EP2171111A1

EP2171111A1 - Extruded product made from aluminium alloy al-mg-si with improved resistance to corrosion

Info

Publication number: EP2171111A1
Application number: EP08835140A
Authority: EP
Inventors: Bruce Morere; Annabelle Bigot; Jérôme PIGNATEL
Original assignee: Alcan Rhenalu SAS
Current assignee: Constellium Issoire SAS
Priority date: 2007-07-27
Filing date: 2008-07-21
Publication date: 2010-04-07
Anticipated expiration: 2028-07-21
Also published as: EP2171111B1; BRPI0814132A2; CN101765669A; JP2010534765A; MX2010000786A; FR2919307B1; FR2919307A1; WO2009043992A1; US20100200205A1; KR20100051081A

Abstract

The invention relates to an extruded product, particularly a drawn tube made from an alloy of the 6XXX series with the following composition (%, by weight) : Mg: 0.4 - 0.7, Si: 0.4 - 0.7, Fe: 0.1 - 0.3, Zn: 0.16 - 0.3, Ti: 0.12 - 0.3, Mn < 0.10, Cu < 0.05, Cr < 0.05, Ni < 0.05. others <0.05 each and <0.15 in total, remainder being aluminium, in which the ratio Si / Mg is between 0.9 and 1.3. Said product offers an advantageous combination of good mechanical properties at operating temperatures for vehicle air-conditioning systems using CO2 as refrigerant fluid and high resistance to perforating corrosion necessary for extended operating life without leaks. Said tubes are advantageously used for cabin air-conditioning systems in motor vehicles using CO2 as refrigerant gas.

Description

AI-Mg-Si aluminum alloy spun product with improved corrosion resistance

Field of the invention

The invention relates to spun aluminum alloy products Al-Mg-Si (series 6000 according to the nomenclature of Aluminumuminum Association) with improved corrosion resistance, in particular drawn tubes intended in particular for pipes or heat exchangers for car manufacturing.

State of the art

Today, three out of four vehicles sold in France have air conditioning. By 2020, nine out of ten vehicles will be air-conditioned. Automotive air conditioning has a significant impact on climate change for two main reasons. The first is the overconsumption of fuel it entails. This depends a lot on the type of vehicle and the use that one makes of it but is estimated on average at 7% of consumption. The second is associated with refrigerant losses. The currently used fluid (HFC-R134a, CH2 FCF3) has an impact on the greenhouse effect approximately one thousand four hundred times greater than the equivalent mass of carbon dioxide (CO2) and it is widely accepted that each vehicle loses each year the third of the content (about 900g) of the refrigeration loop.

Many studies currently concern the replacement of HydroFluoroCarbures (HFCs) with CO2 for air conditioning systems. CO2, even though it is a greenhouse gas, has a much lower impact than HFCs, which would reduce the harmfulness of emissions related to leaks. The operation of an air conditioner using CO2 as a refrigerant gas is based on gas compression and expansion. A compressor compresses the CO2 at high pressure and it then goes into a gas cooler (traditionally called a condenser, but in which condensation does not occur when the refrigerant is CO2), then in an internal heat exchanger (which allows heat exchange with the low pressure zone). The CO2, which is still gaseous, then passes into a regulator from which a liquid flows out which allows the cooling of the passenger compartment by passing through an evaporator. The low pressure gas is then accumulated before circulating in the internal heat exchanger and back into the compressor for a new cycle. The spun aluminum products can be used for the manufacture of heat exchangers (gas cooler, evaporator) and / or for the realization of the pipes allowing the refrigerant to circulate between the various elements of the cooling circuit. The use of CO2 as a refrigerant is made difficult by the pressure at which it must be used. Indeed, the critical temperature of CO2 is lower than that of HFC-134a and its critical pressure is higher which forces the air conditioning system to operate at higher pressures and temperatures than those currently used, whether in the high pressure part or the low pressure part of the circuit. The materials used in the air conditioning circuit must therefore be stronger than current materials while maintaining at least equivalent performance in terms of manufacturing, shaping, assembly and corrosion resistance. For a good refrigerating efficiency, the CO2 thus needs to be compressed at high pressures of the order of 100 to 200 bar. Therefore, to allow the use of CO2 as a refrigerant, the pipes must withstand an operating pressure of 200 bar for high temperatures of 130-170 ⁰ C which is high compared to current conditions, the order of 5 bars at 60 ^° C. Alloys have been proposed for the production of flat tubes for heat exchangers (gas cooler, evaporator) of air conditioning systems using CO2 as a refrigerant gas.

