Patent Application
20110076184
This application claims the benefit of Chinese Patent Application No. 200910177463.4, filed Sep. 29, 2009, which is incorporated herein by reference in its entirety.
The present invention relates to a novel corrosion resistant aluminum alloy and articles thereof, particularly to an AA3000 series aluminum alloy and articles thereof.
1XXX series pure aluminum exhibits excellent formability and weld properties. Its corrosion resistance is the best among aluminum alloys, but its strength is relative low. 3XXX series aluminum alloy are manufactured by adding Mn in aluminum to form a solid solution so as to strengthen aluminum alloy, enhance the strength of aluminum alloy, maintain good corrosion resistance, electrical conductivity, thermal conductivity, and have excellent welding property and plastic processing property. 3XXX series aluminum alloys have been widely used in automobiles, refrigerating equipments, chemical industry and so on for manufacturing radiating pipes and radiating fins of heat exchangers.
In the past 15 years, standard 3003 aluminum alloy was used generally. This alloy has good formability and mechanical properties, and acceptable corrosion resistance. Recently, with the continuous improvement of aluminum heat exchangers in structure design, the thickness of brazed aluminum alloy pipes has been reduced gradually from 1 mm to not more than 0.4 mm. Studies have shown that the corrosion behavior of aluminum alloys for heat exchangers mainly includes two mechanism, that is pitting corrosion and grain boundary corrosion. If the phases in the alloy are closer to aluminum matrix in electrical potential, their number is less, and their distribution is more uniform, then the corrosion resistance property of the alloy is better. With the improvement of the structure of refrigerating components, the materials of aluminum alloy pipes for heat exchangers have been developed from 1XXX pure aluminum (e.g. 1050, 1060, 1100, 1235) to 3XXX series aluminum alloys (e.g. 3003, 3005, 3102, 3104 and so on), and the thickness of the wall of the pipes has been reduced gradually from 1 mm to not more than 0.4 mm; the outer surface of the pipe was coated by using multiple coating technologies to enhance the corrosion resistance properties of the pipes.
In order to solve the problems that the strength and the corrosion resistance of alloys should be correspondingly improved due to the reduction of the wall thickness of the pipes, 3026 aluminum alloy has been developed in the prior art. This alloy was manufactured by optimizing the composition of the alloy based on corrosion resistance and processability. The optimization includes: exactly adjusting the amounts of each alloying element, such as, reducing the amounts of Mn and Fe in the alloy and simultaneously adding Cu, Zn, Ti and adjusting the amounts thereof, to make the electrical potential of the phases in the alloy close to that of aluminum matrix so as to enhance the corrosion resistance of the alloy and ensure that the alloy has certain mechanical properties, processabilities and excellent welding properties. However, it has been found in practical use that the alloy exhibits disadvantageous deep processing properties due to poor mechanical properties, as compared to 3003 alloy.
Studies have shown that addition of small amounts of Cr, Mn, Zr, Ti, Si, etc. into aluminum can reduce the pitting corrosion of alloys, while decreasing and controlling Fe, Cu, Ni and so on can effectively enhance the corrosion resistance of alloys, and appropriately increasing the amounts of special alloying elements to form a greater amount of reinforcing phases so as to prevent the coarsening of grains in hot working and heat treatment thereby refining microstructure. 3XXX series alloys with Cr and Zr added therein may cause the formation of dispersed phases such as Al(MnFeCr)Si or Al(FeMnCr)Si and Al3Zr, etc. during homogenization. As the amount of the dispersed phases is increased, the recrystallization temperature of alloys is elevated. Very high density and thermal stability of these dispersed phases will seriously affect the recovery, recrystallization and growth of grains during the solution heating of alloys, even can act as nucleation site for the precipitation of reinforcing phases. It has been proved that dispersed phases can promote homogeneous sliding, enhance the strength, plasticity and bending properties of aluminum alloys, and prevent the growth of recrystallized grains by pinning the migration of grain boundaries, and the effective action of the refining of grains thereof increase in the order of Cr, Mn, Zr. Fine grain structures benefit the enhancement of mechanical properties and corrosion resistance properties of alloys, however, excessive Cr will render the degradation of processability of alloys. Ti is an effective grain refiner. Studies have shown that in addition to serving as a heterogeneous nucleus to promote the nucleation, it is also distributed in grain boundary to inhibit the growth of α(Al) grains so as to effectively refine structure and improve formability.
In summary, there are still demands of aluminum alloys having excellent mechanical strength and corrosion resistance in this art.
