KR100549389B1 - High corrosion resistant aluminium alloy containing zirconium - Google Patents

Abstract

An aluminium-based alloy consisting of 0,10 - 0,40% by weight of iron, 0,05 - 0,25% by weight of silicon, 0.05 - 0,20% by weight of zirconium and the balance aluminium and incidental impurities, said aluminium-based alloy exhibiting high corrosion resistance and high tensile strength. Optional elements are 0,05 - 0,40% by weight of manganese and 0,05 - 0,30% by weight of chromium.

Description

High corrosion-resistant aluminum alloy containing zirconium {HIGH CORROSION RESISTANT ALUMINIUM ALLOY CONTAINING ZIRCONIUM}

The present invention relates to an improved aluminum alloy, and more particularly to an aluminum alloy containing a predetermined amount in a controlled amount, in combination with high extrudability and high corrosion resistance.

In the automotive industry, aluminum alloys are used in a variety of applications, particularly in piping, because of their low weight, high strength properties and extrudability.

Aluminum alloys are particularly useful for use in heat exchangers or condensers for air conditioning. In these applications the aluminum alloy should have good strength, sufficient corrosion resistance and good extrudability.

A typical alloy used for this application is AA 3102. This alloy typically contains about 0.43% iron, 0.12% silicon, 0.25% manganese.

The aluminum alloys described in WO97 / 46726 include up to 0.03 wt% copper, 0.05 to 0.12 wt% silicon, 0.1 to 0.5 wt% manganese, 0.03 to 0.30 wt% titanium, 0.06 to 1.0 wt% zinc. , Less than 0.01% magnesium, less than 0.50% iron, less than 0.01% nickel and less than 0.50% chromium.

International Publication No. WO97 / 46726 claims that there is no positive effect of chromium on corrosion resistance. It should also be noted that the minimum content of manganese in the same publication is 0.1% by weight.
According to International Publication WO 91/14794, a number of elements, including zinc, zirconium, nickel, vanadium and chromium, may be present up to 0.05% by weight per element as common impurities. In the table of the fifth page of the specification, an example is shown in which the total content of impurities is 0.041% by weight and zirconium contains only 0.001% by weight. Increasing the total content of impurities to 0.15% by weight will result in a maximum content of zirconium to 0.0036585% by weight. Clearly, some impurities such as zinc and chromium may be present up to 0.05% by weight locally, but not all elements.
According to US-A-4749627 it is described that manganese can be contained up to 0.03% by weight as impurities.
The alloy according to D2 is intended to be used as finstock and there is no indication of its extrudability. Corrosion resistance from Table 6 is due to the high zinc content present in the alloy (see nos. 10, 11 and 19), which results from the harmonious presence of different elements as described for alloys A to E according to the invention. no.

There has been a steady need for aluminum alloys that combine excellent extrudability with excellent corrosion resistance. Good extrudability is required to minimize production costs in the extrusion plant, including lower extrusion pressures and higher extrusion rates.

Accordingly, it is an object of the present invention to provide an aluminum alloy with a composition which exhibits excellent corrosion resistance and improved extrudability while maintaining the strength of the commercial aluminum alloy at this time. For this reason the aluminum alloy according to the invention comprises iron, silicon, manganese, zirconium, chromium and zinc in controlled amounts.

Another object of the present invention is to provide an aluminum base alloy suitable for use in heat exchanger extrusion piping.

It is a further object of the present invention to provide an aluminum based alloy suitable for use in foil packaging applications which are corroded by, for example, brine or in finstocks for heat exchangers.

These objects and advantages include about 0.06 to 0.25 weight percent iron, 0.05 to 0.15 weight percent silicon, 0.70 weight percent or less copper, 0.10 weight percent or less manganese, 0.02 to 0.20 weight percent zirconium, By an aluminum-based alloy composed of 0.18% by weight or less of chromium, 0.70% by weight or less of zinc, 0.005 to 0.02% by weight of titanium for fine grains, 0.02% or less of unavoidable impurities, and the balance of aluminum. This aluminum alloy has high corrosion resistance, good extrudability and acceptable tensile strength.

