U.S. patent application number 10/413158 was filed with the patent office on 2006-06-29 for aluminum base alloy containing boron and manufacturing method thereof.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho. Invention is credited to Yasuhiro Aruga, Katsura Kajihara, Yasuaki Sugizaki.
Application Number | 20060137783 10/413158 |
Document ID | / |
Family ID | 26586777 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060137783 |
Kind Code |
A1 |
Aruga; Yasuhiro ; et
al. |
June 29, 2006 |
ALUMINUM BASE ALLOY CONTAINING BORON AND MANUFACTURING METHOD
THEREOF
Abstract
A aluminum base alloy containing boron and manufacturing method
thereof, said alloy exhibiting good mechanical properties (such as
high-temperature strength and creep strength) over a long period of
time and also having a neutron absorbing capacity owing to boron
present therein in the form of a compound without segregation. The
alloy contains 0.5-10 mass % of boron with an isotopic element
satisfying a relation of .sup.10B/(.sup.10B+.sup.11B).gtoreq.30%,
said boron being present in the form of a boron compound which is
300 .mu.m or below in size. The alloy is obtained by melting at a
temperature in excess of 950.degree. C. and cast at a temperature
in the range of 800.degree. C. to 950.degree. C., in such a way
that the molten metal is kept for 60-1800 seconds until it cools
from 950.degree. C. to the casting temperature.
Inventors: |
Aruga; Yasuhiro; (Kobe-shi,
JP) ; Kajihara; Katsura; (Kobe-shi, JP) ;
Sugizaki; Yasuaki; (Kobe-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko
Sho
Kobe-shi
JP
|
Family ID: |
26586777 |
Appl. No.: |
10/413158 |
Filed: |
April 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09797871 |
Mar 5, 2001 |
|
|
|
10413158 |
Apr 15, 2003 |
|
|
|
Current U.S.
Class: |
148/689 ;
148/437 |
Current CPC
Class: |
C22C 21/00 20130101;
C22C 32/0073 20130101; C22C 1/026 20130101; Y02E 30/30 20130101;
G21C 19/40 20130101; G21F 1/08 20130101 |
Class at
Publication: |
148/689 ;
148/437 |
International
Class: |
C22F 1/04 20060101
C22F001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2000 |
JP |
2000-059433 |
Oct 23, 2000 |
JP |
2000-323142 |
Claims
1. An aluminum base alloy containing 0.5-1.8 mass % of boron with
an isotopic element satisfying a relation of
95%>.sup.10B/(.sup.10B+.sup.11B).gtoreq.75%, wherein said boron
is present in the form of particles of a boron-compound,
containing, in addition to aluminum and boron, at least one element
selected from the group consisting of Mg, Mn, Si and Cu; the total
amount in said boron-compound of the at least one element selected
from the group consisting of Mg, Mn, Si and Cu is 0.01-50 atom %;
and said particles are 250 .mu.m or below in size.
2-4. (canceled)
5. The aluminum base alloy according to claim 1, wherein the
difference between the maximum and minimum values of the B quantity
of the specimens taken after dividing the alloy into a plurality of
specimens is 1.0% or less.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an aluminum base alloy
containing boron having a neutron absorbing capacity and an ability
to maintain the sub-criticality of fuel assemblies which is
effective for a structural material (basket material) for a
transporting packaging (cask) for transporting spent nuclear fuel
or a storage cask container and the like, and its manufacturing
method.
[0003] 2. Description of the Related Art
[0004] Spent nuclear fuel has to be stored stable for a long period
of time without the possibility of recriticality and radiation
leakage. To this end, various investigations have been made on the
design and the basket material of its cask containers. Such a
material is required to have a capacity to shield and absorb
neutrons and to effectively cool spent fuel. Spent fuel is as hot
as 100-300.degree. C., and spent fuel needs storage for a long
period of time (tens of years). Therefore, the basket material for
cask has to be made from a material which keeps creep strength and
mechanical properties at high temperatures.
[0005] A conventional material in general use for the basket
material for a transporting cask and a storage cask container is an
aluminum base alloy containing boron which is considered to be
superior in capacity to shield and absorb neutrons. Attempts have
been made to protect the original mechanical and physical
properties of the aluminum base alloy from being adversely affected
by boron contained thereinto for neutron shield and absorption.
[0006] For example, boron added to an aluminum base alloy
containing magnesium as a constituent forms an intermetallic
compound with magnesium which crystallizes and precipitates,
thereby decreasing the amount of magnesium in the form of solid
solution, with the result that the decrease in strength of the
aluminum base alloy is caused. A method of addressing this problem
was disclosed Japanese Patent Laid-open No. 312043/1989. This
method involves the addition of in the form of powder of
magnesium-free AlB.sub.12 compound, so as to suppress the reaction
between boron and magnesium, thereby preventing a possible decrease
in strength due to the formation of these intermetallic compounds.
In addition, Japanese Patent Laid-open No. 312044/1989 discloses
another method in which a melting processing is carried out in a
high temperature region of 1200.degree. C. or more in order to
restrict a reaction between B and Mg by adding boron in the form of
powder. Furthermore, Japanese Patent Laid-open No. 333542/1992
discloses a method of producing an aluminum base alloy containing
boron which has a low viscosity and hence is superior in
castability. This method involves reacting KBF.sub.14 with Al
within a temperature range of 680 to 850.degree. C. and
subsequently adding a small amount of K.sub.2TiF.sub.6 in the melts
of Al--B alloy containing the generated AlB.sub.2 crystal. In this
way it is possible to eliminate a high viscosity of the melts and
improve a castability.