The present invention uses following technical solutions: on the basis of Al—Mn alloy, reducing the amounts of Fe, Cu and Zn in the alloy, adjusting the amounts of Si and Mn in the alloy, and adding Cr, Zr and Ti to the alloy in combination. At the meantime, the production process should guarantee that the products achieve stable fine grain fiber structure, the alloying elements in the grain are sufficiently solutionized and disadvantageous precipitation phases do not occur in grain boundary, and the products have higher corrosion resistance and good mechanical properties or formability.
In one aspect, the present invention provides a novel aluminum alloy which satisfies the demands mentioned above. In order to solve the problem that the strength and corrosion resistance of alloy should be enhanced correspondingly brought by the reduction of the thickness of the wall of cooling pipe materials, the present invention achieves high corrosion resistance and good mechanical properties and technological properties by reducing the amounts of Fe, Cu and Zn, adjusting the amounts of Si and Mn, and adding Cr, Zr, Ti, etc. in combination on the basis of the composition of Al—Mn series alloys.
The alloy of the present invention consists essentially of (by weight %): 0.30-1.25% Mn, 0.10-1.20% Si, 0.05-0.25% Cr, 0.05-0.20% Zr, 0.08-0.30% Ti, less than 0.03% Zn, less than 0.03% Cu, and up to 0.20% Fe, balance aluminum and inevitable impurities.
In the embodiments of the present invention, the Mn content in the alloy of the present invention is preferably 0.50-1.00%, and more preferably 0.70-0.90%.
In the embodiments of the present invention, the Si content in the alloy of the present invention is preferably 0.20-0.80%, and more preferably 0.30-0.60%.
In the embodiments of the present invention, the Cr content in the alloy of the present invention is preferably 0.06-0.18%, and more preferably 0.08-0.12%.
In the embodiments of the present invention, the Zr content in the alloy of the present invention is preferably 0.08-0.20%, and more preferably 0.10-0.15%.
In the embodiments of the present invention, the Ti content in the alloy of the present invention is preferably 0.10-0.25%, and more preferably 0.12-0.20%.
In the embodiments of the present invention, the Fe content in the alloy of the present invention is preferably up to 0.15%, and more preferably up to 0.10%.
The aluminum alloys of the present invention are adapted to be made into various forms of articles, including but being not limited to the articles in the form of pipes, wires, strips, plates, sheets or rods. Preferably, the inventive aluminum alloys are particularly suitable for using as materials for heat exchangers.
The present invention will be described in detail with reference to following drawings.
In the context of the present invention, as to the composition of the aluminum alloys, all the percents mentioned mean weight percent (wt %) unless indicated otherwise. Besides, the nomenclature of the aluminum or aluminum alloys referred to in the present invention means the nomenclature of Aluminum Association (AA).
Additionally, when any numerical value range is referred to, it should be understood that this range includes each number and/or subrange between the minimum and maximum in said range. For example, the range of 0.30-1.25% Mn should include all intermediate values, e.g. 0.31%, 0.32%, 0.33%, . . . 1.23%, 1.24% and 1.25% Mn. This is also suitable for the ranges of all other elements mentioned below.
Present invention obtained an aluminum alloy with excellent corrosion resistance and good mechanical performance by decreasing the contents of Fe, Cu and Zn, adjusting the contents of Si and Mn, and adding Cr, Zr and Ti, etc. in combination on the basis of the composition of Al—Mn series alloy. The basic composition of the inventive alloy is (by weight %): 0.30-1.25% Mn, 0.10-1.20% Si, 0.05-0.25% Cr, 0.05-0.20% Zr, 0.08-0.30% Ti, less than 0.03% Zn, less than 0.03% Cu, and up to 0.20% Fe, balance aluminum and inevitable impurities.
Mn can prevent the recrystallization of aluminum and its alloys, elevate recrystallization temperature, and can refine the grains of recrystallization significantly. At the meantime, Mn can enhance the strength of the alloys, but excessive Mn may form coarse compounds and damage the properties of materials. Hence, Mn content should be 0.30-1.25%, preferably 0.5-1.00%, and more preferably 0.70-0.90%.
Si can reduce the solubility of Mn in aluminum, accelerate the precipitation of Mn from supersaturated solid solution during thermal deformation, and improve the mechanical properties of alloys. Therefore, Si content is required to be between 0.10% and 1.20%, preferably between 0.20% and 0.80%, and more preferably between 0.30% and 0.60%.
