrusion. In one embodiment, an alloy
as described herein
may achieve a yield strength of at least 350 MPa or at least 360 MPa, with a
tensile elongation
of at least 8%, at least 9%, or at least 10%, after extrusion and artificial
ageing.
[351 Below are several examples illustrating the beneficial properties and
advantageous
performance of alloys according to aspects of the disclosure, as well as
comparative alloys.
1361 EXAMPLE 1
1371 The alloy compositions listed in Table 1, representing existing
commercial high
strength AA 6XXX alloys, were direct chill cast as 101.6 mm diameter ingots,
and a 5% Ti ¨
1% B grain refiner was added prior to casting to ensure a fine as-cast grain
size.
type Si Fe Cu Mn Mg Cr V Zr Ti
6111 0.66 0.20_0.70
0.20 0.70 0.00 0.01 <001 0.02 0.002
6056 0.96 0.18_0.56 0.79 0.67 0.00 0.01 0.10 0.02 0.002
6066 1.26 0.20 0.76
0.45_0.87 0.09 0.01 <.001 0.00 0.001
Table 1: Commercial Alloy Compositions
1381 The ingots were cut into 400 mm billet lengths and homogenized. The
billets of
AA6111 and AA6056 were homogenized for 2 hours at 560 C, and the AA6066 billet
was
homogenized for 4 hours at 545 C. The billets were cooled at 400 C/hr after
homogenization.
1391 The billets were extruded into a 40x30x2 mm hollow profile with a 5 mm
external
corner radius using a billet temperature of 475 C and a ram speed of 4-6 mm/s.
The ram speed
was varied to find the maximum speed attainable before surface cracking
occurred. This
maximum ram speed is reported in Table 2. The extrusion ratio was 32/1, such
that
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corresponding exit speeds ranged from 8-12m/min. The extrusion was water
quenched at a
rate of ¨1000 C/sec using a standing wave water quench unit positioned about
2.5m from the
extrusion die. The extrusions were floor aged at room temperature for 24 hours
before artificial
ageing for 8hrs/175 C.
[40] Crush tests were performed by axially crushing a 150 mm length to 30 mm
at a cross
head speed of 20 mm/s. The load displacement curve was recorded and the mean
crush force
(MCF) was calculated using an averaging technique. The extent of cracking
(crush rating CR)
during the crush test was assessed on a scale of 1 to 9, where 1 represented a
crack free sample
and 9 represented full disintegration. Longitudinal tensile testing was
performed, the area of
the final fracture was measured, and the true fracture strain was calculated
as ef = -Ln (final
area/initial area). The true fracture strain (ef) has been shown to be a good
measurement of
ductility at high plastic strains. The mechanical property and crush testing
results are also
reported in Table 2, where RX signifies a fully recrystallized grain structure
and F signifies a
predominantly fibrous grain structure. Some of these results are also depicted
graphically in
FIGS. 2-3.
Alloy YS UTS %El ef MCF C.R grain structure max ram speed
MPa MPa kN rn m is
6111 338 367 12 0.6 33.1 3 R X >6
6056, 384 403 11 0.4 36.4 8 F 5
6066 417 443 12 0.2 33 9 4
Table 2: Mechanical Properties
[41] The AA6066 alloy exhibited the lowest extrusion speed, followed by the
AA6056 alloy.
The AA6111 alloy had the highest maximum ram speed, and was the most
extrudable of the
three alloys. AA6111, which is widely used as an automotive sheet alloy,
resulted in a fully
recrystallized grain structure and did not meet the 350 MPa minimum yield
strength target.
Both the AA6056 and AA6066 alloys exhibited yield strengths in excess of the
350MPa target,
along with a predominantly fibrous or non-recrystallized grain structure.
However, the higher
strengths of these alloys did not translate into increased energy absorption,
and AA6056 and
AA6066 both performed poorly in crush testing. In particular, the AA6066 alloy
experienced
premature onset of cracking in the crush test and had a low fracture strain.
