MXPA01000608A - High conductivity aluminum fin alloy - Google Patents

Abstract

An improved aluminum alloy fin stock is described having both a high strength and a high thermal conductivity. The fin stock contains 1.2 - 1.8%Fe, 0.7 - 0.95%Si, 0.3 - 0.5%Mn, and the balance Al, and is produced by continuously strip casting the alloy at a cooling rate greater than 10°C/sec., cold rolling the re-roll sheet to an intermediate gauge, annealing the sheet and cold rolling the sheet to final gauge. This fin stock has a conductivity after brazing of greater than 49.0%IACS.

Description

HIGH CONDUCTIVITY ALUMINUM ALLOY FOR FINS Technical Field This invention relates to an improved product of aluminum alloys for making heat exchange fins, and more particularly to a fin material having high strength and high thermal conductivity. BACKGROUND ART Aluminum alloys have been used in the production of heat exchange fins, for example, automotive radiators, condensers, evaporators, etc. The fins alloys in traditional radiators are designed to give high strength after strong strong welding, good weldability and good resistance to collapse during strong strong welding. The alloys used for this purpose generally contain a high level of manganese. An example is the AA3003 aluminum alloy. Such alloys provide a good strong strong welding performance. However, the thermal conductivity is relatively low. This low thermal conductivity was not a serious problem in the past because the main thermal wall in automotive heat exchange performance was the transfer of heat with fins to the air. Recently, there has been a demand for radiators that have an increased heat transfer efficiency. This new generation of radiators requires a new material for fins that has a high resistance as well as a high thermal conductivity. The new fin material properties demanded by the automotive industry for heat exchangers includes a high ultimate strength (UTS) after strong strong welding, a high strong strong welding temperature and a high conductivity for fin material having a thickness of no more than about 0.1 mm. Morris et al., U.S. Patent No. 3,989,548 discloses an aluminum alloy containing Fe, Si, Mn and Zn. These alloys are preferably high in Mn which should result in adequate strength but poor conductivity. Alloys are not described as useful material for fins. In Morris et al., British Patent 1,524,355, products of Al-Fe-type dispersion-reinforced aluminum alloy which commonly contains Fe, Si, Mn and Cu are described. Cu is present in amounts of up to 0.3 percent and this has a negative effect on conductivity and causes pitting by corrosion, which are particularly detrimental to the performance of very fine fins. An alloy that is said to be useful for material for Heat exchange fins are described in Morris et al., U.S. Patent No. 4,126,487. This aluminum alloy contains Fe, Si, Mn and Zn. Preferably it also contains some additional resistance for Cu and Mg. As with GB 1,524,355, Cu can be present in amounts up to 0.3 percent, which could impair the performance of very thin fins. It is an object of the present invention to produce a new fin material of aluminum alloy having high strength and high thermal conductivity. Description of the invention The present invention relates to a new material for fins that is suitable for manufacturing welded heat exchangers using fins that are thinner than the previous possible ones. This is achieved by retaining adequate strength and conductivity in the fins to allow their use in heat exchangers. The above combination of features has surprisingly been obtained according to the present invention by the balance of three somewhat contradictory properties in the material, namely, strength (UTS) after strong strong welding, electrical / thermal conductivity after strong welding strength and strong strong welding temperature (the melting point of the fin material during an operation of strong welding). A problem in the development of this type of alloy is to find the conductivity requirements. So, if the conductivity is improved by the modification of a traditional alloy composition, for example, by reducing the Mn content of the AA3003 alloy, then the strength of the alloy becomes too low. It was found that the desired balance of the characteristics could be obtained starting with a material in which there was a certain amount of reinforcement based on particles, which normally do not have a negative effect on the conductivity. Then the elements were added to contribute to the reinforcement in the solution of a careful way of selection to increase the resistance without lowering the conductivity or melting temperature to a degree that should make the material unusable. A microstructure was developed that provides an optimal combination of particle hardening and reinforcement in a solids solution by introducing a high volume fraction of fine intermetallic particles evenly distributed. In order to increase the effect of the reinforcement of the particles and in solution to a given composition, so that the desired properties were achieved, a high cooling rate was required in the process of strips, but not so high as to retain excess conductivity by destroying solids solution elements in the final fin element (ie, after emptying, laminating and welding). The aluminum alloy of the invention has the composition (all the percentages are in that): The Zn when present is preferably present at less than 1.5% by weight and more preferably at less than 1.2% by weight. The strip product formed of this alloy according to the present invention has a strength (UTS) after strong welding greater than about 127 MPa, preferably greater than about 130 MPa, a conductivity after strong welding greater than 49.0% IACS, more preferably greater than 49.8% IACS, more preferably greater than 50.0% IACS and a strong soldering temperature greater than 595 ° C, preferably greater than 600 ° C. These properties of the strips are measured under