U.S. patent application number 12/927062 was filed with the patent office on 2011-03-10 for aluminium alloy for lithographic sheet.
Invention is credited to Jeremy Mark Brown, Richard Gary Hamerton, Theodore Rottwinkel, John Andrew Ward, David Skingley Wright.
Application Number | 20110056595 12/927062 |
Document ID | / |
Family ID | 26073381 |
Filed Date | 2011-03-10 |
United States Patent
Application |
20110056595 |
Kind Code |
A1 |
Rottwinkel; Theodore ; et
al. |
March 10, 2011 |
Aluminium alloy for lithographic sheet
Abstract
The invention discloses an Al alloy suitable for processing into
a lithographic sheet, the alloy having a composition in wt %: Mg
0.05 to 0.30, Mn 0.05 to 0.25, Fe 0.11 to 0.40, Si up to 0.25, Ti
up to 0.03, B up to 0.01, Cu up to 0.01, Cr up to 0.03, Zn up to
0.15, unavoidable impurities up to 0.05 each, 0.15 total, Al
balance. Also disclosed is a method of processing the Al alloy.
Inventors: |
Rottwinkel; Theodore;
(Adelebsen, DE) ; Wright; David Skingley;
(Rosdorf-Dramfeld, DE) ; Hamerton; Richard Gary;
(Chipping Norton, GB) ; Brown; Jeremy Mark;
(Banbury, GB) ; Ward; John Andrew; (Leamington
Spa, GB) |
Family ID: |
26073381 |
Appl. No.: |
12/927062 |
Filed: |
November 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11486733 |
Jul 14, 2006 |
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12927062 |
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10433078 |
Oct 8, 2003 |
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PCT/GB01/05434 |
Dec 11, 2001 |
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11486733 |
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Current U.S.
Class: |
148/552 |
Current CPC
Class: |
C22F 1/04 20130101; C22C
21/00 20130101; C22C 21/06 20130101; C22F 1/047 20130101; B41N
1/083 20130101 |
Class at
Publication: |
148/552 |
International
Class: |
C22F 1/04 20060101
C22F001/04; C22F 1/047 20060101 C22F001/047; C22F 1/05 20060101
C22F001/05; C22F 1/043 20060101 C22F001/043 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2000 |
EP |
00311029.3 |
Jul 25, 2001 |
GB |
0118100.7 |
Claims
1. A method of processing an Al alloy having a composition in wt %:
TABLE-US-00011 Mg 0.05 to 0.30 Mn 0.06 to 0.25 Fe 0.11 to 0.40 Si
up to 0.25 Ti up to 0.03 B up to 0.01 Cu up to 0.01 Cr up to 0.03
Zn up to 0.15 Zr up to 0.005
Unavoidable impurities up to 0.05 each, 0.15 total Al balance,
which method consists of the steps of: casting by DC casting,
homogenising, optional hot rolling, cold rolling, and optional
interannealing, to give material in H18 or H19 condition, wherein
the homogenisation step is carried out by heating the cast alloy to
a temperature of 550 to 610.degree. C. for 1 to 10 hours and
subsequently cooling to a hot rolling temperature of between 450
and 550.degree. C.
2. A method according to claim 1, wherein the method consists of
the steps of: casting by DC casting, homogenising, optional hot
rolling, and cold rolling, to give material in H19 condition,
wherein the homogenisation step is carried out by heating the cast
alloy to a temperature of 550 to 610.degree. C. for 1 to 10 hours
and subsequently cooling to a hot rolling temperature of between
450 and 550.degree. C.
3. A method according to claim 1, which does not include the
optional interannealing step.
4. A method according to claim 1, wherein the interannealing is
batch interannealing.
5. A method according to claim 4, wherein the interannealing is
carried out at 300 to 500.degree. C. for 1 to 5 hours.
6. A method according to claim 1, wherein the interannealing is
continuous interannealing.
7. A method according to claim 6, wherein the continuous
interannealing is carried out at 450 to 600.degree. C. for less
than 10 minutes.
8. A method according to claim 1, wherein said material in H18 or
H19 condition is capable of being electrograined in hydrochloric
acid.
