WO1991014794A1

WO1991014794A1 - Improved aluminum alloy

Info

Publication number: WO1991014794A1
Application number: PCT/CA1991/000098
Authority: WO
Inventors: Ernest Eugene Hajcsar
Original assignee: Alcan International Limited
Priority date: 1990-03-27
Filing date: 1991-03-26
Publication date: 1991-10-03
Also published as: AU7544091A

Abstract

The present invention provides a novel aluminum based alloy which provides good resistance to corrosion, good brazeability, good workability or extrudability during fabrication of product, and imparts good mechanical strength to the fabricated articles. The invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.02 % to 0.12 % silicon, 0.07 % to 0.27 % iron, 0.05 % to 0.45 % copper, 0.06 % to 0.26 % manganese, and 0.05 % to 0.25 % titanium, with the balance being aluminum with normal impurities. The present invention also provides an improved process for heat treating and extruding the foregoing aluminum alloy.

Description

Improved Aluminum Alloy Technical Field

The present invention relates to an improved aluminum alloy having increased corrosion resistance properties, good mechanical strength, workability and extrudability, and good brazeability. Background Art and Industrial Applicability

The use of extruded tubing to form serpentine condensers as heat exchanges particularly for automobile, van and truck air conditioners and radiators is well known. The most common alloys currently used in such condensers are AA3102 and a Japanese alloy commonly known as MR162. MR162 contains a significant amount of copper making it cathodic to fins, thereby extending its resistance to corrosion through cathodic protection. However, the alloy itself has insufficient inherent corrosion resistance and thus like AA3102, another common alloy, lasts only about 5 days as an unpainted brazed condenser in an ASTM G85 A3 corrosion test. Numerous previous attempts have been made to improve upon the corrosion resistance of aluminum alloys without sacrificing its strength, extrudability or workability. For example, United States Patent No. 4,649,087 (Scot et al.) discusses an alloy which attempts to provide corrosion resistance with strength. The alloy has a relatively high manganese content which helps increase its strength, but also makes it difficult to extrude or work the alloy. U.S. Patent No. 3,960,208 discloses an alloy containing increased amounts of manganese, chromium, and zirconium. Despite the addition of these metals, the alloy does not seem to provide improved workability or corrosion resistance.

Each of the foregoing alloys suffers from disadvantages in either corrosion resistance or workability. It is therefore an object of the invention to provide an aluminum alloy material having improved corrosion resistance, without sacrificing mechanical strength, workability, extrudability or its ability to be brazed.

Disclosure of Invention

The present invention provides a novel aluminum based alloy which provides good resistance to corrosion, good brazeability, good workability or extrudability during fabrication of product, and imparts good mechanical strength to the fabricated articles. The invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.02% to 0.12% silicon, 0.07% to 0.27% iron, 0.05% to 0.45% copper, 0.06% to 0.26% manganese, and 0.05% and 0.25% titanium, with the balance being aluminum with normal impurities.

In another embodiment, the invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.13% to 0.19% manganese, 0.11% to 0.15% titanium, with the balance being aluminum with normal impurities. In yet another embodiment, the invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.05% to 0.11% manganese, and 0.11% to 0.15% titanium, with the balance being aluminum with normal impurities.

In each of the preferred embodiments, the sum of the amounts of copper and titanium, by weight percent, should preferably be less than about 0.50, and the ratio of the weight percent of copper to the weight percent of titanium should preferably be between about 1.5 and about 2.5. The invention also provides a tube made from the aluminum alloy of the embodiments of the present invention summarized as above and the tube has improved resistance to corrosion, making it particularly well suited to duty in corrosive environments, such as serpentine condensers for car, van and truck air conditioners and radiators, as well as residential and commercial air conditioners. Best Modes For Carrying Out The Invention

The present invention provides a novel aluminum based alloy which provides good resistance to corrosion, good brazeability, good workability or extrudability during fabrication of a product, and imparts good mechanical strength to the fabricated articles. The invention provides an aluminum alloy which can be fabricated relatively easily into mechanically strong tubes, and which demonstrates improved effectiveness in resisting corrosion in use. The invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.02% to 0.12% silicon, 0.07% to 0.27% iron, 0.05% to 0.45% copper, 0.06% to 0.26% manganese, 0.05% to 0.25% titanium, with the balance being aluminum with normal impurities.

In another embodiment, the invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.13% to 0.19% manganese and 0.11% to 0.15% titanium, with the balance being aluminum with normal impurities.

In a further alternative embodiment, the invention provides an aluminum alloy material consisting essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.05% to 0.11% manganese and 0.11% to 0.15% titanium, with the balance being aluminum with normal impurities. In each embodiment, the sum of the amounts of copper and titanium, by weight percent, should preferably be less than 0.50, and the ratio of the weight percent of copper to the weight percent of titanium should preferably be between about 1.5 and about 2.5.

