Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ARMOUR COMPONENT PRODUCED FROM A 7XXX-SERIES
ALUMINIUM ALLOY
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of and priority to U.S. Provisional Patent
Application No. 63/224,618, filed July 22, 2021, the contents of which are
herein
incorporated by reference in its entirety.
FIELD
Described herein are armour components for civil or military vehicles made of
high-
strength 7XXX-series aluminium alloys requiring ballistic protection. More
particularly,
described herein are armour components used for manufacturing armour hulls and
add-on
appliqués, which are removable panels to be mounted on the external faces of
the military
vehicles.
BACKGROUND
Generally, an armour shield includes a metal panel, typically of steel,
aluminium,
titanium or alloys thereof Such panels have an excellent ability to absorb
kinetic energy of a
penetrator during impact. However, particularly if they are made of a steel
alloy, such panels
are heavy and have a low effectiveness in terms of absorption of energy
related to the weight
carried by a vehicle. Because of their light weight, aluminium alloys have
found wide use in
military applications, including military vehicles such as personnel carriers.
The light weight
of aluminium allows for improved performance and ease of transporting
equipment,
including air transport of military vehicles. In some vehicles it is advisable
to provide
shielding or protection against assault, by providing armour plate to protect
the occupants of
the vehicle. Aluminium has enjoyed substantial use as armour plate, and there
are a number
of armour plate specifications for the use of different aluminium alloys.
The most relevant requirements for aluminium alloy armour plate are resistance
to
projectiles, good corrosion resistance and stress corrosion resistance in
particular, and in
some applications, good weldability. Ballistic tests are often conducted with
armour piercing
("AP") projectiles such as the 7.62 mm AP M2 and with fragment simulating
projectiles
("FSP") such as the common 20 mm projectile. The first test is intended to
characterize the
resistance to perforation and the second test is intended to quantify to
withstand the impacts
which generate fragmented debris. During these tests, the armour panels are
the target of
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projectiles of different shapes and sizes (spindle shape for the AP test, a
more squat form for
the FSP test). In each test type, several geometries are used in the
projectile according to the
thickness of the test panel and the nature of the threats that said armour
panel is intended to
protect. For example, according to US military specification MIL-DTL-46063H,
plates made
of 7039 alloy and thicker than 1.5 inches are submitted to AP tests with 0.5
inches calibre AP
M2 bullets while plates thinner than 1.5 inches are submitted to AP tests with
0.3 inches
calibre AP M2 bullets. However, in practice, 0.3 inches calibre AP M2 bullets
are still used
for AP tests on plates slightly thicker than 1.5 inches.
For both tests, the ability to stop bullets and absorb their kinetic energy is
quantified by
a parameter called "V50 ballistic limit" having a speed dimension. V50 is
defined for
example in MIL-STD-662 (1997) standard: it is the velocity at which the
probability of
penetration of an armour material is 50%. It is established by calculating the
average of
speeds attained by the projectiles on impact resulting from taking the same
number of results
having the highest speeds corresponding to a partial penetration and results
having the lowest
speeds corresponding to a complete penetration. A complete penetration occurs
when the
impacting projectile or any fragment (of the projectile or of the test
specimen) perforates a
thin witness plate located behind the test specimen.
Aluminium alloys which satisfy all the requirements for armour plate are
desirable, and
these desires have been met to varying degrees. For example, aluminium alloys
AA5083,
AA5456 and AA5059 are covered in the U.S. Military Specification for armour
plate MIL-
DTL-46027K (July 2007), and the alloy AA7039 is covered in the U.S. Military
Specification
MIL-DTL-46063H (September 1998). It is generally recognized that for many
applications
the alloy AA7039 armour plate is better than AA5083 and AA5456 armour plate,
although
the advantage is more for armour piercing ballistic performance and less so
for fragment
simulation performance, at least according to the military specifications.
However, the alloy
AA7039 can present corrosion or stress corrosion problems to a much greater
degree than
AA5083 and AA5456. The AA7039 alloy when used for armour plate applications is
commonly in a T6 temper and the AA5083 and AA5456 alloys when used for armour
plate
applications is used in the H131 temper.
Patent document US-8,206,517-B1 discloses an armour component in the form of a
plate having a thickness of 1-4 inches (25.4-101.6 mm) made of a 7xxx-series
aluminium
alloy, which contains essentially (in wt.%): 7.0-9.5% Zn, 1.3-1.68% Mg, 1.2-
1.9% Cu, up to
0.4% of at least one grain structure element, the rest being aluminium and
incidental elements
and impurities. Said 7XXX-series aluminium alloy is over-aged via a three-step
ageing
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process such that it should comply simultaneously with three conditions
relating to yield
strength of not greater than 68 ksi (455.6 MPa), FSP performance and spall
resistance. The
chemistry of the 7XXX-series alloy in US Patent No. 8,206,517 largely overlaps
with that of
alloy AA7085. US military specification MIL-DTL-32375 (MR) covers 7085 wrought
aluminium armour plate for non-fusion welded applications in nominal
thicknesses from
0.500 to 3.000 inches.