9. A method according to claim 1, wherein said material in H18 or
H19 condition is capable of being electrograined in nitric
acid.
10. A method according to claim 1, wherein said material in H18 or
H19 condition is capable of being electrograined in both
hydrochloric and nitric acids.
11. A method of processing an Al alloy having a composition in wt
%: TABLE-US-00012 Mg 0.05 to 0.30 Mn 0.06 to 0.25 Fe 0.11 to 0.40
Si up to 0.25 Ti up to 0.03 B up to 0.01 Cu up to 0.01 Cr up to
0.03 Zn up to 0.15 Zr up to 0.005
Unavoidable impurities up to 0.05 each, 0.15 total Al balance,
which method consists of the steps of: casting, homogenising,
optional hot rolling, cold rolling, optional interannealing,
optional cleaning, electrograining, anodizing and stoving, wherein
the homogenisation step is carried out by heating the cast alloy to
a temperature of 550 to 610.degree. C. for 1 to 10 hours and
subsequently cooling to a hot rolling temperature of between 450
and 550.degree. C.
12. A method of processing an Al alloy having a composition in wt
%: TABLE-US-00013 Mg 0.05 to 0.30 Mn 0.06 to 0.25 Fe 0.11 to 0.40
Si up to 0.25 Ti up to 0.03 B up to 0.01 Cu up to 0.01 Cr up to
0.03 Zn up to 0.15 Zr up to 0.005
Unavoidable impurities up to 0.05 each, 0.15 total Al balance,
which method consists of the steps of: casting, homogenising,
optional hot rolling, cold rolling, optional interannealing,
optional cleaning, electrograining, anodizing and stoving, wherein
the homogenisation step is carried out by heating the cast alloy to
a temperature of 550 to 610.degree. C. for 1 to 10 hours and
subsequently cooling to a hot rolling temperature of between 450
and 550.degree. C., and wherein the steps of casting, homogenising,
optional hot rolling, cold rolling, and optional interannealing
give material in H18 or H19 condition.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of application Ser. No. 11/486,733
filed Jul. 14, 2006, as a division of application Ser. No.
10/433,078 filed Oct. 8, 2003, as the U.S. National Stage of
PCT/GB01/05434 filed Dec. 11, 2001.
[0002] This invention relates to an Al alloy suitable for
processing into a lithographic sheet, which exhibits good
mechanical properties with good electrograining
characteristics.
[0003] At present the lithographic sheet market largely consists of
products in the 1XXX and 3XXX alloy range. During electrograining
the 1XXX alloys are used with both nitric and hydrochloric acid
electrolytes and generally have the better graining response. The
3XXX alloys, mainly AA3103, are used where greater strength is
demanded by the printer but can only be grained in hydrochloric
acid, and even then not by all platemakers.
[0004] With the advent of larger, faster presses being used for the
high quality end of the market, the Applicants have perceived a
need for an alloy for a plate, which combines the good graining
response of AA1050A with the strength properties of AA3103.
[0005] Existing alloys such as AA1050A are adversely affected by
the "stoving" step used to provide the finished lithographic plate.
Stoving has been found to reduce the strength and cause distortion
of lithographic sheet material by causing recovery or
recrystallisation of the heavily cold worked metal. A useful
indication of the likely amount of distortion that may occur is
provided by measuring the change in ultimate tensile strength (UTS)
or proof strength (PS) caused by stoving. A large loss in strength
indicates an unacceptable level of distortion, and difficulties in
handling and mounting for use in service.
[0006] Thus, according to the first aspect of the present
invention, there is provided an Al alloy suitable for processing
into a lithographic sheet, the alloy having a composition in wt
%:
TABLE-US-00001 Mg 0.05 to 0.30 Mn 0.05 to 0.25 Fe 0.11 to 0.40 Si
up to 0.25 Ti up to 0.03 B up to 0.01 Cu up to 0.01 Cr up to 0.03
Zn up to 0.15
[0007] Unavoidable impurities up to 0.05 each, 0.15 total
[0008] Al balance.
[0009] As well as exhibiting good mechanical and electrograining
characteristics, the alloy is relatively cheap to produce as it
contains alloying elements in smaller amounts compared with AA3103.
