ALUMINUM ALLOYS FOR LONG RUN PRINTING PLATES

ALLIAGES D'ALUMINIUM POUR CLICHES DE LONGUE DUREE

English Abstract

ABSTRACT OF THE DISCLOSURE
The present invention consists of an aluminum alloy
having a high fatigue strength which is particularly suited
for use in the fabrication of printing plates for offset
lithography. The alloy contains form 0.2 to 0,75 wt.%
magnesium, from 0.45 to 0.7 wt.% copper, from 0.1 to 0.7
wt.% iron and up to 0.3 wt.% silicon. The alloy, when
processed according to the process of the present invention
possesses a uniquely high fatigue strength.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:-
1. A high fatigue strength aluminum base alloy consist-
ing essentially of from 0.2 to 0.75 wt.% magnesium, from 0.45
to 0.7 wt.% copper, from 0.1 to 0.7 wt.% iron, 0 to 0.3 wt.%
silicon, 0 to 0.05 wt.% manganese, 0 to 0.05 wt.% zinc, 0 to
0.03 wt.% titanium, 0 to 0.05 wt.% chromium, 0 to 0.02 wt.%
boron, and the balance aluminum.
2. A high fatigue strength aluminum base alloy according
to claim 1 having a maximum of 0.9 wt.% of material out of solid
solution.
3. A high fatigue strength aluminum base alloy according
to claim 2 having a maximum of 0.7 wt.% of material out of solid
solution.
4. A high fatigue strength aluminum base alloy according
to claim 2 containing from 0.4 to 0.6 wt.% magnesium.
5. A high fatigue strength aluminum base alloy according
to claim 2 containing from 0.5 to 0.6 wt.% copper.
6. A high fatigue strength aluminum base alloy according
to claim 2 containing from 0.4 to 0.65 wt.% iron.
7. A high fatigue strength aluminum base alloy according
to claim 2 including a layer of electroplated copper on the
surface thereof, wherein said layer has a thickness from 0.0005
to 0.005''.
8. A high fatigue strength aluminum base alloy consisting
essentially of from 0.2 to 0.75 wt.% magnesium, from 0.45 to
0.7 wt.% copper, from 0.1 to 0.7 wt.% iron, from 0.001 to 0.3
wt.% silicon, from 0.001 to 0.05 wt.% manganese, from 0.001 to
11

0.05 wt.% zinc, from 0.001 to 0.03 wt.% titanium, from 0.001 to
0.05 wt.% chromium, from 0.001 to 0.02 wt.% boron, balance
aluminum, wherein said alloy contains a maximum of 0.9 wt.%
of material out of solid solution.
9. A high fatigue strength aluminum base alloy according
to claim 8 containing from 0.0075 to 0.015 wt.% titanium and
from 0.005 to 0.015 wt.% boron.
10. A method of preparing a high fatigue strength
aluminum alloy comprising:
(A) casting an aluminum alloy consisting essentially of
from 0.2 to 0.75 wt.% magnesium, from 0.45 to 0.7 wt.%
copper, from 0.1 to 0.7 wt.% iron, from 0.001 to 0.3
wt.% silicon, 0 to 0.05 wt.% manganese, 0 to 0.05 wt.%
zinc, 0 to 0.03 wt.% titanium, 0 to 0.05 wt.% chrom-
ium, 0 to 0.02 wt.% boron, balance aluminum,
(B) homogenizing at a temperature of between 900 and
1150°F, but below the solidus temperature of the alloy,
for a period of time of between 2 and 24 hours,
(C) hot rolling at a temperature of between 750 and
900°F;
(D) cold rolling and annealing to penultimate gauge;
(E) applying a final cold reduction of at least 20%, and
(F) partially annealing to produce a high fatigue
strength aluminum alloy.
11. A method according to claim 10 wherein said alloy
contains a material selected from the group consisting of from
0.001 to 0.05 wt.% manganese, from 0.001 to 0.05 wt.% zinc,
from 0.001 to 0.03 wt.% titanium, from 0.001 to 0.05 wt.%
chromium, from 0.001 to 0.02 wt.% boron, and mixtures thereof.
12