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1421 EXAMPLE 2
1431 The alloys listed in Table 3 were direct chill cast as 101.6 mm diameter
ingots and cut
into 400 mm billet lengths, and a 5% Ti - 1% B grain refiner was added prior
to casting to
ensure a fine as-cast grain size.
type Si Fe Cu Mn Mg Cr V Zr TiB
A 0.87 0.15
<.001 0.50 0.64 0.13 0.01 <.001 0.0030.0003
B 0.91 0.18
0.01 0.50 0.64 0.14 0.12 <.001 0.010 0.002
C 0.90 0.16
0.32 0.51 0.66 0.12 0.01 <.001 0.020 0.007
D 0.89 0.17
0.61 0.49 0.68 0.13 0.01 <.001 0.007 0.001
0.90 0.17 0.30 0.07 0.64 0.00 0.01 <.001 0.012 0.002
F 0.88 0.17
0.30 0.77 0.64 0.14 0.01 0.001 0.014 0.002
Table 3: Alloy Compositions
1441 The billets were homogenized for 2 hours at 550 C and cooled at 400
C/hour after
homogenization. The billets were extruded into a 40x30x2 mm hollow profile
using a billet
temperature of 500 C and a fixed ram speed of 5 mm/s. The extrusion was water
quenched at
a rate of -1000 C/sec using a standing wave water quench unit positioned about
2.5m from the
extrusion die. The extrusions were floor aged at room temperature for 24 hours
before artificial
ageing for 8 hours at 175 C. Tensile and crush testing was performed, the
extrusion hydraulic
pressure was monitored and the maximum (breakthrough) pressure value and the
value at 50%
of the ram stroke were extracted. The percentage difference in breakthrough
pressure compared
to alloy A (AP) was calculated to give an indication of the relative
extrudability. The increase
in yield strength per each % increase in extrusion pressure compared to alloy
A was also
calculated to assess the strengthening efficiency as compared to the effect on
extrudability.
The test results are summarized in Table 4, where RX signifies a fiilly
recrystallized grain
structure and F signifies a predominantly fibrous grain structure. Some of
these results are also
depicted graphically in FIGS. 2-4.
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Alloy YS UTS %El ef MCF C.R grain structure YS per inc. P AP
MPa MPa kN MPa/%P
A 312 331 10.7 0.73 29.92 3
B 311 329 10.9 0.73 29.11 2 F -0.20 4.9
C 361 377 11.1 0.57 33.75 5 F 27.57 1.8
D 379 403 11.8 0.54 35.57 4 F 11.28 5.9
E 346 360 9.9 0.28 28.91 9 RX -2.56 -13.3
F 348 369 11.2 0.54 32.35 2 F 5.22 6.9
Table 4: Mechanical Properties
1451 Alloy A, which is used for comparative purposes, is based on an
automotive grade
AA6082, gave good ductility and a good crush rating, but only achieved a yield
strength of
312 MPa. The alloy contained additions of Mn and Cr to form submicron
dispersoid particles
during homogenization and this resulted in a predominantly fibrous/non-
recrystallized grain
structure after extrusion. Alloy B, with a V addition relative to Alloy A,
exhibited similar
strength and ductility with a small (1 grade) improvement in crush rating.
Alloy C, with an
addition of 0.32% Cu relative to Alloy A, exhibited a yield strength in excess
of the 350 MPa
target with some deterioration in ductility as measured by the fracture strain
and crush rating.
Alloy D, with an addition of 0.61% Cu relative to Alloy A, exhibited an
excellent yield strength
of 379MPa with only slightly lower fracture strain and inferior crush rating
to Alloy C. Alloy
E, with an addition of 0.30% Cu relative to Alloy A, but no addition of Cr and
only 0.07% Mn,
resulted in a recrystallized grain structure. While Alloy E only exhibited a
yield strength of
346 MPa, it also gave the lowest fracture strain and highest (worst) crush
rating of 9,
representing full disintegration. Finally, Alloy F, which was similar to alloy
C but with the Mn
content increased to 0.77, gave slightly lower strength than alloy C, nearly
meeting the 350
MPa target, but a significantly better crush rating.
1461 The fracture strain and crush rating results for Examples 1 and 2 are
plotted in FIG. 2
as a function of the yield strength. From examination of this plot, it is
apparent that Alloys C
and D offer a yield strength in excess of 350 MPa and reasonable ductility in
terms of crush
rating and fracture strain. Although the existing commercial alloys AA6066 and
AA6056 are
capable of higher strengths, this increased strength is accompanied by a
significant
deterioration in fracture strain and crush rating relative to Alloys C and D.
