EP0224016B1 - Wrought aluminium alloy of the type al-cu-mg having a high strength in the temperature range between 0 and 250o c - Google Patents

Description

The invention is based on a wrought aluminum alloy according to the preamble of claim 1.

Aluminum alloys of the AUCu / Mg type have been known for decades. Attempts have been made again and again to improve this classic hardenable alloy with further additives and to adapt its properties optimally to the respective intended use. Alloying silver to cast alloys of this type has been proposed, inter alia, to improve strength properties (see, e.g., US-A-3,288,601; US-A-3,475,166; US-A-3,925,067). Similar proposals have also been made in the field of wrought alloys (see GB-A-1 320 271). The alloys have other additives to improve the structure, e.g. Manganese, titanium etc.

Al / Cu / Mg wrought alloys with additions of iron and nickel have been developed for operating temperatures up to about 100 ... 150 ° C (see alloy 2618 according to the US standard). These alloys are usually the result of appropriate casting alloys with nickel additives. However, since they suffer a comparatively well-defined drop in strength above 150 _° C, it is not actually possible to speak of "heat-resistant" aluminum alloys in today's sense. The known alloys do not fully exploit the possibilities of improving the strength properties. In particular, they do not meet the requirements at higher temperatures (up to, for example, 250 _° C.), as are required for numerous technical uses.

There is therefore a great need for a further improvement in wrought aluminum alloys, in particular their strength properties at elevated temperatures.

The invention is based on the object of specifying an aluminum wrought alloy which can be produced by melt metallurgy using simple, conventional methods and which in the temperature range from 0 to 250 _° C. in the hardened state has significantly higher strength properties than conventional alloys.

This object is achieved by the features specified in the characterizing part of claim 1.

The invention is described on the basis of the following exemplary embodiments which are explained in more detail by means of figures.

• Fig. 1 ein Diagramm der Brinellhärte in Funktion des Ag-Gehalts für eine AI/Cu/Mg- bzw. AVCu/Mg/Ag-Legierung,
• Fig. 2 ein Diagramm des Verlaufes der Brinellhärte in Funktion der Aushärtezeit für eine neue Legierung im Vergleich zu einer bekannten, kommerziellen Legierung,
• Fig. 3 ein Diagramm des Verlaufes der Streckgrenze und der Zugfestigkeit in Funktion der Prüftemperatur für eine neue Legierung im Vergleich mit zwei bekannten, kommerziellen Legierungen,
• Fig. 4 ein Diagramm der Zeitstandfestigkeit für eine neue Legierung im Vergleich mit einer bekannten, kommerziellen Legierung.

It shows:

• 1 shows a diagram of the Brinell hardness as a function of the Ag content for an Al / Cu / Mg or AVCu / Mg / Ag alloy,
• 2 shows a diagram of the course of the Brinell hardness as a function of the hardening time for a new alloy in comparison with a known, commercial alloy,
• 3 shows a diagram of the course of the yield strength and the tensile strength as a function of the test temperature for a new alloy in comparison with two known, commercial alloys,
• 4 shows a diagram of the creep rupture strength for a new alloy in comparison with a known, commercial alloy.

The Brinell hardness as a function of the Ag content of an Al / Cu / Ag or Al / Cu / Mg / Ag alloy is shown diagrammatically in FIG. 1. The Mg content is plotted as a parameter. Curve 1 relates to a Mg-free alloy, curve 2 to a Mg content of 0.3% by weight, curve 3 to 0.4% by weight and curve 4 to 0.5% by weight. The alloy had a constant proportion of 6.3% by weight of Cu; Rest aluminum. The values refer to the state obtained after solution heat treatment, water quenching and heat curing. With increasing content of alloying elements, the Brinell hardness rose to a flat maximum.

