EP2171114A1

EP2171114A1 - Extruded products in aluminium alloy al-mn with improved mechanical strength

Info

Publication number: EP2171114A1
Application number: EP08835982A
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: WO2009043993A1; EP2171114B1; KR20100065289A; FR2919306B1; US20100190027A1; JP2010534766A; MX2010000785A; BRPI0814138A2; FR2919306A1; CN101765674A

Abstract

The invention relates to an extruded product, in particular a tube, made from an alloy of composition (%, by weight): Si: < 0.30, Fe: < 0.30, Cu: < 0.05, Mn: 0.5 - 1.2, Mg. 0.5 - 1.0, Zn: < 0.20, Cr: 0.10 - 0.30, Ti < 0.05, Zr < 0.05, Ni < 0.05, others <0.05 each and <0.15 in total, remainder being aluminium. The invention further relates to a method for producing extruded tubes with said composition, comprising casting a billet, optional homogenisation thereof, the extruding of a tube, the drawing of said tube, in one or more passes and continuous annealing at a temperature between 350 and 500°C with a temperature rise of less than 10 seconds. Said tubes are used to advantage in cabin air-conditioning systems for motor vehicles using CO2 as refrigerant gas.

Description

AI-Mn aluminum alloy spun products with improved mechanical strength.

Field of the invention

The invention relates to spun aluminum alloy products Al-Mn (3000 series according to the nomenclature of the Aluminum Association) with improved mechanical strength, in particular tubes intended in particular for pipes or heat exchangers for the automotive industry. .

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 current currently used fluid (HFC-Rl 34a, CH2 FCF3) has an impact on the greenhouse effect approximately one thousand four hundred times higher 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 if it is a greenhouse gas, has a much lower impact than HFCs ₃ , 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 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 exchanges 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 ° 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 coolers, evaporators) of air conditioning systems using CO2 as a refrigerant gas.

JP 2005-068557 discloses a composition alloy (% by weight)

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 an alloy of composition (% 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. In addition, several alloys of the 3XXX series are known for the production of tubes intended for air conditioning using traditional refrigerants.

The patent application WO 97/46726 of Reynolds Metals relates to an alloy, known under the name X3030, of composition (% by weight): Mn: 0.1 - 0.5, Cu <0.03, Mg <0.01 , Zn: 0.06 - 1.0, Si: 0.05 - 0.12, Fe <0.50,

Ti: 0.03 - 0.30, Cr <0.50, remains aluminum. The addition of Zn and Ti contributes to the improvement of the corrosion resistance. Cr is preferably maintained below 0.20%.

The patent application WO 99/18250 of the same company relates to an alloy designated X3020 having a better formability than the X3030 by addition of Mg

(up to 1%) and Zr (up to 0.30%). Cr is preferably maintained below

0.02%, or even 0.01%, Ti is preferably maintained above 0.12% and Zn above 0.1%.

The patent application WO 00/50656 of Norsk Hydro relates to an alloy of composition: Si: 0.05 - 0.15, Fe: 0.06 - 0.35, Cu <0.10, Mn: 0.01 - 1.0, Mg: 0.02

0.60, Cr <0.25, Zn: 0.05-0.70, Ti <0.25, Zr <0.20.

Cr is preferably maintained below 0.15% and is only allowed for reasons of recycling of manufacturing scrap other alloys. Zn is preferably maintained above 0.1%. The patent application WO 02/055750 of the Applicant 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.

The problem addressed by the present invention is to provide a 3XXX alloy spun product of improved mechanical strength, so as to be able to withstand high pressures and in particular for operating temperatures between 130 and 170 ^° C., and having identical or superior performance in terms of manufacturing, shaping, assembly and corrosion resistance to those of current products. Object of the invention

The subject of the invention is a spun product, in particular a stretched tube, of alloy of composition (% by weight): Si <0.30, Fe <0.30, Cu <0.05, Mn: 0.5 - 1 , 2, Mg 0.5 - 1.0, Zn <0.20, Cr: 0.10 - 0.30, Ti <0.05, Zr <0.05, Ni <0.05, others <0, 05 each and <0.15 total, remains aluminum.