Cr is an alloying element commonly used in aluminum alloys. It can hinder the nucleation and the growth of recrystallized grains, refine the recrystallized grains, strengthen the alloys, and simultaneously improve the toughness of the alloys and reduce stress corrosion cracking sensitivity, but increase the quenching sensitivity. Additionally, the addition of Cr in the aluminum alloys is generally not greater than 0.35%. Hence, Cr content should be 0.05-0.25%, preferably 0.06-0.18%, and more preferably 0.08-0.12%.
Ti can refine cast structure and weld structure remarkably, reduce cracking tendency, and enhance the mechanical properties of materials. Hence, Ti content should be 0.08-0.30%, preferably 0.10-0.25%, and more preferably 0.12-0.20%.
Zr can also refine cast microstructure, exhibit less quenching sensitivity than Cr and Mn, but decrease the grain refinement effect of Ti. Thus, a small amount of Zr is used to substitute Cr and Mn for refining recrystallized microstructure and reducing the quenching sensitivity of the alloys. Therefore, Zr content is required to be 0.05-0.20%, and preferably 0.10-0.15%.
Zn has no significant affect on the mechanical properties and corrosion resistance of the alloys, but exhibits disadvantages to the weldability of the alloys. In order to enhance the weldability of materials, Zn content should be less than 0.03%.
Cu can enhance the tensile strength of the alloys significantly, however, a small amount of Cu will decrease the corrosion resistance of the alloys. Thus, Cu content should be not greater than 0.03%.
Fe can effectively refine the annealed grains, but excessive Fe may form a great deal of coarse platlet intermediate phase compounds, and decrease the corrosion resistance of the alloys remarkably. Hence, Fe content is required to be up to 0.2%.
The aluminum alloys according to the present invention have excellent corrosion resistance and mechanical strength, are suitable for making the articles in various forms of pipes, wires, strips, plates, sheets or rods. Particularly, the inventive alloys are suitable for using as materials for heat exchangers.
The present invention is further described by following examples. It should be indicated that following examples are only used to illustrate the present invention, but not intended to limit the present invention in any way.
According to the alloy composition of present invention, 99.7Al ingot and Al-10Mn, Al-12Si, Al—SCr, Al-10Zr, Al-10Ti intermediate alloys were used to make an alloy according to the weight % described as follows: Al-1.2Mn-0.2Si-0.15Cr-0.15Zr-0.15Ti, which was named as alloy A-1 (the composition of the alloy is shown in Table 1). The alloy was smelt and refined in a graphite crucible furnace, and then cast in an iron mould at a temperature of 700-730° C. to form an ingot. The ingot was subjected to homogenization at 600° C./20 h, water quenched, machined into bars of φ80 mm, and then extruded into rods of φ10 mm on 800T extruder, wherein the heating temperature of the ingot was 480° C., the outlet temperature was about 520° C., the ingot was directly cooled with water. The rods were extruded into pipes of Φ8×0.4 mm on LJ300 type CONFORM continuous extruder, the outlet temperature was about 450° C., and then the rods were directly cooled with water.
The properties of the pipes made of the alloy A-1 were tested, wherein the melting point was determined by DSC (Differential Scanning calorimetric), the tensile property was determined in accordance with ISO 6892: 1998 (Room Temperature Tensile Test of Metal Materials), the SWAAT corrosion resistance test was conducted in accordance with ASTM/G85-1998 A3 of “Modified Salt Mist Test Method” (sea water acidification recirculation test), bulging was performed in accordance with EN ISO 8493 (bulging test method of metal material pipes), bending test was conducted in accordance with ISO 8491-1998 (bending test of metal material pipes (total cross section)), welding test was conducted by welding 3003/4045 composite soldered aluminum alloy plates and new alloy pipes. Detailed test results were shown in Table 2.
Additionally, the subsequent bending processed surface of the pipes did not have tangerine hull thereon, and the pipes and 3003/4045 complex soldered aluminium alloy plates exhibit excellent soldering properties.
According to the alloy composition of the present invention, 99.7Al ingot and Si solvent, Al-10Mn, Al—SCr, Al-10Zr, Al-10Ti intermediate alloys were used to make an alloy according to the weight percent described as follows: Al-0.9Mn-0.4Si-0.12Cr-0.15Zr-0.20Ti, which was named as alloy A-2 (the concrete composition of the alloy is shown in Table 3). The alloy was melt and refined in a double 500 kg level flame furnaces, and then machined into rods of φ12 mm by horizontal continuous casting method, the casting temperature was 690-730° C., and then the rods were extruded into pipes of Φ8×0.4 mm on C315 type CONFORM continuous extruder, the outlet temperature was about 450° C., and then the pipes were directly cooled with water.