The iron content of the alloy according to the invention is preferably about 0.06 to 0.15% by weight. In this case, the corrosion resistance and the extrudability are optimal, and these two properties decrease greatly as the iron content increases.

In order to optimize corrosion resistance, it is preferable to make zirconium content 0.10 to 0.18 weight%. The extrudability of the alloy in this range is practically unaffected by any change in the amount of zirconium.

The chromium content is also preferably 0.10 to 0.18% by weight. Increasing the chromium content improves the corrosion resistance and within this range the extrudability is somewhat reduced but still in the acceptable range.

Zinc, even in small amounts, adversely affects the anodizing properties of the AA 6000 alloy. In view of this contamination effect of zinc, the level of zinc should be kept low to increase the recyclability of the alloy and to reduce the cost at the foundry. On the other hand, zinc has a good effect on the corrosion resistance up to at least 0.7% by weight, but for the above reason it is preferable that the amount of zinc is 0.10 to 0.18% by weight.

Copper may contain up to 0.50% by weight, but in order to have the highest extrudability possible, it is preferred to have a content of less than 0.01% by weight. In some situations, it may be necessary to add copper to the alloy to control galvanic potential to reduce galvanic corrosion of the product by reducing the electrical negativeness of the product. It was found that the addition of copper every 1% increases the corrosion potential of several hundred mV, while at the same time the extrudability is substantially reduced.

The invention also relates to an aluminum product based on the aluminum alloy according to the invention and obtained through extrusion.

After casting, the alloy is usually homogenized, for example by heat treatment for 3 to 10 hours at a high temperature of 550 to 610 ° C. Extrusion is somewhat improved by such heat treatment, but corrosion resistance has been found to be adversely affected.

According to the present invention, the aluminum product is characterized in that the only heat treatment performed on the aluminum product after casting is a preheating treatment immediately before extrusion.

Since such preheating is carried out only for a few minutes at a lower temperature than in the homogenization step, the properties of the alloy related to extrudability and corrosion resistance are hardly affected.

In order to demonstrate the improvement in the aluminum-based alloy of the present invention over known prior art alloys, the properties related to mechanical properties, corrosion resistance and extrudability were investigated.

A discussion of the methods used to investigate the aforementioned characteristics and the results of such investigations is described in detail below.

A number of alloys according to the invention were prepared. These alloys are shown as Alloy A to Alloy E in Table 1 below. In Table 1, the compositions of these alloys are expressed in weight percent, taking into account that each alloy may contain up to 0.02 weight percent of unavoidable impurities. Table 1 also shows the composition of a traditional 3102 alloy.

All of these alloys were made by traditional methods. The alloy was prepared and preheated to a temperature of 460-490 ° C. before extrusion into the billet.

Chemical composition of various alloys alloy iron silicon manganese zirconium chrome zinc titanium A 0.10 0.08 0.07 0.18 0.11 0.00 0.013 B 0.12 0.07 0.07 0.12 0.11 0.10 0.011 C 0.12 0.07 0.07 0.14 0.14 0.17 0.012 D 0.13 0.07 0.07 0.10 0.13 0.19 0.009 E 0.11 0.07 0.09 0.07 0.00 0.24 0.011 3102 0.43 0.12 0.25 - - - 0.010

In order to evaluate the improvement obtained by the alloy according to the present invention, a number of tests were conducted and the results are shown in Table 2.

Properties of the alloys listed in Table 1 alloy Tensile strength (MPa) Yield strength (MPa) Elongation (%) Die force (tons) Max force (tons) Corrosion Test SWAAT (days) A 87.60 67.60 38.50 5094 6319 35 B 84.20 64.70 35.00 5115 6245 83 C 87.60 68.00 35.50 5130 6305 90 D 85.00 65.20 35.50 5078 6168 67 E 80.50 56.00 36.00 4734 5078 35 3102 86.20 65.50 37.20 5008 6025 10

In order to investigate the properties of these alloys, a set of billets were cast and their composition was measured under an electron microscope. A BAIRD VACUUM instrument was used for this analysis, and the standard used was provided by Pechiney.