[0007] The present inventors had carried out investigations on the
development of the above-mentioned aluminum base alloy containing
boron. One result of the investigations was disclosed in U.S. Pat.
No. 5,925,313. The disclosed an aluminum base alloy containing
boron, which has an enhanced capacity to absorb neutrons, is
characterized in having a content of isotope .sup.10B of 95% or
more (satisfying a relation of .sup.10
B/(.sup.10B+.sup.11B).gtoreq.95%. Originally, boron has an isotope
composition composed of .sup.10B and .sup.11B, and boron having a
superior neutron absorbing capacity is mainly .sup.10B. In
addition, the aluminum base alloy contains boron in the form of
AlB.sub.2 dispersed in the alloy, so that the alloy exhibits a
stable neutron shielding capacity and an ability to recycle the
scrap alloy.
[0008] Unfortunately, the aluminum base alloy containing boron (or
boron-containing aluminum) proposed so far suffers the disadvantage
of being unable to maintain its high-temperature strength and creep
strength for a long period of time which are characteristic
properties required of the basket material for cask to store spent
fuel. Another disadvantage is that the basket material (sheet or
extended pipe and the like) as a whole does not fully function to
absorb neutrons because of the microscopic segregation or the
gravity segregation in the ingot.
OBJECT AND SUMMARY OF THE INVENTION
[0009] The present invention was completed in view of the
foregoing. It is an object of the present invention to provide an
aluminum base alloy containing boron and the manufacturing method,
said alloy being characterized by its mechanical properties (such
as strength and creep strength) that last for a long period of time
at high temperatures and by its ability to absorb neutrons and to
maintain the sub-criticality of fuel assemblies and, with boron
remaining in the form of compound in the alloy without
segregation.
[0010] The present invention is directed to an aluminum base alloy
containing boron which contains 0.5-10% of boron with an isotopic
composition satisfying a relation of
.sup.10B/(.sup.10B+.sup.11B).gtoreq.30%, said boron being present
in the form of a boron compound which is 300 .mu.m or less in
size.
[0011] The present invention is also directed to an aluminum base
alloy containing boron which contains 0.5-10% of boron with an
isotopic composition satisfying a relation of
.sup.10B/(.sup.10B+.sup.11B).gtoreq.30%, said boron being present
in the form of a compound containing aluminum and boron which is
300 .mu.m or less in size.
[0012] The present invention is also directed to an aluminum base
alloy containing boron which contains 0.5-10% of boron with an
isotopic composition satisfying a relation of
.sup.10B/(.sup.10B+.sup.11B).gtoreq.30%, said boron being present
in the form of a compound containing, in addition to aluminum and
boron, at least one element selected from the group composed of Mg,
Mn, Si, and Cu, which is 300 .mu.m or less in size. In a preferred
embodiment, the aluminum base alloy containing boron contains boron
such that the boron compounds (in which the total amount of those
elements selected from the group composed of Mg, Mn, Si, and Cu is
0.01-50 atom %) occupy 50% or more with the number proportion in
all the boron compounds.
[0013] An aluminum base alloy containing boron, which the
difference is 1.0% or less in the maximum and minimum value of the
B quantity of the specimen that divided the alloy in the
plural.
[0014] The manufacturing method of the present invention has a
feature that (1) a melting temperature is controlled in excess of
950.degree. C. and a casting temperature is in the range of
800.degree. C. to 950.degree. C., and the holding or cooling time
from 950.degree. C. to the casting temperature is in the range of
60-1800 seconds, (2) the hot rolling or hot forging temperature is
in the range of 250-600.degree. C. in such a way that the rate of
reduction per pass is 40% or below and the total reduction is 50%
or more, and (3) temperature extruded is in the range of
400-550.degree. C. If necessary, the above-mentioned three
requirements may be combined with one another. [For example,
(1)+(2) or (1)+(3).] The method that mentioned above causes the
boron compound to be fine in size 300 .mu.m or less and hence
contributes to its uniform distribution in the aluminum base
alloy.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] In order to complete the present invention, the present
inventors carried out a series of researches which led to the
finding that the aluminum base alloy containing boron exhibits good
high-temperature strength and creep strength if it is contained
boron satisfying the relation of .sup.11B/(.sup.10B+.sup.11B) is
larger than a certain value and it processes melting, casting and
hot working (such as rolling and extrusion) under adequate
conditions so that the boron compound in the alloy is not larger
than 300 .mu.m in size.
[0016] The neutron absorbing capacity of an aluminum base alloy
containing B is secured even if it depends on large amount of
original boron (which is a isotope composition composed of 20% of
.sup.10B). Unfortunately, boron in the aluminum base alloy exists
in the form of compound and the amount of the boron compound
increases as the content of boron increases. This boron compound
exerts the influence on the decline of the high-temperature
strength and creep strength of the aluminum base alloy. Therefore,
it is necessary that the content of boron be 10% or less in the
aluminum base alloy of the present invention. With a boron content
higher than 10%, the aluminum base alloy will be remarkably poor in
mechanical properties.
[0017] On the other hand, with a boron content less than 0.5%, the
aluminum base alloy does not absorb as many neutrons as required
even though all of the boron contained is composed of .sup.10B. One
way to cope with this situation is to increase the wall thickness
of the basket material. However, this is not practical because the
cask container becomes large in size (which is uneconomical) and
less efficient in heat removal.