The properties of the pipes made of the alloy A-2 were tested, wherein the melting point was determined by DSC (Differential Scanning calorimetric), the tensile property was determined in accordance with ISO 6892:1998 (Room Temperature Tensile Test of Metal Materials), the SWAAT corrosion resistance test was conducted in accordance with ASTM/G85-1998 A3 of “Modified Salt Mist Test Method” (sea water acidification recirculation test), bulging was performed in accordance with EN ISO 8493 (bulging test method of metal material pipes), bending test was conducted in accordance with ISO 8491-1998 (bending test of metal material pipes (total cross section)), welding test was conducted by welding 3003/4045 composite soldered aluminum alloy plates and new alloy pipes. Detailed test results were shown in Table 4.
Additionally, the subsequent bending processed surface of the pipes did not have tangerine hull thereon, and the pipes and 3003/4045 complex soldered aluminium alloy plates exhibit excellent soldering properties.
Alloys A-Q within the compositions range of the present inventive alloys were manufactured, and processed into pipes by the method of Example 1. Detailed alloy compositions were shown in Table 5.
The properties of the pipes made of the alloys A-Q were tested, wherein the melting point was determined by DSC (Differential Scanning calorimetric), the tensile property was determined in accordance with ISO 6892: 1998 (Room Temperature Tensile Test of Metal Materials), the SWAAT corrosion resistance test was conducted in accordance with ASTM/G85-1998 A3 of “Modified Salt Mist Test Method” (sea water acidification recirculation test), bulging was performed in accordance with EN ISO 8493 (bulging test method of metal material pipes), bending test was conducted in accordance with ISO 8491-1998 (bending test of metal material pipes (total cross section)), welding test was conducted by welding 3003/4045 composite soldered aluminum alloy plates and new alloy pipes. Detailed test results were shown in Table 6.
The results show:
The melting points of the inventive alloys were higher than 640° C.;
the tensile strengths of the inventive alloy pipes were 89-134 Mpa;
the elongations of the inventive alloy pipes were 28-38%;
the Bulging ratio of the inventive alloy pipes were greater than 30%;
tangerine hull disappeared on the subsequent bending processed surface of the pipes;
pipe leakages were not occurred in the inventive alloy pipes after they were corroded in SWAAT salt spray corrosion test for 30 days;
the inventive alloy pipes exhibit excellent soldering properties when being soldered with 3003/4045 aluminium alloy composite plates.
In order to compare with the inventive alloy, pipes of Φ8×0.4 mm were manufactured with 3003 alloy of the prior art by the same manner of Example 2, and their properties were tested by the same methods. The test results of the chemical composition and properties of 3003 alloy were shown in Tables 7 and 8, respectively.
Corrosion Test
Comparative test of SWAAT corrosion resistance was conducted in accordance with ASTM/G85-1998 A3 of “Modified Salt Mist Test Method” (sea water acidification recirculation test).
Comparison of Hot Working Property
In order to compare with the alloys of the present invention, pipes of Φ8×0.4 mm were manufactured with 3026 alloy of the prior art by the same manner of Example 2, and their properties were tested by the same methods. The test results of the chemical composition and properties of 3026 alloy and the inventive alloy A-2 were shown in Tables 9 and 10, respectively.
The tensile property and elongation rate were determined in accordance with ISO 6892: 1998 (Room Temperature Tensile Test of Metal Materials); the SWAAT corrosion resistance test was conducted in accordance with ASTM/G85-1998 A3 of “Modified Salt Mist Test Method” (sea water acidification recirculation test); the Bulging ratio was performed in accordance with EN ISO 8493 (bulging test method of metal material pipes); the bending test was conducted in accordance with ISO 8491-1998 (bending test of metal material pipes (total cross section)), and the explosive pressure was tested using pipes of D5×0.45 mm by “hydraulic pressure test method of metal pipes” of GB/T241-2007.
It can be seen from above tables that the inventive alloy products exhibit equivalent corrosion resistance as compared to the 3026 alloy products, but their explosive pressure was evidently higher than the 3026 alloy products. The explosive pressure of the new alloy products was higher than that of the 3026 alloy products by 9.7%. The causes were: the adjustment of chemical components of new alloys rendered that the tensile strength of the new alloy products were higher than that of 3026 alloy, so that the safe properties of the new alloy products were enhanced, and the phenomenon of 3026 alloy is relative soft during machining was solved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200910177463.4 | Sep 2009 | CN | national |