Extrudeability is related to the die force and the maximum extrusion force indicated by the maximum force. These parameters are recorded by a pressure transducer installed on the press, so that their numerical values are immediately read.

In order to measure the corrosion resistance of these alloys, the so-called SWAAT-test is used. Test samples used extruded tubing with 0.4 mm thick walls. This test was performed by alternating 30 minutes of spraying and 90 minutes of soaking at 98% humidity in accordance with ASTM Standard G85-85 Annex A3. The electrolyte is acidified to pH 2.8 to 3.0 by acetic acid and is artificial seawater of composition according to ASTM standard D1141. The temperature is maintained at 49 ° C. The test was performed in a Liebisch KTS-2000 salt spray chamber.

To study the development of the corrosion behavior, samples of different materials were taken out of the chamber every three days. The material was then washed with water and tested for leaks at an applied pressure of 10 bar. For example, if 35 days passed and a hole was found in a predetermined sample, a comparative sample was introduced into the chamber and maintained for 35 days, followed by initial irradiation to confirm the result. The SWAAT column shows the number of days until the hole is drilled.

The test mentioned above is generally used in the automotive industry, and when 20 or more, it is recognized as a passing performance.

Testing of the mechanical properties was carried out according to the European standard on the Zweck Universal Testing Instrument (Module 167500). In the test, the elastic module was fixed at 70000 N / mm ² . The test speed up to Rp0.2 was constant at 10 N / mm ² , and the test speed from Rp0.2 to failure was 40% Lo / min, where Lo is the initial gage distance.

The results in Table 2 show that both mechanical properties, extrudability in terms of die force and maximum force, and corrosion resistance depend on the alloy. Above all, the corrosion resistance of alloys A to E is superior to that of the 3102 alloy. Extrudeability is comparable to that of 3102 alloys overall, and the same applies to mechanical properties. Analyzing the SWAAT data of alloys C, D, and E reveals the best harmony with chromium, zirconium, and zinc (alloy C).
Alloy E without chromium and Alloy A without zinc have much better results than the pass limit of 20 days, but the corrosion resistance is significantly lower than that of alloys B, C and D. This clearly shows that the presence of chromium and zinc is essential for long service life alloys to optimize corrosion resistance. In addition, comparing the results from alloys C and D reveals the importance of zirconium. Increasing the zirconium content significantly improves the corrosion behavior.

Therefore, it is emphasized that the optimum conditions and especially the corrosion resistance are the result of the proper combination of the elements chromium, zirconium, manganese and zinc.

Extrudeability is affected by the addition of small amounts of various alloying elements. By introducing chromium and zirconium, it can be seen that the die force and the maximum force are increased (ie, the extrudability is reduced). On the other hand, zinc does not significantly affect extrudability, which is known per se.

The mechanical properties expressed in terms of tensile strength and yield strength can be seen to be significantly increased with the addition of chromium. In that case, the new alloy formed is comparable to that of the 3102 alloy.

Corrosion tests were done on samples taken at different locations of the coil. About 10 samples were taken at the coil start (billet front), 10 samples at the coil middle (billet middle), and 10 samples at the coil end (billet end). Each sample was about 50 cm in length. The test results were very consistent, meaning that in the extrusion parameters used, there was no impact on the extrusion rate and the corrosion resistance associated with the flow of material during the extrusion of one billet.

Further work was done to evaluate the effects of different alloying elements, which effects are also shown in FIGS. 1 to 6 of the accompanying drawings.

1 shows the effect of iron content on the properties of the alloy according to the invention.

Figure 2 shows the effect of manganese content on the properties of the alloy according to the invention.

Figure 3 shows the effect of zirconium content on the properties of the alloy according to the invention.

4 shows the effect of chromium content on the properties of the alloy according to the invention.

5 shows the effect of zinc content on the properties of the alloy according to the invention.

