JP2004536223A - Pressure cast parts made of high ductility aluminum alloy - Google Patents

Abstract

The present invention is directed to a security part or a structural part for an automobile made of a ductile aluminum alloy and to be pressure-cast, and its composition (% by weight) is: Si <2-6 Mg <0.40 Cu <0. 30 Zn <0.30 Fe <0.50 Ti <0.30, Mn (0.3-2%), Cr (0.1-0.3), Co (0.1-0.3), At least one element, such as V (0.1-0.3) and Mo (0.1-0.4), for reducing welding defects of the mold, and also Sr (50-500 ppm), Na At least one eutectic modifying element, such as (20-100 ppm) and Ca (30-120 ppm), other elements each less than 0.05 and less than 0.10 in total, the balance being aluminum; The part is tempered at a temperature lower than 220 ° C. After exhibits an elastic limit R _p0.2> 110 MPa and elongation A> 10%.

Description

【００３２】
熱処理のされていないこれらの板において、引っ張り力の試験片を加工して、破断強度Ｒ_m（単位ＭＰａ）、０．２％に定められた伸びの弾性限界Ｒｐ０．２（単位ＭＰａ）、および破断伸びＡ（単位％）を測定した。結果（１０の試験片の平均）は、表２と図１ａ，１ｂ，および１ｃに再現されている。
【００３３】
【表２】

【００３４】
シリコンが３％と７％の間でマグネシウムが０．１％と０．２％の間の合金について、破断強度および弾性限界が、シリコン含有量とともにしだいに増してゆき、伸びが減少していることが確認される。弾性限界がまた、マグネシウム含有量とともに次第に増してゆく一方で、マグネシウムの伸びに対する効果は明白ではない。
【００３５】
（実施例２、冷却速度の効果）
シリコンが７％で、マグネシウムがそれぞれ０％，０．１３％，および０．２０％の合金において、規格ＮＦ Ａ ５７−１０２に従って直径１３．８ｍｍに加工された試験片を、重力により鋳型の中で鋳造し、合金Ｇ，Ｈ，およびＩについて、機械的特性を実施例１の機械的特性と比較した。結果は、表３および図２に再現されている。
【００３６】
【表３】