Furthermore, the alloy has an added commercial benefit by providing
the potential for reduced inventories for manufacturers and their
customers. The alloy has also been found to resist the softening
encountered during stoving or heating at temperatures of about
240.degree. C. or even 270.degree. C.
[0010] It is particularly surprising that relatively small amounts
of magnesium and manganese are sufficient to attain much improved
mechanical properties while still allowing adequate electrograining
in hydrochloric acid, and preferably in nitric acid in some
embodiments.
[0011] Magnesium is preferably present in an amount of 0.06 to 0.30
wt %, even more preferably 0.10 to 0.30-wt %. Magnesium is the
element influencing work hardening in the alloy. However, if the
magnesium level is raised too far, then electrograining becomes
increasingly difficult especially in nitric acid electrolyte.
[0012] Manganese is present in an amount of 0.05 to 0.25 wt %,
preferably in an amount of 0.05 to 0.20 wt %. In either case, the
lower limit of Mn may optionally be 0.06 wt %. Manganese provides
maximum stoved strength, and a minimum drop in strength compared
with the as cold rolled sheet. The optimum upper level of manganese
is determined by a balance between the desirable stoving resistance
on the one hand and the onset of an undesirable level of streaking
and discolouration after electrograining on the other hand.
[0013] Preferably, copper is present in an amount up to 0.005%,
more preferably up to 0.003%.
[0014] Ti is present in total amounts of up to 0.03 wt %.
Preferably, up to 0.028 wt % of the titanium is free i.e. present
in solid solution and not tied up for example as the boride,
TiB.sub.2. Preferably, titanium is present in a total amount up to
0.015 wt %, even more preferably 0.010 wt %. Generally, a lower
titanium level favours better graining. Grain refiner may or may
not be present; if it is, some additional titanium is present over
that found in virgin metal. It has been found that if the free
titanium content is too high, this may have a detrimental effect on
the ability to grain the formed lithographic sheet in nitric acid,
although it may still be grainable in hydrochloric acid. The level
of titanium preferably needs to be controlled. If too much free
titanium is present it is detrimental to graining; titanium
combined with boron is not detrimental.
[0015] B is preferably present in an amount up to 0.002.
[0016] In one embodiment, zinc may be present in an amount of up to
0.05 wt %. Alternatively, a zinc content in the range of 0.01 to
0.15 wt % has been found to be advantageous in order that the alloy
can be satisfactorily grained by electrograining in nitric acid. In
such an embodiment, the zinc content of the alloy will typically be
in the range of from 0.01 to 0.1 wt % and more preferably from
about 0.01 to 0.08 wt %. Especially preferred zinc contents will be
in the range of from 0.015 to 0.06 wt % and most preferably from
about 0.02 to about 0.05 wt %.
[0017] Zirconium may typically be present in amounts up to 0.019 wt
%, for example up to 0.015 wt %, particularly up to 0.005 wt %. In
a preferred embodiment, there is no deliberate addition of
zirconium.
[0018] In one embodiment, iron is present in an amount of 0.20 to
0.40%. Silicon may be present in an amount of 0.05 to 0.15%, for
example 0.09 to 0.15%. Such alloys have been found to exhibit good
strength properties in both the as-rolled and stoved embodiments,
and are reasonably cost effective for use in high volume production
of lithographic sheet.
[0019] Silicon in solution alters the reactivity of the sheet
during electrograining. If the amount of silicon present is too
small, too many pits form during graining and the surface is not
suitable for lithographic sheet. If the amount of silicon present
is too great, too few pits form during electrograining and they are
too large.
[0020] Iron in solution has a similar effect to silicon as regards
electrograining. In addition, iron forms intermetallic phases
present as particles in the sheet. The presence of too many of
these iron containing particles is detrimental to graining.
[0021] According to a second aspect of the present invention, there
is provided a lithographic sheet formed from the alloy. In such a
lithographic sheet, titanium may be present in an amount sufficient
to enable the sheet to be capable of being electrograined in nitric
acid, although it should be borne in mind that in some embodiments
of the invention the presence of titanium is not essential to the
ability to electrograin in nitric acid. Preferably, free Ti is
present up to 0.028 wt % in general but only up to 0.019 wt %, for
example up to 0.015 wt %, for nitric acid graining. TiB.sub.2 is,
in one embodiment, present up to 170 ppm, but it can be higher.