12. A method according to claim 10 wherein the annealing
in step (D) is at a temperature of from 600 to 750°F for from
1 minute to 6 hours.
13. A method according to claim 10 wherein said partial
annealing in step (F) is at a temperature of from 250 to 500°F
for from 1 minute to 4 hours.
14. A method according to claim 13 wherein said partial
annealing in step (F) produces a high fatigue strength aluminum
alloy having a 0.2% offset yield strength of between 22,000 and
28,000 psi.
13

Description

, 3077-MAL
BACX~ROUND OF THE INVENTION
Of~set lithography is a widely used printing process which
utilizes a printing plate which has been treated so that certain
portions of the plate are water receptive and other portions of
the plate are receptive to an oil base ink. The printing pro~
cess consists of f~rst applying water to the sheet and then an
oil base ink. After the alternate application of water and ink
the aluminum sheet is then placed in contact with a rubber roll
and a portion of the ink on the aluminum sheet is transferred to
the rubber ro].1. The rubber roll is then placed in contact with
a sheet of paper and the image which results on the paper ls dir-
ectly related to the original surface condition of the aluminum
sheet. The aluminum sheet is usually prepared through the use of
a photographic process. In one variation of this process, a
photosensitive polymer is applied to the surface of the sheet and
a pattern of light corresponding to the desired printed image is
caused to impinge on the photosensitive polymer. Subsequently, a
developer removes all the photosens,itive polymer which was not
exposed to light. Because of surface tension effects the oil base
ink will adhere to the areas where the photosensitive polymer re-
mains and the water will adhere to areas where the original sur-
face of the aluminum sheet is exposed. Large numbers of copies
may be made from one printing plate, sometimes`in excess of one
mlllion. Because the resultant printed image depends on the sur-
face condition of the aluminum sheet, it is highly important that
the original surface of the sheet be smooth, flat and free from
de~ects.
Aluminum alloys are widely used in the production of print-
ing plates for use in offset lithography. Difficulties are en-
countered when aluminum alloy printing plates are used in ex-
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tremely long production runs. These difficulties include fatigue
cracking o~ the alloys and excessive wear of the alloy. These
problems of low fatigue strength and excessive wear are both
related to the inability of the alloy to further work harden
in service. CorNmonly used aluminum alloys, Aluminum Association
designation 3003 and 1100 have a fatigue strength in hard tempers
of about 10,000 psi at 500,000,000 reversals.
These problems cannot be solved by the substitution of
higher strength alumimum alloys because present commercial
processes cannot produce material having the requi'red width,
flatness and surface f~.nish in alloys having a tensile strength
in excess of 35l000 psi.
The prececling difficultles may be largely overcorne
through the us~ of the alloy of the present inventlon. I'he
alloy of the present invention has a fatigue strength of between
13,000 and 15,000 psi and a tensile strength of about 25,000 psi.
When used in a partially annealed condition, these strengths may
be obtained while the alloy retains suf~icient work hardening
capabilities so as to minimize wear.
SUMMARY OF THE I~VENTION
The alloy of the present inventioll contains in wt.% from
.2 to .75% magnesium, from .45 to .7% copper, from .1 to .7%
iron and up to .3% silicon, balance essentially aluminum. This
alloy in the partially annealed condition possesses a moderate
tensile strength of about 25 ,000 psi. The tensile strength is
comparable to that of the commonly used aluminum alloys t~hile
the fatigue strength of 13,000 to 15,000 psi, is from 30 to 50%
greater than the fatigue strength of other alloys commonly used
for litho plates.
The alloy of the present invention may be fabricated us-
ing conventional techniques and may be surface grained for litho-
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~"~f~{~
graphy purposes using techni~ues similar to those used for
current alloys. Additional advantages and ben2fits of the
present invention will be made more app;~rent with referen(~e
to the foLlowing Description of the Preferred Em~odiments in
combination with the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The composition of the present invention i.s given i.n
weight percent in the following description unless otherwise
specified.
The broad and preferred compos:ition limits for the alloy
o.f the present invention are gi.ven in Table I below:
TABL~ I
Broad Preferred
Magnesium .2 - .75 .4 - .6
Copper .45 - .7 .5 - .6
Iron .1 ~ .7 .4 - .65
Silicon o - .3
Manganese O - .05 0 - .05
Zinc O - .05 0 - .05
Titanium O ~ .03.0075- .Q15
Chromium O - .OS O - .05
Boron O - .02 .OOS - .015
The essential components of the alloy are magnesium,
copper and iron. The other component,s listed in Table I may
be present in concentrations up to those listed in the Table
without adverse effect. Titanium may be present as a purpose-
ful addition for the purposes of grain refinement. Naturally,
any of the foregoing non-essential elements may be present in
levels as low as .001%.
The alloying elements of the present alloy have been sel-
ected so that the resultant alloy in its final condition has a
,.~ )