strong welding conditions simulated as follows. The UTS after strong welding is measured according to the following procedure that simulates strong welding conditions. The raw material processed for the fins at the end as laminated thickness (for example, after rolling to 0.06 mm thick) is placed in a preheated oven at 570 ° C then heated to 600 ° C in approximately 12 minutes, maintained (soaked) at 600 ° C for three minutes, cooled to 400 ° C at 50 ° C / min. then air cooled to room temperature. Then the ductility test is performed on this material. The conductivity after strong welding is measured as electrical conductivity on a sample processed as for the UTS test that simulates the conditions of strong welding, using conductivity tests that are described in JIS-H0505. Brief Description of the Drawing The attached Figure 1 is an elevation view of a configuration test for determining the strong welding temperature of the fin material. The strong welding temperature is determined in a test configuration which is shown in Figure 1 in which a corrugated fin 1 is created from the processed material 2.3 mm high x 21 mm wide, with a distance of 3.4 mm. The sample is placed against a strip of material tube 2 consisting of a layer 3 of alloy AA4045 placed on a piece 4 of alloy AA3003, where strip 2 is 0.25 mm thick and layer 3 AA4045 is 8% of the total thickness . A flow of Nocolok ™ is sprayed on the assembled test at a rate of 5 to 7 gm2. An additional set of 3"template" assembled 5 is placed on top of the assembled test, with a final sheet and a weight 6 of 98 grams on top. The assembled test is heated to selected final test temperatures (eg, 595 ° C, 600 ° C or 605 ° C) at 50 ° C / min., Then held at that temperature for three minutes. The material has a strong welding temperature of "x" when none of the corrugations of the test fin melt during the test procedure at a higher final temperature of "x". For example, if none of the corrugations of the test fin melt at a final temperature of 600 ° C, but some or all of them melt at a final temperature of 605 ° C, then the strong welding temperature is taken at 600 ° C. C. To find the above characteristics, the alloy must be melted and formed under quite specific conditions. First, the alloy must be melted continuously in strips at an average cooling speed greater than 10 ° C / sec. It is preferable that the average cooling rate is less than 250 ° C / sec, more preferably less than 200 ° C / sec. The melt is preferably made in a melt cavity that does not deform the plate formed during solidification. This plate preferably has a thickness of less than 30 mm. The molten plate is cold rolled to an intermediate gauge, after tempered rolled to a final gauge. The cold rolling to a final gauge after the tempering step is preferably less than 60% reduction, more preferably less than 50% reduction. The plate can, if necessary, be hot rolled to a re-rolled or re-corrugated gauge (1 to 5 mm in thickness), but such hot rolling should be done without previous homogenization. The average cooling rate means that the average cooling speed through the thickness of the molten plate, and the cooling rate is determined from the average separation of the interdendritic cells taken through the thickness of the molten plate as for example, in an article by RE Spear, et al., in the Transactions of the Amercian Foundrymen's Society, Proceedings of the Sixty-Seventh Annual Meeting, 1963, Vol. 71, published by the American Foundrymen's Society, Des Plaines, Illinois. , USA, 1964, pages 209 to 215. The average size of the interdendritic cells corresponding to the preferred average cooling speed is in the range of 7 to 15 microns. BEST MODE FOR CARRYING OUT THE INVENTION In accordance with this invention, the amounts of the individual elements in the alloy must be controlled fairly carefully. The iron in the alloy forms intermetallic particles of a eutectic composition during melting that are relatively small and contribute to the reinforcement of the particles. With iron contents below 1.2%, there is insufficient iron to form the desired number of reinforcing particles, while with iron content above 1.8% a large phase of primary intermetallic particles are formed which prevent lamination to the desired sizes for very thin fin material. The silicon in the alloy in the range of 0.7 to 0.95% contributes to both, reinforcement by particles and solids solution. Below 0.7% there is insufficient silicon for this strengthening purpose while above 0.95%, the conductivity is reduced. More significantly, at high silicon contents the melting temperature of the alloy is reduced to the point at which the material can not be welded. To provide optimum reinforcement, silicon in excess of 0.8% is particularly preferred. - When manganese is present in the range of 0.3 to 0.5%, it contributes significantly to the reinforcement of the solids solution and some measure to the reinforcement by particles of the material. Below 0.3% the amount of manganese is insufficient for the purpose. Above 0.5% the presence of manganese in solids solution becomes strongly detrimental to conductivity. The balance of iron, silicon and manganese contributes to the achievement of the desired strength, the execution of strong welding and conductivity in the finished material. The zinc content, which remains between 0.3 and 2%, preferably less than 1.5% and more preferably less than 1.2%, provided for corrosion protection of a heat exchanger by making the sacrificial fins reducing the corrosion potential of the alloy. Zinc does not have a significant positive or negative effect on strength or conductivity. A zinc content below 0.3% is insufficient for corrosion protection, while no benefit is achieved by increasing zinc to contents above 2.0%. Titanium, when present in the alloy as TiB2, acts as a refiner of the grain during melting. When present in amounts greater than 0.02%, it tends to have a negative impact on conductivity.