JP 2005-068557 discloses a composition alloy (wt%) Mn: 0.8 - 2, Cu: 0.22 - 0.6, Ti: 0.01 - 0.2, Fe: 0.01 - 0, 4, Zn <0.2, Sn <0.018, In <0.02. JP 2007-070699 discloses a composition alloy (% by weight)

Si: 0.31 - 0.7, Fe: 0.3 - 0.6, Mn: 0.01 - 0.4, and optionally Ti 0.01 - 0.3, Zr 0.05 - 0.3, Cr 0.05 - 0.3. These alloys do not seem to achieve some of the required hardness performance, especially for pipes intended for pipelines. Traditionally, alloys used in the manufacture of pipe tubing are part of the 3XXX series. Patent application WO 02/055750 of the Applicant thus relates to an alloy having an improved corrosion resistance of composition Si <0.30, Fe: 0.20 - 0.50, Cu <0.05, Mn: 0, 5 - 1.2, Mg

<0.05, Zn <0.50, Cr: 0.10 - 0.30, Ti <0.05, Zr <0.05.

Patent application WO 99/18250 also discloses an alloy of the 3XXX series of composition Cu <0.03, Mn: 0.1 - 1.5, Ti 0.03 - 0.35, Mg <1.0 , Ni <0.01, Zn: 0.05 - 1.0, Zr <0.3, Fe <0.50, Si <0.50 Cr <0.20.

In addition, certain alloys of the 6XXX series are known from the EN 754-2 standard for the production of drawn tubes.

Among the alloys having a good spinnability, mention may be made of alloys AA6060, AA6061 and AA6063.

AA6060 alloy has the composition:

Mg: 0.35 - 0.6, Si: 0.30 - 0.6, Fe: 0.10 - 0.30, Cu <0.10, Mn <0.10, Cr <0.05, Zn

<0.15, Ti <0.10, other <0.05 each and <0.15 total, remains aluminum. The AA6061 alloy has the composition: Mg: 0.8 - 1.2, Si: 0.40 - 0.8, Fe: <0.7, Cu: 0.15-0.40, Mn <0.15, Cr 0, 04-0.35, Zn <0.25, Ti <0.15, other <0.05 each and <0.15 total, remains aluminum. AA6063 alloy has the composition:

Mg: 0.45 - 0.9, Si: 0.20 - 0.6, Fe: <0.35, Cu <0.10, Mn <0.10, Cr <0.10, Zn <0.10 , Ti <0.10, other <0.05 each and <0.15 total, remains aluminum. Application EP 0 251 180 mentions alloys AA6061 and AA6063 for the manufacture of tubes intended for automotive applications. Moreover, the alloy AA6106 of composition:

Mg: 0.40 - 0.8, Si: 0.30 - 0.6, Fe <0.35, Cu <0.25, Mn <0.05 - 0.20, Cr <0.20, Zn < 0.10, other <0.05 each and <0.15 total, remains aluminum is also known from the applicant for the production of drawn tubes.

The problem addressed by the present invention is to provide a 6XXX alloy spun product of improved corrosion resistance and mechanical properties to withstand high pressures, particularly for operating temperatures between 130 ^° C and 170 ^° C while having the same or better performance in terms of manufacturing, forming, assembly and corrosion resistance than current 3XXX, 5XXX and 6XXX series products .

Object of the invention

The subject of the invention is a spun product, in particular a stretched tube, made of alloy of the 6XXX series of composition (% by weight): Mg: 0.4 - 0.7, Si: 0.4 - 0.7, Fe : 0.1 - 0.3, Zn: 0.16 - 0.3, Ti 0.12 - 0.3, Mn <0.10, Cu <0.05, Cr <0.05, Ni <0, 05 other <0.05 each and <0.15 total, remaining aluminum, in which the Si / Mg ratio is between 0.9 and 1.3.

The preferred contents are (% by weight): Mg: 0.5 - 0.6, Si: 0.5 - 0.6, Fe: 0.15 - 0.25, Zn: 0.16 - 0.25, , Ti 0.16 - 0.25, Mn <0.05, Cr <0.03, Cu <0.03, Ni <0.03 other <0.05 each and <0.15 total, remaining aluminum, in wherein the Si / Mg ratio is between 1.0 and 1.2.

Another object of the invention is the use of a spun product according to the invention in the manufacture of motor vehicles.