[0022] According to a further aspect of the present invention,
there is provided a DC cast ingot comprising the alloy.
[0023] According to a further aspect of the present invention there
is provided a method of processing an Al alloy as defined above,
which method comprises the steps of: casting, optional
homogenising, optional hot rolling, cold rolling, optional
interannealing.
[0024] The casting step is, in one embodiment, a DC casting step.
The DC cast ingots are scalped prior to the homogenising step.
Homogenising is used to get the right amount of Fe and Mn in solid
solution. Other casting options include roll casting or belt
casting. If these continuous casting processes are used, then
homogenising and scalping may not be necessary. This is because the
rapid cooling in continuous casting holds a lot of Fe and Mn in
solid solution.
[0025] Heat treatment after casting and before hot rolling affects
both the strength loss during stoving and the response to
electrograining. To some extent the effects are contradictory and
an optimum treatment has to be found. Two alternative homogenising
treatments are envisaged. Firstly, there is a two stage
homogenisation designated Type 2. This involves slow heating of the
alloy to a temperature higher than the rolling temperature and
holding at this temperature. During heating to this temperature and
during holding, Mn is taken into solution. The ingot is then cooled
to the hot rolling temperature and rolled either after holding for
a period or immediately on reaching the hot rolling temperature.
Some Mn will come out of solution during cooling but the process is
slow and most will remain in supersaturated solution. This reduces
the strength loss during subsequent stoving but tends to be
detrimental to the electrograining response. An example of this
treatment is: slow heat to 550 to 610.degree. C. and holding in
that temperature range for typically 1 to 10 hours. This is
followed by cooling to the rolling temperature and hot rolling at a
temperature of between 450 to 550.degree. C. Alternatively, the
homogenisation may be carried out with a heat-to-roll practice
(designated Type 1). This involves heating the alloy as cast (and
scalped) to the hot rolling temperature, typically 450 to
550.degree. C., by ramped heating and holding at that temperature
for 1 to 16 hours prior to hot rolling. This treatment consumes
less energy and take less time than the Type 2 treatment and is
therefore less expensive. However, the Type 1 treatment minimises
the amount of Mn taken into solution. This benefits electrograining
but the strength loss during subsequent stoving is greater.
Variations or combinations of these two treatments may be required
to achieve the optimum combination of strength after stoving and
good electrograining response.
[0026] Where an intermediate annealing step is present, it may be
carried out immediately after hot rolling or during cold rolling.
The interannealing may be carried out as batch interannealing, in
which case it is preferably carried out at 300 to 500.degree. C.,
for example for 1 to 5 hours. Alternatively, the interannealing may
be continuous, in which case it is preferably carried out at 450 to
600.degree. C., preferably for less than 10 minutes, for example
for up to 5 minutes, even more preferably up to 1 minute.
Preferably, at least forced air quenching is used. It is preferred
to cool rapidly in order to hold Mn and Fe in solid solution.
[0027] In one embodiment, the cold roll reduction of the sheet
thickness is greater than 30%, preferably greater than 50%.
[0028] An electrograining step may also be provided. Preferably the
alloy is capable of being electrograined in hydrochloric acid, even
more preferably in both hydrochloric and nitric acids.
[0029] Further steps which may be provided are anodising and
stoving. Stoving trials are typically carried out at 240.degree. C.
for 10 minutes or even 270.degree. C. for 10 minutes to harden the
photosensitive coating prior to printing. In the Examples below,
stoving is simulated by heating the plate to 240.degree. C. for 10
minutes or, where noted, to 270.degree. C. for 10 minutes. Printers
use less time than 10 minutes, typically 3 minutes in continuous
ovens, up to 7 minutes in others, and therefore the simulated
stoving is a particularly severe test because the degree of
softening increases with both time and temperature of stoving. The
plate softens via the mechanisms of recovery and recrystallisation
of the microstructure and the inherent anisotropy in the plate can
lead to off-flatness problems. As mentioned above, the present
invention minimises such problems. Generally, as low a drop in
proof strength as possible is required.