The preferred contents are (% by weight): Si 0.05 - 0.15, Fe: 0.05 - 0.25, Cu <0.01, Mn: 0.9 - 1.1, Mg 0.6 - 0.9, Zn: <0.05, Cr: 0.15 - 0.25, Ti <0.04, Zr <0.04, Ni <0.01.

The subject of the invention is also a process for manufacturing spunbonded alloy tubes according to the invention comprising casting a billet, optionally homogenizing this billet, spinning a tube, stretching said tube one or more passes, and annealing continuously at a temperature between 350 and 500 ° C with a rise in temperature of less than 10 s.

Yet 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 otherwise indicated, all the indications relating to the chemical composition of the alloys are expressed in percent by weight. 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, ie the tensile strength R _m , the yield strength R. _p o _{, 2} , and the elongation at break A, are determined by a tensile test. according to EN 10002-1 and EN 754-2. The term "spun product" includes so-called "stretched" products, i.e., 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 3XXX series according to the invention has a relatively high magnesium content and a zinc content reduced to the level of impurity. Contrary to the teaching of the prior art which recommends the addition of zinc and titanium to the alloys of the 3XXX series to improve their resistance to corrosion, the alloy according to the invention has a good corrosion behavior with a content zinc and a titanium content reduced to the level of impurities. Thus the zinc content should be less than 0.20% by weight, more preferably less than 0.05% by weight and even more preferably less than 0.04% by weight. Likewise, the titanium content must be less than 0.05% by weight, preferably less than 0.04% by weight and even more preferably less than 0.03% by weight. Moreover, the low zinc and titanium contents are an advantage as regards the recycling of the alloy products according to the invention.

The magnesium content is between 0.5 and 1.0% by weight and preferably between 0.6 and 0.9% by weight. The addition of magnesium at a content of at least 0.5% by weight and preferably at least 0.6% by weight makes it possible to increase the mechanical strength very significantly. The magnesium content should, however, be limited to a maximum of 1.0% by weight and preferably 0.9% by weight to ensure satisfactory brazeability of the products, as well as good performance in terms of extrusionability. The addition of chromium at a concentration of between 0.10 and 0.30% by weight and preferably at a concentration of between 0.15 and 0.25% by weight makes it possible to improve the corrosion resistance of the alloy.

Manganese is the main alloying element, its addition is carried out at a concentration of between 0.5 and 1.2% by weight and preferably at a concentration of between 0.9 and 1.1% by weight.

The content of iron and silicon must be less than 0.30% by weight. Advantageously, the iron content is at most 0.25% by weight and the silicon content is at most 0.15% by weight. Too high a content of these elements contributes to the degradation of the corrosion resistance. It is preferable, mainly for economic reasons of recycling, that the silicon and iron contents are at least 0.05% by weight.

The addition of other elements may have a detrimental effect on the alloy and must therefore have a content of less than 0.05% by weight and less than 0.15% in total. In In particular, the presence of zirconium, nickel or copper can degrade the corrosion resistance properties and the content of these elements should be less than 0.05% by weight. In a preferred manner, the nickel and copper content is less than 0.01% by weight and the zirconium content is less than 0.04% by weight.

The method of manufacturing the spun products, including tubes, comprises casting billets of the indicated alloy, optionally homogenizing the billets, heating them and spinning to obtain a tube in straight length or crown, and optionally one or several stretching passes to bring the product to the desired dimensions. The tube can, if it is stretched, then advantageously continuously annealed by high velocity scrolling through a passage oven, preferably an induction furnace. Heating the spun product is very fast, less than 10 seconds, and preferably 2 seconds, and the product scrolls at a speed between 20 and 200 m / min. The oven temperature is maintained between 350 and 500 ° C. The product can after the annealing undergo a new stretching to increase the mechanical strength (state H).

This continuous annealing leads to a fine-grain equiaxed microstructure, of a mean grain size, measured by the intercepts method, of less than 40 μm, and typically of the order of 25 μm. The fine-grained microstructure is particularly advantageous with respect to the mechanical properties and corrosion resistance of the tubes.