Any incidental element in the alloy should be less than 0.05% each and less than 0.15% in aggregate. In particular, the magnesium must be present in amounts of less than 0.10%, preferably less than 0.05%, to ensure weldability by the Nocolok process. Copper should be kept below 0.05% because it has a manganese-like effect on conductivity and also causes pitting by corrosion. In the melting process, if the average cooling speed is less than 10 ° C / sec, the intermetallic particles formed during melting will be too large and will cause rolling problems. A lower cooling rate will generally include DC casting and homogenization and under such circumstances, the elements leave the supersaturated matrix alloy and the mechanism of solution reinforcement is reduced, resulting in an inadequate resistance material. This means that a continuous strip melting process should be used. A variety to such process exists, including laminated casting, cast tape and casting block. For laminated casting, the average cooling speed should not exceed approximately 1,500 ° C / sec. The melt of tapes and blocks operate at lower maximum cooling rates than less than 250 ° C / sec, more preferably less than 200 ° C / sec.

The continuous melt process creates a larger number of fine intermetallic particles (less than 1 micrometer in size), and therefore a strip produced by the process of this invention will have, in the final melt and laminated strips, a population of intermetallic particles equal to or smaller than 1 miera equal to or greater than 3 x 104 particle over mm3. It is also preferable that the alloy be a molten strip in a manner that prevents deformation of the material while still in the "soft" state. If the deformation occurs during solidification, it can result in excessive segregation of the center line and problems when laminated to form very thin fin material required for modern applications. It is also preferred that the melt cavity be elongated since the high Si content in the present alloy results in a large freezing range which preferably requires an elongated melt cavity to properly solidify. This means, in effect, that the strip cast by the tape or block melters is preferred where the cooling rate is preferably less than 250 ° C / sec, and more preferably less than 200 ° C / sec. According to the preferred feature characteristic of the invention, the fin material is produced by the continuous cast alloy strips to form a plate 6 to 30 mm thick at a cooling rate of 10 ° C / sec or greater, but less than 200 ° C / sec, then hot rolling as the pouring plate at 1-5 mm sheet thickness , cold rolled to 0.08-0.20 mm thick sheet, tempering at 340-450 ° C for 1-6 hours, and cold rolled to a final gauge (0.05-0.10 mm). It is preferable that the pouring plate enters the hot rolling process at a temperature between about 400-550 ° C. The step of hot rolling helps in the thermomechanical process, contributing to the precipitation of manganese from the solids solution which then contributes to the achievement of the desired conductivity in the final product. It is particularly preferred that the melt plate be 11 mm or larger in thickness. The final cold rolling should preferably be done using less than 60% reduction and more preferably less than 50% reduction. The amount of cold rolling in the final rolling step is adjusted to give an optimum grain size after strong welding, ie, a grain size of 30 to 80 μm, preferably 40 to 80 μm. If the reduction of the cold rolling is too high, the UTS after the strong welding becomes high, but the grain size becomes too small and the strong welding temperature becomes low. Otherwise, if