Heat-resistant Al—Cu—Mg—Ag alloy and process for producing a semifinished part or product composed of such an aluminum alloy

Abstract

A heat-resistant AlCuMgAg alloy for producing semi-finished parts or products, which is suitable for use at elevated temperatures and has good static and dynamic strength properties combined with an improved creep resistance and comprises: 0.3-0.7% by weight of silicon (Si), not more than 0.15% by weight of iron (Fe), 3.5-4.7% by weight of copper (Cu), 0.05-0.5% by weight of manganese (Mn), 0.3-0.9% by weight magnesium (Mg), 0.02-0.15% by weight of titanium (Ti), 0.03-0.25% by weight of zirconium (Zr), 0.1-0.7% by weight of silver (Ag), 0.03-0.5% by weight of scandium (Sc), 0.03-0.2% by weight of vanadium (V), not more than 0.05% by weight of others, individually, not more than 0.15% by weight of others, total, balance aluminum, is described. A process for producing a semi-finished part or product composed of the above-mentioned aluminum alloy is described.

Claims

1. A semi-finished part or semi-finished product produced from a heat-resistant AlCuMgAg alloy, suitable for use at high temperatures and with high static and dynamic strength properties combined with an improved creep resistance, characterized in that: the aluminum alloy comprises 0.45-0.55 wt % silicon (Si) max. 0.15 wt % iron (Fe) 4.1-4.7 wt % copper (Cu) 0.05-0.5 wt % manganese (Mn) 0.3-0.9 wt % magnesium (Mg) 0.02-0.15 wt % titanium (Ti) 0.05-0.07 wt % zirconium (Zr) 0.1-0.7 wt % silver (Ag) 0.03-0.5 wt % scandium (Sc) 0.03-0.2 wt % vanadium (V) max. 0.05 wt % others, individually max. 0.15 wt % others, total remainder aluminum; and the semi-finished part or product can endure a creep test conducted at a temperature of 190 C. and a creep tension of 200 MPa for 500 hours or more without breaking.

2. The part or product of claim 1, wherein the sum of the elements zirconium, titanium, scandium and vanadium is less than or equal to 0.4 wt %.

3. The part or product of claim 1, wherein the aluminum alloy contains: 0.04 to 0.06 wt % titanium (Ti), 0.08 to 0.10 wt % scandium (Sc) and 0.10 to 0.12 wt % vanadium (V).

4. The part or product of claim 1, wherein the aluminum alloy contains: 4.10-4.30 wt % copper (Cu) 0.15-0.25 wt % manganese (Mn) 0.5-0.7 wt % magnesium (Mg) and 0.40-0.55 wt % silver (Ag).

5. The part or product of claim 1, wherein the sum of the elements silver, zirconium, scandium and vanadium is at least 0.60 wt % and maximally 1.1 wt %.

6. The part or product of claim 1, wherein the aluminum alloy contains the elements silver and scandium in a ratio of Ag:Sc=5-23.

7. The part or product of claim 1, wherein the aluminum alloy contains the elements scandium and zirconium in a ratio of Sc:Zr=1-17.

8. The part or product of claim 1, wherein the aluminum alloy contains the elements silver and vanadium in a ratio of Ag:V=0.5-14.

9. The part or product of claim 1, wherein the aluminum alloy contains an iron content of max. 0.09 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described using exemplary embodiments and by comparison to previously known aluminum alloys, with reference made to the attached figures. In the figures:

(2) FIG. 1: shows a diagram with the chemical composition of the claimed alloy in comparison to the chemical compositions of previously known aluminum alloys,

(3) FIG. 2: shows a comparison of the creep properties of the claimed alloy with a previously known alloy considered to be especially creep-resistant, and

(4) FIG. 3: shows a Larsen-Miller diagram for representing the creep behavior of the claimed alloy in comparison to previously known ones.

DETAILED DESCRIPTION

(5) FIG. 1 shows a comparison of the chemical composition of the claimed alloy with previously known aluminum alloys. These alloys include those from which semi-finished parts or products with high static and dynamic strength properties can be produced in a known manner, and specifically AA2014, AA2014A and AA2214. In addition, two known alloys associated with an especially good long-time stability under thermal influences are provided, namely AA2618 and AA2618A. The known alloy AA2016 is also given. The data in the table for the amounts of the particular alloy elements is taken from the International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys, The Aluminum Association Inc., 1525 Wilson Boulevard, Arlington, April 2006.

(6) The table of FIG. 1 indicates the disclosed alloy according to the invention with a W designation. Comparison of the alloy compositions clearly demonstrates the differences of the claimed heat-resistant aluminum alloy, specifically by the addition of the elements vanadium and scandium and the special selection of the remaining alloy components including its particular amount. It is also clear from this comparison that the claimed alloy W cannot be derived as the sum or in some other manner from these previously-known alloys.

(7) Two typical alloy compositions of the claimed alloy were produced and investigated for the production of test pieces and for carrying out investigations of strength at room temperature and an elevated temperature. The two alloys W1 and W2 had the following chemical composition:

(8) TABLE-US-00001 W1 W2 Element wt % wt % Si 0.51 0.50 Fe 0.092 0.084 Cu 4.06 4.22 Mn 0.186 0.207 Mg 0.591 0.586 Cr 0.009 0.013 Ni 0.002 0.009 Zn 0.009 0.007 Ti 0.128 0.059 Zr 0.146 0.059 V 0.131 0.115 Sc 0.137 0.089 Ag 0.46 0.49 Others individually 0.05 0.05 Others total 0.15 0.15 Al Remainder Remainder

(9) Furthermore, test pieces of the comparison alloys AA2016 and AA2618 were produced and correspondingly investigated. For the theoretical composition of these alloys, see the data in FIG. 1.