[0018] For the reasons mentioned above, the aluminum base alloy
containing boron of the present invention should contain boron in
an amount of 0.5-10%. For the alloy to have the same mechanical
properties as the original aluminum base alloy (before contained
boron), the amount of boron should preferably be 9% or less.
[0019] If a desired neutron shielding capacity is to be attained by
containing original boron having an isotope composition composed of
about 20% of .sup.10B, it is necessary to increase the thickness of
the aluminum base alloy containing boron or to increase the boron
content in the alloy. Such countermeasures, however, offer the
disadvantages mentioned above. Thus, for the aluminum base alloy
containing B to have a satisfactory neutron absorbing capacity with
a boron content from 0.5% to 10% which has no adverse effect on its
mechanical properties, it is necessary that the relation of
.sup.10B to the total amount of .sup.10B and .sup.11B should be 30%
or more.
[0020] If this relation is less than 30%, the alloy with a normal
thickness will not have the desired neutron absorbing capacity. On
the other hand, as this ratio increases, the alloy has a larger
neutron absorbing capacity; however, the alloy as a structural
component needs a certain measure of thickness. In addition,
containing .sup.10B (which is very expensive) in large amounts
leads to a cost increase. Therefore, the ratio of
.sup.10B/(.sup.10B+.sup.11B) should preferably be less than
95%.
[0021] As mentioned above, the present invention requires that the
boron content and the ratio of .sup.10B in the aluminum base alloy
containing boron should be properly controlled, so that the
resulting alloy has an adequate neutron absorbing capacity and the
same mechanical properties as the original aluminum base alloy
before incorporation with boron. However, these requirements are
not enough; depending on the state in which boron exists, the alloy
used for the basket material may not have an adequate neutron
absorbing capacity and mechanical properties required for storage
of spent fuel for a long period of time.
[0022] For the aluminum base alloy containing boron to retain
stable, good mechanical properties (such as high-temperature
strength and creep strength) over a long period of time, it is
necessary that the compound containing boron in the aluminum base
alloy should have a size of 300 .mu.m or less. The shape of the
boron compound may be bulk, needle, plate, etc. The term "the size
of the boron compound" as used in this specification means the
maximum length in any direction (regardless of thickness or width).
The boron compound larger than 300 .mu.m in size will impair the
mechanical properties (such as high-temperature strength and creep
strength) of the alloy. It is desirable that the boron compound
should be uniformly dispersed from the standpoint of neutron
absorption. This object is easily accomplished if the boron
compound is 300 .mu.m or less in size. If the size exceeds this
limit, the aluminum base alloy will not have a uniform neutron
absorbing capacity.
[0023] The term "boron compound" as used in this specification
means any boron compounds such as AlB.sub.2, AlB.sub.12, TiB, CrB,
FeB, B.sub.2O.sub.3, and B.sub.4C, which are not specifically
restricted. These compounds are formed when boron is added to
molten pool of Al alloy (Al-bath), or they may be previously
prepared from raw materials (in powder form) and then added to the
Al-bath. They are not restricted by their origin. Incidentally, it
is not always necessary that all of the boron compounds have a size
of 300 .mu.m or less; the present invention will produce its effect
if 80% or more of the boron compounds have a size of 300 .mu.m or
less.
[0024] The present inventors investigated the relation between the
kind of the boron compound and the mechanical properties, paying
special attention to Al--B compounds (such as AlB.sub.2 and
AlB.sub.12) which dominate in the boron compounds that mentioned
above. As the result, it was found that the present invention
produces its effect when the compound has the size of 300 .mu.m or
less.
[0025] By the way, it is a general method to add the alloy elements
such as Mg and Mn to the aluminum alloy to improve its mechanical
properties. For example, Japanese Patent Laid-open No. 312043/1989
(mentioned above) specifies that the melting temperature should be
higher than 1200.degree. C. or more because "the Al--B--Mg
intermetric compounds are formed at the melting temperature of
700-800.degree. C., which causes the decrease in strength".
[0026] The present inventors carried out investigations in
anticipation of containing the alloy elements (such as Mg and Mn)
into the aluminum base alloy. As the result, it was found that the
present invention produces its effect even though the Al--B--Mg
intermetallic compounds are formed, if they are made extremely
small in size under strict melting conditions. It was also found
that the effect that mentioned above is achieved not only in the
case of Al--B--Mg compounds but also in the case of boron compounds
containing at least any of Mn, Si, Cu, etc. In other words, the
effect of the present invention is achieved when applied to not
only 5000 series or 6000 series aluminum alloy containing Mg as a
major element but also 3000 series aluminum alloy containing Mn as
a major element and 2000 series aluminum alloy containing Cu as a
major element, if the boron compounds including such alloy elements
into oneself have the specified size (300 .mu.m or less) and the
specified type (phase) of the intermetric compounds.
[0027] The boron compound containing at least one of the alloy
elements that mentioned above (e.g., Mg, Mn, Si, and Cu) varies in
boron distribution and size depending on its type. This in turn
affects the neutron absorbing capacity and the high-temperature
characteristics of the resulting alloy. According to the present
invention, the type of the compound should preferably be such that
the boron compound in which the total amount of these alloy
elements is 0.01-50 atom % accounts for 50% or more (in terms of
number) of the total amount of the boron compounds.
