U.S. patent application number 10/432625 was filed with the patent office on 2004-03-11 for safety component moulded in a1-si alloy.
Invention is credited to Cosse, Francois, Garat, Michel.
Application Number | 20040045638 10/432625 |
Document ID | / |
Family ID | 8857635 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040045638 |
Kind Code |
A1 |
Garat, Michel ; et
al. |
March 11, 2004 |
Safety component moulded in a1-si alloy
Abstract
The invention concerns a safety component with high mechanical
strength and good ductility, moulded in Al--Si alloy consisting (in
wt. %) of: Si: 2-11; Mg: 0.3-0.7; Cu: 0.3 0.9; other elements <1
each and <2 in total, the rest being aluminium, and solution
heat treated, tempered and hardened resulting in Brinell hardness
of more than 125. The invention also concerns a safety component
with high mechanical resistance and good ductility, moulded in
Al--Si alloy consisting (in wt. %) of: Si: 2-6; Mg: 0.3-0.7; Fe
<0.20; other elements <0.3 each and <1 in total; the rest
being aluminium; solution heat treated, hardened and tempered
resulting in a quality index Q=Rm+log A>485 MPa.
Inventors: |
Garat, Michel; (Moirans,
FR) ; Cosse, Francois; (Grenoble, FR) |
Correspondence
Address: |
DENNISON, SCHULTZ & DOUGHERTY
1745 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
8857635 |
Appl. No.: |
10/432625 |
Filed: |
July 22, 2003 |
PCT Filed: |
December 12, 2001 |
PCT NO: |
PCT/FR01/03966 |
Current U.S.
Class: |
148/417 ;
420/534 |
Current CPC
Class: |
C22C 21/02 20130101;
C22C 21/04 20130101; C22F 1/043 20130101 |
Class at
Publication: |
148/417 ;
420/534 |
International
Class: |
C22C 021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2000 |
FR |
00/16282 |
Claims
1. Safety part with high mechanical strength and good ductility,
cast from an Al--Si alloy with the following composition (% by
weight): Si 2-11; Mg 0.3-0.7; Cu 0.3-0.9; other elements <1 each
and <2 total, remainder aluminium, and solution heat treated,
quenched and aged to give a hardness of more than 125 Brinell.
2. Safety part according to claim 1, characterised in that the Mg
content is between 0.5 and 0.7%.
3. Safety part according to claim 1 or 2, characterised in that the
Cu content is between 0.3 and 0.6%.
4. Safety part according to one of claims 1 to 3, characterised in
that the Ti content is between 0.05 and 0.3%.
5. Safety part according to one of claims 1 to 4, characterised in
that the iron content is less than 0.15%, and preferably less than
0.12%.
6. Safety part according to one of claims 1 to 5, characterised in
that it contains at least one element modifying or refining the
eutectic such as sodium (with a content of between 0.001 and
0.020%), strontium (between 0.004 and 0.050%) and antimony (between
0.03 and 0.30%).
7. Safety part according to one of claims 1 to 6, characterised in
that the Si content is between 2 and 7%.
8. Safety part according to claim 7, characterised in that it is
cast using one of the following casting processes: casting in the
semi-solid state (thixocasting), squeeze casting, casting followed
by forging or stamping, casting with lost foam models under
isostatic pressure, vacuum die casting, and casting followed by hot
isostatic compaction (HIP).
9. Safety part according to one of claims 1 to 6, characterised in
that the Si content is between 7 and 11%.
10. Safety part according to claim 9, characterised in that it is
moulded using a casting process with a high solidification rate,
such that the spacing between dendrite arms is less than 20
.mu.m.
11. Safety part according to one of claims 1 to 10, characterised
in that ageing is done within the 170-190.degree. C. temperature
range for a duration of between 4 h and 20 h.
12. Safety part with high mechanical strength and good ductility,
cast from an Al--Si alloy with the following composition (% by
weight): Si 2-6; Mg 0.3-0.7; Fe <0.20; other elements <0.3
each and <1 total, remainder aluminium, and solution heat
treated, quenched and aged to give a quality index Q=R.sub.m+150
log A>485 MPa.
13. Safety part according to claim 12, characterised in that the Mg
content is between 0.45 and 0.65%.
14. Safety part according to claim 12 or 13, characterised in that
the Ti content is between 0.05 and 0.3%.
15. Safety part according to one of claims 12 to 14, characterised
in that the iron content is less than 0.15%, and preferably less
than 0.12%.