• Cu = 6,0 Gew-%
• Mg = 0,5 Gew-%
• Ag = 0,4 Gew-%
• Mn = 0,5 Gew-%
• Zr = 0,15 Gew-%
• V = 0,1₀ Gew-%
• Si = ₀,₀4 Gew-%
• Fe = 0,15 Gew-%
• AI ₌ Rest

2 shows a diagram of the course of the Brinell hardness as a function of the hardening time for a new alloy (corresponding to curve 5) compared to a known, commercial alloy (corresponding to curve 6). The new alloy had the following composition:

• Cu = 6.0% by weight
• Mg = 0.5% by weight
• Ag = 0.4% by weight
• Mn = 0.5% by weight
• Zr = 0.15% by weight
• V = 0.1 ₀ % by weight
• Si = _{0, 0} 4% by weight
• Fe = 0.15% by weight
• AI ₌ rest

• Cu = 2,3 Gew-%
• Mg = 1,5 Gew-%
• Fe = 1,0 Gew-%
• Ni = 1,0 Gew-%
• Si = 0,2 Gew-%

The known commercial comparative alloy according to US standard No. 2618 had the following composition:

• Cu = 2.3% by weight
• Mg = 1.5% by weight
• Fe = 1.0% by weight
• Ni = 1.0% by weight
• Si = 0.2% by weight

Both alloys were treated in an analogous manner and were in a similar state: solution annealing, quenching in cold water, hardening (hot aging) at 195 _° C. After 5 hours of hardening, the new alloy reached a maximum hardness of 165 Brinelle units, while the comparative alloy No. 2618 after approx. 30 hours curing only achieved approx. 145 Brinelle units.

• Mn = 0,3 Gew-%
• Zr = 0,18 Gew-%
• V = 0,10 Gew-%
• Fe = 0,30 Gew-% (max)
• Mg = 0,02 Gew-% (max)
• Si = 0,20 Gew-% (max)

In Fig. 3 the course of the yield point (0.2% limit, corresponding to curve 7) and the tensile strength (corresponding to curve 8) as a function of the test temperature under the assumption of a holding time of 0.5 hours at this temperature for a new alloy in Comparison with two known, commercial alloys. The composition of the new alloy corresponded to that which was described under FIG. 2. The composition of the comparative alloy No. 2618 can be found in the description of FIG. 2. The composition of the comparison alloy according to US Standard No. 2219 is as follows: Cu = 6.3% by weight

• Mn = 0.3% by weight
• Zr = 0.18% by weight
• V = 0.10% by weight
• Fe = 0.30% by weight (max)
• Mg = 0.02% by weight (max)
• Si = 0.20% by weight (max)

Curve 9 relates to the course of the yield point (0.2% limit) of alloy No. 2618, curve 10 to that of alloy No. 2219. The values of the yield point of the new alloy are significantly higher than those of the known, commercial alloys.

4 shows a representation of the creep rupture strength at 180 _° C. for a new alloy in comparison to a known, commercial alloy. The new alloy had the composition shown in Fig. 2, while the comparative alloy was No. 2618 described above. Curve 11 relates to the new alloy, while curve 12 applies to the known alloy No. 2618. The achieved values of the new alloy are consistently approx. 20% higher than those of the comparison alloy.

Example 1:

• Cu = 6,0 Gew-%
• Mg = 0,5 Gew-%
• Ag = 0,4 Gew-%
• Mn = 0,5 Gew-%
• Zr= 0,15 Gew-%
• V = 0,10 Gew-%
• Si = 0,₀₄ Gew-%
• AI = Rest

An aluminum alloy of the following composition was melted in a crucible in the induction furnace:

• Cu = 6.0% by weight
• Mg = 0.5% by weight
• Ag = 0.4% by weight
• Mn = 0.5% by weight
• Zr = 0.15% by weight
• V = 0.10% by weight
• Si = 0, _04% by weight
• AI = rest

The pure elements were melted down as raw materials for the components aluminum, copper, magnesium and silver. The purity of the aluminum was 99.9%. The components manganese, zirconium and vanadium were added as aluminum master alloys, each with 50% by weight of the element in question. The total melted mass was approx. 2 kg. The melt was brought to a casting temperature of 740 _° C. and poured into a slightly conical, water-cooled copper mold. The raw cast ingot had a smallest diameter of approx. 70 mm and a height of approx. 160 mm. After cooling, it was homogenized at a temperature of 485 _° C. for 24 hours. After mechanical removal of the cast skin, cylindrical pressing bolts 36 mm in diameter and 36 mm high were screwed out of the ingot. These were pressed individually on an extrusion press at a temperature of 420 _° C. to form a round rod with a diameter of 9 mm. The effective reduction ratio was 13: 1. Sections of 50 mm in length were cut off from this bar and further processed individually. First, the test specimens thus obtained were subjected to solution heat treatment at a temperature of 530 _° C. for a period of 3 hours and then quenched in cold water. The test specimens were then cured for 7 hours at a temperature of 195 _° C. (hot aging).