【００３７】
はるかに低い冷却速度で鋳型の中で鋳造された部品について、破断強度および弾性限界は、とりわけマグネシウム含有量が少ない場合には、はるかに低く、また伸びがより大きいことが確認される。【Technical field】
[0001]
The present invention relates to the field of manufacturing aluminum / silicon alloy parts having a relatively small thickness formed by pressure casting, particularly to the field of manufacturing structural parts or security parts for automobiles. It is.
[Background Art]
[0002]
The use of aluminum alloys for casting is growing rapidly in automobiles, especially for security components and structural elements, such as welded joints to floorboards, which allows for vehicle weight reduction. This weight reduction is even more important as high mechanical strength can be obtained. Known alloys such as alloys Al-Si9Cu3Mg in a state F which has not been processed, breaking strength force of at least 300 MPa R _m and makes it possible to obtain the elastic limit R _p0.2 of at least 230 MPa. In contrast, the breaking elongation A does not exceed 2%. However, structural or security components for motor vehicles need sufficient ductility to absorb energy, avoid fracture in the event of an impact, and adapt to different assembly configurations.
[0003]
On the other hand, a high content of copper, while having a beneficial effect on mechanical strength, makes the alloy more susceptible to corrosion. However, resistance to corrosion, especially under stress, is necessary to avoid component damage in corrosive environments, such as snow removal salts.
[0004]
Various methods of making alloys have been proposed to meet these needs.
[0005]
For example, U.S. Pat. No. 3,726,672, filed in 1970 by US Reduction, describes an alloy for a pressure cast wheel having the following composition (% by weight):
Si: 11-13.5 Mg: 0.25-0.6 Cu: 0.25-0.6 Mn <0.5 Zn <3 Fe: 0.5-1.5 Cr: 0.25-0. 4
[0006]
U.S. Pat. No. 4,104,089, filed in 1976 by Nippon Light Metal Co., Ltd., discloses a porous, non-porous nestless, pressure-cast component for automobiles having high mechanical strength, stable against impact. Wherein the part has the following composition:
Si: 7-12 Mg: 0.2-0.5 Mn: 0.55-1 Fe: 0.65-1.2
[0007]
The parts are treated by infiltration between 450 ° C. and 530 ° C., quenched and undergo tempering between 150 ° C. and 230 ° C. for one hour or more.
[0008]
EP 0 687 742, filed in 1994 by Aluminum Rheinfelden, describes an alloy for pressure casting intended for casting security parts, which has the following composition (% by weight):
Si: 9.5-11.5 Mg: 0.1-0.5 Mn: 0.5-0.8 Fe <0.15 Cu <0.03
[0009]
WO 96/27686, filed by Alcoa in 1995, describes a pressure-cast part for automotive structures of the "space frame" type, made of an alloy having the following composition: Si: 8 .5-11 Mg: 0.10-0.35 Mn: 0.4-0.8 Fe <0.50
[0010]
Austrian patent invention 404844, filed in 1997 by Aluminum Lend, relates to an alloy for pressure casting having the following composition:
Si: 9-12.5 Mg: 0.10-0.60 Mn: 0.30-0.45 Cr: 0.05-0.40 Fe <0.18 Cu <0.05 Zn <0.10 Ti : 0.01-0.20
[0011]
EP 0992601 and EP 0997550, filed in 1998 by Alusuisse, describe the production of parts by pressure casting of alloys having the following composition:
Si: 9.5-11.5 Mg: 0.1-0.4 Mn: 0.3-0.6 Fe: 0.15-0.35 Ti <0.1 Sr: 90-180 ppm In some cases, Cr : 0.1-0.3 Ni: 0.1-0.3 Co: 0.1-0.3
[0012]
The parts are subject to partial infiltration between 400 and 490 ° C.
[0013]
These various alloys require heat treatment by infiltration and quenching to reach the required mechanical strength, which results in significant deformation of the part, which must be subjected to strain correction, and significantly increases costs. Cause a significant increase.
[0014]
U.S. Patent No. 6,132,531, filed by Alcoa in 1997, relates to alloys for pressure casting and is specifically directed to "space frame" type automotive body structural joints and has the following composition: Has: Si <0.20 Fe <0.20 Mg: 2.80-3.60 Mn: 1.10-1.40 Ti <0.15 Be: 0.0005-0.0015. Excellent mechanical properties are obtained without heat treatment of the cast parts. Lack of silicon adversely affects the castability of the alloy.
[Patent Document 1]
US Patent No. 3,726,672 [Patent Document 2]
US Patent No. 4,104,089 [Patent Document 3]
European Patent No. 0687742 [Patent Document 4]
WO 96/27686 pamphlet [Patent Document 5]
Austrian Patent Invention No. 404844 [Patent Document 6]
European Patent No. 0992611 [Patent Document 7]
European Patent No. 0997550 [Patent Document 8]
US Patent No. 6,132,531 [Disclosure of the Invention]
[Problems to be solved by the invention]
[0015]
It is an object of the present invention to provide an aluminum alloy for the pressure casting of structural and security parts for motor vehicles, which alloy does not necessarily require a complete heat treatment of the T6 or T7 type, It combines excellent mechanical strength, high ductility, excellent corrosion resistance, and excellent suitability for casting, and enables parts to be manufactured in a mass production system under acceptable economic conditions.
[Means for Solving the Problems]
[0016]
SUMMARY OF THE INVENTION The present invention is directed to a security or structural component made of a ductile aluminum alloy that is pressure cast, the composition (% by weight) of the alloy being:
Si: 2-6 Mg <0.40 Cu <0.30 Zn <0.30 Fe <0.50 Ti <0.30;
Mn (0.3-2%), Cr (0.1-0.3), Co (0.1-0.3), V (0.1-0.3) and Mo (0.1-0) .4) at least one element aimed at reducing welding defects in the mold,
At least one eutectic modifying element, such as Sr (50-500 ppm), Na (20-100 ppm) and Ca (30-120 ppm);