16. Safety part according to one of claims 12 to 15, characterised
in that it contains at least one element modifying or refining the
eutectic such as sodium (between 0.001 and 0.020%), strontium
(between 0.004 and 0.050%) and antimony (between 0.03 and 0.30%).
Description
FIELD OF THE INVENTION
[0001] The invention relates to the manufacture of cast safety
parts intended particularly for automobiles, for example such as
suspension parts made of hypoeutectic Al--Si alloys, these parts
having high mechanical strength, sufficient ductility, good
corrosion resistance and good metallurgical soundness, after heat
treatment.
STATE OF THE ART
[0002] The use of aluminium alloys for cast parts is developing
quickly in automobiles, particularly for safety parts such as
connections to the ground, in order to reduce the weight of the
vehicle. This weight reduction is particularly significant because
a high mechanical strength can also be obtained after heat
treatment. Furthermore, for this type of part, it is essential to
have sufficient ductility to prevent a brittle failure after a
shock, good corrosion resistance, particularly stress corrosion, to
prevent deterioration of the part in a corrosive environment such
as road salt, and lack of shrinkage, particularly on the surface,
which could generate cracks causing failure of the part.
[0003] Processes typically used for the production of such parts
include casting in metallic moulds by gravity or at low pressure,
"squeeze casting", casting in metallic moulds followed by forging,
or stamping as described in U.S. Pat. No. 5,582,659 (Nippon Light
Metal and Nissan Motor) or in certificate of utility FR 2614814
(Thomas DI SERIO), or forming in the semi-solid state by pressure
injection or forging (thixocasting or rheocasting depending on
whether the initial metal is in the solid state or the liquid
state).
[0004] Casting with lost foam models under isostatic pressure, high
quality die casting, possibly under a vacuum, and sand casting or
casting in metallic moulds followed by hot isostatic compaction are
also applicable.
[0005] The most frequently used alloys for this type of part are
Al--Si-Mg alloys, particularly of the AlSi7Mg, AlSi9Mg or AlSi10Mg
type. In the F, T5 and particularly T6 tempers, these alloys
produce a good compromise between mechanical strength and
elongation, and excellent resistance to corrosion. However, the
mechanical strength is limited by the hardening capacity of the
Mg.sub.2Si phase.
[0006] Several patents illustrate the use of this type of alloy.
U.S. Pat. No. 4,104,089 filed by Nippon Light Metal in 1976 applies
to non-porous die cast parts for automobiles with high mechanical
strength and shock resistance, and with the following composition
(% by weight):
[0007] Si 7-12; Mg 0.2-0.5; Mn 0.55-1; Fe 0.65-1.2
[0008] Parts are solution heat treated at between 450.degree. C.
and 530.degree. C., quenched and then aged for more than 1 hour at
between 150 and 230.degree. C.
[0009] U.S. Pat. No. 5,582,659, filed by Nippon Light Metal and
Nissan Motor in 1993, discloses a process for manufacturing cast
parts including casting of a blank containing the following (% by
weight):
[0010] Si 2.0-3.3; Mg 0.2-0.6; Fe <0.15 and possibly Cu
0.2-0.5
[0011] Zr 0.01-0.2; Mn 0.02-0.5; Cr 0.01-0.3.
[0012] Homogenisation of this blank between 500 and 550.degree. C.,
forging of the blank and solution heat treatment for 0.5 to 2 h
between 540 and 550.degree. C., quenching in water and T6 ageing
for between 2 and 20 h between 140 and 180.degree. C.
[0013] Patent EP 0687742 filed by Aluminum Rheinfelden in 1994
describes a die casting alloy for use in making cast safety parts
with the following composition (% by weight):
[0014] Si 9.5-11.5; Mg 0.1-0.5; Mn 0.5-0.8; Fe <0.15;
Cu<0.03.
[0015] If a strength greater than that obtained by the
precipitation of Mg.sub.2Si is required while maintaining the
appropriate casting properties, AlSiMgCu type alloys that can be
hardened by the Al.sub.2Cu, Al.sub.2CuMg and w (AlCuMgSi) series of
phases have to be used. There are many known and standardised
alloys with a copper content equal to or exceeding 1%, and
particularly AlSi5 alloys such as:
[0016] EN AC 45300 (type AlSi5Cu1Mg, similar to AA C355) containing
between 1.0 and 1.5% Cu EN AC 45100 (type AlSi5Cu3Mg, similar to AA
319) containing between 2.6 and 3.6% Cu or AlSi8 or AlSi9 alloys
such as:
[0017] EN AC 46000 (type AlSi9Cu3), 46200 (type AlSi8Cu3) or 46500
(type AlSi9Cu3FeZn). The alloy EN AC 46400 has a Cu content of
between 0.8 and 1.3%. In general, it is accepted that Cu contents
equal to or greater than 1% are necessary to increase the hardness
and the yield strength at ambient temperature compared with AlSiMg
alloys. But, due to the hardening caused by these Cu contents, the
elongation becomes low and resistance to corrosion mediocre, and
usually insufficient for automobile safety parts.