6 shows the effect of copper content on the properties of alloys according to the invention.

In Figures 1 to 5, the x-axis represents the content of alloying elements in weight percent, while the y-axis is a relative expression for different properties, the square point is used to represent the tensile strength in MPa and the black triangular point is representative. The die force is used as a measure to represent the extrudability expressed in ktons, and the white triangle point is used to represent the SWAAT-test results expressed in days.

As shown in FIG. 1, the corrosion resistance is significantly reduced with increasing iron content (silicon content is maintained at the same level of 0.08% by weight). This effect occurs especially at iron contents in the range of 0.2 to 0.3% by weight. At the same time, extrudability is significantly reduced with increasing iron content. It should be noted that as the extrudability decreases by 2-3% (expressed as an increase in break through pressure of 2-3%), the through pressure increases to an unacceptable level for the extrusion plant. On the other hand, an increase in iron content leads to an increase in tensile strength.

As is evident in FIG. 2, any change in manganese content at a manganese content of less than 0.30% by weight actually does not affect corrosion resistance (keeping iron and silicon content at 0.15% and 0.08% by weight, respectively). An increase in manganese content leads to a decrease in extrudability, which in turn tends to have unacceptable extrudability. On the other hand, mechanical properties improve with increasing manganese content.

When the contents of iron, silicon, and manganese are maintained at a constant level of 0.15%, 0.08%, and 0.08% by weight, respectively, when the zirconium content is increased from 0.07% by weight to 0.15% by weight, as shown in FIG. It brings an improvement. At the same time, the extrudability only slightly decreases while the tensile strength increases.

If the chromium content is changed from 0.08% to 0.12% by weight while maintaining iron, silicon and manganese at the same level as in FIG. This is shown in FIG. 4.

The effect of zinc with the contents of iron, silicon and manganese maintained at the same level of 0.15%, 0.08% and 0.08% by weight is shown in FIG. 5. In this figure, titanium (Ti) is also present at a constant level of 0.15% by weight (titanium and zirconium are believed to affect corrosion resistance in the same way, as supported by the results presented in Table 2 above).

Zinc practically does not affect extrudability and mechanical properties, but increasing zinc content improves corrosion resistance.

The use of copper is optional and depends on the actual use of the alloy. 6 is a diagram showing the effect of copper content on extrudability and corrosion potential. The x-axis represents the copper content in weight percent, the left y-axis represents the extrusion force in kN and the right y-axis represents the corrosion potential in mV according to ASTM G69. The upper line of the graph shows the development of corrosion potential and the lower line shows the development of extrusion force.

From this graph, it is evident that a decrease in the copper content leads to an improvement in the extrudability, while an increase in the copper content of 1% by weight makes the corrosion potential less negative by 100 mV.
Typically, it is desirable to use alloys with the lowest possible amount of copper, since copper adversely affects the intrinsic corrosion resistance of bare tubes and strongly affects extrudeability negatively.

However, if an extruded product, such as a heat exchanger tubing, must be connected to another product, such as a header with a zinc free clad, the addition of copper prevents the tube from corroding the header material (less negatively). ) Corrosion potential of extruded products can be controlled. This can suppress any galvanic corrosion occurrence on the tube.

Claims (8)

0.06 to 0.25 weight percent iron, 0.05 to 0.15 weight percent silicon, 0.70 weight percent or less copper, 0.03 to 0.10 weight percent manganese, 0.02 to 0.20 weight percent zirconium, and 0.18 weight percent or less And, up to 0.70% by weight of zinc, 0.005 to 0.02% by weight of titanium (as a grain refiner), up to 0.02% by weight of unavoidable impurities, and the balance of aluminum. Aluminum alloy showing extrudeability. The aluminum-based alloy of claim 1, wherein the iron content is 0.06 to 0.15 wt%. delete The aluminum-based alloy of claim 3, wherein the zirconium content is 0.07 to 0.15 wt%. The aluminum-based alloy of claim 4, wherein the chromium content is 0.08 to 0.12 wt%. delete delete delete

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