U.S. patent application number 13/522940 was filed with the patent office on 2012-12-27 for method for manufacturing 6xxx alloy materials for vacuum chambers.
This patent application is currently assigned to CONSTELLIUM VALAIS SA. Invention is credited to Cedric Gasqueres, Joost Van Kappel.
Application Number | 20120325381 13/522940 |
Document ID | / |
Family ID | 42646369 |
Filed Date | 2012-12-27 |
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United States Patent
Application |
20120325381 |
Kind Code |
A1 |
Gasqueres; Cedric ; et
al. |
December 27, 2012 |
METHOD FOR MANUFACTURING 6XXX ALLOY MATERIALS FOR VACUUM
CHAMBERS
Abstract
The invention relates to a manufacturing process for an aluminum
block of at least 250 mm thick designed for the manufacture of
elements for vacuum chambers in which the following operations are
carried out successively: an alloy block is cast by semi-continuous
casting, the composition of this block in weight % being: Si
0.5-1.5; Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10;
Ti<0.15, other elements <0.05 each and <0.15 in total, the
rest aluminum; solution heat treatment is performed at a
temperature ranging between 450 and 560.degree. C. directly on the
cast block and optionally homogenized; the block that has undergone
solution heat treatment is quenched at a cooling speed between the
solution heat treatment temperature and 200.degree. C. of at least
200.degree. C./h; the block quenched and optionally stress-relieved
is artificially aged. The blocks obtained in this way are
advantageous for the production of vacuum chambers for the
manufacture of integrated electronic circuits containing
semiconductors, flat screens and/or photovoltaic panels.
Inventors: |
Gasqueres; Cedric; (Issoire,
FR) ; Van Kappel; Joost; (Sierre, CH) |
Assignee: |
CONSTELLIUM VALAIS SA
Sierre
CH
CONSTELLIUM FRANCE
Paris
FR
|
Family ID: |
42646369 |
Appl. No.: |
13/522940 |
Filed: |
January 19, 2011 |
PCT Filed: |
January 19, 2011 |
PCT NO: |
PCT/FR2011/000029 |
371 Date: |
September 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61296593 |
Jan 20, 2010 |
|
|
|
Current U.S.
Class: |
148/552 ;
148/417; 148/549 |
Current CPC
Class: |
C22F 1/05 20130101; C22C
21/08 20130101; C22C 21/02 20130101 |
Class at
Publication: |
148/552 ;
148/549; 148/417 |
International
Class: |
C22F 1/047 20060101
C22F001/047; C22C 21/02 20060101 C22C021/02; C22F 1/043 20060101
C22F001/043; C22C 21/08 20060101 C22C021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 20, 2010 |
FR |
10/00212 |
Claims
1. A Manufacturing process for a block of aluminum at least 250 mm
thick designed for manufacture of an element for a vacuum chamber,
said process comprising successively: (a) casting an alloy block
with a composition in weight % Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3;
Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other elements
<0.05 each and <0.15 in total, the rest aluminum by
semi-continuous casting; (b) optionally, homogenizing the cast
block at a temperature ranging from 500.degree. C. to 590.degree.
C.; (c) performing solution heat treatment at a temperature ranging
from 450 to 560.degree. C. directly on the cast and optionally
homogenized block; without carrying out before solution heat
treatment a hot or cold working step; (d) quenching the block that
has undergone solution heat treatment between the solution heat
treatment temperature and 200.degree. C. at a cooling speed of at
least 200.degree. C./h; (e) optionally stress-relieving the block
quenched in this way; (f) artificially aging the block quenched and
optionally stress-relieved.
2. The process according to claim 1, wherein the manganese content
is lower than 0.6 wt. % and optionally lower than 0.05 wt. %
3. The process according to claim 1, wherein the chromium content
is lower than 0.05 wt. % and optionally lower than 0.03 wt. %.
4. The process according to claim 1, wherein the Cr, Mn and Zr
contents are simultaneously lower than 0.05 wt. % and optionally
lower than 0.03 wt. %.
5. The process according to claim 1, wherein the iron content is at
least 0.1 wt. %.
6. The process according to claim 1, wherein the silicon content is
from 0.5 to 0.8 wt. % and the magnesium content is from 0.8 to 1.2
wt. %.