[0030] According to a further aspect of the present invention,
there is provided a method of forming a lithographic sheet
comprising electrograining an aluminium metal sheet formed of the
above-mentioned alloy in a nitric acid electrolyte until a total
charge input of above 82 kC/m.sup.2 is applied, wherein the surface
of the lithographic sheet comprises a pitted structure. Preferably,
the total charge input is about 87 kC/m.sup.2. The pitted structure
may provide total coverage of the surface of the material and
sufficient roughness to allow good adhesion of a light-sensitive
coating, together with good wear resistance and water retention
following anodising and post anodic treatment.
[0031] The invention will now be described with reference to, and
as illustrated in, the accompanying drawings, and in which:
[0032] FIGS. 1a and 1b show, respectively, the proof strength and
ultimate tensile strength at final gauge in the as-rolled
(H18--that is with an interanneal) condition and after stoving for
Mg or Mn additions;
[0033] FIGS. 2a and 2b show, respectively, the proof strength and
ultimate tensile strength at final gauge in the as rolled condition
and after stoving for other Mg and/or Mn additions;
[0034] FIGS. 3a and 3b show similar properties in the H19 condition
(without interanneal);
[0035] FIGS. 4a to 4d show proof strength and nitric acid graining
response for various alloy compositions for different homogenising
and annealing conditions;
[0036] FIGS. 5a and 5b show, respectively, the proof strength and
ultimate tensile strength for various treatments in the H18
condition against total Ti content;
[0037] FIGS. 6a and 6b show similar properties in the H19
condition;
[0038] FIG. 7 shows the ultimate tensile strength of various alloys
under varying treatment conditions;
[0039] FIG. 8 shows the ultimate tensile strength of various alloys
under various treatment conditions against the annealing
temperature.
[0040] FIGS. 9a-c show the softening behaviour of various alloys
against stoving temperature.
EXAMPLE 1 (COMPARATIVE)
[0041] A series of alloys based on the standard AA1050A composition
were cast, rolled and electrograined in the laboratory to see the
effects of single additions of various elements on tensile
properties and electrograining response. The compositions used are
shown in Table 1:
TABLE-US-00002 TABLE 1 Composition and TEP for Alloy trials of
AA1050A + Mn or Mg Total Free Cast ID Si Fe Mn Mg Ti Ti* B Std 0.08
0.30 0.003 <0.001 0.006 0.003 0.0012 Std + Mg0.01 0.08 0.30
<0.003 0.010 0.006 0.004 0.0010 Std + Mg0.02 0.08 0.30 <0.003
0.020 0.006 0.004 0.0010 Std + Mg0.3 0.08 0.30 <0.003 0.300
0.008 0.003 0.0022 Std + Mn0.1 0.08 0.30 0.100 0.001 0.006 0.004
0.0011 Std + Mn0.2 0.08 0.30 0.200 <0.001 0.007 0.004 0.0012 Std
+ Mn0.5 0.08 0.30 0.500 <0.001 0.006 0.003 0.0013 Zn, Cu, Cr and
Zr all = 0.001 wt % for all variants shown in Table 1. *Free Ti is
the Ti in the Al solid solution and not including Ti combined with
B as TiB.sub.2 particles.
[0042] Compositions given in Table 1 are rounded to the nearest
significant figure and Std means typical AA1050A with the
compositions shown.
[0043] Rolling blocks approximately 70 mm thick by 180 mm wide by
200 mm long were scalped from ingots cast in large book moulds. The
rolling blocks were homogenised by heating slowly to 600.degree. C.
and holding for several hours followed by a 2 hour cool to
500.degree. C. for 10 hours to allow equilibration of solute to
occur, prior to hot rolling. This two-stage homogenisation is an
example of a Type 2 pre-heat. The rolling blocks were hot rolled to
an intermediate gauge of about 9 mm with a finish temperature of
about 150.degree. C. and allowed to air cool. Subsequent cold
rolling to a final gauge of 0.3 mm was done with an intermediate
anneal at about 2 mm gauge by heating to 450.degree. C. and holding
for 2 hours. The tensile properties of the final gauge sheet,
before and after a simulated stoving treatment for 10 minutes at
240.degree. C., were measured in the longitudinal and transverse
orientations (with respect to the rolling direction).