The results for the
other alloy variants would suggest that a predominantly fibrous (non-
recrystallized) grain
structure is preferred, and that reduced levels of Mn and the absence of Cr,
as in the case of
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Alloy E, are undesirable. The improved crush rating and reasonably high yield
strength for
Alloy F suggests that increasing the Mn level to about 0.8% in addition to the
Cr addition could
also be beneficial.
1471 FIG. 3 shows a similar plot for MCF vs. yield strength for the alloys in
Examples 1 and
2. In general, the /vICF increases in line with the yield strength, with the
exception of Alloys
E and AA6066, due to their reduced ductility and premature failure in the
crush test. Similar
conclusions can be drawn from the data in FIGS. 2 and 3.
1481 FIG. 4 shows the extrusion pressure results for the breakthrough pressure
(upper curve)
and the pressure at mid stroke (lower curve), again plotted against the yield
strength to give an
indication of the penalty in extrudability incurred by increasing the alloy
strength. Adding extra
solute to an alloy to gain extra strength from artificial ageing would be
expected to increase the
high temperature flow stress, making the alloy more difficult to extrude. In
general, the higher
the extrusion pressure of an alloy, the lower the maximum extrusion speed that
can be achieved
for a given billet temperature. Using Alloy A as the baseline, FIG. 4
indicates that Alloy E was
the only variant to exhibit lower extrusion pressure than the base alloy.
However, as described
above, this also corresponded to significantly inferior ductility. Alloy B,
containing the V
addition, required ¨ 5% higher breakthrough pressure than Alloy A, with no
corresponding
increase in yield strength. Alloys C and D required extrusion pressure
increases of 1.8 and
5.9% respectively for useful yield strength increases of 49 and 67 MPa
relative to Alloy A.
Alloy F required a 6.9% increase in breakthrough pressure for a yield strength
gain of 36 MPa
relative to Alloy A. When the yield strength increase per % increase in
breakthrough pressure
values are compared in Table 4, it is clear that alloys C and D containing
additions of about 0.3
and 0.6 Cu are the most efficient in terms of achieving the target strength
level with minimum
loss of extrudability.
1491 EXAMPLE 3
1501 The alloy compositions G and H shown in Table 5 were direct chill cast as
228 mm
diameter ingots, cut into billets, homogenized for 2 hours at 560 C, and
cooled at 450 C/hour
after homogenization. Five billets of each alloy were extruded on a commercial
extrusion press
into a two-cavity bumper profile with wall thicknesses varying between 2.6 and
3.6 mm. A
billet preheat temperature of 500 C was used with a ram speed of 3 mm/s. The
profile was
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spray water quenched and artificially aged for 8 hours at 175 C. Alloys G and
H contained
Cu, Mn, and Cr contents similar to those of Alloy D from Example 2, but the Mg
and Si
contents of these alloys were increased relative to Alloy D. Tensile testing
was conducted on
the top and bottom of the profile, and the results are shown in Table 5.
All ____________________________________________________________ YS (MPa) UTS
(MPa) %El
oy
Si Fe Cu Mn Mg Cr V Zr Ti B
top bottom top bottom top bottom
0.91 0.18 0.70 0.60 0.79 0.12 0.014 0.001 0.03 0.002 383 363 416 399 12.2
10
H 1.01 0.17 0.58 0.60 0.70 0.14 0.016 0.001 0.03 0.004 378 360 406 392 12.4
10.6_
Table 5: Alloy Compositions and Mechanical Properties
1511 The grain structure was checked by optical metallography, and all
extrusions had a
predominantly fibrous/non-recrystallized grain structure. The strength of both
Alloys G and H
varied between the top and bottom locations, most likely due to variations in
quench rate
associated with the spray quench settings. Both alloys achieved yield
strengths of 360 MPa or
greater for the bottom locations with the lower quench rate and near or
exceeding 380 MPa at
the faster quenched top location.
1521 EXAMPLE 4
1531 Alloy I, shown in Table 6, was direct chill cast as 101.6 mm ingots and
cut into billets.