The strength properties were tested both at room and at elevated temperatures after a previous holding time of 0.5 h or 1000 h at the relevant test temperature. The results for the 0.5 hour hold time are shown in the diagrams corresponding to FIGS. 2, 3 and 4. This results in the following values: Brinell hardness HB: flat maximum of 165 units in the range from approx. 4 to 7h curing time. Curing temperature 195 _° C. Curve 4.

Example 2:

• Mg = 0,6 Gew-%
• Ag = 0,3 Gew-%
• Mn = 0,5 Gew-%
• Zr = 0,25 Gew-%
• V = ₀,₁₅ Gew-%
• Si = 0,08 Gew-%
• AI = Rest

Analogously to Example 1, an alloy according to the following composition was melted and processed into rod sections: Cu = 5.3% by weight

• Mg = 0.6% by weight
• Ag = 0.3% by weight
• Mn = 0.5% by weight
• Zr = 0.25% by weight
• V = _{0, 15%} by weight
• Si = 0.08% by weight
• AI = rest

The alloy specimens were solution annealed at a temperature of 533 _° C and quenched in boiling water. The thermosetting was carried out at 175 _° C for a period of 50 hours.

The strength values were on average approx. 5% below those of Example 1.

Example 3:

• Cu = 6,7 Gew-%
• Mg = 0,4 Gew-%
• Ag = 0,8 Gew-%
• Mn = 0,8 Gew-%
• Zr = 0,15 Gew-%
• V = ₀,0₅ Gew-%
• Si = ₀,₀₆ Gew-%
• AI = Rest

Analogously to Example 1, an alloy of the following composition was melted and further processed into rod sections:

• Cu = 6.7% by weight
• Mg = 0.4% by weight
• Ag = 0.8% by weight
• Mn = 0.8% by weight
• Zr = 0.15% by weight
• V = _0, 0 _5% by weight
• Si = _{0, 06%} by weight
• AI = rest

The specimens of the alloy were solution annealed at a temperature of 525 _° C and quenched in cold water. The heat curing took place at a temperature of 205 _° C for a period of 2 hours.

The strength values were comparable to those of Example 1.

Example 4.

Analogous to embodiment 1, an aluminum alloy corresponding to this example was melted. The melt was brought to a temperature of 700 _° C. and atomized to fine powder in a device using a gas jet. The gas was nitrogen, which was under a pressure of 60 bar. Of the fine-grained powder produced, only the fractions with a particle diameter below 50 µm were used further.

The powder was poured into aluminum cans and degassed at 450 _° C. for 5 hours. Then the filled cans were hot-pressed and the press bolts produced in this way were further processed in an extrusion press at 420 _° C. into bars with a diameter of 9 mm. The material was 100% density. Sections of the bars were then solution annealed at a temperature of 530 _° C for 3 hours and then quenched in cold water. The test specimens were aged at 195 _° C for 7 hours. The maximum strength was reached after about 5 hours. The mechanical properties of the test specimens produced by powder metallurgy were on average still slightly higher than those produced by melt metallurgy.

• Streckgrenze (0,2 %-Grenze): 520 MPa
• Bruchfestigkeit: 620 MPa
• Dehnung: 8,5 %
• Zu der legierungstechnischen Seite ist folgendes zu bemerken:

The following values were achieved at room temperature:

• Yield strength (0.2% limit): 520 MPa
• Breaking strength: 620 MPa
• Elongation: 8.5%
• The following should be noted on the alloying side:

In general, the additional impurities to be accepted in the industrial manufacture of the alloys should remain as low as possible and should not exceed a total of 0.25% by weight for all elements taken together. The silicon content should be kept as low as possible to avoid the formation of low-melting eutectics in the grain boundaries. In addition, intermetallic compounds with the magnesium, which would mean a loss of the latter metal for its beneficial effect together with silver, should be switched off (see FIG. 1). The silicon content should therefore remain below 0.10% by weight. The transition metals manganese, zircon and vanadium serve to refine the grain and form intermetallic phases, which, in finely divided form, cause dispersion hardening and, above all, contribute to increasing the heat resistance. Other similarly acting additions of iron, nickel and chromium to the claimed alloy compositions are conceivable. However, these elements have the disadvantage that they form additional intermetallic compounds with copper, which reduces the content of this latter element available for precipitation hardening and the strength of the matrix. In any case, when using iron and / or nickel, which is at most in the range of 0.1 to max. 1.5% by weight can be added, caution is advised.