The products according to the invention have a high mechanical strength. Thus, in the H12 state, the breaking strength at room temperature is increased by at least 40% relative to a product according to the application WO 02/055750 having a comparable manganese content. Surprisingly, the advantage is even more marked for the tests carried out at high temperature. Thus, in the H12 state, the breaking strength at 170.degree. C. is increased by nearly 60% relative to a product according to the application WO 02/055750 having a comparable manganese content. In particular, the spun products according to the invention have, in the H12 state, a resistance to rupture Rm greater than 150 MPa at room temperature and greater than 140 MPa at 170 ^° C. In addition, the products spun in accordance with the preferred composition of the invention exhibit in the H12 state a breaking strength Rm greater than 160 MPa at room temperature and greater than 150 MPa at 170 ° C.

The relative plastic difference R _p o _{/ o} , defined by the ratio R _p o _{/ o} = (R _m -R _p02 ) / R _p0 , ₂ , makes it possible to evaluate the plastic deformation ability without rupture. The products according to the invention have, in the H12 state, a plastic gap at room temperature slightly lower than that of the products according to the application WO 02/055750 but surprisingly an improved relative plastic gap for test temperatures greater than or equal to 130 ° C. Thus, in the H12 state, the relative plastic difference obtained with the products according to the invention is greater than 5% for a test temperature of 140 ° C. Moreover, even after aging at 130 ° C., the relative plastic difference at the H 12 state remains greater than 5%. The products according to the invention also have good corrosion performance. 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. It is possible that this favorable result results, at least in part, from the absence of MgZn ₂ precipitates which may form in the event of the simultaneous presence of Mg and Zn and which may have a detrimental effect, in particular on the corrosion resistance.

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 preferably comprising only one cavity for the fluid transfer lines used in the cabin air-conditioning systems. of motor vehicles using CO2 as a refrigerant gas. Example

Bindings were cast and homogenized in 3 alloys listed A to C. The alloys A and B respectively correspond to compositions of alloy AA3103 and according to the application WO 02/055750 of the prior art. Alloy C is in accordance with the invention. The compositions of the alloys (% by weight) are shown in Table 1.

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

The billets were spun into tube crowns and then stretched to obtain tubes 12 mm in diameter and 1.25 mm thick. No significant differences were recorded for the three alloys with respect to their spinning and drawing properties. These rings were annealed continuously in an induction furnace at a temperature set at 470 ⁰ C, with a speed of passage between 60 and 120 m / min. The crowns were then subjected to a new stretching pass to bring them to H12 according to EN 515. Measurements of the 3 tubes were measured for the breaking strength R _m (in MPa) and the limit of elasticity R _{p0; 2} (in MPa), at room temperature and, for tubes B and C, at 140 ° C and 170 ° C so as to simulate the conditions of use of the tube in an air conditioning installation using the CO2 as a refrigerant. The results are shown in Table 2.

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

It is found that alloy C according to the invention leads ^"in mechanical strength greatly improved as compared that of the alloy B for a test performed at room temperature and even more vastly improved for a test carried out at 170 0C. Thus the resistance at break is improved by about 40% at room temperature and about 60% at 170 ^° C. The plastic gap for tests performed at at least 140 ° C is also largely improved from 0% for the alloy B greater than 5% for alloy C for temperatures of 140 ° C. and 170 ° C. The properties of breaking strength and the yield strength of alloy C were also measured at 130 ° C. aging 72h at 130 ° C and 100Oh at 130 ⁰ C, and measured at 165 ° C after aging from 72h to 165 ° C and from 100Oh to 165 ⁰ C. For comparison, the alloy B has been characterized only in the the most severe conditions, ie measured at 165 ⁰ C after aging 100Oh to 165 ° C. The results are shown in Table 3.

Table 3. Mechanical characteristics obtained after aging at high temperature.

It is found that the alloy C according to the invention retains after aging the mechanical properties of resistance to fracture and yield strength significantly improved since increased by 40% relative to the alloy B.