[0028] In other words, the present invention produces its effect as
the boron compound is made smaller, if the total amount of alloying
elements in the boron compound is 0.01 atom % or more, preferably
0.1 atom % or more. With a total content in excess of 50 atom %,
the alloy elements do not demonstrate the effect of strengthening
the parent material and hence the resulting alloy is poor in
high-temperature strength. A more preferable upper limit value of
the total content of the alloy elements is about 40 atom %.
[0029] The boron compound in which the total amount of the alloy
elements is 0.01-50 atom % should account for 50% or more with
number proportion of the total amount of the boron compounds, so
that the effect of the present invention produced by making the
boron compound make extremely small in size. A preferred lower
limit of this ratio is about 55%.
[0030] The content of alloying elements (one or more species
selected from Mg, Mn, Si, and Cu) in the boron compound and the
ratio of the boron compound may be determined by using EPMA, SEM,
FE-SEM, TEM, FE-TEM, etc. For accurate determination, it is
desirable to select more than 100 samples.
[0031] The aluminum base alloy containing boron of the present
invention has improved mechanical properties (such as
high-temperature strength and creep strength) owing to the
controlled size and type of the boron compounds. It is necessary
that the alloy as a whole should have this effect uniformly. In
other words, when the aluminum base alloy containing boron is
applied to the practical use, the boron content should be uniform
from one part to the other in the alloy component. The aluminum
base alloy containing boron of the present invention involves the
boron compound uniformly dispersed therein and hence contains boron
almost uniformly throughout the alloy. For better reliability and
more efficient design, it is necessary to adequately control the
variation of the boron content in each part of the component.
[0032] The aluminum base alloy containing boron of the present
invention is rolled, extruded, or forged according to use. No
matter what the working process and the shape and dimension, the
alloy should meet the requirement that the difference is 1.0% or
less in the maximum and minimum value of the B quantity of the
specimen that divided the alloy in the plural. Failure to meet this
requirement leads to an alloy which varies in neutron absorbing
capacity and mechanical properties. Such an alloy necessitates to
increase the thickness of the component made from it, and thick of
component are high in production cost and poor in efficiency of
heat removal. This in turn requires that the component should have
greater high temperature strength.
[0033] The manufacturing method according to the present invention
is explained in the following. The aluminum base alloy containing
boron of the present invention should be melted at 950.degree. C.
or above and cast at 800-950.degree. C. The molten metal should be
kept for 60-1800 seconds until it cools from 950.degree. C. to its
casting temperature.
[0034] According to the method mentioned above, the melting
temperature should be 950.degree. C. or above so that the boron
compound has a size of 300 .mu.m or less and is dispersed as
uniformly as possible. For uniform dispersion of added boron, it is
necessary that the added boron should be melted once in Al-melt at
950.degree. C. or above. At a temperature 950.degree. C. or below,
the boron compound does not melt in the molten aluminum base alloy
but remains in the coarse form in the ingot, adversely affecting
the mechanical properties. The melting temperature should
preferably be 960.degree. C. or above.
[0035] In the case that it adds with the type of powder such as TiB
or CrB as the addition form of the B material, here, the melting
temperature is not necessarily limited to the temperature that
exceeds 950.degree. C. However, above temperature has technical
significance with this viewpoint, because it is prefer to melt B in
the powder material into Al-bath as a high temperature.
[0036] Casting that follows melting should be carried out at
800-950.degree. C. If the casting temperature is lower than
800.degree. C., the ingot solidifies in a short time, which
contributes to uniform boron distribution in the ingot. On the
other hand, the disadvantage of the low casting temperature is that
the boron compound grows and becomes large in size before the
casting temperature is reached. This adversely affects the decline
of strength and elongation. By contrast, if the casting temperature
is higher than 950.degree. C., the ingot takes a long time before
it solidifies and hence the boron compound settles down and
aggregates (resulting in uneven boron distribution) although the
boron compound becomes small in size. The casting temperature
should preferably be about 820.degree. C. at its lower limit and
930.degree. C. at its upper limit.
[0037] The molten pool of aluminum base alloy should be kept for a
specified period of time before it cools from 950.degree. C. to the
casting temperature, so as to effectively control the size of the
boron compound. If this period is longer than specified, the boron
compound grows in size. In other words, if this period is longer
than 1800 seconds, the boron compound becomes larger than 300 .mu.m
and the resulting alloy is poor in mechanical properties. On the
other hand, it is not sufficient to be demonstrate the effect
stably in below 60 seconds. This period should preferably be about
120 seconds at its lower limit and about 1500 seconds at its upper
limit.
[0038] The present invention specifies the melting temperature, the
casting temperature, and the period for cooling from 950.degree. C.
to the casting temperature as mentioned above, so that the boron
compound has an adequate size and boron is uniformly distributed in
the aluminum base alloy containing boron. In addition to these
requirements, it is also necessary to control the cooling rate of
the molten alloy so as to improve the distribution of boron.
[0039] After casting, the molten alloy cools from the casting
temperature to liquidus point at a certain rate. Low cooling rate
causes the gravity segregation and aggregation of the boron
compound. Most boron compounds have a larger specific gravity than
the aluminum base alloy, and hence the boron compound settles
during soldefication and this contributes to uniform distribution
of boron in the aluminum base alloy. For this reason the cooling
rate should be as large as possible, preferably 0.05.degree.
C./second or above.