Patent document US-8,747,580-B1 discloses a method of manufacturing a
ballistic
resistant aluminium alloy, comprising forging an aluminium alloy into an
armour component
having a thickness of 1-4 inches (25.4-101.6 mm) wherein the 7XXX-series
aluminium alloy,
which contains essentially (in wt.%) 7.0-9.5% Zn, 1.3-1.68% Mg, 1.2-1.9% Cu,
up to 0.4%
of at least one grain structure element, the rest being aluminium and
incidental elements and
impurities, solution heat treating the forged armour component followed and
quenching and
artificial over-ageing such that it should comply simultaneously with a
longitudinal yield
strength of not greater than 70 ksi (469 MPa) and a defined spall resistance.
The chemistry of
the 7XXX-series alloy in US Patent No. 8,747,580 largely overlaps with that of
alloy
AA7085.
Patent document US-8,758,530-B1 discloses a method of manufacturing an armour
component made from 2XXX- or 7XXX-series aluminium alloys and wherein the
aluminium
alloy product is being underaged to produce a certain ballistic performance
which is said to
be better than that of a peak strength aged version of the aluminium alloy
products. It is
reported that in particular the FSP resistance is improved by the under-ageing
treatment. AP
resistance and FSP resistance are antagonist properties: when an armour
material has a high
FSP resistance, it has a reduced AP resistance. Under-ageing of 7XXX-series
aluminium
alloy leads to a reduced corrosion resistance compared to over-ageing.
Patent document US-10,308,998-B2 discloses an armour component produced from a
7XXX-series aluminium alloy, wherein the aluminium alloy consists essentially
of (in wt.%):
8.4-10.5% Zn, 1.3-2% Mg, 1.2-2% Cu, at least 0.05-0.3% of a dispersoid forming
element
from the group consisting of (Zr, Sc, V, Hf, Ti, Cr, and Mn), the remainder
substantially
aluminium, incidental elements and impurities, wherein the 7XXX alloy is in
the form of a
plate having a thickness of 0.5 to 3 inches (12.7-76.2 mm), and wherein the
7XXX alloy is
aged to achieve a defined lower-limit for both the AP and FSP resistance. The
chemistry of
the 7XXX-series alloy in US Patent No. 10,308,998 largely overlaps with that
of alloy
AA7056. US military specification MIL-DTL-32375 (MR) covers 7056 wrought
aluminium
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armour plate for non-fusion welded applications in nominal thicknesses from
0.500 to 3.000
inches.
Patent document WO-2017/044471-A1 discloses a method of producing an armour
component, comprising casting a 7XXX-series aluminium alloy to obtain an
ingot, wherein
the 7XXX-series aluminium alloy comprises or consists essentially of (in
wt.%), 8.4-10.5%
Zn, 1.3-2% Mg, 1.2-2% Cu, at least 0.04-0.3% of a dispersoid forming element
from the
group consisting of (Zr, Sc, V, Hf, Ti, Cr, and Mn), the remainder
substantially aluminium,
incidental elements and impurities, homogenization; hot working the
homogenised ingot to
obtain a plate having a first thickness Ti; cold working the plate having the
first thickness to
obtain a plate having a second thickness T2, wherein T2 = Ti ¨ (xl*T2)/100 and
0.5<xl<15); solution heat treating; quenching and ageing. The combination of
the cold
working operation, i.e., a combination of cold rolling and stretching, and
using Zr as the
dispersoid forming element in a range of 0.04-0.10%, preferably 0.05-0.08%,
provides in
particular an improved spall resistance. The chemistry of the 7XXX-series
alloy in WO-
2017/044471-Al largely overlaps with that of alloy AA7056.
SUMMARY
Covered embodiments of the invention are defined by the claims, not this
summary.
This summary is a high-level overview of various aspects of the invention and
introduces
some of the concepts that are further described in the Detailed Description
section below.
This summary is not intended to identify key or essential features of the
claimed subject
matter, nor is it intended to be used in isolation to determine the scope of
the claimed subject
matter. The subject matter should be understood by reference to appropriate
portions of the
entire specification, any or all drawings, and each claim.
Described herein is an armour component produced from a 7XXX-series aluminium
alloy, wherein the aluminium alloy comprises:
Zn 7.1% to 7.5%,
Mg 1.90% to 2.25%,
Cu 1.3% to 1.8%,
at least 0.05-0.4% of a dispersoid forming element selected from the group
consisting of Zr, Sc, V, Hf, Ti, Cr, and Mn,
Ti 0.01% to 0.06%,
Si up to 0.15%,
Fe up to 0.15%,
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balance unavoidable impurities and aluminium,
wherein the 7XXX-series aluminium alloy is in the form of a plate having a
thickness
of 12.7 mm to 76.2 mm;
wherein the 7XXX-series aluminium alloy is over-aged to achieve a combination
of:
(i) tensile yield strength in LT-direction > 497 MPa,
(ii) ultimate tensile strength in LT-direction > 538 MPa,
(iii) elongation in LT-direction > 9%, and
(iv) an armour piercing V50 ballistic limit such that meets the requirements
of
US military spec MIL DTL-32375B (MR) (2021).
Optionally, the Zn content is in a range of 7.20% to 7.5% or 7.30% to 7.5%. In
some
cases, the Zn/Mg ratio is less than 4 (e.g., less than 3.9). Optionally, the
dispersoid forming
element comprises Zr in a range of 0.06% to 0.15% (e.g., 0.08% to 0.14% or
0.09% to
0.13%). In some cases, the Mg content is in a range of 1.9% to 2.25% (e.g.,
1.95% to
2.20%).
