ES2399234T3 - Copper and zinc alloy stable against degalvanization as well as a procedure for its production - Google Patents

Abstract

Copper and zinc alloy stable against degalvanization, in particular for use in the health sector, characterized in that it comprises 50 to 80% by weight of Cu, 0 to 5% by weight of Pb, from 0.01 to 0.10% by weight of As, from 0.03 to less than 0.3% by weight of Si, from 0 to 0.3% by weight of Fe, from 0 to 0.04% by weight of Mn and optionally from 0.15 to 0.3% by weight of Al being the remainder Zn as well as the inevitable impurities, and because the equivalent of effective Cu is from 60 to 70% by weight.

Description

Copper and zinc alloy stable against degalvanization as well as a procedure for its production

The invention relates to a stable copper and zinc alloy against zinc degalvanization or elimination, which is particularly suitable for use in the sanitary sector, eg for drinking water taps, drinking water pipes or connectors. tubes The invention further relates to a production process for such a copper and zinc alloy.

The usual copper and zinc alloys, also called brass or brass alloys, can be presented

in two different metal phases. In the so-called phase α, the brass alloy has an fcc structure (from English "Face - Centered - Cubic" = cubic centered on the faces), while in phase β it has a Bcc structure (from English "Body - Centered - Cubic "= cubic centered on the body). In the phase diagram of a brass alloy, the pure α phase appears in the case of a copper proportion of more than 62% by weight. In the case of a proportion of copper comprised between 54 and 62% by weight, the brass alloy has certain proportions of both the α phase and also the β phase. In the case of the presence of additional metal components, the limits of the above mentioned phases are shifted.

For sanitary uses, a brass alloy due to constant contact with water must have a high stability against corrosion. Brass, and also copper, in aqueous electrolytic solutions of a weakly acidic to alkaline character, form copper oxide-based coating layers, which generally offer some general corrosion protection. In soft waters, which contain chlorides, in the case of brass alloys a special form of corrosion can be presented, which is designated as degalvanization. In this case, the zinc is released from the brass alloy, and a porous copper sponge is left behind. In addition, the β phase is attacked more strongly than the α phase, since the first cited is less electropositive than the cited

in the last place. For the improvement of the corrosion resistance of a brass alloy, the resource is therefore known to avoid as far as possible the formation of a β phase by heat treatment during its production. In addition, it is also known to add additional metal components to a brass alloy, which protect the α phase against degalvanization. As such metal components, phosphorus, arsenic, antimony, bismuth and silicon are known from international patent application document WO 89/08725. From the German patent application document DE 197 22 827 A1, the addition of arsenic or phosphorus to a brass alloy is known.

The addition of a single additional metal component can however drastically modify other characteristic features of the brass alloy. Thus, according to WO 89/08725, the addition of arsenic certainly improves the corrosion protection for the α phase, but in the case of the presence of the α and β phases, corrosion stability is worsened in the presence of water containing sulfates. Since the composition of a drinking water, that is, the type and concentration of the ions dissolved in it, is greatly dependent on its geographical origin, long and tedious investigations are required to find a composition of a brass alloy, which does not it is corroded even after use and contact with water for several decades.

As a brass alloy with low degalvanization and which is stable against corrosion, a copper and zinc alloy is known from WO 89/08725, containing up to 0.8% nickel by weight, between 0.5 and 3% by weight of lead, between 0.3 and 1% by weight of silicon and between 0.07 and 0.8% by weight of iron. Arsenic is considered in principle as disturbing, since it favors intercrystalline corrosion, so its proportion must be below 0.02% by weight.

A mission of the present invention is to indicate a copper and zinc alloy that has a particularly high stability against degalvanization and intercrystalline corrosion, and which is particularly suited for uses in the healthcare sector. In addition, it is another mission of the invention to indicate a production process for such a copper and zinc alloy.

The problem posed by the mission cited in the first place is solved according to the invention for a copper and zinc alloy by means of the resource that it comprises from 50 to 80% by weight of copper, from 0 to 5% by weight of lead, of 0.01 to 0.1% by weight of arsenic, from 0.03 to less than 0.3% by weight of silicon, from 0 to 0.3% by weight of iron, from 0 to 0.04% by weight of manganese, the remainder being zinc as well as unavoidable impurities, and that the equivalent of effective copper is 60 to 70% by weight.