7. The process according to claim 1 wherein the silicon content is
from 0.8 to 1.2 wt. % and the magnesium content is from 0.6 to 1.0
wt. %.
8. The process according to claim 7, wherein the silicon content
ranges from 0.8 to 1 wt. % and optionally from 0.85 to 0.95 wt. %,
and said magnesium content ranges from 0.6 to 0.8 wt. % and
optionally from 0.65 0.75 wt. %.
9. The process according to claim 1, wherein said cooling speed
from the temperature of solution heat treatment to 200.degree. C.
lies from 200.degree. C./h to 400.degree. C./h.
10. The process according to claim 1, wherein said cooling speed
from the temperature of solution heat treatment to 200.degree. C.
is at least 800.degree. C./h.
11. The process according to claim 1, wherein stress-relieving is
carried out by cold compression with permanent set ranging from 1%
to 5%.
12. A block comprising in weight %: Si: 0.5-1.5, Mg: 0.5-1.5;
Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other
elements <0.05 each and <0.15 in total, the rest aluminum,
said block being at least 250 mm thick, and, in T6 or T652 temper,
with a ultimate tensile strength Rm at 1/4 thickness of at least
280 MPa and an tensile yield strength Rp0.2 at 1/4 thickness of at
least 240 MPa, obtained by semi-continuous casting, optionally
homogenizing at a temperature ranging from 500.degree. C. to
590.degree. C., solution heat treating at a temperature ranging
from 450.degree. C. to 560.degree. C. directly on a cast and
optionally homogenized block, without carrying out before solution
heat treatment a hot or cold working step, quenching with a cooling
speed from the solution heat treatment temperature to 200.degree.
C. of at least 200.degree. C./h, optionally stress-relieving and
artificial aging.
13. Block obtained by the process according to of claim 1.
14. The block according to claim 12, wherein the composition is, in
weight %, Si: 0.5-1.2; Mg: 0.6-1.0; Fe 0.1-0.3; Cu<0.2;
Mn<0.05; Cr<0.05; Ti<0.15; other elements <0.05 each
and <0.15 in total, and in that in temper T6 or T652 said block
comprises an ultimate tensile strength Rm at 1/4 thickness of at
least 300 MPa and a tensile yield strength Rp0.2 at 1/4 thickness
of at least 270 MPa.
15. The block according to claim 12, capable of being used in
producing a vacuum chamber for manufacture of an integrated
electronic circuit containing a semiconductor, a flat screen and/or
a photovoltaic panel.
16. The process according to claim 2, wherein the chromium content
is lower than 0.05 wt. % and optionally lower than 0.03 wt. %.
17. The block according to claim 13, wherein the composition is, in
weight %, Si: 0.5-1.2; Mg: 0.6-1.0; Fe 0.1-0.3; Cu<0.2;
Mn<0.05; Cr<0.05; Ti<0.15; other elements <0.05 each
and <0.15 in total, and in that in temper T6 or T652 the block
has an ultimate tensile strength Rm at 1/4 thickness of at least
300 MPa and a tensile yield strength Rp0.2 at 1/4 thickness of at
least 270 MPa.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the manufacture of 6xxx alloy
products, in particular designed to be used in the production of
vacuum chambers for the manufacture of integrated electronic
circuits containing semiconductors, flat screens and photovoltaic
panels.
BACKGROUND OF RELATED ART
[0002] In the manufacture of aluminum alloy blocks designed to be
used in the production of vacuum chambers for the manufacture of
integrated electronic circuits containing semiconductors, flat
screens and photovoltaic panels, it is important to obtain a set of
properties, while limiting the cost of operations.
[0003] The blocks must first of all have satisfactory mechanical
characteristics to allow machine production of parts of the
required dimensions and rigidity in order to be able to obtain a
vacuum generally at least of the level of the average vacuum
(10.sup.-3-10.sup.-5 Torr) without bending. The required ultimate
tensile strength (R.sub.m) is therefore generally at least 260 MPa
and even more if possible. In addition, residual stresses in blocks
designed to be bulk machined must be low in order to obtain the
required dimensions without difficulty and without bending due to
machining. As the dimensions of vacuum chambers are continuously
increasing, in particular for the production of liquid crystal
screens or large size photovoltaic panels, it is necessary to
produce increasingly thick aluminum alloy blocks, in particular at
least 250 mm or even 300 mm thick. The thicker the blocks are, the
more it is difficult it is to obtain adequate mechanical properties
while maintaining excellent stability during machining.