the cold reduction is too low, then the strong welding temperature is high but UTS after strong welding is too low. The preferred method of continuous die casting is strip casting. Example 1 Two alloys A and B having the compositions given in Table 1 were melted in a belt melter at an average cooling rate of 40 ° C / sec. to a thickness of 16 mm, and were then hot-rolled to a thickness of 1 mm, rolled and allowed to cool. The re-rolled sheet was then cold-rolled to a thickness of either 0.10 mm (A) or 0.109 mm (B), tempered in a tempering furnace in batches at 390 ° C for 1 hour, then cold-rolling a final thickness of 0.060 mm (reducing the final cold rolling of 40% for A and 45% for B). The strong welding temperature and UTS conductivity were determined by the methods described above, and the result is shown in Table 2. Both alloys processed by continuous strip melting meet the specifications for the final sheet. The density of intermetallic particles was determined by alloy B by taking SEM images of 12 sections of the longitudinal and transverse section of the cold rolled sheet of 0.060 mm and using image analysis, counting the number of particles less than 1 micrometer in size. The number of particles less than 1 micrometer in size was found to be 5.3 x loVmm2.

Example 2 An alloy C having a composition given in Table 1 was cast DC to an ingot (508 mm x 1080 mm x 2300 mm), homogenized at 480 ° C and hot rolled to form a re-rolled sheet having a thickness of 6. mm, then rolled and allowed to cool. The sheet was then cold rolled at 0.100 mm, tempered at 390 ° C for 1 hour, then cold rolled to a final thickness of 0.60 mm (a 40% reduction on the final cold roll). The properties of this sheet are given in Table 2. Although the composition and practice of lamination falls within the requirements of the present invention, the UTS was lower than that required and the strong welding temperature was less than 595 ° C, both with a consequence of melting at low cooling speeds of the DC melt followed by homogenization before hot rolling. The density of intermetallic particles was determined in the same way as for alloy B and was found to be only 2.7 x loVmm2. EXAMPLE 3 The alloys D and E have their composition provided in Table 1 were processed as in Example 1 with an initial cold rolled thickness of 0.1 mm and a final cold rolled reduced to 40%. The UTS values in Table 2 show that the low content of Mn and Si in these Alloys produce material with inadequate resistance. Example 4 Alloy F has a composition provided in Table 1 (with Fe and Si close to the average range of the preferred composition and Mn slightly above the preferred composition) was processed as in Example 1 with reduced final cold rolling 50% to a thickness of 0.06 mm. The conductivity that is provided in Table 2 was lower than the preferred value of 49.8% IACS indicating the negative effect of the still slightly elevated Mn on the properties. Example 5 The alloy G having a composition provided in Table 1 was processed as in Example 1 with a reduced final cold rolling of 40% at a thickness of 0.06 mm. The strong welding temperature as illustrated in Table 2 was not acceptable in view of the fact that Si was very high. Example 6 Alloy A having a composition provided in Table 1 was processed as in Example 1 except that the alloy was melted in a ribbon melter at an average cooling rate of 100 ° C / sec. UTS, conductivity and strong welding temperatures all fall within the acceptable ranges but the highest average Cooling rate (but still within the range of the invention) tends to result in a slightly higher strength and conductivity.