Description of the invention

Unless stated otherwise, all the information relating to the chemical composition of the alloys is expressed in percent by weight. In a mathematical expression "Si" means the silicon content expressed in percent by weight, this applies mutatis mutandis to the other chemical elements. The designation of the alloys follows the rules of The Aluminum Association, known to those skilled in the art as well as the EN 573-1 standard. The metallurgical states are defined in the European standard EN 515. The chemical composition of standardized aluminum alloys is defined for example in the standard EN 573-3. Unless otherwise stated, the static mechanical characteristics, that is the breaking strength R _m , the yield point R _p o _{, 2} , and the elongation at break A, are determined by a tensile test according to the standards EN 10002-1 and EN 754-2. The term "spun product" includes so-called "stretched" products, that is products that are made by spinning followed by stretching.

Unless otherwise stated, the definitions of the European standard EN 12258-1 apply. The alloy of the 6XXX series according to the invention comprises, with respect to alloys AA6060 and AA6063, an addition of zinc and titanium. Thus, the zinc content must be between 0.16 and 0.3% by weight and preferably between 0.16 and 0.25% by weight. The titanium content must be between 0.12 and 0.3% by weight, and preferably between 0.16 and 0.25% by weight. Furthermore, the content of Cr, Cu and Ni must be maintained at an impurity level: less than 0.05% by weight and preferably less than 0.03% by weight. The alloy according to the invention thus differs from the alloy AA6061 which contains 0.04 - 0.35% by weight of Cr and 0.15 - 0.40% by weight of Cu. The combination of the addition of Zn and Ti makes it possible both to improve the mechanical properties and the resistance to corrosion. The magnesium content is between 0.4 and 0.7% by weight and preferably between 0.5 and 0.6% by weight. The silicon content is between 0.4 and 0.7% by weight and preferably between 0.5 and 0.6% by weight. The addition of magnesium and silicon at a content of at least 0.4% by weight and preferably at least 0.5% by weight makes it possible to achieve the desired mechanical characteristics. The magnesium content must however be limited to a maximum of 0.7% by weight and preferably 0.6% by weight to ensure satisfactory brazeability of the products, as well as a good performance in terms of extrusionability. . The silicon content must also be limited to a maximum of 0.7% by weight and preferably 0.6% by weight. The Si / Mg ratio is between 0.9 and 1.3 and preferably between 1.0 and 1.2.

The manganese content must be less than 0.10% by weight and preferably less than 0.05% by weight.

The iron content must be between 0.1 and 0.3% by weight and preferably between 0.15 and 0.25% by weight. Too high a content of iron contributes to the degradation of the corrosion resistance and a maximum content of 0.3% by weight is required, a maximum content of 0.25% by weight being preferred. For economic reasons of recycling, the iron content must be at least 0.1% by weight and preferably at least 0.15% by weight. The addition of other elements may have a detrimental effect on the alloy and they must therefore have a content of less than 0.05% by weight each and less than 0.15% by weight in total.

The process for producing the spun products according to the invention, in particular tubes, involves the casting of billets of the indicated alloy, the homogenization of the billets, their heating and their spinning in order to obtain a tube in straight length or in a crown, the solution and quenching and optionally one or more stretching passes to bring the product to the desired dimensions. The tube may advantageously be annealed at a temperature between 400 ° C. and 550 ^° C. to improve its ductility. Preferably, the spun products according to the invention are used in the T4 state, that is to say that the maturation is carried out at room temperature. The products according to the invention can be obtained by quenching on a press. In another embodiment of the invention, the spun products according to the invention undergo a return which leads them to the T6 state, so as to maximize the mechanical strength.

The products according to the invention have a grain size of less than 45 μm and preferably less than 25 μm.

The products according to the invention have in the T4 state a high mechanical strength. Thus, in the T4 state, the breaking strength at ambient temperature is increased by more than 50% with respect to a 3XXX alloy product according to the application WO 02/055750 in the H12 state and by more than 10% with respect to a 6060 alloy product in the T4 state. The advantage is confirmed for tests carried out at high temperature. Thus, in the T4 state, the tensile strength at 170 ^° C. is increased by nearly 60% relative to a 3XXX alloy product according to the application WO 02/055750 in the H12 state and by almost 10% relative to to an alloy product 6060 in the T4 state. In particular, the tubes according to the invention have, in the T4 state, a tensile strength R _m greater than 170 MPa at room temperature and greater than 140 MPa at 170 ^° C. In addition, the tubes according to the preferred composition of The invention has in the T4 state a breaking strength Rm greater than 180 MPa at room temperature and greater than 150 MPa at 170 ° C. The elongation at break A% obtained with the products according to the invention is high: greater than 25%, both at room temperature and at 170 ^° C. The product according to the invention thus has important advantages in terms of suitability. to shaping and resistance to the rupture especially with respect to 3XXX alloy products according to demand

WO 02/055750.