In some cases, the over-ageing treatment comprises the following 2-step
treatment: 4-
12 hours at 110 C-130 C followed by 4-20 hours at 140 C-160 C. Optionally, the
over-
ageing treatment comprises the following 2-step treatment: 4-12 hours at 110 C-
130 C
followed by 12-20 hours at 140 C-160 C. Optionally, the over-ageing treatment
comprises
the following 2-step treatment: 4-12 hours at 110 C-130 C followed by 12-18
hours at
140 C-160 C.
The 7XXX-series aluminium alloy can optionally be manufactured with the
following
steps:
a. casting said alloy into an ingot form;
b. homogenizing said ingot;
c. hot working said ingot to obtain a plate;
d. solution heat treating;
e. quenching;
f stretching to obtain a permanent elongation from 1% to 3%; and
g. over-ageing at least in two steps, the over-ageing treatment
corresponding
to the following 2-step treatment: 4-12 hours at 110 C-130 C followed by
12-20 hours at 140 C-160 C.
Optionally, the 7XXX-series alloy comprises or consists of, in wt.%:
Zn 7.1% to 7.5%, preferably 7.20% to 7.5%,
Mg 1.90% to 2.25%, preferably 1.95% to 2.25%,
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Cu 1.3% to 1.8%,
Zr 0.06% to 0.15%, preferably 0.08% to 0.13%,
Ti 0.01% to 0.06%,
Si up to 0.15%
Fe up to 0.15%,
balance unavoidable impurities and aluminium.
The Si content or the Fe content can optionally be up to 0.10 wt. %. In some
cases, the
elongation in LT-direction is > 9 %.
Further described herein is a method of producing an armour component as
described
herein, comprising:
a. casting said alloy into an ingot form;
b. homogenizing said ingot;
c. hot working said ingot to obtain a plate;
d. solution heat treating;
e. quenching;
f stretching to obtain a permanent elongation from 1% to 3%; and
g. over-ageing at least in two steps, the over-ageing heat treatment
corresponding to the following two-step heat treatment: 4-12 hours at
110 C-130 C followed by 12-20 hours at 140 C-160 C.
Optionally, the over-ageing treatment corresponds to the following 2-step
treatment: 4-
12 hours at 110 C-130 C followed by 12-20 hours at 140 C-160 C. Optionally,
the over-
ageing treatment corresponds to the following 2-step treatment: 4-12 hours at
110 C-130 C
followed by 12-18 hours at 140 C-160 C.
Also described herein is an armour component produced from a 7XXX-series
aluminium alloy, wherein the aluminium alloy consists essentially of:
Zn 7.1% to 7.5%,
Mg 1.90% to 2.25%,
Cu 1.3% to 1.8%,
at least 0.05-0.4% of a dispersoid forming element selected from the group
consisting of Zr, Sc, V, Hf, Ti, Cr, and Mn,
Ti 0.01% to 0.06%,
Si up to 0.15%,
Fe up to 0.15%,
balance unavoidable impurities and aluminium,
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wherein the 7XXX-series aluminium alloy is in the form of a plate having a
thickness
of 12.7 mm to 76.2 mm;
wherein the 7XXX-series aluminium alloy is over-aged to achieve a combination
of:
(i) tensile yield strength in LT-direction > 497 MPa,
(ii) ultimate tensile strength in LT-direction > 538 MPa,
(iii) elongation in LT-direction > 9%, and
(iv) an armour piercing V50 ballistic limit such that meets the requirements
of
US military spec MIL DTL-32375B (MR) (2021).
Optionally, the Zn content is in a range of 7.20% to 7.5% or 7.30% to 7.5%. In
some
cases, the Zn/Mg ratio is less than 4 (e.g., less than 3.9). Optionally, the
dispersoid forming
element is essentially Zr in a range of 0.06% to 0.15% (e.g., 0.08% to 0.14%
or 0.09% to
0.13%). In some cases, the Mg content is in a range of 1.9% to 2.25% (e.g.,
1.95% to
2.20%).
In some cases, the over-ageing treatment corresponds to the following 2-step
treatment: 4-12 hours at 110 C-130 C followed by 4-20 hours at 140 C-160 C.
Optionally,
the over-ageing treatment corresponds to the following 2-step treatment: 4-12
hours at
110 C-130 C followed by 12-20 hours at 140 C-160 C. Optionally, the over-
ageing
treatment corresponds to the following 2-step treatment: 4-12 hours at 110 C-
130 C followed
by 12-18 hours at 140 C-160 C.
The 7XXX-series aluminium alloy can optionally be manufactured with the
following
steps:
a. casting said alloy into an ingot form;
b. homogenizing said ingot;
c. hot working said ingot to obtain a plate;
d. solution heat treating;
e. quenching;
f stretching to obtain a permanent elongation from 1% to 3%; and
g. over-ageing at least in two steps, the over-ageing treatment
corresponding
to the following 2-step treatment: 4-12 hours at 110 C-130 C followed by
12-20 hours at 140 C-160 C.