[0004] The level of porosity of the blocks must in addition be
sufficiently low to obtain a high vacuum (10.sup.-6-10.sup.-8 Torr)
if required. In addition, the gases used in vacuum chambers are
frequently very reactive and in order to avoid the risks of
pollution of the silicon wafers or liquid crystal devices by
particles or substances coming from the walls of the vacuum
chambers and/or frequent part replacement, it is important to
protect the surfaces of the chambers. Aluminum proves to be an
advantageous material from this point of view because it is in
general possible to produce a hard anodized oxide coating on the
surface of the blocks, resistant to reactive gases. However, the
resistance of the anode layer is affected by many factors in
particular related to the microstructure of the product (grain
size, phase precipitation, porosity) and it is always desirable to
improve this parameter.
[0005] Lastly, as for any industrial process, it is desirable to
obtain the targeted properties via an economic process. Large scale
development of vacuum chambers for many mass-marketed applications
(flat screens, solar panels) has recently led to increased interest
in simplifying the manufacturing processes.
[0006] U.S. Pat. No. 6,565,984 (Applied Materials Inc.) describes
an alloy suitable for the manufacture of chambers for the
manufacture of semiconductors composed as follows (in weight %):
Si: 0.54-0.74, Cu: 0.15-0.30; Fe: 0.05-0.20; Mn.ltoreq.0.14;
Zn.ltoreq.0.15; Cr: 0.16-0.28; Ti.ltoreq.0.06; Mg: 0.9-1.1. The
parts are obtained by extrusion or machining to reach the required
shape. The composition makes it possible to check the size of the
impurity particles which improves the performance of the anode
layer.
[0007] U.S. Pat. No. 6,982,121 (Kyushyu Mitsui Aluminum) describes
an alloy suitable for anodizing and suitable for plasma treatment
chambers, containing (in weight %): Mg: 2.0 to 3.5; Ti: 0.004 to
0.01% and the rest aluminum, 99.9% pure. The alloy does not require
heat treatment, unlike alloys requiring the precipitation of
Mg.sub.2Si. In addition, the alloy does not require the presence of
Cr and Mn which must be added to alloys 5052 and 6061 to control
the grain size, but which are likely to cause heavy metal pollution
of the semiconductors treated. The mechanical characteristics of
the alloy are not, however, indicated. In addition the cost of
99.9% pure aluminum is high.
[0008] US patent application 2009/0050485 (Kobe Steel, Ltd.)
describes an alloy of composed as follows (in weight %): Mg:
0.1-2.0, Si: 0.1-2.0, Mn: 0.1-2.0; Fe, Cr, and Cu.ltoreq.0.03,
anodized so that the hardness of the anode oxide coating varies
throughout the thickness. The very low iron, chromium and copper
content leads to a high excess cost for the metal used.
[0009] Patent applications US 2001/019777 and JP2001 220637 (Kobe
Steel) describe an alloy for chambers comprising (in weight %) Si:
0.1-2.0, Mg: 0.1-3.5, Cu: 0.02-4.0 and impurities, the Cr content
being less than 0.04%.
[0010] Patent application EP 2 003 219 A2 (Kobe Steel) describes a
forging alloy comprising (in weight %) Mg 0.5-1.25%, Si: 0.4-1.4%,
Cu: 0.01-0.7%, Fe: 0.05-0.4%, Mn: 0.001-1.0%, Cr 0.01-0.35%, Ti et
Zr 0.005-0.1%. This document discloses in particular products
obtained by carrying out before solution heat treatment a hot
forging step.
[0011] The document "The effect of processing and Mn content on the
T5 and T6 properties of AA6082 profiles", Journal of Materials
Processing Technology, 173 (2006) 84-91 describes profiles in alloy
AA6082. This document discloses in particular products obtained by
carrying out before solution heat treatment a hot extruding
step.