The products according to the invention also have a high resistance to perforating corrosion, which makes it possible to obtain high durations of use without leakage. In particular, the products according to the invention do not exhibit deep pits during a salt spray test of SWAAT type according to the ASTM G85A3 standard, whereas under the same conditions, they are observed for AA6106 alloy products. , AA6060 and even for AA6060 alloy products in which titanium has been added. Unexpectedly, the combined addition of zinc and titanium enables the products according to the invention to achieve a corrosion resistance in the T4 state equivalent to that obtained with the 3XXX alloy products according to the application WO 02/055750. .

A preferred form of the spun product according to the invention is a cylindrical tube having only one cavity. The spun products according to the invention can be used especially as tubes in the manufacture of motor vehicles. In particular, the spun products according to the invention can be used as tubes for fuel lines, oil, brake fluid or refrigerant for automobiles and as tubes for heat exchangers for engine cooling and / or air conditioning systems. passenger compartment, especially if they use CO2 as a refrigerant gas. The tubes, in particular the drawn tubes, according to the invention are more particularly adapted to be used in the form of cylindrical tubes having only one cavity for the fluid transfer lines used in passenger compartment air-conditioning systems of motor vehicles using CO2 as a refrigerant gas.

Example

Logs were cast and homogenized in 5 alloys listed from A to F. The alloys A, B, C and D correspond to compositions of the prior art, alloy A is part of the 5xxx series, alloy B according to the application WO02 / 055750 is part of the 3XXX series, the alloys C and D are part of the 6XXX series. The alloy E is an alloy 6060 in which titanium has been added and the alloy F is in accordance with the invention.

The compositions (% by weight) are indicated in Table 1.

Table 1. Composition of the alloys A to F (% by weight).

The alloy billet A was spun into finished lengths of straight tubes, which were then drawn and annealed to a diameter of 16 mm and a thickness of 1.25 mm in the final state O.

The alloy billets B, C, D, E and F were spun into tube crowns. The 6XXX alloy products (C, D, E and F) were hardened on press. These crowns

10 were then stretched and annealed at a temperature between 400 and 550 ⁰ C to obtain a diameter of 10 or 11 mm and a thickness of 1.25 or 1.5 mm. No significant differences were recorded between the five alloys B, C, D, E and F for their spinning and drawing properties. The crowns of sample B were then subjected to a new stretching pass to bring them to state H12 according to

According to EN 515 standard, the tensile strength R _m (in MPa), the yield strength R _p o _{, 2} (in MPa) and the elongation at break A% were measured on samples of the 6 tubes. , at room temperature and at 140 ⁰ C and 170 ⁰ C so as to simulate the conditions of use of the tube in an air conditioning system using CO2 as a refrigerant. The results are shown in Table 2.

20

Table 2. Mechanical characteristics obtained at ambient temperature and at high temperature.

II 121 I 206 iI 31 jI 116 II 185 I 27 II 109 I 168 I 27 I

The spun products obtained with the four alloys C, D, E, F of the 6xxx series have mechanical characteristics that are quite similar to each other and comparable to those obtained with alloy A of the 5XXX series. The alloy F according to the invention has among the 6XXX alloys tested the best properties, in particular with a higher tensile strength of more than 10% for a test carried out at ambient temperature and of nearly 10% for a test carried out at 170 ^° C. C, compared to that obtained with AA6060 alloy. The alloy F according to the invention has, in particular, improved mechanical characteristics with respect to the alloy B according to WO02 / 055750 of the prior art: a rupture strength R _m increased by more than 50% both at room temperature at 140 ^° C. or 170 ° C., and an elongation at break of more than 25% at room temperature as well as at 140 ^° C. or 170 ° C. The average grain size was measured by the intercepts method on samples of tubes B, D, E and F. The results are shown in Table 4. The tubes obtained with the alloy according to the invention have fine grains. equiaxes of the order of 25 microns.

Table 4. Average grain size measured by the intercepts method.