3077-MAL
:`
minimum of alloylng elements present out of solid solution.
Table II lists the approximate solid solubility of the alloyin~
addltions of the present invention at a temperature of 625F.
This temperature was chosen since it is representative of the
final full annealing temperature disclosed in the present appli-
cation. Also shown in Table II are the approximate percentages
of alloying elements of the present invention out of solution
under the worst possible condition which is when the alloying
elements are present in their maximum amounts. The sum of the
alloying elements out of solution at 625F is seen to be less
than .9%. The alloying composition of the presenk invention is
preferably chosen to have a maximum amount of alloying additions
out of solution to be less than .9% and most preferably less than
,7%. The ~lloying composition must, of course, still fall with-
in the limits set forth in Table I.
TABLE II
Solubility Max. out of
in Aluminum Solution in
at 625FMax~ Allowed in Present Alloy
Element (approx.)Present Alloy at 625F
Mg 8.0 .75
Cu 2.G ,7
Fe .02 .7 .68
Si .15 .3 .15
Mn .05 .05
zn 45.0 .05
Ti .01 .03 .02
Cr .01 .05 .04
B .005 .015 .010
The present invention will be made more clear through ref-
erence to the following illustrative examples.

3077-MA~
, .
EXA~PLE I
A series of alloys containing various amounts of magnesium,
copper and silicon were cast for evaluation. The composition of
the ingots i5 given in Table III, along with the details of the
initial homogenization given the ingots. The ingots were hot
rolled from 1.5" to a final gage of .2l' at a temperature of
825F. The ingots were reheated for 5 minutes after each .1"
reduction. The ingots were then cold rolled frcm .2 to .1" us
ing a reduction of about 10% per pass. The cold rolled ingots
were then annealed for 3 hours at 625~. Some of the ingots
received controlled heating and cooling at a rate of 25F/hr.
before and after this anneal to simulate commercial large coll
practice. Those ingots whlch received controlled cooling and
heating are designated in Table III.
The annealed ingots were then cold rolled at 10% per pass
to .o60" or to .043". The cold worked ingots were then annealed
at 625F for 3 hours. For this anneal all alloys received the
control cooling and heating rate of 25F/hr. The annealed mate-
rial was then cold rolled 10% per pass to a thickness of .030".
This represents a 50% reduction for the .o60" gage material and
a 30% reduction for the .043" gage material. As a final anneal
the alloys received a partial anneal as described in Table III.
EXAMPLE II
_
The alloys prepared in Example I were evaluated for mech-
anical properties, yield strength, ultimate tensile strength
and elongation. The results are listed in Table III. The
alloys were also tested for fatigue strength and the fatigue
strength listed in Table III is the stress in ksi which the
alloy withstood for 107 cycles.
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3077-MAL
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It is noteworthy tnat the alloys of the present invent~on
have average fatigue strengths on the order o~ 14,000 psi whereas
conventional alloys used for the fabrication of lit,hography plates
and listed in Table III have fatigue strengths on the order of'
10 ksi. The improvemen~ in fatigue strength is achieved without
significant change in other mechar.ical properties. The yield
strength and ultimate tensile strength of the alloys of the pre-
sent invention are slightly higher than the conventional alloys,
while the elongation of the present alloys i8 somewhat less than
the elongation of the commercial alloys tested. 1'he y'l.eld
strength may be controlled by controlling the flnal partial an-
neal. The data in Table III indicates the importance of the