[0040] High soldification rate (cooling rate from liquidus
temperature to solidus temperature) is contribute to decrease the
macro-segregation micro-segregation and gravity segregation of the
boron compound which is crystallized as the aluminum matrix
solidifies. Therefore, the freezing rate should be 0.01.degree.
C./second or above.
[0041] The method of casting of the aluminum base alloy containing
boron according to the present invention is not specifically
restricted so long as the requirements as mentioned above are met.
Casting may be accomplished by ordinary semi-continuous casting,
continuous casting, or mold casting. In the last case, it is
desirable to use a cast iron mold, copper mold, or water-cooled
mold.
[0042] The aluminum base alloy containing boron according to the
present invention should be rolled or forged at 250-600.degree. C.
in such a way that the rate of reduction per pass is 40% or below
and the total reduction is 50% or above. Working in this way causes
the boron compound to reduce in size 300 .mu.m or below and hence
contributes to its uniform distribution in the aluminum base alloy.
The working conditions that mentioned above are necessary for the
alloy to uniformly contain the boron compound without cracking that
might occur under ordinary working conditions. Uniform distribution
of the boron compound is desirable for the improved neutron
absorbing capacity and mechanical properties.
[0043] According to the manufacturing process of the present
invention, the working temperature should be 250-600.degree. C. At
a working temperature lower than 250.degree. C., the aluminum base
alloy containing the boron compound is liable to edge cracking
during rolling. On the other hand, working at a temperature higher
than 600.degree. C. causes seizing, thereby deteriorating the
surface quality. Therefore, the working temperature should
preferably be about 300.degree. C. at its lower limit and about
550.degree. C. at its upper limit.
[0044] The manufacturing method according to the present invention
requires the specific working temperature as well as the specific
reduction per pass as mentioned above. That is, the reduction per
pass should be 40% or below so as to avoid edge cracking. The
smaller is the reduction, the less is the aluminum base alloy
subject to surface roughening. On the other hand, the small
reduction causes the final working temperature to decrease.
Therefore, the upper limit of the reduction should preferably be
about 35%. However, the total reduction should be larger than 50%
so that the boron compound is made 300 .mu.m or below in size and
is uniformly distributed in the aluminum base alloy.
[0045] The aluminum base alloy containing boron according to the
present invention may be extruded at 400-550.degree. C. so that the
boron compound is dispersed uniformly in the form of fine particles
300 .mu.m or below in size. Extrusion is an effective way of
producing various products varying in cross section, ranging from
simple plates and hollow pipes (rectangular pipes and the like) to
complex profiles having R-corners. The method of extruding process
is contribute to omission of the machine processing process and
hence to cost reduction.
[0046] The aluminum base alloy containing boron of the present
invention cannot be extruded by the method used for conventional
extrusion method of aluminum base alloys into hollow pipes through
a port hole die. (Extrusion through a port hole die forces more
than one billet through an extrusion die in which extrudates are
deposited together into a pipe.)
[0047] This method is process of making pipe form that one billet
is divided into several parts in the entry die, and every parts
pushes out by the die of pushing out exit, and join by
pressure.
[0048] The condition for extrusion as mentioned above was
established for satisfactory pressure welding. Extrusion at a
temperature lower than 400.degree. C. is poor in pressure welding
performance and is subject to result extrusion clogging due to
increased deformation stress. Extrusion at a temperature higher
than 550.degree. C. causes seizure which aggravates surface quality
and dimensional accuracy.
[0049] The present invention does not specifically restrict the
basic components of the aluminum base alloy. It covers ordinary
aluminum base alloys, such as 6000 series, 5000 series, 4000
series, 3000 series, 2000 series, and 1000 series. These aluminum
base alloys may contain Zn, Cr, Fe, etc. in small amounts not
harmful to their characteristic properties. They may also contain
inevitable impurities such as Mo, Nb, and Ni.
[0050] The aluminum base alloy containing boron in the form of
ingot, plate, or extruded material may undergo heat treatment or
cold rolling depending on its applications and strength required,
as in the case of ordinary aluminum base alloys. Heat treatment
produces good mechanical properties (such as tensile strength and
ductility). For example, 6000 series alloys will acquire a very
high tensile strength (300 MPa or above) if their hot working (such
as rolling and extrusion) is followed by solution treatment (at
515-550.degree. C.), quenching (water hardening), and age hardening
(at 155-165.degree. C.).
[0051] An ingot of the aluminum base alloy containing boron should
be faced (3 mm or more from surface, preferably 3.5 mm) so that it
can be processed into ingot, plates and extruded material having a
good surface. Facing is necessary because the boron compound tends
to segregate in the vicinity of the ingot surface and the segregate
phase differs from the compound specified in the present invention.
Moreover, the segregate phase causes an irregular surface in the
anodizing surface treatment.
[0052] The invention will be understood more readily by reference
to the following examples; however, these examples are intended to
illustrate the invention and are not to be construed to limit the
scope of the invention.
EXAMPLES
Example 1
[0053] 6000 series alloys having the composition shown in Table 1
were changed into blocks of 300 mm in thickness under the
conditions.