The average grain size was measured by the intercepts method on samples from the 3 tubes. The results are shown in Table 4. The tubes obtained with the 3 alloys have equiaxized fine grains of the order of 20 microns. 10

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 of each alloy A ₃ B and C. At the end of the test, the tubes were taken out of the tube. pregnant and stripped in a solution of nitric acid concentrated to 68% in order to dissolve the products of corrosion. On each tube, the depth of the pits is then measured optically on the surface by defocusing and the average depth of the deepest pits is calculated. The average Pmoy of the values obtained for the 3 tubes is then calculated. The corrosion resistance is even better than Pmoy is weak. The results of 5 successive SWAAT test campaigns are shown in Table 5. The number of signs * indicates the number of tubes drilled in the batch of three tubes tested.

Table 5. Results obtained in the SWAAT corrosion test.

It is found that alloy C according to the invention has a corrosion resistance equivalent to that of alloy B of the prior art and significantly improved compared to that of alloy A. Thus alloy C does not present no deep sting, it being understood that in the context of the present invention the term deep sting means a Pmoy value greater than 0.5 mm. The composition according to the invention, and in particular the addition of Mg, the absence of Zn thus makes it possible to dramatically improve the mechanical strength, in particular for temperatures between 130 ° C. and 170 ° C., without compromising corrosion resistance, compared to alloy B.

Claims

claims

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

If <0.30, Fe: <0.30, Cu <0.05, Mn: 0.5 - 1.2, Mg 0.5 - 1.0, Zn <0.20, Cr: 0.10 - 0.30, Ti <0.05, Zr <0.05, Ni <0.05, other <0.05 each and <0.15 total, remains aluminum.

2. Product according to claim 1, characterized in that Zn <0.05% by weight.

3. Product according to one of claims 1 or 2, characterized in that Ti <0.04% by weight and preferably Ti <0.03% by weight.

4. Product according to one of claims 1 to 3, characterized in that Mn: 0.9 - 1.1% by weight.

5. Product according to one of claims 1 to 4, characterized in that Cr: 0.15 - 0.25% by weight.

6. Product according to one of claims 1 to 5, characterized in that Mg: 0.6 - 0.9% by weight.

7. Product according to one of claims 1 to 6, characterized in that Fe: 0.05 - 0.25% by weight.

8. Product according to one of claims 1 to 7, characterized in that Si: 0.05 - 0.15% by weight.

9. Product according to one of claims 1 to 8, characterized in that (% by weight) Cu <0.01, NK O ₅ Ol.

10. Spun product according to one of claims 1 to 9 characterized in that its grain size is less than 40 microns.

11. Spun product according to one of claims 1 to 10 characterized in that in the H12 state its breaking strength Rm is greater than 150 MPa at room temperature and greater than 140 MPa at 170 ° C.

12. Spun product according to claim 11, of composition (% by weight) Si 0.05 - 0.15, Fe: 0.05 - 0.25, Cu <0.01, Mn: 0.9 - 1.1 , Mg 0.6 - 0.9, Zn: <0.05, Cr: 0.15 - 0.25, Ti <0.04, Zr <0.04, Ni <0.01, characterized in that at the H12 state, its breaking strength Rm is greater than 160 MPa at room temperature and greater than 150 MPa at 170 ^° C.

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

14. A method of manufacturing spun tubes according to one of claims 1 to 13, comprising the casting of a billet, optionally the homogenization of the billet, the spinning of a tube, the drawing of this tube in one or several passes, and annealing continuously at a temperature between 350 and 500 ° C with a rise in temperature of less than 10 s.

15. The method of claim 14, characterized in that the rise in temperature is less than 2 s.

16. Method according to one of claims 14 or 15, characterized in that the annealing is done in an induction furnace.

17. Method according to one of claims 14 to 16, characterized in that the annealing is followed by stretching.

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

19. Use according to claim 18 as a tube of fuel lines, oil, brake fluid or refrigerant.

20. Use according to claim 18 as a tube of an engine cooling system heat exchanger and / or cabin air-conditioning in which CO2 is used as a refrigerant gas.

21. Use according to claim 18, 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.