Optionally, the 7XXX-series alloy consists of, in wt.%:
Zn 7.1% to 7.5%, preferably 7.20% to 7.5%,
Mg 1.90% to 2.25%, preferably 1.95% to 2.25%,
Cu 1.3% to 1.8%,
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Zr 0.06% to 0.15%, preferably 0.08% to 0.13%,
Ti 0.01% to 0.06%,
Si up to 0.15%
Fe up to 0.15%,
balance unavoidable impurities and aluminium.
The Si content or the Fe content can optionally be up to 0.10 wt. %. In some
cases, the
elongation in LT-direction is > 9 %.
Further described herein is a method of producing an armour component as
described
herein, comprising:
a. casting said alloy into an ingot form;
b. homogenizing said ingot;
c. hot working said ingot to obtain a plate;
d. solution heat treating;
e. quenching;
f stretching to obtain a permanent elongation from 1% to 3%; and
g. over-ageing at least in two steps, the over-ageing heat treatment
corresponding to the following two-step heat treatment: 4-12 hours at
110 C-130 C followed by 12-20 hours at 140 C-160 C.
Optionally, the over-ageing treatment corresponds to the following 2-step
treatment: 4-
12 hours at 110 C-130 C followed by 12-20 hours at 140 C-160 C. Optionally,
the over-
ageing treatment corresponds to the following 2-step treatment: 4-12 hours at
110 C-130 C
followed by 12-18 hours at 140 C-160 C.
Other objects and advantages of the invention will be apparent from the
following
detailed description of non-limiting examples.
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DETAILED DESCRIPTION
As will be appreciated herein below, except as otherwise indicated, aluminium
alloy
designations and temper designations refer to the Aluminium Association
designations in
Aluminium Standards and Data and the Registration Records, as published by the
Aluminium
Association in 2019, and frequently updated, and are well known to the person
skilled in the
art. The temper designations are laid down in European standard EN515. Unless
mentioned
otherwise, static mechanical characteristics, in other words the ultimate
tensile strength UTS,
the tensile yield stress TYS and the elongation at fracture A, are determined
by a tensile test
according to standard ASTM B557.
For any description of alloy compositions or preferred alloy compositions, all
references to percentages are by weight percent unless otherwise indicated.
The term "up to" and "up to about", as employed herein, explicitly includes,
but is not
limited to, the possibility of zero weight-percent of the particular alloying
element to which it
refers. For example, up to 0.03% Mn may include an aluminium alloy having no
Mn.
Provided herein is an armour component product from a 7XXX-series aluminium
alloy
in the form of a plate and having been over-aged to achieve a combination of a
high strength,
high elongation at fraction and good AP resistance.
Also provided herein is a method for manufacturing an armour component product
from
a 7XXX-series aluminium alloy in the form of a plate and having been over-aged
to achieve a
combination of a high strength, high elongation at fraction and good AP
resistance.
These and other objects and further advantages are met or exceeded by the
present
disclosure providing an armour component produced from a 7XXX-series aluminium
alloy,
wherein the aluminium alloy comprises or consists essentially of:
Zn 7.1% to 7.5%,
Mg 1.90% to 2.25%,
Cu 1.3% to 1.8%,
at least 0.05-0.4% of a dispersoid forming element selected from the group
consisting of Zr, Sc, V, Hf, Ti, Cr, and Mn,
Ti 0.01% to 0.06%,
Si up to 0.15%,
Fe up to 0.15%,
balance unavoidable impurities and aluminium. Typically, inevitable impurities
are
each up to 0.05% maximum and in total 0.15% maximum. The 7XXX-series aluminium
alloy
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is in the form of a plate having a thickness of 12.7 mm to 76.2 mm (0.5 to 3
inches); and the
7XXX-series aluminium alloy is over-aged to achieve a combination of target
properties:
(i) tensile yield strength in long transverse-direction (LT-direction) >
504 MPa
for thicknesses of 1.501 to 2.000 inch incl. and > 497 MPa for thicknesses
of 2.001 to 3.000 inch incl.
(ii) ultimate tensile strength in LT-direction > 545 MPa for thicknesses of
1.501 to 2.000 inch incl. and > 538 MPa for thicknesses of 2.001 to 3.000
inch incl.
(iii) elongation in LT-direction >10% for thicknesses of 1.501 to 2.000
inch
incl. and >9% for thicknesses of 2.001 to 3.000 inch incl.
(iv) an armour piercing V50 ballistic limit such that:
the minimum requirements of MIL-DTL-32375B Class I Type A are met.
Compared to AA7085, the alloys as described herein have a higher tensile
strength of at
least 1 Ksi for each thickness range. Compared to AA7056, the alloys as
described herein
generally have an elongation of at least a minimum 2-3% or higher. Compared to
7081 and
7056, the alloys as described herein have a lower density, which is beneficial
for
lightweighting, as further described herein.
Another advantage is also the improved Mass Efficiency compared to AA7056-T711
counterparts. Due to amongst others a significantly lower Zn content, the 7XXX-
series
aluminium alloy product described herein has a lower specific density measured
at 20 C
compared to AA7056 alloys resulting in a favourable strength-to-weight ratio
or specific
strength (tensile strength divided by specific density). The Mass Efficiency
is a measure for
the AP performance and relates also to the specific density and allows for a
fair comparison
of various armour plate materials of similar gauge against each other. Mass
Efficiency or
"Em" is defined as the weight per unit area of a reference material, for
example an AA7056-
T761 counterpart alloy, required for defeating a given ballistic threat
divided by the weight
per unit area of the subject material. The improved mass efficiency of the
armour plate
component allows for the construction of a lighter vehicle while offering the
same resistance
against incoming projectiles. Weight saving in an armoured vehicle can
translate amongst
other advantages, into vehicle mobility. Alternatively, when constructing an
armoured
vehicle an unchanged plate thickness can be used while offering a
significantly improved
resistance against incoming projectiles and thereby an increased
survivability.