[0012] The processes used in these documents lead to a high cost
(because of the purity of the aluminum used, and the many steps
involved in the process). There is a need for an improved and
inexpensive process for the manufacture of aluminum alloy blocks
designed to be used in the production of vacuum chambers, with high
mechanical characteristics, low residual stresses and allowing,
after machining, the formation of anode layers resistant to
reactive gases.
SUBJECT OF THE INVENTION
[0013] A first subject of the invention is a manufacturing process
for a block of aluminum at least 250 mm thick designed for the
manufacture of elements for vacuum chambers wherein the following
operations are carried out successively:
(a) an alloy block with a composition in weight % Si: 0.5-1.5, Mg:
0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15,
other elements<0.05 each and <0.15 in total, the rest
aluminum is cast by semi-continuous casting; (b) optionally, the
cast block is homogenized at a temperature ranging between
500.degree. C. and 590.degree. C.; (c) solution heat treatment is
performed at a temperature ranging between 450 and 560.degree. C.
directly on the cast and optionally homogenized block; without
carrying out before solution heat treatment a hot or cold working
step, (d) the block that has undergone solution heat treatment is
quenched at a cooling speed between the solution heat treatment
temperature and 200.degree. C. of at least 200.degree. C./h; (e)
optionally the block quenched in this way can be stress-relieved;
(f) the block quenched and optionally stress-relieved is
artificially aged.
[0014] Another subject of the invention is a block composed as
follows (in weight %): Si: 0.5-1.5, Mg: 0.5-1.5; Fe<0.3;
Cu<0.2; Mn<0.8; Cr<0.10; Ti<0.15, other
elements<0.05 each and <0.15 in total, the rest aluminum, at
least 250 mm thick, and, in T6 or T652 temper, with a ultimate
tensile strength Rn, at 1/4 thickness of at least 280 MPa and an
tensile yield strength R.sub.p0.2 at 1/4 thickness of at least 240
MPa, obtained by semi-continuous casting, optionally homogenizing
at a temperature ranging between 500.degree. C. and 590.degree. C.,
solution heat treating at a temperature ranging between 450.degree.
C. and 560.degree. C. directly on the cast and optionally
homogenized block, without carrying out before solution heat
treatment a hot or cold working step, quenching with a cooling
speed between the solution heat treatment temperature and
200.degree. C. of at least 200.degree. C./h, optionally
stress-relieving and artificial aging.
[0015] Yet another subject of the invention is the use of a block
according to the invention in the production of vacuum chambers for
the manufacture of integrated electronic circuits containing
semiconductors, flat screens and/or photovoltaic panels.
DESCRIPTION OF THE FIGURES
[0016] FIG. 1: Granular structure of the blocks obtained by the
process according to invention 11 (FIG. 1a) and 21 (FIG. 1b).
[0017] FIG. 2: Granular structure of the block reference 31 (FIG.
2a) and of the block obtained by a process according to prior art
(working by forging before solution heat treatment) (FIG. 2b).
DETAILED DESCRIPTION OF THE INVENTION
[0018] The designation of alloys is compliant with the rules of The
Aluminum Association (AA), known to those skilled in the art. The
definitions of the metallurgical tempers are indicated in European
standard EN 515.
[0019] Unless otherwise stated, the static mechanical
characteristics, in other words the ultimate tensile strength Rm,
the conventional tensile yield strength at 0.2% of elongation Rp
0.2 and elongation at rupture A %, are determined by a tensile test
according to standard EN 10002-1, sampling and test direction being
defined by standard EN 485-1. Hardness is measured according to
standard EN ISO 6506.