The invention also provides a tube made from the aluminum alloy of the foregoing embodiments, and the tube appears to have improved formability or extrudability characteristics, and appears to resist corrosion better than available alloys. The composition limits for the inventive alloy were established as follows:

Manganese (Mn) is included in minimal amounts. Its content in the inventive alloys is preferably maintained at about 0.26 percent by weight or less in order to increased extrudability, but may vary from about 0.06 to about 0.26 by weight percent. To compensate for decreased manganese content in the alloy, a balanced composition of copper and titanium are provided. Silicon, although present as an impurity in some aluminum alloys, increases strength in the alloy of the present invention, if the silicon content is maintained in the range of about 0.02 to 0.12 weight percent.

The addition of copper also contributes to the increased strength of the present alloy. Preferably, the total copper content should range from about 0.05 to about 0.45 by weight percent in order to increase strength without sacrificing brazeability or corrosion resistance, and should be balanced with titanium such that the ratio of the weight percent of copper to titanium is between about 1.5 and 2.5.

The iron content of the alloy of the present invention is preferably about 0.07 to about 0.27 by weight percent; the addition of iron increases strength. Titanium is an important addition to the inventive alloys. When added in an amount ranging from 0.05 to 0.25 by weight percent, it helps enhance corrosion resistance of the alloys of the present invention. In making the alloy of the present invention, a balance should be maintained between the amounts of copper and titanium contained therein. Preferably, the sum of the weight percents of titanium and copper should be less than about 0.50, and the ratio of weights copper to titanium should be between about 1.5 and 2.5. Additional elements may be present as normal impurities, including zinc (Zn) , zirconium (Zr) , nickel (Ni) , vanadium (V) , and chromium (Cr) . Each of these impurity elements should be present in an amount of about 0.05 by weight percent or less, and the total of impurities should preferably be kept at about 0.15 weight percent or less. The impurities found in the alloy composition of the present invention typically include the following elements in the following percents by weight:

Zn 0.015

Zr 0.001

Ni 0.005 V 0.005

Cr 0.02

Mg < 0.005

The balance of the composition is aluminum to make up a total of 100%. The alloy of the present invention is particularly useful in the manufacture of tubing for use in brazed serpentine condensers found in automobile air conditioners, where exposure to rain, snow and road salt tend to corrode the tubing. Condenser tubing made of the alloy of the present invention tends to resist corrosion better than available alloys in an industry standard test (ASTM Test G85-A3, issued January 3, 1985). Because of its superior corrosion resisting properties, tubing made from the alloy of the present invention may also be used in other environments where the tubing serves as a conduit for corrosive fluids or where the tubing may be employed in a corrosive environment. Examples include automobile radiators, as well as in commercial and residential air conditioning equipment. The alloy is preferably fabricated according to conventional techniques, that is, by stirring the additional metallic ingredients into the molten aluminum until the mixture is homogenous. The use of TiB₂ grain refiner helps improve the properties of the resulting alloy. While TiB₂ is the grain refiner preferred for use in fabricating the alloys of the present invention, other grain refiners such as zirconium can be used, although the titanium content of the alloy may interfere with the action of zirconium as a grain refiner.

After casting the alloy, the material should preferably be subjected to heat treatment. Depending upon desired properties and end use, the type of heat treatment may be chosen from a wide range of temperatures (400 to 625°C) for up to several hours. To obtain a homogenized alloy, the heat treatment should preferably be at about 600 to 625°C for approximately two to six hours, preferably four hours. The alloy can then be extruded at a temperature of about 490° to 510°C, although the tube can also be extruded at 450° to 480°C. A lower temperature heat treatment (400 to 425°C) gives a nonhomogenized alloy, but improved corrosion resistance can still be noticed. Of course, the higher the temperature of the extrusion, the more expensive is the operation due in part to faster extrusion die wear. However, gains in corrosion resistance may offset any such production cost increases for some applications. Once the tube is extruded, it can be assembled into serpentine condensers using the NOCOLOK™ process (Alcan International Ltd.) having AA 4343/3003/4343 fins brazed thereto. The fins have a high silicon content to facilitate brazing. The tube is significantly cathodic fins and this has an extended life partially due to cathodic protection. The low manganese content increases extrudability of the alloy.

The following examples are presented for the purposes of illustration only, and are not to be construed as limiting the scope of invention in any manner.