Zinc (Zn), magnesium (Mg), and copper (Cu) are the major alloying elements of
the
7XXX-series aluminium alloy armour component. Zn combined with Mg and Cu
within the
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defined compositional ranges provide simultaneously high static mechanical
properties in
combination with good AP ballistic test results.
The Zn content should be in a range of 7.1% to 7.5%. In a preferred embodiment
the Zn
content is at least 7.20%, and more preferably at least 7.30%.
The Mg content should be in a range of 1.90% to 2.25%. In a preferred
embodiment the
Mg content is at least 2.0%. In an embodiment the Mg content is not more than
about 2.20%.
In an embodiment the 7XXX-series aluminium alloy has a Zn/Mg ratio (in wt.%)
of less
than 4. In an embodiment the Zn/Mg ratio is less than 3.9, and preferably less
than 3.8.
Exfoliation corrosion tests according to ASTM G34 exhibit a rating of EB or EA
regardless if the test is performed on the as-rolled surface or if the surface
has been milled
down to 90% of its thickness (s/10). A rating of EA indicates superficial
corrosion, while a
rating of EB indicates moderate corrosion.
Furthermore, it has been found that by controlling the Zn/Mg ratio the
resistance to
hydrogen embrittlement is improved. Hydrogen embrittlement is where brittle
cracking of an
aluminium alloy can occur when a susceptible aluminium alloy is subjected to a
sustained
stress in particular in the short transverse (ST) direction for longer periods
of time in a humid
atmosphere. This phenomenon, also known as environmentally assisted cracking
("EAC"),
can be a challenge for component manufacturers since under certain conditions
the structural
integrity can be affected. Sensitivity to this form of EAC has been observed
especially in high
Zn containing high strength aluminium alloys.
In an embodiment the 7XXX-series aluminium alloy product has a Cu-content of
maximum about 1.8%, and preferably of maximum about 1.75%, and more preferably
of
maximum about 1.70%. The minimum Cu-content is about 1.3%, and more preferably
1.35%
to provide sufficient strength and elongation at fracture, AP resistance, good
stress corrosion
cracking (SCC) resistance in combination with a low sensitivity to EAC under
conditions of
high stress and humid environment.
The aluminium alloy comprises at least about 0.05%-0.4% of a dispersoid
forming
element selected from the group consisting of Zr, Sc, V, Hf, Ti, Cr, and Mn to
control the
grain structure during thermo-mechanical processing. Two or more dispersoid
forming
elements can be added but the sum should not exceed 0.4%. In a preferred
embodiment the
dispersoid forming element is Zr. Preferably the Zr content is maximum about
0.15%, and
more preferably about 0.14%. In an embodiment the Zr content is at least
0.06%, and more
preferably about 0.08%.
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The iron (Fe) and silicon (Si) contents should be kept low, for example not
exceeding
about 0.15% Fe, and preferably less than about 0.10% Fe, and not exceeding
about 0.15% Si
and preferably about 0.10% Si or less.
In the aluminium alloy the balance is made by aluminium and unavoidable
impurities,
typically each up to 0.05% maximum and in total 0.15% maximum.
In an embodiment the aluminium alloy includes or consists of: Zn 7.1% to 7.5%,
Mg
1.90% to 2.25%, Cu 1.3% to 1.8%, Zr 0.06% to 0.15%, Ti 0.01% to 0.06%, Si up
to 0.15%,
Fe up to 0.15%, balance unavoidable impurities and aluminium, and with
preferred narrower
ranges as herein described and claimed.
The 7XXX-series aluminium alloy of the armour component has been over-aged in
at
least two steps to achieve the combination of properties.
In an embodiment, the over-ageing heat treatment corresponds to the following
2-step
treatment: about 4 to 12 hours at 110 C to 130 C followed by 1 to about 2 to
20 hours at
140 C to 160 C, and preferably about 12 to 18 hours at 140 C to 160 C.
In an embodiment the armour component from the 7XXX-series aluminium alloy
plate
achieves an armour piercing V50 ballistic limits described by MIL-DTL-32375B
Class 1
Type A.
In an embodiment the armour component from the 7XXX-series aluminium alloy
achieves a tensile yield strength in LT-direction > 497 MPa, and preferably >
504 MPa.
In an embodiment the armour component from the 7XXX-series aluminium alloy
achieves an ultimate tensile strength in LT-direction > 538 MPa, and
preferably > 545 MPa.
In an embodiment the armour component from the 7XXX-series aluminium alloy
achieves an elongation in the LT-direction > 10 %.
According to the present description, the 7XXX-series aluminium alloy plate of
the
armour component has a thickness in the range of about 12.7 mm to about 76.2
mm (about
0.5 to about 3 inches), and preferably of about 25.4 mm to about 76.2 mm
(about 1 to about 3
inches).