[0018] The article by F. J. Feikus "Optimization of Al--Si cast
alloys for cylinder head applications" AFS Transactions 98-61, pp.
225-231, studies the addition of 0.5% and 1% of copper to an
AlSi7Mg0.3 alloy to make cylinder heads for internal combustion
engines. No improvement in the yield strength and no increase in
the hardness at ambient temperature was observed after conventional
T6 treatment involving 5 h solution heat treating at 525.degree. C.
followed by quenching in cold water and ageing for 4 h at
165.degree. C. The added copper only makes a significant
improvement to the yield strength and creep resistance at usage
temperatures of more than 150.degree. C.
[0019] The former French standard NF A57-702, February 1960,
mentioned the A-S4G alloy with a very wide tolerance in iron
(<0.65%), a wide range for the magnesium content (0.40-0.95%)
and fairly low mechanical properties in the Y33 state:
R.sub.m>25 kgf/mm.sup.2 (245 MPa) R.sub.p0.2>18 kgf/mm.sup.2
(176 MPa) A>1.5%.
[0020] These properties were lower than the properties of the
A-S7G0.6 alloy, standardised in the February 1981 edition of the
same standard, that were as follows respectively:
[0021] R.sub.m>290-320 MPa; R.sub.p0.2>210-240 MPa;
A>4-6%
[0022] The purpose of this invention is to provide safety parts
that can be cast using all casting processes and have a high
mechanical strength, good resistance to stress corrosion and good
ductility.
[0023] Purpose of the Invention
[0024] The purpose of the invention is a safety part with high
mechanical strength and good ductility, cast from an Al--Si alloy
with the following composition (% by weight):
[0025] Si 2-11; Mg 0.3-0.7; Cu 0.3-0.9; other elements <1 each
and <2 total, remainder aluminium,
[0026] and solution heat treated, quenched and aged to give a
hardness of more than 125 Brinell.
[0027] The alloy preferably contains 0.5 to 0.7% Mg and 0.3 to 0.9%
Cu.
[0028] If the casting process can tolerate alloys with a greater
tendency to shrinkage, for example die casting, "squeeze casting",
casting followed by hot isostatic compaction, casting in the
semi-solid state (thixocasting or rheocasting), casting followed by
forging or die stamping, and casting with lost foam models under
isostatic pressure, the alloy composition includes 2 to 7% of
Si.
[0029] Another purpose of the invention is a safety part with high
mechanical strength and good ductility, cast from an Al--Si alloy
with the following composition (% by weight):
[0030] Si 2-6; Mg 0.3-0.7; Fe <0.20; other elements <0.3 each
and <1 total, remainder aluminium,
[0031] and solution heat treated, quenched and aged to give a
quality index Q=R.sub.m+150 log A>485 MPa.
DESCRIPTION OF THE FIGURES
[0032] The single figure shows the variation of the HB hardness for
AlSi alloys with 7% of silicon containing 0.45% and 0.9% of copper
respectively, as a function of the ageing time in hours, for 3
ageing temperatures equal to 170.degree. C., 180.degree. C. and
190.degree. C.
DESCRIPTION OF THE INVENTION
[0033] The invention is based on the observation that the addition
of copper with a content of between 0.3 and 0.9% to an AlSiMg
alloy, is not only acceptable in terms of resistance to stress
corrosion, but also improves the yield strength and the ultimate
tensile strength under particular ageing conditions, without
deteriorating elongation compared with an alloy with the same
composition without copper.
[0034] If a conventional AlSi7Mg0.6 type alloy is compared with the
same alloy with 0.45% of copper in the same T6 temper obtained by
ageing for 6 h at 160.degree. C., it is observed for the copper
alloy that there is no variation in the yield strength, there is a
slight increase in the elongation, a slight reduction in the HB
hardness which changes from 119 to 114, and particularly there is a
severe degradation in the resistance to stress corrosion measured
according to the ASTM G49 standard. However, if ageing is done for
example for 16 h at 170.degree. C. instead of conventional ageing
for 6 h at 160.degree. C., such that the hardness of the treated
part is of the order of 130 HB, it is observed that the yield
strength for the copper alloy increases (from 309 to 320 MPa), and
that surprisingly this occurs without any degradation to the
elongation, and particularly to the resistance to stress
corrosion.