Table 1 The balance of the alloy composition is aluminum and incidental impurities.

Table 2 The UTS and conductivity determined on the samples processed as described above.

Claims (24)

1. A method of producing aluminum alloy fin material from an alloy containing 1.2-1.8% Fe, 0.7-0.95% Si, 0.3-0.5% Mn, and the Al balance, consisting of continuous strip casting alloy to a cooling speed greater than 10 ° C / sec., the cold rolling of the strip to an intermediate gauge, tempering the sheet and cold rolling the sheet to a final gauge.

2. The method according to claim 1 wherein the alloy further contains 0.3 to 2.0% Zn.

3. The method according to claim 2 wherein the alloy contains 0.3 to 1.5% Zn.

4. The method according to any of claims 1-3 wherein the alloy contains in addition to

0. 005 to 0.02% Ti.

5. The method according to any of claims 1-4 wherein the cooling rate is less than 250 ° C / sec.

The method according to any of claims 1-5 wherein the molten strip is hot rolled, without prior homogenization, for a re-laminated strip before cold rolling.

7. The method according to claim 1 wherein the alloy contains in addition to 0.3 to 1.2% Zn, the speed of cooled is less than 200 ° C / sec., and the molten strip is hot rolled, without previous homogenization, to a re-laminated strip before cold rolling.

8. The method according to any of claims 1-7 wherein the plate is cast to a thickness of no more than about 30 mm.

9. The method according to claim 8 wherein the plate is cast to a thickness of about 6-30 mm.

10. The method according to claim 9 wherein a molten plate as such is hot rolled, without prior homogenization, to form a sheet with a thickness of 1-5 mm.

The method according to claim 10 wherein the hot rolled sheet is tempered at 340-450 ° C for 1-6 hours.

The method according to any of claims 1-11 wherein the tempered sheet is cold rolled to a final strip gauge of less than 0.10 mm.

The method according to any of claims 1-11 wherein the tempered sheet is cold rolled to a final strip using a reduction of less than 60%.

14. The method according to any of claims 1-13 wherein the melting of the strip is performed using a tape or block melter.

15. The method according to claim 14 wherein the The strip product obtained has a final ductile strength after strong welding greater than about 127 MPa, a conductivity after strong welding greater than 49.0% IACS and a strong welding temperature greater than 595 ° C.

16. An aluminum alloy fin material having a composition: Fe 1.20 - 1.80% Si 0.70 - 0.95% Mn 0.30 - 0.50% On balance the aforementioned strip has a conductivity after strong welding greater than 49.0% IACS.

17. The aluminum alloy fin material according to claim 16 having a conductivity after strong welding greater than 49.8% IACS.

18. The aluminum alloy fin material according to claim 17 which also contains 0.3 to 2.0% Zn.

19. The aluminum alloy fin material according to claim 18 containing 0.3 to 1.5% Zn.

20. The aluminum alloy fin material according to any of claims 16-19 which also contains 0.005 to 0.02% Ti.

21. The aluminum alloy fin material according to claim 16 which also contains 0.3 to 1.2% Zn and has a conductivity after strong welding greater than 49.8% IACS.

22. The aluminum alloy fin material according to any of claims 16-21 having a final ductile strength after strong welding greater than about 127 MPa and a strong welding temperature greater than 595 ° C.

23. The aluminum alloy fin material according to claim 22 having a thickness less than 0.10 mm.

24. The aluminum alloy fin material according to claim 23 obtained by continuously casting the alloy strips at a rate of cooling greater than 10 ° C / sec. but less than 200 ° C / sec., the hot rolled strip to a re-laminated sheet without homogenization, cold rolling the re-laminated sheet to an intermediate gauge, tempering the sheet and cold-rolling the sheet to a final gauge .