The 7XXX-series plate product forming part of the armour component is
manufactured
in the conventional method, the method comprising the steps, in that order,
of:
a. casting stock of a rolling ingot of the AA7XXX-series aluminium alloy
according to the
present disclosure;
b. homogenizing the rolling ingot;
c. hot working by means of rolling the ingot to obtain a plate;
d. solution heat treating ("SHT") of the plate;
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e. cooling the SHT plate, preferably by one of spray quenching or
immersion quenching
in water or other quenching media;
f stretching or compressing of the cooled SHT plate or otherwise cold
working of the
cooled SHT plate to relieve stresses, for example levelling or drawing or cold
rolling of the
cooled SHT stock;
g. artificial over-ageing at least in two steps to obtain the
combination of target properties.
The 7XXX-series aluminium alloy can be provided as an ingot or slab or billet
for
fabrication into a suitable wrought product by casting techniques regular in
the art for rolling
ingots, e.g., Direct-Chill (DC)-casting, Electro-Magnetic-Casting (EMC)-
casting, Electro-
Magnetic-Stirring (EMS)-casting. Slabs resulting from continuous casting,
e.g., belt casters
or roll casters, also may be used, which in particular may be advantageous
when producing
thinner gauge plate products. Grain refiners such as those containing titanium
(Ti) and boron
(B), or titanium and carbon (C), can be used. The Ti-content in the aluminium
alloy is up to
0.15%, and preferably in a range of about 0.01% to 0.06%. Optionally a cast
ingot can be
stress relieved, for example by holding it at a temperature in a range of
about 350 C to 450 C
followed by slow cooling to ambient temperature. After casting the ingot can
be scalped to
remove segregation zones near the as-cast surface of the ingot and to improve
product
flatness.
The purpose of a homogenization heat treatment has at least the following
objectives:
(i) to dissolve as much as possible coarse soluble phases formed during
solidification, and (ii)
to reduce concentration gradients to facilitate the dissolution step. A
preheat treatment
achieves also some of these objectives.
First, the soluble eutectic phases and/or intermetallic phases such as the S-
phase, T-
phase, and M-phase in the aluminium alloy ingot are dissolved using regular
industry
practice. This is typically carried out by heating the stock to a temperature
of less than 500 C,
typically in a range of 450 C to 485 C, as S-phase (Al2MgCu-phase) has a
dissolution
temperature of about 489 C in AA7XXX-series alloys and the M-phase (MgZn2-
phase) has a
dissolution temperature of about 478 C. This can be achieved by a
homogenization treatment
in said temperature range and allowed to cool to the hot rolling temperature,
or after
homogenization the stock is subsequently cooled and reheated before hot
rolling. The
homogenization process can also be done in two or more steps if desired, and
which are
typically carried out in a temperature range of 440 C to 490 C for the AA7XXX-
series alloy.
In a particular favourable embodiment a two-step homogenization process is
applied. There
is a first step between 455 C and 470 C, and a second step between 470 C and
485 C, to
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optimise the dissolving process of the various phases depending on the exact
aluminium alloy
composition.
The soaking time at the homogenization temperature is in the range of 1 to 50
hours,
and more typically for 2 to 20 hours. The heat-up rates that can be applied
are those which
are regular in the art.
The hot working, and hot rolling in particular, may be performed to a near
final gauge,
which is between 12.7 mm and 76.2 mm.
In an embodiment the plate material is hot rolled in a first hot rolling step
to an
intermediate hot rolled gauge, followed by an intermediate annealing step and
then hot rolled
in a second hot rolling step to near final hot rolled gauge.
In another embodiment the plate material is hot rolled in a first hot rolling
step to an
intermediate hot rolled gauge, followed by a recrystallization annealing
treatment at a
temperature up to the SHT temperature range and then hot rolled in a second
hot rolling step
to near final hot rolled gauge.
A next process step is solution heat treating ("SHT") of the hot rolled plate.
The product
should be heated to bring as much as possible, all or substantially all
portions of the soluble
zinc, magnesium and copper into solution. The SHT is preferably carried out in
the same
temperature range and time range as the homogenization treatment according as
set out in this
description, i.e. about 460-490 C. However, it is believed that also shorter
soaking times can
.. still be very useful, for example in the range of about 2 to 180 minutes.
The SHT is typically
carried out in a batch or a continuous furnace. After SHT, it is important
that the aluminium
alloy be cooled with a high cooling rate to a temperature of 90 C or lower,
preferably to
ambient temperature, to prevent or minimise the uncontrolled precipitation of
secondary
phases, e.g., Al2CuMg and Al2Cu, and/or MgZn2. On the other hand cooling rates
should
preferably not be too high to allow for a sufficient flatness and low level of
residual stresses
in the product. Suitable cooling rates can be achieved with the use of water,
e.g. water
immersion or water jets. The cooling rate is preferably in a range of about 1
C/sec to 9 C/sec,
and preferably about 2 C/sec to 5 C/sec when measured at mid-thickness of the
product.
The plate is further cold worked, for example, by stretching in the range of
about 1% to
6% to relieve residual stresses therein and to improve the flatness of the
plate product.
Preferably the stretching is in the range of about 1% to 3%. After cooling the
plate is
artificially over-aged, in at least two steps to achieve the combination of
properties. In an
embodiment the over-ageing treatment corresponds to the following two-step
ageing heat
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treatment: about 4 to 12 hours at 110 C to 130 C followed by about 12 to 20
hours, and about
preferably 12-18 hours, at 140 C to 160 C.