final partial anneal in achieving superior fatigue strength. For
example, the alloy identified as 26 has a fatigue strength of
13 ksi in the non-partially annealed condition and a fatigue
strength of 15.7 ksi after the partial anneal, an improvement of'
1~.7%. The partial anneal also increased the elongation, which
is a measure of residual work hardened capacity, ~rom 2.0 to 5.5%.
The yield strength was not slgnificantly affected by the stabil-
ization while the ultimate tensile strength was only slightly in-
creased ~3 5,000 psi). Thus, it can be seen that the partial
anneal plays an important role in producing material having a
high fatigue strength. The partlal anneal condltions were selec-
ted to provide a yield strength of approximately 25,000 ksi. Ma-
terial having a yield strength of 25,000 ksi may reaaily be fab-
ricated using conventional commercial techniques.
EXAMPLE III
The samples of Alloys 12A, 12B, 26A and 26B were further
' evaluated for su~tability ~or use in lithography plates by fab-
ricating the lithographic printing plates from these alloys.
.

3077-MAL
The e~aluation of the resultant printed images indicated that the
alloys were highly suited for the fabrication of printing plates.
The printed image was extremely sharp and there was no evidenee
of defects caused by the surface condition of the alloy.
In summary, the process which is preferred for preparation
of the alloys of the present invention consists of the following
steps:
1) Cast the alloy useing conventional processes such as
used for the casting of 1100 type alloys. Titanium
may be added ~or ~rain refinernent in the amounts
listed in Table I.
2) Homogeni7e at a temperature of between 900 and 1150F
for a time of between 2 and 24 hours. Care must be
taken to avoid exceeding the solidus temperature
~hich is dependent on the e~act composition of the
alloy.
3) Hot roll at a te~perature between 750 ancl 900F.
4) Cold roll and anneal to penultimate gage. Intermed-
iate anneals should be performed at temperatures
between 600 and 750F for periods from 1 minute to
6 hours.
5) The final cold reduction should be at least 20%.
6) The final partial anneal should be performed so
that the resultant material has a .2% offset yield
strength of between 22 and 28~000 psi. In general~
the final anneal will be performed at temperatures
between 250 and 500F for times of between :L minute
and 4 hours.

¢~ ,2
The resultant alurnlnum a:Lloy is characterized by haviny
a non-recrystallized cJrain structure, preferab:Ly a yield strength
of between 22 and ~,000 psi. The elongation of the resultant
alloy is preferabl,v at least 5%.
The aluminum alloy of the present invention treated
according to the process of the present invention has superior
fatigue properties and is hiyhly suited for use in the product-
ion of long run aluminum lithography printing plates. For
extremely long run printing plates it is common commercial
practice to apply a layer of electroplated copper~to the surface
of the aluminum printing plate so as to provide a wear resistant
8urEace. The alloy of the pr~sent invention can be easily
plated with copper and the resulting copper plated swrface is
free from defects. The thickness of the copper plate layer
will generally fall between .0005 and .005" and may be applied
by any of several well known conventional techniques.
This invention may be embodied in other forms or carried
out in other ways without departing from the spirit or essential
characteristics thereof. The present embodiment is therefore to
be considered as in all respects illustrative and not restrict-
ive, the scope of the invention being indicated by the appended
claims, and all changes which come within the meaning and range
of equivalency are intended to be embraced therein.
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