Other elements each less than 0.05 and less than 0.10 in total, the balance being aluminum;
The part exhibits an elastic limit Rp _0.2 > 110 MPa and an elongation at break A> 10% after tempering T5 below 220 ° C.
[0017]
Preferably, the following limits are aimed at for the composition:
Si: 3.5-5 Mg: 0.05-0.20 Mn: 0.7-1.5 Ti: 0.05-0.15 Cu <0.10 Zn <0.10
[0018]
FIGS. 1a, 1b and 1c show the silicon content in a 2.5 mm thick sample plate which was pressure-cast using a vacuum aid and unheated (state F) for various magnesium contents. 3 shows changes in the breaking strength, the elastic limit, and the elongation according to.
[0019]
FIG. 2 shows the mechanical properties of parts cast under pressure (SP) and parts cast in a mold by gravity (Coq) for a 7% silicon alloy with their magnesium content. It is shown accordingly.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020]
The invention is, inter alia, a reduction in the silicon content compared to prior art alloys intended for the same application, whereby the pressure-cast parts, while still having an acceptable castability, are in particular only tempered ( It is based on a proper compromise between mechanical strength and ductility at T5) and confirmation that cracks and shrinkage-free can be obtained.
[0021]
The silicon content is at least 2% for good castability and up to 6% for high ductility in state T5. The silicon content is preferably comprised between 3.5% and 5%. The effect of the silicon content on the elastic limit and elongation is shown in FIG. 1 a and FIG. 1 b in state F (untreated) and in FIG. It shows a rapid decline in growth at times.
[0022]
Magnesium itself has the same effect as silicon because it forms Mg ₂ Si particles that have a hardening effect during heat treatment. However, applicants have surprisingly found that at the cooling rates inherent in pressure casting of thin parts, this hardening effect, when not infiltrated and not quenched, probably due to the supersaturation effect of a solid solution of aluminum. Confirmed that it will partially survive. In this way, the magnesium content can be limited to 0.4%, even 0.3% or 0.25%, which improves elongation and still retains a good elastic limit. .
[0023]
Iron, manganese, chromium, cobalt, vanadium, molybdenum, and nickel, individually or in combination with aluminum, form intermetallic compounds that cause embrittlement, so their content must be limited . However, these components have a smaller size and more advantageous morphology, so less embrittlement when the cooling rate upon removal from the mold is significant.
[0024]
Conversely, these same elements contribute to reducing "welding defects" in casting molds by reducing the chemical potential of the alloy compared to steel.
[0025]
Since iron has a detrimental effect on elongation and must be limited to 0.5% and preferably to 0.2%, it is essential that at least one of the other elements be present in addition to iron. It is. If this element is manganese, its content must be comprised between 0.3% and 2%, and preferably between 0.7% and 1.5%. Titanium combines with boron to reduce the size of the crystal grains of the primary particles, thereby making the solid solution of aluminum finer. Furthermore, the titanium increases the acceleration of volume shrinkage during solidification, which contributes to improving the compactness of the part.
[0026]
Copper must be kept below 0.3%, preferably below 0.1%, to avoid susceptibility to corrosion, since copper reduces elongation. Lead, tin, and antimony inhibit the action of modifying elements.
[0027]
Eutectic modifying and refinement elements such as strontium, sodium, and calcium modify the size and morphology of small silicon plates by giving them a fibrous structure. They can also act as fine particles for certain intermetallic compounds.
[0028]
Parts pressed from the alloy according to the invention, with or without vacuum, can be used without heat treatment (state F) or, conversely, by a complete heat treatment T6 including infiltration, quenching and tempering. Alternatively, T7 or natural aging treatment T3 after quenching can be applied. The pressed part is characteristically adapted to a simple tempering treatment (state T5) at a temperature below 220 ° C. for a length comprised between 15 minutes and 1 hour. This treatment is realized during the heat curing operation of the paint, which is generally carried out for automotive parts at a temperature comprised between 150 ° C. and 220 ° C.
[0029]
The alloys according to the invention make it possible to produce parts which simultaneously exhibit excellent mechanical strength and high elongation, which lead to excellent impact resistance and to assemblies requiring high ductility, such as joint fixing. To The part also exhibits excellent suitability for TIG, MIG or laser welding, and excellent compatibility with the aluminum alloy 6000 used for the body. The alloy is less susceptible to oxidation in the liquid state, is very easy to recycle, and has low remelting loss of debris.
【Example】
[0030]
(Example 1, effect of composition on static mechanical properties)
Nine different alloy sample plates from A to I were produced by pressure casting with the aid of vacuum (residual pressure in a mold of 80 hPa), the compositions of which are given in Table 1. The plates were 120 x 220 mm in size and 2.5 mm thick. The casting was performed on a press with a closing force of 3200 kN, with a piston injection speed of 0.7 m / s. The temperature of the metal in the furnace was 780 ° C.
[0031]
[Table 1]