[0035] The invention is applicable to all AlSiMgCu alloys
containing (by weight) from 2 to 11% of silicon, 0.3 to 0.7% of
magnesium and 0.3 to 0.9% of copper, the other additive elements or
impurities not exceeding 1% each and 2% total. Preferably, the
magnesium content is between 0.5 and 0.7%, and the copper content
is between 0.3 and 0.6%. Advantageously, the alloy may contain 0.05
to 0.3% of titanium for refining purposes, and one or several
elements to modify or refine the eutectic, such as sodium (between
0.001 and 0.020%), strontium (between 0.004 and 0.050%) or antimony
(between 0.03% and 0.3%).
[0036] The iron content is preferably kept below 0.15%, or even
better below 0.12%, so as to prevent the formation of iron phases
that are detrimental to elongation.
[0037] If a casting process is used that has better tolerance to
alloys with a greater tendency to shrinkage, the compromise between
the required properties can be improved even further. These casting
processes that have been developed recently are particularly
casting in the semi-solid state (thixocasting or rheocasting),
squeeze casting, casting followed by forging or stamping, casting
with lost foam models under isostatic pressure, vacuum die casting,
and casting followed by hot isostatic compaction (HIP). In these
cases, the silicon content can be reduced to significantly below 7%
without affecting the soundness of the produced parts, which gives
a significant increase in ductility. The drop in the silicon
content can be as much as 2% and its magnitude depends on casting
parameters; it is only limited by the castability, the behaviour in
terms of shrinkage and the crackability.
[0038] When alloys according to the invention are used with a
silicon content of between 7 and 11%, and when ageing is done
according to the invention, for example for making thin parts
requiring good castability, the loss of ductility induced by the
high silicon content can be avoided by using a casting process such
as squeeze casting, die casting, vacuum casting, thixocasting or
rheocasting with a high solidification rate, such that the spacing
between dendrite arms is less than 20 .mu.m.
[0039] The degree of structural hardening leading to an HB hardness
of more than 125 obtained by ageing within the 170-190.degree. C.
temperature range for a duration of between 4 h and 20 h, the
duration decreasing when the temperature increases, as shown in the
figure which shows hardnesses obtained at temperatures of 170, 180
and 190.degree. C. respectively as a function of time for an alloy
with 7% of silicon containing 0.45 or 0.9% of copper.
[0040] The invention also relates to use of a low silicon content
alloy containing between 2 and 6% of silicon, 0.3 to 0.7% of
magnesium and less than 0.20% of iron, for the same type of safety
parts, together with other additive elements and impurities not
exceeding 0.3% each and 1% in total. The magnesium content is
preferably between 0.45 and 0.65%. The iron content is preferably
kept below 0.15%, or even better below 0.12%. The alloy may contain
0.05 to 0.30% of titanium for refining purposes, and one or several
eutectic modifying or refining elements such as sodium with a
content of between 0.01 and 0.20%, strontium between 0.004 and
0.050%, or antimony between 0.03 and 0.3%.
[0041] Parts cast from such an alloy have an ultimate tensile
strength when treated in the T6 temper at least equivalent to the
ultimate tensile strength of an alloy with 7% silicon, and better
elongation, giving them a significantly better quality index Q of
the order of 515 MPa instead of 480 to 485 MPa. This quality index
Q=R.sub.m+150 log A was defined in the article by M. Drouzy, S.
Jacob and M. Richard at the Centre Technique des Industries de la
Fonderie (Foundry Industries Technical Centre) entitled <<Le
diagramme charge de rupture allongement des alliages d'aluminium.
L'indice de qualit. Application aux A-S7G>> ("The ultimate
load--elongation diagram for aluminium alloys. The Quality Index.
Application to A-S7G"), Fonderie, No. 355, April 1976, pp. 139-147.
This index is a good indicator of the global mechanical performance
of this type of alloy.
EXAMPLES
Example 1
[0042] The three alloys A, B and C with the composition (by weight
%) shown in Table 1 below, which differ essentially in their copper
content, were cast in the form of 18 mm diameter test shell pieces
according to standard NF A 57-702.
1 TABLE 1 Alloy Si Fe Cu Mg Ti A 6.95 0.12 0.01 0.60 0.12 B 6.85
0.13 0.47 0.58 0.13 C 6.87 0.13 0.94 0.59 0.13
[0043] After casting, the test pieces are hot isostatically
compacted in order to eliminate all microporosity, this compaction
being representative of the different moulding processes including
a high pressure compaction phase during solidification such as die
casting, squeeze casting, thixocasting, rheocasting or casting with
lost foam models under isostatic pressure, or after solidification,
such as casting--die stamping.