[0020] The parts for vacuum chambers are in particular vacuum
chamber bodies, valve bodies, flanges, connecting elements, sealing
elements, passages, and flexible pipes. In the process according to
the invention, an alloy of the 6xxx family is transformed into a
block that can be used for the production of parts for vacuum
chambers without hot or cold working before solution heat
treatment. So according to the invention, a block at least 250 mm
thick made of an alloy, composed as follows (in weight %): Si:
0.5-1.5, Mg: 0.5-1.5; Fe<0.3; Cu<0.2; Mn<0.8; Cr<0.10;
Ti<0.15, other elements<0.05 each and <0.15 in total, the
rest aluminum, is obtained by semi-continuous casting, optionally
homogenizing the cast block at a temperature ranging between
500.degree. C. and 590.degree. C.; solution heat treating at a
temperature ranging between 450 and 560.degree. C. directly on the
cast and optionally homogenized, without carrying out before
solution heat treatment a hot or cold working step, block;
quenching with a cooling speed between the temperature of solution
heat treatment and 200.degree. C. of at least 200.degree. C./h;
optionally stress-relieving and aging. Solution heat treatment
directly on the cast block, without carrying out before solution
heat treatment a hot or cold working step, is, within the scope of
this invention, taken to mean that there is no hot or cold working
step before the solution heat treatment. However, conventional
steps such as surface machining or sawing an end may be performed,
in particular before or after homogenization. The iron content must
be lower than 0.3 wt. % because above this figure the anode layer
obtained to protect the metal from reactive gases does not reach
the required resistance. The present inventors did, however, note
that it is not necessary to reach a very high level of purity to
obtain anode layers displaying the required characteristics using
the process according to the invention. The iron content is
therefore advantageously at least 0.1 wt. %, which makes the
process according to the invention particularly economical.
[0021] The copper content must be lower than 0.2 wt. % because too
high a copper content increases quench sensitivity. It is however
advantageous in certain cases to add a limited amount of copper to
improve the mechanical characteristics, in particular when the
cooling speed after solution heat treatment is greater than
800.degree. C./h. A copper content ranging between 0.03 and 0.15
wt. % is preferred in one embodiment of the invention.
[0022] The present inventors noted that if the chromium content is
not lower than 0.10 wt. %, the required mechanical properties, in
particular the minimal mechanical resistance, are not obtained. It
is commonly accepted that to produce a wrought product for a vacuum
chamber made of 6xxx family alloy the presence of chromium and/or
manganese is necessary in order to control the grain size. The
present inventors noted that, within the scope of this invention,
the absence of chromium is, on the contrary, favorable because
without damaging the granular structure it makes it possible to
limit quench sensitivity and to improve the mechanical
characteristics of thick products. In an advantageous embodiment of
the invention, the chromium content is lower than 0.05 wt. % and
preferably lower than 0.03 wt. %. The manganese content must be
lower than 0.8 wt. %, a content higher than 0.8 wt. % being
detrimental, in particular with regard to the properties of the
anode layer and contamination of the vacuum chamber. Advantageously
the manganese content is lower than 0.6 wt. % to avoid the
formation of coarse phases that may be detrimental to the
properties of the anode layer. In an advantageous embodiment of the
invention, the manganese content is even lower than 0.05 wt. %. The
present inventors noted that, surprisingly, even in the absence of
Cr, Mn and Zr, the granular structure obtained by the process
according to the invention is controlled and makes it possible to
obtain satisfactory characteristics in terms of mechanical
properties and resistance to reactive gases. The simultaneous
absence of Cr, Mn and Zr therefore makes it possible to very
significantly decrease the alloy's quench sensitivity and therefore
to improve the mechanical properties of thick products, without
detriment to the granular characteristics and the properties of the
anode layers. In an advantageous embodiment of the invention, the
Cr, Mn and Zr contents are simultaneously lower than 0.05 wt. % and
preferably lower than 0.03 wt. %.
[0023] The silicon and magnesium contents are between 0.5 and 1.5
wt. %. Advantageously, either the combination of 0.5 to 0.8 wt. %
of silicon with 0.8 to 1.2 wt. % of magnesium, or the combination
of 0.8 to 1.2 wt. % of silicon with 0.6 to 1.0 wt. % of magnesium
is used. In a preferred embodiment of the invention making it
possible to obtain particularly high mechanical characteristics,
the silicon content ranges between 0.8 and 1 wt. %, and preferably
between 0.85 and 0.95 wt. %, and the magnesium content ranges
between 0.6 and 0.8 wt. % and preferably between 0.65 and 0.75 wt.
%.
[0024] The alloy is cast using the direct chill casting process in
the form of a block. Typically, a block format of between 300 and
450 mm thick is used.
[0025] The cast block may, optionally, be homogenized at a
temperature ranging between 500.degree. C. and 590.degree. C. for
at least one hour. Performing homogenization is advantageous
because it generally makes it possible to obtain more advantageous
mechanical properties and better properties of the anode layer, and
in addition to reduce the length of solution heat treatment. The
homogenization can be carried out during a separate heat treatment
operation or alternatively during the solution heat treatment.