[0054] Melting temperature: 1050.degree. C. Casting temperature:
900.degree. C. TABLE-US-00001 TABLE 1 Sample .sup.10B/(.sup.10B +
.sup.11B) Chemical composition (mass %) No. (mass %) B Si Mn Cr Cu
Zn Mg Ti Fe Example 1 90 0.90 0.71 0.01 0.22 0.29 0 1.10 0.03 0.39
2 90 0.90 0.71 0.01 0.22 0.29 0 1.10 0.03 0.39 3 90 0.90 0.71 0.01
0.22 0.29 0 1.10 0.03 0.39 4 75 6.40 0.69 0.02 0.20 0.27 0.01 1.06
0.02 0.40 5 88 1.20 0.70 0.01 0.19 0.31 0.01 1.18 0.03 0.38
Comparative 6 25 2.60 0.71 0.01 0.22 0.29 0 1.10 0.03 0.39 Example
7 85 11.50 0.71 0.01 0.22 0.29 0 1.10 0.03 0.39 8 90 0.30 0.71 0.01
0.22 0.29 0 1.10 0.03 0.39 9 75 13.50 0.70 0.01 0.21 0.30 0.01 1.18
0.03 0.40 10 20 2.30 0.69 0.02 0.24 0.28 0.01 1.11 0.02 0.40
[0055] The ingots obtained in this way were soaked and they were
hot rolled at 500.degree. C. (starting temperature). There was
obtained a 10-mm thick plate. The sequence of soaking and facing
may be reversed; however, facing that follows soaking effectively
removes surface oxides and hence contributes to a plate having a
good surface. The hot-rolling may be preceded by forging to give a
desired shape. Incidentally, these 6000 series alloys were
processed by T6 treatment (a solution treatment at 530.degree. C.,
for 1 hour and age hardening at 180.degree. C. for 24 hours). The
thus obtained plate of aluminum base alloy was examined for the
following items.
[Measurement of the Size and Type (Phase) Shape of the Boron
Compound]
[0056] Samples taken from the plate were examined for the size and
type (phase) of the boron compound by using an SEM or SEM-EDX. The
presence of boron in each compound was confirmed by EDX. The
content (in terms of atom %) of components (such as Mg, Mn, Si, and
Cu) in each boron compound was measured. The size of the boron
compound is defined as the length of the longer axis (in the case
of rectangular shape) or the maximum diameter (in the case of
spherical shape). Incidentally, the number of measurements was
200.
[Tensile Test at Room Temperature]
[0057] A specimen conforming to JIS Z2201 No. 5 (25 w.times.50
GL.times.plate thickness) was taken from the plate as mentioned
above in such a way that the length of the specimen is
perpendicular to the rolling direction. This specimen was examined
by tensile test at room temperature. The pulling rate was 1 MPa/sec
until the offset yield strength for 0.2% elongation and then 20
mm/min. The specimen was also tested for offset yield strength (for
0.2% elongation) and elongation at room temperature (20.degree. C.)
according to JIS Z2241 (1980) describing the method of tensile test
for metal materials.
[Tensile Test at High Temperatures]
[0058] Since nothing is specified in JIS for tensile test of
aluminum base alloy at high temperatures, the method according to
JIS G0567 (6 mm in diameter.times.30 GL) was employed. A specimen
was taken in such a way that its length is perpendicular to the
rolling direction. The pulling rate was 0.3%/min until the offset
yield strength for 0.2% elongation and then 7.5%/min. The number of
measurements was 9. The test was carried out at 200.degree. C. The
specimen was also tested for offset yield strength (for 0.2%
elongation) and elongation.
[Creep Characteristics]
[0059] Creep rupture test at high temperatures was carried out
according to JIS Z2271 (1978). The specimen is a round rod, 6 mm in
diameter, and the specimen was taken in such a way that its length
is perpendicular to the rolling direction. The test was carried out
at 200.degree. C. under a load of 5 kg/mm.sup.2, and time required
for rupture to occur was measured. The specimen was rated according
to the following criterion.
[0060] .largecircle.: rupture occurred after 10 hours.
[0061] X: rupture occurred within 10 hours.
[Assessment of Boron Distribution]
[0062] Samples were taken from the head and tail ends and the
center and edges (in the widthwise direction) of the plate. They
were analyzed by ICP emission spectroscopy. They were rated in
terms of the difference between the maximum and minimum values
according to the following criterion.
.circleincircle.: 0.05% or below
.largecircle.: 1.0% or below
X more than 1.0%
[0063] The results of the tests are shown in Table 2. It is noted
from the table that the samples Nos. 1 to 5 (which are aluminum
base alloy containing boron meeting the requirements of the present
invention) are good in high-temperature strength and creep
characteristics. By contrast, those samples Nos. 6 to 10 (which are
aluminum base alloys not meeting the requirements of the present
invention) contain the boron compound in coarse form, alloy
elements in large amount, and unevenly distributed boron.
TABLE-US-00002 TABLE 2 Strength at High-temperature room
temperature strength Size of Amount Offset Offset boron of alloying
Major yield Elon- yield Elon- compound elements alloying Strength
strength gation Strength strength gation Creep Boron No. (.mu.m)
(atom %) element (MPa) (MPa) (%) (MPa) (MPa) (%) characteristics
distribution Problem 1 190 24 Mg 325 291 13.3 220 203 12.5
.largecircle. .largecircle. -- 2 80 8 Mg 340 310 14.4 230 215 13.6
.largecircle. .largecircle. -- 3 250 35 Mg 320 278 12.1 217 200
11.4 .largecircle. .largecircle. -- 4 45 3 Mg 345 312 14.8 236 219
14.0 .largecircle. .largecircle. -- 5 130 13 Mg 337 307 13.0 224
208 12.9 .largecircle. .largecircle. -- 6 50 7 Mg 341 309 14.6 232
217 14.0 .largecircle. .largecircle. 1) 7 360 47 Mg 301 273 9.7 210
192 9.6 X .largecircle. 2) 8 200 29 Mg 323 289 13.1 220 202 11.9
.largecircle. .largecircle. 1) 9 420 68 Mg 295 269 8.9 204 188 9.0
X .largecircle. 2) 10 40 4 Mg 346 314 14.7 237 222 14.2
.largecircle. .largecircle. 1) 1) Neutron absorbing capacity 2)
Strength and elongation
Example 2
[0064] The same procedure as in Example 1 was repeated to produce
ingots, except that the aluminum base alloy was replaced by 5000
series one having the composition as shown in Table 3.