The billets were homogenized for 2 hours at 560 C and cooled at 450 C/hour
after
homogenization, and were then extruded into a 50 x 2.5mm strip using a billet
temperature of
500 C and a ram speed of 5 mm/s. The extrusion was water quenched at a rate of
1000 C/sec
at the press exit and then artificially aged for 8 hours at 175 C. After this
treatment, Alloy I
achieved a yield strength of 391 MPa, an ultimate tensile strength of 419 MPa,
and 12.7%
elongation in tensile testing.
Si Fe Cu Mn Mg Cr V Zr Ti B
, 0.93 0.17 0.63 0.48 0.73 0.14 0.013 .001 0.03 0.002
Table 6: Alloy Composition
1541 Alloy J, shown in Table 7, was direct chill cast as 254 mm diameter
billet and
homogenized for 3 hours at 560 C and cooled at 400 C/hour after
homogenization.
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Si Fe Cu Mn Mg Cr V Zr Ti
094 0.17 0.63 0.71 0.73 0.13 0.010 0.001 0.03 0.003
Table 7 : Alloy Composition
1551 This billet was extruded on a commercial press into a bumper profile with
an extrusion
ratio of 50.1 and wall thicknesses from 2.5 to 5mm using a billet temperature
of 490 C and an
exit speed of 81n/min. The profile was spray quenched at the press exit. After
artificial ageing
for 8 hours at 175 C, Alloy J achieved a yield strength of 395 MPa, an
ultimate tensile strength
of 421.9 MPa, and an elongation of 10.4%.
1561 EXAMPLE 5
1571 The alloy compositions listed in Table 8 were direct chill cast as
101.6mm ingots and
cut into 200mm billet lengths. The billets were grain refined using a 5%Ti-1%B
grain refiner
added prior to casting. The billets were homogenized for 3 hours at 560 C and
cooled at
400 C/hour, with the exception of alloy M, which had a lower equilibrium
solidus and as a
result was homogenized for 3 hours at 545 C to avoid melting, followed by
cooling at
400 C/hour. Groups of 6 billets of each alloy were extruded into 3 x 42mm
profiles with sharp
corners, using a billet temperature of 480 C. The ram speed for each group was
increased
incrementally on successive billets from 4mm/s to 9mm/s until speed cracking
was observed
at the corners, and, based on this observation, the maximum extrusion speed
(Vt) without
tearing was established. The extrusions were water quenched at the press exit
using a standing
wave water quench unit giving a quench rate of ¨ 1000 C/sec. The maximum
breakthrough
pressure was recorded during extrusion. Lengths of extrusion were then aged
for 8 hours at
175 C and tensile testing was performed. Table 8 presents the results for each
alloy in terms
of tearing speed (Vt), yield strength (YS), ultimate tensile strength (UTS),
breakthrough
pressure (Pmax). FIG. 5 illustrates the Mg and Si compositions of Alloys G-M
in Table 6 as
compared to the Mg/Si plots I-IV and I-IV' as shown in FIG. 1 and the ranges
of 0.60 ¨ 0.80
wt.% Mg and 0.85¨ 1.10 wt.% Si described in the specification. As shown in
FIG. 5, Alloys
G, H, I, and J are within these ranges, and Alloys K, L, and M are outside
these ranges.
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alloy Si Fe Cu Mn Mg Cr V Zr Ti B ,Vt
YS MPa LOTS MPa Pmax psi AP%
G 0.92 0.15 , 0.66, 0.47 0.66 0.08 0.01
<001 0.034, 0.001 6.5 373 405 , 1512 -4.8
H 1.05 0.19 , 0.64, 0.44 0.64 0.08 0.01
<001 0.035, 0.002 3.8 372 408 , 1491 -6.1
1 0.90 0.16 0.63 0.46 0.75 0.08 0.01 <001
0.033 0.001 6 381 412 1588 0.0
1.02 0.16 0.65 0.46 0.75 0.08 0.01 <001 0.033 0.002 3.8 379 421
K 0.72 0.16 0.64 0.46 0.64 0.08 0.01 <001 0.035 0.0017 7 352 383
1528 -3.8
0.79 0.17 0.65 0.48 0.83 0.08 0.01 <001 0.034 0.0015 6 367 398
1621 2.1
M 1.14 0.16 0.64 0.46 0.65 0.08 0.01 <001 0.034 0.0016 3.5 360 404
Table 8: Alloy Compositions and Test Results
[58] Alloys G, H, I and I all achieved yield strength levels in excess of 370
MPa, meeting
and comfortably exceeding the target strength of 350 MPa. Alloys H and .1 have
higher Si
contents, and these alloys exhibited significantly lower tearing speeds than
alloys G and I.