In another embodiment, the 7XXX-series plate product forming part of the
armour
component can be manufactured by:
a. casting stock of a rolling ingot of the AA7XXX-series aluminium alloy
according to this disclosure;
b. homogenizing the rolling ingot;
c. sawing or machining the ingot;
d. preheating the ingot;
e. rolling the ingot to form a plate;
sawing the plate;
g. solution heat treating (or SHT) the plate at approximately 470 C;
h. stretching the plate approximately 2% to 3% with respect to length;
i. heat treatment of the plate at 120 C for a period (e.g., up to eight
hours) and
then at 155 C for a period (e.g., up to six hours);
j. marking or sawing the plate;
k. testing properties and performance of the plate; and
1. inspection, and packaging, of the plate.
The 7XXX-series aluminium alloy can be provided and cast as described above.
The
homogenization can be performed on the ingot as described above. The ingot can
be sawed or
machined as described above or using other suitable sawing or machining
techniques. The
ingot can be preheated using a pit furnace or by other suitable techniques,
for heating the
ingot to a suitable temperature for rolling. The ingot can be rolled to form a
plate as described
above or using other suitable rolling techniques. The plate can be solution
heat treated (or
SHT) at approximately 470 C and can be stretched to between 2% and 3%. The
plate can be
heat treated using the techniques described herein, or using other suitable
techniques. The
plate can be marked, or sawed, using suitable techniques. The plate can be
tested for ballistic
properties or performance, static properties or performance, or for other
suitable properties or
performance. The plate can be inspected to verify the plate is free from
defects and can be
.. packaged.
In yet another embodiment, the 7XXX-series plate product forming part of the
armour
component can be manufactured by:
a. casting stock of a rolling ingot of the AA7XXX-series
aluminium alloy as
described herein;
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b. homogenizing the rolling ingot;
c. sawing or machining the ingot;
d. preheating the ingot;
e. rolling the ingot to form a plate;
f sawing the plate;
g. solution heat treating (or SHT) the plate at approximately 470 C;
h. stretching the plate approximately 2% to 3% with respect to length;
i. heat treatment of the plate at 120 C for a period (e.g., up to eight
hours) and
then at 155 C for a period (e.g., 14, 16, or 18 hours);
j. marking or sawing the plate;
k. testing properties and performance of the plate;
1. inspection, and packaging, of the plate.
The 7XXX-series aluminium alloy can be provided and cast as described above.
The
homogenization can be performed on the ingot as described above. The ingot can
be sawed or
machined as described above or using other suitable sawing or machining
techniques. The
ingot can be preheated using a pit furnace, or by other suitable techniques,
for heating the
ingot to a suitable temperature for rolling. The ingot can be rolled to form a
plate as described
above or using other suitable rolling techniques. The plate can be solution
heat treated (or
SHT) at approximately 470 C and can be stretched to between 2% and 3%. The
plate can be
heat treated using the techniques described herein, or using other suitable
techniques, at
120 C for a period (e.g., eight hours) and then at 155 C for a period (e.g.,
14, 16, or 18
hours). The plate can be marked, or sawed, using suitable techniques. The
plate can be tested
for ballistic properties or performance, static properties or performance, or
for other suitable
properties or performance. The plate can be inspected to verify the plate is
free from defects
and can be packaged.
In some examples, the plate can be manufactured by any of the above-described
processes and can be tempered to a T76 temper or a T79 temper. The T76 temper
can include
solution heat treating the plate and having the plate artificially overaged
for achieving a high
degree of exfoliation corrosion resistance. The T79 temper can include
solution heat treating
the plate and having the plate artificially overaged, to a lesser degree than
the T76 temper, for
achieving a high degree of exfoliation corrosion resistance.
The invention will now be illustrated with reference to non-limiting examples
according
to the invention.
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Example 1.
Aluminium alloy plates have been produced having different thicknesses (38.1,
50.8
and 76.2 mm) and subjected to varying over-ageing heat treatment followed by
testing for the
various properties.
All aluminium alloy plates had of nominal composition (in wt. %) of 7.38% Zn,
2.03%
Mg, 1.55% Cu, 0.12% Zr, 0.03% Ti, 0.07% Fe, 0.04% Si, <0.001% Mn, balance
aluminium
and unavoidable impurities. The alloy composition of the 7XXX-series aluminium
alloy plate
is according to this disclosure. The alloy has a Zn/Mg-ratio of 3.63.
The industrial manufacturing process includes DC casting of rolling ingots,
homogenizing the ingot, hot rolling the homogenized ingot to arrive at an
intermediate
thickness, solution heat treating the plates at about 470 C, quenching,
stretching of the plates
for about 2.5% to arrive at final thickness, artificial over-ageing of the
stretched plate as
indicated in Tables 1, 2, 3, and 4.
The plate products have been tested for their ballistic properties, in
accordance with US
military standard MIL DTL-32375B (MR) (2021). In accordance to this standard
Cal. 50 AP
M2 projectiles were used for ballistic testing of the 38.1 and 50.8 mm plates
and 14.5-mm
BS-41 projectiles were used for ballistic testing of the 76.1 mm plates
respectively. The
results are listed in Tables 1 and 4.