[0026] Between casting and solution heat treating, before or after
homogenization when performed, surface machining is generally
performed, of approximately at least 5 mm per face, in order to
eliminate the segregated surface layer and prevent cracking.
[0027] Solution heat treatment is then performed directly on the
cast and optionally, homogenized block at a temperature ranging
between 450 and 560.degree. C., and preferably between 520 and
550.degree. C. directly, without any hot or cold working step
beforehand. Hot working, conventionally one of the processes of
prior art, is in general carried out by rolling and/or forging
and/or extruding. Thus the block does not undergo between casting
and solution heat treating any significant working step. By working
it is understood typically operations of rolling and/or forging
and/or extruding. Thus, according to the invention, none of the
dimensions of the cast block (length, width, thickness) undergoes a
significant change, that is typically of at least 10% by working
between cast and solution heat treatment. The duration of solution
heat treatment is preferably greater than one hour. The process
according to the invention, which makes it possible to avoid hot or
cold working before solution heat treatment, is particularly
advantageous from an economic point of view because this step is an
expensive one. According to prior art, this type of process had not
been considered, especially for blocks designed for the production
of elements for vacuum chambers made of 6xxx alloy, probably
because it was feared that, without hot working, the mechanical
characteristics, the resistance of the anode layers and the level
of porosity, necessary to manufacture elements for vacuum chamber,
would not be obtained. In addition, certain particularly thick
products were not accessible using the processes according to prior
art. Surprisingly, the present inventors noted that the process
simplified in this way not only makes it possible to obtain
properties equivalent to those obtained by the process according to
prior art, but in certain cases to improve upon them.
[0028] After solution heat treatment, the quenching step is
critical, and must be performed with a cooling speed between the
temperature of solution heat treatment and 200.degree. C. of at
least 200.degree. C./h. The cooling speed is calculated midway
through the thickness of the blocks. If the cooling speed is too
low, the present inventors noted that the required mechanical
properties are not obtained.
[0029] In a first advantageous embodiment of the invention, the
cooling speed ranges between 200.degree. C./h and 400.degree. C./h.
Surprisingly, when the cooling speed lies between 200.degree. C./h
and 400.degree. C./h, satisfactory mechanical characteristics and
low residual heat are simultaneously obtained making it possible to
avoid the step of stress-relieving by compression. Such a cooling
speed can be obtained by mist spraying.
[0030] In a second advantageous embodiment of the invention, the
cooling speed is at least equal to 800.degree. C./h. Such a cooling
speed can be obtained by sprinkling or immersing in water. Since
too high a cooling speed may generate too great internal stresses
in the blocks, water at a temperature of at least 50.degree. C. is
preferably used for cooling.
[0031] Optionally, the block quenched in this way is
stress-relieved, preferably by cold compression with permanent set
ranging between 1% and 5%. In the second embodiment for which the
cooling speed is greater than 800.degree. C./h, stress-relieving
proves to be particularly advantageous. Stress-relieving makes it
possible to decrease the residual stresses in the metal and to
avoid bending during machining.
[0032] Finally, the block quenched and optionally stress-relieved
is artificially aged. The aging temperature preferably lies between
150 and 190.degree. C. and preferably between 165 and 185.degree.
C., the duration of aging ranging between 5 and 40 hours and
preferably between 8 and 20 hours. Advantageously, aging is
performed to reach T6 or T652 temper, corresponding to the peak of
the static mechanical properties (Rn, and R.sub.p0.2).
[0033] The blocks obtained by the process according to the
invention are characterized by high mechanical properties. Ultimate
tensile strength R.sub.m at 1/4 of the thickness of the products
obtained by the process according to the invention is at least 280
MPa and the tensile yield strength R.sub.p0.2 at 1/4 of the
thickness is at least 240 MPa in temper T6 or T652. In an
advantageous embodiment, an alloy is used composed as follows: Si:
0.5-1.2, Mg: 0.6-1.0; Fe 0.1-0.3; Cu<0.2; Mn<0.05;
Cr<0.05; Ti<0.15; other elements <0.05 each <0.15 in
total, and in temper T6 or T652 a ultimate tensile strength R.sub.m
at 1/4 of the thickness of at least 300 MPa and an tensile yield
strength R.sub.p0.2 at 1/4 of the thickness of at least 270 MPa are
obtained; and in addition if the silicon content lies between 0.8
and 1 wt. % and preferably between 0.85 and 0.95 wt. % and the
magnesium content lies between 0.6 and 0.8 wt. % and preferably
between 0.65 and 0.75 wt. %, a ultimate tensile strength R.sub.m at
1/4 of the thickness of at least 320 MPa an tensile yield strength
R.sub.p0.2 at 1/4 of the thickness of at least 300 MPa, in temper
T6 or T652.