[0044] FIGS. 1a and 1b show, respectively, the proof strength and
tensile strength at final gauge in the as rolled (H18) condition
and after stoving for the Mn and Mg additions. It can be seen that
even small Mg additions give significant work hardening effect and
thus a higher as rolled strength. However on stoving the drop in
strength is also large. The maximum stoved strength (and minimum
drop in strength) is seen in the Mn containing alloys.
EXAMPLE 2
[0045] Further experiments were carried out to investigate a wider
range of Mg and Mn additions in combination.
[0046] A series of cast book mould alloys are shown in Table 2:
TABLE-US-00003 TABLE 2 AA1050A + Mg + Mn Alloy Trials Total Free
Cast ID Si Fe Mn Mg Ti Ti* Zn B Std 0.08 0.30 <0.003 <0.001
0.006 0.003 0.006 0.0012 0.1Mg0.1Mn 0.08 0.30 0.100 0.100 0.006
0.003 0.006 0.0013 0.1Mg0.5Mn 0.08 0.30 0.500 0.100 0.006 0.003
0.006 0.0015 0.3Mg0.1Mn 0.08 0.30 0.100 0.300 0.006 0.002 0.006
0.0019 1.0Mg0.1Mn 0.08 0.30 0.100 1.000 0.006 0.002 0.006 0.0017
Cu, Cr and Zr all = 0.001 wt % for all variants shown in Table 2.
*Free Ti is the Ti in the Al solid solution and not including Ti
combined with B as TiB.sub.2 particles.
[0047] Compositions given in Table 2 are rounded to the nearest
significant figure and Std means typical AA1050A with the additions
shown.
[0048] Rolling blocks were manufactured in a similar manner to that
described in Example 1. In addition to the standard two-stage
preheat (Type 2) described above, a set of blocks were homogenised
with a heat-to-roll practice (Type 1). This consists of a ramped
heating to the rolling temperature of 500.degree. C. and holding
for a few hours (total heating cycle about 16 hours). The blocks
were either rolled to final gauge with an interanneal, as above, to
give material in the H18 condition, or without any interanneal to
give material in the H19 condition. The H19 route is more
economical while the H18 route gives an opportunity to control
solute and grain structure, and hence stoving response and surface
streakiness in the final gauge product.
[0049] The mechanical properties of these materials at final gauge,
before and after the stoving treatment, are shown in FIGS. 2 (H18)
and 3 (H19). It can be seen that for most compositions the H18
strength after stoving is lower than for the H19 material.
[0050] Other conclusions are: [0051] Pre-heat Type 1 in general
gives lower stoved strength as compared with pre-heat Type 2 [0052]
H19 treatment gives consistently higher as-rolled strength; and
[0053] Type 2 pre-heat results in the lowest drop during softening.
This is consistent with the recovery being controlled via solute
rather than dispersoids.
EXAMPLE 3
[0054] Final gauge samples prepared in a similar manner to that
described in Examples 1 and 2 and from the same casts were
pre-cleaned in a 3% sodium hydroxide solution at 60.degree. C. for
10 seconds and grained in a laboratory twin cell system operated in
the liquid contact mode. The electrolyte was 1% nitric acid. The
voltage applied was 14V AC (conventional sine wave source). The
spacing between each electrode was 15 mm and the counter electrodes
were conventional impregnated graphite used industrially. This
arrangement has been shown to produce surfaces similar to those
produced commercially using standard 1050A lithographic quality
material. The time taken to produce a fully grained surface on such
a material is approximately 30 seconds and the total charge input
is about 87 kC/m.sup.2. Due to the symmetrical nature of the
arrangement the forward and reverse current density is
approximately equal.