With the equivalent of copper or the effective copper content, the effects of the different elements of the alloy are taken into account in the case of brass alloys in terms of texture formation. If, for example, lead or iron is contained in the copper and zinc alloy, then their proportions add up in terms of effectiveness versus the actual proportion of copper. In this case, the actual proportion of copper is lower than the equivalent of effective copper. If the effective copper equivalent is approximately 60% by weight and if a lead ratio of 2% by weight is additionally contained, then the actual proportion of copper is (1 - 0.02) x 60% by weight = 58 , 8% by weight.

Extensive research has shown that a copper and zinc alloy with the aforementioned composition has both high stability against degalvanization as well as very small intercrystalline corrosion, hereinafter called IK. The invention starts in this case from the recognition that a certain arsenic content is decisive for the prevention of intercrystalline corrosion. In addition, the invention assumes that iron is not necessary for the corrosion resistance of the brass alloy, but acts in a disturbing manner. The disturbing influence of iron can, however, be avoided to a limited extent by the addition of silicon.

Other advantageous embodiments are found in the dependent claims 2-5.

The problem posed by this mission with regard to the production process for a copper and zinc alloy, in which the starting materials are mixed according to the desired composition, cast and cast molded to give a metal alloy, and The metal alloy is annealed at 500-650 ° C for the formation of the α phase, it is resolved according to the invention by the resource that the annealed metal alloy is actively cooled by means of cooling agents.

Extensive investigations have established that the stability of the alloy against intercrystalline corrosion can be further improved, in accordance with the features of claim 1, when the annealed alloy is actively cooled by means of cooling agents. Such active cooling for the acceleration of natural cooling, with no additional auxiliary agent being used, can be carried out, for example, by a cooling fan, or else it can be cooled rapidly by quenching. Such tempering can be carried out, for example, by a water bath. In the case of the use of a cooling fan, the cooling treatment can be structured as a direct step cooling for larger numbers or quantities of parts.

If a copper and zinc alloy produced in such a way is subsequently treated by cold forming, then it has been shown that in this way the stability against intercrystalline corrosion decreases. This can be advantageously avoided if the cold formed alloy is subjected to annealing with stress removal for 10 min up to 2 hours at a temperature between 250 and 600 ° C

Examples of embodiment of the invention are illustrated in more detail with the aid of the following tests, drawings and tables. In this case they show:

Figure 1: the percentage susceptibility to intercrystalline corrosion of different test alloys depending on the arsenic content,

Figure 2: the percentage susceptibility to intercrystalline corrosion of different test alloys depending on the respective manganese content and

Figure 3: the delivery of lead to drinking water by a test alloy compared to the state of the art alloys, depending on the time.

In total 44 copper and zinc alloys with different compositions were investigated. Table 1 shows the composition of these 44 test alloys for copper, lead, arsenic, iron, silicon, manganese, aluminum and zinc. For the respective metal component of each alloy, the nominal proportion and the actual proportion in% by weight are reproduced. The test alloys are designated in each case with four-digit figures. This designation is used hereafter for the respective alloy.

The test alloys shown in Table 1 were produced as follows:

one.

 Casting of molten alloy at a temperature of 1,050 to 1,100 ° C on a steel ingot with dimensions of 110 mm x 40 mm

2.

Milling of the sample until it reaches a thickness of 14 mm

3.

Lamination of the sample until it reaches 5 mm, with intermediate annealing in each case for 1 hour at temperatures of approximately 700 ° C

Four.

 Annealing α for 2 hours at a temperature of 550 degrees Celsius

Alloy No.