[0065] The thus obtained ingots were soaked and they were hot
rolled at starting temperature of 500.degree. C. into 10-mm thick
plates. Incidentally, the 5000 series alloys were processed by a
H34 treatment and then evaluated according to the same criterion as
in Example 1. The results are shown in Table 4. It is noted that
the results are the same as those in Example 1. TABLE-US-00003
TABLE 3 Sample .sup.10B/(.sup.10B + .sup.11B) Chemical composition
(mass %) No. (mass %) B Si Mn Cr Cu Zn Mg Ti Fe Example 1 83 1.10
0.21 0.02 0.18 0.08 0.05 2.50 0.01 0.30 2 83 1.10 0.21 0.02 0.18
0.08 0.05 2.50 0.01 0.30 3 83 1.10 0.21 0.02 0.18 0.08 0.05 2.50
0.01 0.30 4 90 0.85 0.23 0.01 0.17 0.09 0.04 2.53 0.02 0.32 5 75
8.20 0.19 0.01 0.18 0.10 0.05 2.49 0.01 0.29 Comparative 6 20 2.10
0.21 0.02 0.18 0.08 0.05 2.50 0.01 0.30 Example 7 70 0.30 0.21 0.02
0.18 0.08 0.05 2.50 0.01 0.30 8 90 13.80 0.21 0.02 0.18 0.08 0.05
2.50 0.01 0.30 9 80 11.45 0.23 0.01 0.19 0.09 0.04 2.53 0.02 0.29
10 25 2.36 0.20 0.01 0.17 0.08 0.03 2.48 0.01 0.31
[0066] TABLE-US-00004 TABLE 4 Strength at High-temperature room
temperature strength Size of Amount Offset Offset boron of alloying
Major yield Elon- yield Elon- compound elements alloying Strength
strength gation Strength strength gation Creep Boron No. (.mu.m)
(atom %) element (MPa) (MPa) (%) (MPa) (MPa) (%) characteristics
distribution Problem 1 120 8 Mg 268 231 9.5 165 125 8.9
.largecircle. .largecircle. -- 2 30 19 Mg 280 240 10.4 170 130 9.3
.largecircle. .largecircle. -- 3 190 6 Mg 266 229 9.1 160 120 8.4
.largecircle. .largecircle. -- 4 50 17 Mg 275 237 10.1 173 127 9.3
.largecircle. .largecircle. -- 5 100 10 Mg 271 233 9.7 166 125 9.0
.largecircle. .largecircle. -- 6 90 6 Mg 271 234 9.8 167 125 9.0
.largecircle. .largecircle. 1) 7 150 65 Mg 267 230 9.3 163 122 8.7
.largecircle. .largecircle. 1) 8 410 21 Mg 245 205 7.4 143 106 6.9
X .largecircle. 2) 9 350 18 Mg 250 216 7.9 150 115 7.3 X
.largecircle. 2) 10 40 5 Mg 278 238 10.0 171 128 9.3 .largecircle.
.largecircle. 1) 1) Neutron absorbing capacity 2) Strength and
elongation
Example 3
[0067] The same procedure as in Example 1 was repeated to produce
ingots, except that the aluminum base alloy was replaced by 3000
series one having the composition as shown in Table 5.
[0068] The thus obtained ingots were soaked and they were hot
rolled at the starting temperature of 500.degree. C. into 10-mm
thick plates. Incidentally, the 3000 series alloys were processed
by a H34 treatment and then evaluated according to the same
criterion as in Example 1. The results are shown in Table 6. It is
noted that the results are the same as those in Example 1.