[0032]
In these unheated plates, tensile strength test specimens were machined to obtain a breaking strength R _m (in MPa), an elastic limit of elongation Rp 0.2 defined in 0.2% (in MPa), and The breaking elongation A (unit%) was measured. The results (average of 10 specimens) are reproduced in Table 2 and FIGS. 1a, 1b and 1c.
[0033]
[Table 2]

[0034]
For alloys between 3% and 7% silicon and between 0.1% and 0.2% magnesium, the breaking strength and elastic limit increase progressively with silicon content and elongation decreases. It is confirmed that. While the elastic limit also increases progressively with magnesium content, the effect on magnesium elongation is not apparent.
[0035]
(Example 2, effect of cooling rate)
Specimens machined to 13.8 mm in diameter according to standard NF A 57-102 in alloys of 7% silicon and 0%, 0.13% and 0.20% magnesium, respectively, were placed in a mold by gravity. For alloys G, H, and I, the mechanical properties were compared with those of Example 1. The results are reproduced in Table 3 and FIG.
[0036]
[Table 3]

[0037]
For parts cast in molds with much lower cooling rates, the breaking strength and elastic limit are found to be much lower and the elongation higher, especially when the magnesium content is low.

Claims (8)

A security or structural part made of a ductile aluminum alloy that is pressure cast and has the composition (% by weight) of the alloy:
Si: 2-6 Mg <0.40 Cu <0.30 Zn <0.30 Fe <0.50 Ti <0.30;
Mn (0.3-2%), Cr (0.1-0.3), Co (0.1-0.3), V (0.1-0.3) or Mo (0.1-0) .4) at least one element aimed at reducing welding defects in the mold,
At least one eutectic modifying element, such as Sr (50-500 ppm), Na (20-100 ppm) and Ca (30-120 ppm);
Other elements each less than 0.05 and less than 0.10 in total, the balance being aluminum;
A part exhibiting, after tempering T5 at a temperature lower than 220 ° C., an elastic limit R _p0.2 > 110 MPa and an elongation A> 10%. Component according to claim 1, characterized in that the content of silicon is comprised between 3.5% and 5%. Component according to claim 1 or 2, characterized in that the magnesium content is comprised between 0.05% and 0.25%. 4. The component according to claim 1, wherein the content of titanium is comprised between 0.05% and 0.15%. The component according to claim 1, wherein the copper content is less than 0.10%. The component according to claim 1, wherein the iron content is less than 0.20%. 7. The component according to claim 1, wherein the content of zinc is less than 0.10%. 8. The component according to claim 1, wherein the manganese content is comprised between 0.7% and 1.5%.