(10) In order to determine the strength properties, the alloys W1 and W2 were cast on an industrial scale to cast extrusion blocks with a diameter of 370 mm, whereby care was taken that the elements zirconium, scandium and vanadium were sufficiently dissolved during the casting of the bars. To this end, the molten aluminum alloy or melt was put in motion by generating a convection in the melt. The cast extrusion blocks were homogenized in order to compensate the crystal segregations conditioned by the hardening. The blocks were homogenized and cooled off in two stages using a temperature range of 500 C. to 550 C. After twisting off the casting skin, the homogenized blocks were preheated to approximately 400 C. and multiply deformed to free-form forged pieces with a thickness of 100 mm and a width of 250 mm. Subsequently, the free-form forged pieces from alloys W1 and W2 were solution-annealed for at least 2 h at 500 C., quenched in water, and subsequently hot-hardened between 165 C. and 200 C. Tensile tests were taken from the hot-hardened free-form forged pieces on which the strength properties were determined at room temperature in the longitudinal (L) test position. The results are listed in the table below:

(11) TABLE-US-00002 R.sub.p0.2 R.sub.m A.sub.5 Alloy [MPa] [MPa] [%] 2016 446 490 11.1 2618 344 432 10.4 W1 399 449 8.1 W2 383 437 10.6

(12) For purposes of a comparison, the strength properties for free-form forged pieces of the alloys AA2016, followed by W1, W2 and AA2618 in the heat-hardened state are additionally indicated in the table.

(13) The alloy AA2016 shows the greatest strength (stretch limit), followed by W1, W2 and AA2618. A sufficient ductility of >8% is achieved by all alloys. It should be noted at this point that the strength values of the comparison alloy AA2016 were not able to be reached with the test alloys W1, W2. However, the test values achieved clearly exceed those of the other comparison alloy AA2618. For the cases of use in question, the strength values that the test alloys W1, W2 have are sufficient. It is important that the test alloys W1, W2 have a significantly better creep resistance, as described in the following with reference to FIG. 2, in comparison to the comparison alloy AA2618 which is considered to be creep-resistant.

(14) The differences are especially noticeable in a comparison of the creep behavior of the alloy AA2618, known as creep-resistant, with the alloy W2. This comparison is shown in FIG. 2. The diagram of FIG. 2 shows the creep properties of the respective alloys at 190 C. and a creep tension of 200 MPa. While the alloy AA2618 is known as especially creep-resistant and has previously been used for such purposes, breaks after about 320 hours in the prescribed test setup and a plastic expansion of about 1% at about 230 hours were experienced. The examined time period of 500 h was not sufficient to cause the test alloy W2 to break. At the same time of the break of the test piece for alloy AA2618, a plastic deformation of only about 0.2% was able to be determined for the test alloy W2. The improved creep resistance of the claimed alloy in comparison to the alloy AA2618 (considered to be especially creep-resistant) is surprising.

(15) The test pieces of the other test alloy W1 have a creep resistance that corresponds to the one shown in the diagram of FIG. 2 for the test alloy W2.

(16) The special properties of the claimed alloy are also evident by a comparison of this alloy and of the two test alloys W1, W2 with known alloys in a Larsen-Miller diagram. FIG. 3 shows such a diagram. In this representation, the strength properties are shown linked with a temperature resistance. The alloy AA2618, known as especially creep-resistant, is distinguished by a relatively slight inclination of its break line. The alloy AA2014 on the other hand, which meets the high static and dynamic requirements, has a distinctly steeper angle of inclination of its break line. The curves of these two alloys intersect. That means that in the test structure documented in the diagram, the alloy AA2214 first resists higher tensions, namely in the curve section located above the curve of the alloy AA2618, and then decreases much more rapidly with increasing temperature and/or time in regard to its breaking tension than the alloy AA2618. The alloy AA2016 is also entered in this diagram for comparison. Since this curve is located to the right of the curve of the alloy AA2014, it is clear that it is more long-time resistant in comparison to the alloy AA2014. It also becomes clear that the alloy AA2016 requires a higher tension up to a certain point in time in order to bring about a break.

(17) These curves of previously-known aluminum alloys are opposed by the area of the Larsen-Miller diagram in which the values of semi-finished parts or products produced with the claimed alloy are located. The line of the test pieces of the test alloys W1, W2 are concretely entered, whereby it is to be taken into consideration that this line does not represent the break line, but rather the state of the test samples after a test time of 500 hours. A break did not occur within this time frame (see also FIG. 2 in this regard by way of comparison). Therefore, the sketched-in lines are considered to be minimum lines with respect to the test alloys W1, W2. The actual break lines of the test alloys W1, W2 are located much further to the right in the Larsen-Miller diagram. Even the inclination of these two curves should probably be significantly smaller than it is sketched in. For this reason, the representation of a field was selected in order to be able to compare the improved properties of the claimed alloy with the properties of the known alloys discussed. The improved creep behavior of the claimed alloy can be clearly gathered from the Larsen-Miller diagram of FIG. 3.