[0055] The electrograining response of these materials in nitric
acid is indicated in Table 3:
TABLE-US-00004 TABLE 3 Laboratory Nitric Acid Graining Trials H18
H18 H19 H19 % Mg % Mn Type 1 Type 2 Type 1 Type 2 0.000 0.001 0.000
0.10 0.000 0.20 X 0.000 0.50 X X X 0.10 0.10 0.10 0.50 X X X X 0.30
0.001 0.30 0.10 1.00 0.10 X Good Acceptable X Unacceptable XX
poor
[0056] FIGS. 4a to 4d illustrate property-electrograining maps for
homogenising treatments Type 1 and Type 2 in the H18 or H19
condition. FIGS. 4a and 4b show graining and proof strength results
after stoving for 10 minutes at 240.degree. C. for Type 1 and Type
2 homogenisation respectively in H18 conditions. FIGS. 4c and 4d
show similar results for Type 1 and 2 homogenisation respectively
in the H19 condition. There is sufficient overlap between the good
strength properties and the good graining response in the alloy
range tested.
EXAMPLE 4
[0057] Ti is an important element in electrograining response in
nitric acid. So a middle level Mn/Mg variant was chosen and ingots
were cast with a range of Ti levels, as shown in Table 4 and heat
treated and rolled as in Example 2:
TABLE-US-00005 TABLE 4 Ti Unialloy Variants Wt % Wt % Ti Wt % free
Mg Wt % Mn Wt % B (total) Ti* 0.10 0.10 0.0011 0.010 0.008 0.10
0.10 0.0011 0.013 0.011 0.10 0.10 0.0012 0.018 0.015 0.10 0.10
0.0011 0.021 0.019 Cu, Cr and Zr all = 0.001 wt % for all variants
shown in Table 4. *Ti in the Al solid solution and not including Ti
combined with B as TiB.sub.2 particles.
[0058] FIGS. 5 and 6 show that the strength values of this system
are almost independent of Ti within the range of levels explored
(with the exception of <100 ppm Ti for the H19 Type 2 preheat
variant). The following conclusions can be made: [0059] Type 2
pre-heat gives higher strength, most notably for H19 samples; and
[0060] The very slight extra strength attained by the H19 samples
with Ti >100 ppm is due to the extra cold reduction used to
investigate differences between the experimental and anticipated
commercial rolling schedules (0.3 mm compared with 0.7 mm).
[0061] The graining response is shown in Table 5:
TABLE-US-00006 TABLE 5 Ti Unialloy Variants Nitric Acid Graining
Response % Ti Type (total) H18 1 H18 Type 2 H19 Type 1 H19 Type 2
0.006 0.010 X 0.013 X X 0.018 X X X 0.021 X X X X X
[0062] Generally a lower free Ti level favours better graining.
EXAMPLE 5
[0063] Commercial scale trials have been carried out as
follows:
[0064] Two trials have been carried out with the alloys listed in
Table 6. The existing litho alloys are included for comparison.
Ingots of these alloys were DC cast measuring 4250 mm long by 1300
mm wide and 600 mm deep and were scalped. Homogenising before hot
rolling was Type 2, in this case the ingot was heated to
600.+-.10.degree. C. for about 4 hours and then cooled to
500.+-.10.degree. C. and hot rolled.
[0065] Material destined to be in the H18 condition was hot rolled
to 4.2 mm and then cold rolled to a final gauge of 0.28 mm with an
interanneal at about 2.2 mm. Material destined to be in the H19
condition was hot rolled to 3.5 mm and then cold rolled to a final
gauge of 0.28 mm without an inter-anneal.
TABLE-US-00007 TABLE 6 Commercial Unialloy Trials Alloy Composition
Alloy Si Fe Cu Mn Mg Cr Zn Ti B AA3103 0.00- 0.0- 0.00- 0.9- 0.00-
0.00- 0.00- (AlMn1) 0.50 0.7 0.10 1.5 0.30 0.10 0.20 AA1050A 0.00-
0.00- 0.00- 0.00- 0.00- 0.00- 0.00- (Al99.5) 0.25 0.40 0.05 0.05
0.05 0.07 0.05 1.sup.st 0.08 0.34 0.001 0.19 0.06 0.001 0.008 0.013
0.0007 version 2.sup.nd 0.08 0.32 0.001 0.10 0.13 0.001 0.006 0.013
0.0006 version 3.sup.rd 0.09 0.33 0.06 0.19 0.001 0.006 0.016
0.0011 version 4.sup.th 0.09 0.32 0.10 0.14 0.001 0.006 0.004
0.0006 version 5.sup.th 0.08 0.33 0.001 0.09 0.08 0.020 0.009
0.0005 version 6.sup.th 0.08 0.32 0.10 0.13 0.021 0.006 0.0007
version
[0066] Mechanical properties of these alloys are shown in FIG. 7
and again show that the new alloy (in all variants) in the H19
condition has high strength after stoving.