• Cu = 5,0 bis 7,0 Gew-%
• Mg = 0,3 bis 0,8 Gew-%
• Ag = 0,2 bis 1,0 Gew-%
• Mn = 0,3 bis 1,0 Gew-%
• Zr = 0,1 bis 0,25 Gew-%
• V = 0,05 bis 0,15 Gew-%
• Si < 0,10 Gew-%
• AI = Rest plus max. 0,25 Gew.-% Verunreinigungen Vorzugsweise besitzen die Aluminiumlegierungen
• die nachfolgenden Zusammensetzungen:
• Cu = 5,5 bis 6,5 Gew-%
• Mg = 0,4 bis 0,6 Gew-%
• Ag = 0,2 bis 0,8 Gew-%
• Mn = 0,3 bis 0,8 Gew-%
• Zr = 0,1 bis 0,2 Gew-%
• V = 0,₀₅ bis 0,15 Gew-%
• Si < 0,05 Gew-%
• AI = Rest plus max. 0,25 Gew.-% Verunreinigungen

The invention is not restricted to the exemplary embodiments. In principle, the compositions can be selected within the following limits:

• Cu = 5.0 to 7.0% by weight
• Mg = 0.3 to 0.8% by weight
• Ag = 0.2 to 1.0% by weight
• Mn = 0.3 to 1.0% by weight
• Zr = 0.1 to 0.25% by weight
• V = 0.05 to 0.15% by weight
• Si <0.10% by weight
• AI = rest plus max. 0.25% by weight of impurities The aluminum alloys preferably have
• the following compositions:
• Cu = 5.5 to 6.5% by weight
• Mg = 0.4 to 0.6% by weight
• Ag = 0.2 to 0.8% by weight
• Mn = 0.3 to 0.8% by weight
• Zr = 0.1 to 0.2% by weight
• V = _0.05 to 0.15% by weight
• Si <0.05% by weight
• AI = rest plus max. 0.25% by weight of impurities

Solution annealing is preferably carried out in the temperature range from 528 to 533 _° C., the upper temperature limit being given by the requirement to avoid local melting by the occurrence of low-melting phases. In partial deviation from the information given in the examples, the heat curing can be carried out in various ways by using the temperature / time relationship. This is preferably done according to the following scheme:

The wrought alloys according to the invention have created light materials which have good strength properties, in particular in the temperature range from room temperature to 250 ° C., and which can be easily produced by conventional melt metallurgical methods.

Claims (4)

1. A wrought AI/Cu/Mg-type aluminium alloy of high strength in the temperature range between 0 and 250°C, characterized in that it has the following composition:

Cu = 5.0 to 7.0% by weight

Mg = 0.3 to 0.8% by weight

Ag = 0.2 to 1.0% by weight

Mn = 0.3 to 1.0% by weight

Zr = 0.1 to 0.25 % by weight

V = 0.05 to 0.15% by weight

Si < 0.10% by weight

AI = remainder, plus max. 0.25% of impurities

2. A wrought aluminium alloy according to Claim 1, characterized in that it has the following composition:

Cu = 5.5 to 6.5% by weight

Mg = 0.4 to 0.6% by weight

Ag = 0.2 to 0.8% by weight

Mn = 0.3 to 0.8% by weight

Zr = 0.1 to 0.2% by weight

V = 0.05 to 0.15% by weight

Si < 0.05% by weight

AI = remainder, plus max. 0.25% of impurities

3. A wrought aluminium alloy according to Claim 1, characterized in that it has the following composition:

Cu ₌ 6.0% by weight

Mg = 0.5% by weight

Ag = ₀._4% by weight

Mn = 0.5% by weight

Zr = 0.15% by weight

V = 0.10% by weight

Si < 0.05% by weight

AI = remainder, plus max. 0.25% of impurities

4. A wrought aluminium alloy according to Claim 1, characterized in that, in the state after solution annealing, quenching in cold water and artificial aging for precipitation hardening, it has at room temperature a 0.2% yield strength of at least 510 MPa and an ultimate tensile strength of at least 575 MPa and, at a temperature of 200_°C after a holding time of 0.5 hour, a 0.2% yield strength of at least 390 MPa and an ultimate tensile strength of at least 405 MPa.

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