EXAMPLE I Two samples of alloys of the present invention having the compositions listed in Table 1 were laboratory cast as solid cylinder ingots and homogenized at 490° to 510°C for four hours, along with ingots having a composition as disclosed in U.S. Patent No. 4,649,087 (Ingot C) . TABLE 1

EXAMPLE II

The ingots were extruded at 490° to 510°C on a 2200 ton Youngstown press having a 104 cm diameter ram into cylindrical billets 18 cm in diameter and from 38 to 76 cm in length. The formability and productivity of the alloys made in Example I above were compared to an alloy made in accordance with the disclosure in U.S. Patent No. 4,649,087. The parameters measured included the temperature to which the billet must be heated to make it extrude satisfactorily, and the breakthrough pressure, the pressure at which the alloy begins to extrude. Also measured was the extrusion exit speed of the alloy, the rate at which the extruded product leaves the extruding die (a measure of alloy productivity) . The results for Ingots A and B of Example I and billets of the alloy of USP 4,649,087 in both homogenized and non-homogenized form are shown in Table 2 below: TABLE 2 COMPARISON OF FORMABILITY/EXTRUDABILITY CHARACTERISTICS

TABLE 2 COMPARISON OF FORMABILITY/EXTRUDABILITY CHARACTERISTICS

EXAMPLE III Tubing having the composition of alloys A and B (see Table 1 above) , as well as a sample of A3102 and MR 162 tubing and tubing made in accordance with U.S. Patent No. 4,649,087 were fashioned into serpentine condensers with AA4343/3003/4343 fins with no coating of zinc on either clad or core and brazed using the NOCOLO ™ process. The condensers under pressurization were subjected to an industry standard test designated ASTM G85-A3 to measure their corrosion resistance. ASTM G85 A3, issued January 3, 1985, is a cyclic, acidified synthetic sea salt fog test. The two hour cycles consist of 1/2 hour exposure to acidified salt fog at a temperature of 49°C, followed by 1 1/2 hour exposure at this same temperature with the fog off. Salt content of the fog is 42 g/L of synthetic sea salt; acid content is sufficient acetic acid to give a pH of 2.8-3.0 to the salt solution. In the test, the condenser is pressurized to 3.5 kg/cm² during the 1 1/2 hour "salt off" part of the cycle. The pressure is released during the fog exposure, and at the end of this time is reintroduced abruptly by opening a solenoid valve to impart a pressure shock wave to the condenser to dislodge any erosion products which may be blocking the perforations in the condenser. When the test is completed the number of days until failure as well as the number of leaks are noted. The results, shown below in Table 3, state the number of days of exposure until failure and the number of leaks that have developed for the condensers tested.

TABLE 3

COMPARISON OF CORROSION TESTING RESULTS

ON ASSEMBLED SERPENTINE CONDENSERS

ACCORDING TO ASTM G85-A3

Claims

Claims :

1. An aluminum alloy material consisting essentially of, by weight percent, 0.02% to 0.12% silicon, 0.07% to 0.27% iron, 0.05% to 0.45% copper, 0.06% to 0.26% manganese, and 0.05% to 0.25% titanium, with the balance being aluminum with normal impurities.

2. An alloy in accordance with claim l, wherein the sum of the amounts of copper and titanium, by weight percent, is less than about 0.50.

3. An alloy in accordance with claim 2, wherein the ratio of the weight percent of copper to the weight percent of titanium is between about 1.5 and about 2.5.

4. An aluminum alloy material consisting essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.13% to 0.19% manganese, and 0.11% to 0.15% titanium with the balance being aluminum with normal impurities.

5. An aluminum alloy material consisting essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.05% to 0.11% manganese, 0.11% to 0.15% titanium, with the balance being aluminum with normal impurities.

6. An alloy in accordance with claim 4 or 5, wherein the sum of the amounts of copper and titanium, by weight percent, is less than about 0.50.

7. An alloy in accordance with claim 4 or 5, wherein the ratio of the weight percent of copper to the weight percent of titanium is between about 1.5 and about 2.5.

8. An alloy in accordance with claim 1, 4 or 5 in the form of an extruded article.

9. A process for producing an aluminum alloy ingot, comprising: casting an ingot from an aluminum alloy material consisting essentially of, by weight percent, 0.02% to 0.12% silicon, 0.07% to 0.27% iron, 0.05% to 0.45% copper, 0.06% to 0.26% manganese, and 0.05% to 0.25% titanium, with the balance being aluminum with normal impurities; and heat treating said ingot at a temperature of between about 400°C and about 625°C for at least 2 hours.

10. A process in accordance with claim 9 wherein the aluminum alloy material consists essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.13% to 0.19% manganese, and 0.11% to 0.15% titanium with the balance being aluminum with normal impurities.

11. A process in accordance with claim 9 wherein the aluminum alloy material consists essentially of, by weight percent, 0.04% to 0.07% silicon, 0.14% to 0.17% iron, 0.22% to 0.28% copper, 0.05% to 0.11% manganese, 0.11% to 0.15% titanium, with the balance being aluminum with normal impurities.