EXAMPLE 6
[0067] FIG. 8 shows that the final gauge stoving response of the
alloy labelled 1.sup.st version in Table 6 is independent of the
interannealing temperature compared to the AA1050A alloy. This is
consistent with the stoving resistance being controlled by
manganese in solid solution, which has a high solid solubility over
this temperature range. Fe has a very low solubility resulting in a
high driving force for Fe precipitation during inter-anneal.
Consequently a high interannealing temperature is usually used to
keep Fe solute levels high in the AA1050A product. An advantage of
the new alloy is that it could be supplied in the H18 condition for
intermediate strength applications by using a relatively low
inter-anneal temperature thus saving production costs.
[0068] The 1.sup.st version in Table 6 was tested against normal
plates, of which typically 4% fail due to plate breakage. With a
sample of 3,500 plates, only 1.5% failed for this reason; a marked
improvement.
[0069] All of the versions in Table 6 have been trialled for both
nitric and hydrochloric acid electrolytes and the graining and
mechanical properties were found to be acceptable. This is another
surprising advantage over AM 050A, which is often prone to streaky
electrograining defects when supplied in the H19 condition.
EXAMPLE 7
[0070] A further series of commercial alloys were cast, homogenised
and rolled using the conditions described in Example 5. The
compositions used are shown in Table 7.
[0071] The blocks were either rolled to final gauge with an
interanneal, as above, to give material in the H18 condition, or
without interanneal to give material in the H19 condition. Stoving
was carried out for 10 minutes at various temperatures to simulate
the actions of a printer and the results are shown in FIGS. 9a-c.
From this it can be seen that material in the H19 condition for the
alloys shown has a higher strength than in the H18 condition. At
higher baking temperatures the material containing Mn in the H19
condition has much better mechanical properties than the comparison
material in a similar condition.
TABLE-US-00008 TABLE 7 Sample Si Fe Cu Mn Mg Zn Ti B OQ 3051 0.08
0.3 0.001 0.05 0.18 0.007 0.014 0.0003 H18 (H502) OQ 3051 0.08 0.3
0.001 0.05 0.18 0.008 0.015 0.0004 H19 (H502) Comparison 0.07 0.35
0.002 0.002 0.18 0.006 0.005 0.0007
EXAMPLE 8
[0072] Alloys having the compositions I, II and III as set out
below were formed into sheet materials in the same manner as
Example 1 and experiments were carried out to investigate the
electrograining response in nitric acid.
TABLE-US-00009 TABLE 8 Alloy Compositions I II III B 0.0016 0.0015
0.0014 Mg 0.100 0.100 0.100 Mn 0.100 0.100 0.100 Zn 0.005 0.022
0.051 Fe 0.30 0.30 0.30 Si 0.08 0.08 0.08 Ti 0.007 0.006 0.006 Cu
and Cr 0.001 0.001 0.001 Al balance balance balance
Electrograining
[0073] A further set of samples of sheet formed from compositions
I, II and III were prepared using a Type 2 homogenisation and were
electrograined as described in Example 3 with the exception that
the voltage applied was lower than standard, in order to
demonstrate the sensitivity.
[0074] The surfaces of the samples after electrograining were
subjected to visual inspection to assess the graining response. The
results are shown in Table 9. All samples grained with the reduced
voltage had the same amount of charge passed.
TABLE-US-00010 TABLE 9 Electrograining Alloy Composition Voltage I
II III 14 V 13 V X 12 V X 0 11 V X X 0 Key X = poor 0 = borderline
acceptability = acceptable = good
[0075] The results demonstrate that by incorporating zinc into the
alloy at 0.02 and 0.05 wt % additions improves the graining
response in H19 (with Type 2 homogenisation) condition.
* * * * *