The plate products have been tested in their static mechanical properties
(total yield
strength (TYS), ultimate tensile strength (UTS), and percent elongation (A))
in both the LT-
and longitudinal (L)-direction. The results (average over [three] tests) are
listed in
respectively Table 2 and Table 3.
Table 1. Ballistic properties of plates with respect to various thicknesses
and heat treatments.
Sample Thickness Ageing Treatment V50 ft/s
(mm) spec test
1A 38.1 8h@120 C+6h@155 C >2143 2201
8h@120 C+10h@155 C 2215
8h@120 C+14h@155 C 2210
8h@120 C+18h@155 C 2226
8h@120 C+22h@155 C 2204
1B 50.8 8h@120 C+6h@155 C >2577 2627
8h@120 C+10h@155 C 2577
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8h@120 C+14h@155 C 2616
8h@120 C+18h@155 C 2612
8h@120 C+22h@155 C 2605
1C 76.2 8h@120 C+6h@155 C >2924 3020
8h@120 C+10h@155 C 3012
8h@120 C+14h@155 C 2966
8h@120 C+18h@155 C 3001
8h@120 C+22h@155 C 2954
Table 2. Mechanical properties in LT-direction as function of plate thickness
and over-
ageing practice.
Sample Thickness Ageing Treatment Mechanical properties in LT-
(mm) direction
TYS UTS A
(MP a) (MP a) (%)
1A 38.1 8h@120 C+6h@155 C 566.5 600.5 12.7
8h@120 C+10h@155 C 555.5 594.5 12.6
8h@120 C+14h@155 C 537.5 581 12.7
8h@120 C+18h@155 C 527 571 13.3
8h@120 C+22h@155 C 516 564.5 13.2
1B 50.8 8h@120 C+6h@155 C 556 596 12.1
8h@120 C+10h@155 C 546.5 589 12.4
8h@120 C+14h@155 C 524 573 12.5
8h@120 C+18h@155 C 523.5 569.5 12.9
8h@120 C+22h@155 C 507.5 559.5 13.0
1C 76.2 8h@120 C+6h@155 C 544.5 585.5 10.1
8h@120 C+10h@155 C 537 578.5 10.5
8h@120 C+14h@155 C 522 566.5 10.9
8h@120 C+18h@155 C 510.5 558 11.3
8h@120 C+22h@155 C 500.5 551.5 12.1
Table 3. Mechanical properties in L-direction as function of plate thickness
and over-ageing
practice.
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Sample Thickness Ageing Treatment Mechanical
properties in L-
(mm) direction
TYS UTS A
(MP a) (MP a) (%)
1A 38.1 8h@120 C+6h@155 C 580.5 609 12.5
8h@120 C+10h@155 C 568 600.5 12.9
8h@120 C+14h@155 C 549 586.5 13.7
8h@120 C+18h@155 C 533.5 574.5 13.7
8h@120 C+22h@155 C 523 567.5 13.8
1B 50.8 8h@120 C+6h@155 C 571 594.5 13.5
8h@120 C+10h@155 C 559 586 13.2
8h@120 C+14h@155 C 539.5 577 13.8
8h@120 C+18h@155 C 529 567.5 14.3
8h@120 C+22h@155 C 515.5 559.5 14.5
1C 76.2 8h@120 C+6h@155 C 558 580.5 13.2
8h@120 C+10h@155 C 548.5 574.5 12.9
8h@120 C+14h@155 C 530.5 562 13.1
8h@120 C+18h@155 C 518.5 552.5 13.5
8h@120 C+22h@155 C 510.5 555 13.2
Table 4: Ballistic properties of various lots of plates with varying
thicknesses.
Heat Lot Thickness Thickness Avg Projectile Min V50 V50 V50-
Treatment Number (mm) (in) Thickness According (fps) min
(in) to MIL
(fps)
(fps)
120 C/ 1 38.1258 1.5 1.501 Ca150 2125 2202 77
8hr 2 50.8 2.0 2.036 APM2 2566 2614 48
155 C/ 3 63.5 2.5 2.520 2924 3007 83
14hr 4 2.561 14.5 BS 2704 2737 33
69.85 2.75 2.815 41 2865 2893 28
6 76.2 3.0 3.030 2994 3038 44
120 C/ 7 38.1258 1.5 1.501 Ca150 2127 2202 75
8hr 8 50.8 2.0 2.026 APM2 2558 2602 44
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155 C/ 9 63.5 2.5 2.520 2924
3000 76
14hr 10 2.563 14.5 BS 2705
2731 26
11 69.85 2.75 2.811 41 2862
2892 30
12 76.2 3.0 3.030 2994
3043 49
120 C/ 13 38.1258 1.5 1.501 Ca150
2122 2204 82
8hr 14 50.8 2.0 2.026 APM2 2558
2602 44
155 C/ 15 63.5 2.5 2.520 2924
2994 70
14hr 16 2.563 14.5 BS 2705
2748 43
17 69.85 2.75 2.814 41 2864
2916 52
18 76.2 3.0 3.030 2994
3029 35
While various embodiments of the technology described herein have been
described in
detail, it is apparent that modifications and adaptations of those embodiments
will occur to
those skilled in the art. However, it is to be expressly understood that such
modifications and
adaptations are within the spirit and scope of the presently disclosed
technology.
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