[0044] The test pieces are then solution heat treted with
preliminary levels in order to redissolve eutectics containing
copper, and a main level for homogenisation and globulisation of
eutectic silicon lasting for 16 h at 530.degree. C. They are then
quenched in water and the ageing treatments indicated in Table 2
are carried out on them. Ageing for 6 h at 160.degree. C. is
conform with prior art, and 10 h and 16 h ageings at 170.degree. C.
are conform with the invention.
[0045] Table 2 indicates the static mechanical characteristics of
the test pieces treated:
[0046] ultimate tensile strength R.sub.m (in MPa)
[0047] conventional yield strength at 0.2% elongation R.sub.p0.2
(in MPa)
[0048] elongation at failure A (in %)
[0049] Brinell hardness (HB)
[0050] The quality index Q=R.sub.m+150 log A is also given.
2TABLE 2 Alloy Ageing R.sub.m R.sub.p0.2 A HB Q A 6 h-160.degree.
319 243 12.8 119 485 A 10 h-170.degree. 343 304 8.3 124 480 A 16
h-170.degree. 341 309 7.8 125 474 B 6 h-160.degree. 345 246 14.2
114 518 B 16 h-170.degree. 374 320 8.3 128 512 C 6 h-160.degree.
361 244 15.7 115 540 C 16 h-170.degree. 388 320 9.1 131 532
[0051] It is found that the ultimate tensile strength R.sub.m and
the yield strength R.sub.p0.2 for copper alloys B and C are higher
than for alloy A with ageing according to the invention, whereas
R.sub.p0.2 remains almost unchanged from ageing according to prior
art. With ageing according to the invention, elongation is not
reduced, which is contrary to what might have been expected, and
even increases slightly as the copper content increases, which
substantially increases the quality index Q due to the increase in
R.sub.m.
[0052] Test pieces made of the same alloys B and C were used to
machine 2 mm thick flat test pieces on which the stress corrosion
test was carried out by immersion--emersion in artificial sea water
according to standard ASTM G49, with stresses equal to 75% of the
yield strength mentioned in Table 2. The results are summarized in
Table 3:
3 TABLE 3 Cu content Ageing Test piece failure 0.45% 6
h-160.degree. C. 100% fail between 5 and 11 days 0.45% 16
h-170.degree. C. 100% resist more than 60 days 0.90% 6
h-160.degree. C. 100% fail between 5 and 7 days 0.90% 16
h-170.degree. C. 75% resist more than 60 days, 25% fail between 15
and 60 days
[0053] It is found that ageing according to the invention very
significantly improves the resistance to stress corrosion compared
with T6 ageing.
Example 2
[0054] Test pieces with three alloys D, E and F at 4% silicon were
prepared under the same conditions as in example 1. The composition
of each test piece (% by weight) is given in Table 4:
4 TABLE 4 Alloy Si Fe Cu Mg Ti D 4.0 0.11 0.03 0.63 0.13 E 3.9 0.08
0.44 0.63 0.13 F 4.1 0.09 0.85 0.64 0.13
[0055] After the different ageings, the same parameters were
measured as for example 1, and the values are given in Table 5:
5TABLE 5 Alloy Ageing R.sub.m R.sub.p0.2 A HB Q D 6 h/160.degree.
C. 342 266 15.0 119 518 D 10 h/170.degree. C. 358 309 11.2 124 515
E 16 h/170.degree. C. 378 322 11.6 132 538 F 16 h/170.degree. C.
388 319 9.3 132 533
[0056] Firstly, it was observed that the alloy D without any copper
and with 4% silicon has better ultimate tensile strength and better
elongation, and therefore a substantially improved quality index,
than alloy A in example 1 with 7% of silicon.
[0057] It is also observed that with copper alloys and ageing
according to the invention, the ultimate tensile strength, the
yield strength and the quality index are all improved compared with
the copper free alloy, due to the fact that elongation does not
reduce, and even increases slightly, which is contrary to what
would have been expected.
Example 3
[0058] Alloys E and F in example 2 were replaced by alloys E' and
F' with the same composition except for iron, and the iron content
of these two alloys was modified to 0.18 and 0.16% respectively.
With the same heat treatment comprising 16 h ageing at 170.degree.
C., the elongations A obtained were equal to 7.5% and 6.8%
respectively, representing reductions of 35% and 27%
respectively.
* * * * *