TABLE-US-00005 TABLE 5 Sample .sup.10B/(.sup.10B + .sup.11B)
Chemical composition (mass %) No. (mass %) B Si Mn Cr Cu Zn Mg Ti
Fe Example 1 94 0.95 0.22 1.25 0.01 0.18 0.17 1.10 0.02 0.62 2 94
0.95 0.22 1.25 0.01 0.18 0.17 1.10 0.02 0.62 3 94 0.95 0.22 1.25
0.01 0.18 0.17 1.10 0.02 0.62 4 94 1.80 0.22 1.23 0.01 0.16 0.17
1.12 0.03 0.60 5 94 0.75 0.24 1.24 0.02 0.19 0.18 1.08 0.01 0.65
Comparative 6 25 2.90 0.21 1.21 0.01 0.17 0.18 1.11 0.02 0.63
Example 7 85 11.50 0.21 1.21 0.01 0.17 0.18 1.11 0.02 0.63 8 20
2.20 0.21 1.21 0.01 0.17 0.18 1.11 0.02 0.63 9 80 10.50 0.23 1.20
0.01 0.20 0.16 1.13 0.01 0.59 10 70 0.20 0.23 1.20 0.01 0.20 0.16
1.13 0.01 0.59
[0069] TABLE-US-00006 TABLE 6 Strength at High-temperature room
temperature strength Size of Amount Offset Offset boron of alloying
Major yield Elon- yield Elon- compound elements alloying Strength
strength gation Strength strength gation Creep Boron No. (.mu.m)
(atom %) element (MPa) (MPa) (%) (MPa) (MPa) (%) characteristics
distribution Problem 1 225 14 Mg 247 200 8.8 151 115 8.0
.largecircle. .largecircle. -- 2 50 17 Mg 261 217 9.7 160 124 8.8
.largecircle. .largecircle. -- 3 100 13 Mg 257 212 9.3 157 120 8.5
.largecircle. .largecircle. -- 4 190 7 Mg 251 205 8.9 153 116 8.2
.largecircle. .largecircle. -- 5 20 25 Mg 265 220 10.0 162 125 9.0
.largecircle. .largecircle. -- 6 90 6 Mg 258 213 9.4 158 120 8.5
.largecircle. .largecircle. 1) 7 350 15 Mg 238 192 7.7 143 105 7.4
X .largecircle. 2) 8 60 6 Mg 260 215 9.5 159 123 8.6 .largecircle.
.largecircle. 1) 9 400 11 Mg 230 185 7.1 138 98 6.9 X .largecircle.
2) 10 150 58 Mg 254 209 9.1 154 118 8.3 .largecircle. .largecircle.
1) 1) Neutron absorbing capacity 2) Strength and elongation
Example 4
[0070] The 6000 series aluminum base alloy, No. 1, shown in Table 1
was cast into ingots under the conditions shown in Table 7. The
ingots were soaked, and they were hot rolled or hot-extruded to be
made into plates.
[0071] The thus obtained plates were processed by a T6 treatment
(solution treatment at 530.degree. C. for 1 hour and age hardening
at 180.degree. C. for 24 hours) and then evaluated according to the
same criterion as in Example 1. The thus obtained plates were
examined for surface state and rated according to the following
criterion.
[0072] .largecircle.: no cracking occurred.
[0073] X: cracking occurred.
[0074] The results are shown in Table 8. It is noted that all the
aluminum base alloys (designated as A to E) meeting the
requirements of the present invention are superior in strength and
ductility, with the boron compound having a small size. It is also
noted that hot-rolling in the way specified in the present
invention results in uniform boron distribution and good surface
state. By contrast, those aluminum base alloys (designated as F to
J) not meeting the requirements of the present invention suffered
increase in size of the boron compound, decrease in ductility,
surface roughening, and uneven boron distribution. TABLE-US-00007
TABLE 7 Time for cooling Rolling or extruding conditions Melting
Casting from 950.degree. C. Working Maximum temperature temperature
to casting temperature reduction Code (.degree. C.) (.degree. C.)
temperature (s) Process (.degree. C.) (%) Example A 1020 900 690
Rolling 500 30 B 1050 930 360 Rolling 400 24 C 1005 840 1250
Rolling 460 35 D 1035 870 990 Extrusion 520 -- E 1080 900 705
Extrusion 480 -- Comparative F 1030 930 450 Rolling 600 50 Example
G 1050 990 -- Rolling 510 29 H 1010 830 2500 Rolling 430 30 I 920
850 -- Extrusion 490 -- J 1005 900 1000 Extrusion 250 --
[0075] TABLE-US-00008 TABLE 8 Strength at High-temperature room
temperature strength Size of Amount Offset Offset boron of alloying
Major yield Elon- yield Elon- Creep Boron compound elements
alloying Strength strength gation Strength strength gation charac-
distri- Surface Code (.mu.m) (atom %) element (MPa) (MPa) (%) (MPa)
(MPa) (%) teristics bution state Problem A 50 9 Mg 337 306 14.6 255
226 13.9 .largecircle. .circleincircle. .largecircle. -- B 90 14 Mg
331 300 14.2 250 221 13.3 .largecircle. .circleincircle.
.largecircle. -- C 210 34 Mg 320 291 13.0 240 210 12.7
.largecircle. .circleincircle. .largecircle. -- D 160 22 Mg 326 295
13.4 246 215 13.0 .largecircle. .circleincircle. .largecircle. -- E
30 7 Mg 340 308 15.0 260 230 14.1 .largecircle. .circleincircle.
.largecircle. -- F 85 11 Mg 330 300 14.3 250 222 13.4 .largecircle.
.largecircle. X 1) G 25 6 Mg 341 308 15.0 262 230 14.2
.largecircle. X .largecircle. 2) H 500 75 Mg 297 269 9.9 217 188
9.4 X X .largecircle. 3) I 410 58 Mg 305 278 9.2 226 198 8.8 X X
.largecircle. 4) J 120 16 Mg 328 296 13.9 248 218 12.9
.largecircle. .largecircle. X 5) 1) Reduction 2) Casting
temperature 3) Time to casting 4) Melting temperature 5) Working
temperature
EFFECT OF THE INVENTION
[0076] The aluminum base alloy containing boron of the present
invention exhibits good mechanical properties (such as
high-temperature strength and creep strength) over a long period of
time. It also has a neutron absorbing capacity, with boron in the
form of compound uniformly distributed therein without
segregation.
* * * * *