Alloy I achieved the best combination of high strength and high extrusion
speed of the alloys
tested in this Example. Table 8 shows the /'-O breakthrough pressure increase
or decrease (AP%)
compared to Alloy 1. Extrusion pressure values are not shown for alloys .1 and
M, as these
alloys could not be extruded at comparable speeds to the other alloys.
1591 Alloys K, L, and NI have compositions outside the Mg/Si plot I-IV as
shown in FIG. 1,
and these alloys all exhibited lower yield strengths than Alloys G, H, I, and
J that fall within
the Mg/Si plot I-IV. Alloy K has a lower Si content such that the composition
is outside the
Mg/Si plot I-1V as shown in FIG. 1, and this alloy achieved a yield strength
of only 352 MPa.
The yield strength of Alloy K is insufficiently in excess of the target
strength of 350 MPa to
ensure that the target strength is consistently met in a production alloy,
indicating a Si content
higher than 0.72 wt.% achieves superior results. Alloy M has the highest
silicon content such
that the composition is outside the Mg/Si plot I-IV as shown in FIG. 1. Alloy
NI exhibited the
lowest tearing speed, indicating that Alloy M is inferior for extrusion.
Additionally, Alloy M
exceeded the target strength of 350 MPa by only I OMPa, and the yield strength
of Alloy M is
insufficiently in excess of the target strength of 350 MPa to ensure that the
target strength is
consistently met in a production alloy. The loss in extrudability and strength
in Alloy NI
compared to Alloys G, H, I and J indicate that a lower silicon content than
1.14 wt.% achieves
superior results. Alloy L has a high Mg content such that the composition is
outside the Mg/Si
plot as shown in FIG. 1. Alloy L exhibited generally acceptable strength
and tearing
speed. However, Alloy L still exhibited lower strength than Alloys G, H, 1,
and J, in addition
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16
to higher extrusion pressure (and therefore inferior extrudability) compared
to Alloys G, H and
I. Thus, under commercial extrusion conditions, the extrusion speed of Alloy L
could be further
restricted by the need to increase the billet temperature to reduce extrusion
pressure. Alloy L
therefore represents a combination of Mg and Si that exhibits an inferior
combination of
strength and extrudability compared to alloys that are within the Mg/Si plot I-
IV as shown in
FIG. 1 (e.g., Alloys G, H, and I).
[60] Based on the strength and extrudability performance of alloys G, H, I,
and J in this test,
it has been demonstrated that the ranges of Mg and Si in the Mg/Si plot I-IV
as shown in FIG.
1 and the ranges of 0.60 ¨0.80 wt.% Mg and 0.85 ¨ 1.10 wt.% Si described in
the specification
can provide yield strength levels comfortably in excess of the target of
3501vffia, with good
extrudability. These testing results also establish that lower silicon
contents do not provide
adequate strength and higher silicon contents provide inferior strength and
inferior
extrudability. These testing results also establish that higher Mg contents
result in an increase
in extrusion pressure and inferior extrudability, with slightly inferior
strength. The testing
results further establish that the use of Mg and Si in ranges of 0.70 ¨ 0.80
wt.% Mg and 0.85 ¨
0.95 wt.% Si achieve a particularly advantageous combination of strength and
extrudability.
[61] Several alternative embodiments and examples have been described and
illustrated
herein. A person of ordinary skill in the art would appreciate the features of
the individual
embodiments, and the possible combinations and variations of the components. A
person of
ordinary skill in the art would further appreciate that any of the embodiments
could be provided
in any combination with the other embodiments disclosed herein. It is
understood that the
invention may be embodied in other specific forms without departing from the
spirit or central
characteristics thereof. The present examples and embodiments, therefore, are
to be considered
in all respects as illustrative and not restrictive, and the invention is not
to be limited to the
details given herein. Accordingly, while the specific embodiments have been
illustrated and
described, numerous modifications come to mind without significantly departing
from the
spirit of the invention and the scope of protection is only limited by the
scope of the
accompanying claims.