Corrosion resistance was measured using the Sea Water Acetic Acid Test (SWAAT) according to ASTM G85 A3. The measurements were made for periods of 500 cycles at the temperature of 49 ^° C., on three tubes of length 200 mm each of alloys A, B, C, D, E and F. At the end of the test, the tubes were removed from the chamber and stripped in a solution of nitric acid concentrated to 68% in order to dissolve the corrosion products. On each tube, the depth of the pits by defocusing is measured optically on the surface and the average of the depths of the 5 deepest stings. The average Pmoy of the values obtained for the 3 tubes is then calculated. Corrosion resistance is better when Pmoy is weak. The results of 5 successive SWAAT test campaigns are shown in Table 3. The number of signs * indicates the number of tubes drilled in the batch of three tubes tested.

Table 3. Results obtained in the SWAAT corrosion test.

It can be seen that the alloy F according to the invention has a corrosion resistance which is much higher than that of the other alloys C, D, E of the same series 6xxx, and that of the alloy A of the series 5xxx. Thus, the alloy F does not exhibit deep pitting, it being understood that in the context of the present invention the term deep stitch means a Pmoy value greater than 0.5 mm.

The Titanium Test E alloy pits deeper than the F alloy, demonstrating the beneficial effect on the corrosion resistance of the combined addition of Ti and Zn, compared with the addition of titanium. alone.

The alloy F according to the invention offers a corrosion resistance equivalent to that of the alloy B, according to the application WO02 / 055750 of the prior art, known for its advantageous properties of corrosion resistance.

The alloy F according to the invention offers an advantageous combination of high mechanical properties at operating temperatures of automotive air conditioning systems using CO2 fluid, and high resistance to the necessary perforating corrosion so as to obtain high durations of use. without leakage.

Claims

claims

1. Spun product, in particular a stretched tube, made of 6XXX alloy of composition (% by weight):

Mg: 0.4 - 0.7, Si: 0.4 - 0.7, Fe: 0.1 - 0.3, Zn: 0.16 - 0.3, Ti 0.12 - 0.3, Mn <0.10,

Cu <0.05, Cr <0.05, Ni <0.05 other <0.05 each and <0.15 total, remains aluminum, in which the Si / Mg ratio is between 0.9 and 1.3 .

2. Product according to claim 1, characterized in that Zn 0.16 - 0.25% by weight.

3. Product according to one of claims 1 or 2, characterized in that Ti 0.16 - 0.25% wt%.

4. Product according to one of claims 1 to 3, characterized in that Mg: 0.5 - 0.6% by weight.

5. Product according to one of claims 1 to 4, characterized in that Si: 0.5 - 0.6% by weight.

6. Product according to one of claims 1 to 5, characterized in that Mn <0.05% by weight.

7. Product according to one of claims 1 to 6, characterized in that Fe: 0.15 - 0.25% by weight.

8. Product according to one of claims 1 to 7, characterized in that (% by weight) Cr <0.03%, Cu <0.03, Ni <0.03.

9. Spun product according to one of claims 1 to 8 characterized in that its grain size is less than 45 microns.

10. Spun product according to one of claims 1 to 9 characterized in that its tensile strength R _m in the T4 state is greater than 170 MPa at room temperature and greater than 140 MPa at 170 ° C.

11. Spun product according to claim 10, composition (% by weight) Mg: 0.5 - 0.6, Si: 0.5 - 0.6, Fe: 0.15 - 0.25, Zn: 0, 16 - 0.25,, Ti 0.16 - 0.25, Mn <0.05, Cr <0.03, Cu <0.03, Ni <0.03 other <0.05 each and <0.15 total, aluminum balance, in which the Si / Mg ratio is between 1.0 and 1.2, characterized in that in the T4 state its breaking strength R _m is greater than 180

MPa at room temperature and greater than 150 MPa at 170 ^° C.

12. Spun product according to one of claims 1 to 11 characterized in that it does not present deep pits during a salt spray type test according to ASTM G85 A3.

13. Spun product according to one of claims 1 to 12 characterized in that it is a cylindrical tube having only one cavity.

14. Use of a spun product according to one of claims 1 to 13 in the manufacture of motor vehicles.

15. Use according to claim 14 as a tube of fuel lines, oil, brake fluid, or refrigerant.

16. Use according to claim 14 as a tube of an engine cooling system heat exchanger and / or cabin air-conditioning in which CO2 is used as a refrigerant gas.

17. Use according to claim 15, wherein said spun product is in the form of cylindrical tube having only one cavity, as a fluid transfer pipe in a cabin air conditioning system using CO2 as a refrigerant gas.