[0034] A minimal elongation value of at least 0.5% is obtained by
the products according to the invention in temper T6 or T652. In
certain cases a minimal elongation value of at least 4% is obtained
by the products according to the invention.
[0035] The granular structure of the products according to the
invention is characteristic of the absence of working before
solution heat treatment. It is therefore possible to distinguish
the products according to the invention from the products according
to prior art for which hot or cold working is performed before
solution heat treatment, by a simple metallographic test.
Typically, the granular structure of the products according to the
invention is isotropic, with an average grain size of at least 200
.mu.m.
[0036] The blocks obtained by the process according to the
invention are suitable for being used in the production of vacuum
chambers for the manufacture of integrated electronic circuits
containing semiconductors, flat screens and/or photovoltaic panels.
The blocks' behavior with regard to machining is favorable,
particularly on account of the high mechanical characteristics and
the low level of residual stresses. In addition, the anode layers
obtained on the blocks machined by means of the usual anodizing
processes are resistant to the reactive gases used in vacuum
chambers.
[0037] The blocks obtained by the process according to the
invention can also be advantageously used for any other application
in which the properties obtained are favorable.
Example
[0038] In this example the process according to the invention is
compared with a process according to reference examples. The
process according to the invention was applied to two different
alloys.
[0039] The direct chill casting process was used to cast four
blocks made of an alloy composed as shown in table 1. The blocks
were surface-machined down to a thickness of 410 mm
TABLE-US-00001 TABLE 1 Composition of alloys tested (wt. %). Alloy
Block Si Fe Cu Mn Mg Cr Ti 1 11 0.9 0.13 <0.01 <0.01 0.7
<0.01 0.02 and 12 2 21 1.0 0.23 0.05 0.5 0.8 0.03 0.01 3 31 0.7
0.39 0.24 0.1 1.0 0.19 0.02
[0040] The blocks were homogenized at a temperature of between 540
and 590.degree. C. for at least 4 hours.
[0041] The blocks then underwent solution heat treatment at
540.degree. C. After solution heat treatment, blocks 11, 21 and 31
were quenched with water at 60.degree. C. (the average cooling
speed calculated between 540.degree. C. and 200.degree. C. was
approximately 1500.degree. C./h), while block 12 was quenched with
air (the average cooling speed between 540.degree. C. and
200.degree. C. was approximately 90.degree. C./h).
[0042] The various blocks then underwent cold compression from 1.5
to 2.5% and subsequently underwent aging at 165.degree. C. in order
to obtain temper T652.
[0043] The granular structure of the products obtained is shown in
FIGS. 1a (block 11), 1b (block 21) and 2a (block 31). For purposes
of comparison, the granular structure of a product using a process
according to prior art (forging before solution heat treatment) is
shown in FIG. 2b. The mechanical characteristics obtained are given
in table 2
TABLE-US-00002 TABLE 2 mechanical characteristics obtained (T652
temper) after sampling at 1/4 thickness in direction TL. Rm Rp0.2
Hardness (MPa) (MPa) A (%) HB 11 (Inv) 334 315 1 109 21 (Inv) 287
245 5.9 88 31 (Ref) 276 229 6.2 87 12 (Ref) 159 92 16.2
[0044] The blocks obtained by the process according to the
invention (11 and 21), have a higher mechanical resistance (Rm,
Rp0.2) than that obtained with the reference ingots, the mechanical
resistance obtained with ingot 11 being particularly
advantageous.
[0045] The blocks obtained according to the invention had low
residual stresses, which makes it possible to avoid block bending
during machining. The level of porosity observed in the blocks
according to the invention was very low, sufficiently low to obtain
a high vacuum.
* * * * *