Cu Pb Ace Faith Yes Mn To the Zn

2088 nominal actual

62.4 62.6 2.6 2.66 0.04 0.046 -0.01 - <0.005 - <0.005 rest rest

2089 nominal actual

62.4 62.65 2.6 2.66 0.07 0.073 -0.01 - <0.005 - <0.005 rest rest

2090 nominal actual

62.4 62.53 2.65 2.65 0.14 0.14 -0.01 - <0.005 - <0.005 rest rest

2094 actual nominal

62.4 62.59 2.6 2.66 0.07 0.074 0.14 0.14 0.08 0.058 - <0.005 rest rest

2102 actual nominal

64 64.01 2.66 2.59 0.06 0.062 0.10 0.10 0.2 0.20 - <0.005 rest rest

2106 actual nominal

63.7 63.8 2.6 2.64 0.06 0.068 0.2 0.17 0.2 0.18 - <0.005 rest rest

2131 nominal actual

62.4 62.23 2.6 2.66 0.08 0.096 -0.02 - <0.005 - <0.005 rest rest

Real nominal 2132

62.4 62.66 2.6 0.09 0.067 -0.01 - <0.005 - <0.005 rest rest

2133 nominal actual

64.38 64.72 2.6 0.06 0.066 -0.01 0.2 0.19 - <0.005 rest rest

2134 nominal actual

68.0 67.84 2.6 0.06 0.064 0.10 0.11 0.60 0.61 - <0.005 rest rest

Actual nominal 2135

82.2 81.55 2.6 0.06 0.064 -0.01 2.0 1.97 - <0.005 rest rest

Actual nominal 2136

81.89 81.41 2.6 0.06 0.062 0.10 0.093 2.0 1.97 - <0.005 rest rest

2156 nominal

65.0 2.0 0.2 0.5 rest

2157 nominal

65.0 2.0 0.06 0.2 0.5 rest

2158 nominal

65.0 2.0 0.06 - 0.5 rest

2159 nominal actual

62.5 62.59 2.0 0.06 0.067 0.1 0.082 -0.004 - <0.002 - <0.002 rest rest

2160 nominal actual

62.5 62.46 2.0 0.06 0.064 0.1 0.097 0.01 0.009 - <0.002 - <0.002 rest rest

Actual nominal 2161

62.5 63.2 2.0 0.06 0.065 0.1 0.079 0.03 0.024 - <0.002 - <0.002 rest rest

2162 nominal actual

63.08 63.26 2.0 0.06 0.054 0.1 0.089 0.06 0.053 - <0.002 - <0.002 rest rest

2163 nominal actual

63.9 64.24 2.0 0.06 0.065 0.1 0.092 0.1 0.097 - <0.002 - <0.002 rest rest

2164 nominal actual

65.88 65.86 2.0 0.06 0.064 0.1 0.10 0.2 0.18 - <0.002 - <0.002 rest rest

Actual nominal 2165

67.88 67.96 2.0 0.06 0.060 0.1 0.098 0.3 0.28 - <0.002 - <0.002 rest rest

2166 nominal actual

71.88 71.98 2.0 0.06 0.060 0.1 0.089 0.5 0.47 - <0.002 - <0.002 rest rest

2167 nominal actual

75.87 75.93 2.0 0.06 0.060 0.1 0.088 0.7 0.67 - <0.002 - <0.002 rest rest

2168 nominal actual

66.51 66.73 2.0 0.06 0.065 -0.010 0.2 0.19 0.01 0.006 - <0.002 rest rest

2169 nominal actual

66.54 66.70 2.0 0.06 0.062 -0.009 0.2 0.19 0.03 0.017 - <0.002 rest rest

2170 nominal actual

66.16 66.25 2.0 0.06 0.064 -0.009 0.2 0.19 0.06 0.037 - <0.002 rest rest

2171 nominal actual

65.88 66.00 2.0 0.06 0.062 -0.009 0.2 0.19 0.1 0.055 - <0.002 rest rest

2172 nominal actual

65.67 66.08 2.0 0.06 0.060 0.1 0.085 0.2 0.19 0.03 0.003 - <0.002 rest rest

2173 nominal actual

65.46 65.69 2.0 0.06 0.065 0.1 0.069 0.2 0.19 0.06 0.003 - <0.002 rest rest

2174 nominal actual

66.81 66.72 2.0 0.06 0.062 0.1 0.080 0.2 0.18 -0.003 0.3 0.30 rest rest

Alloy No.

Cu Pb Ace Faith Yes Mn To the Zn

2175 nominal actual

61.3 61.85 2.0 1.77 0.08 0.084 0.1 0.073 - <0.002 - <0.002 - <0.002 rest rest

2176 nominal actual

61.3 61.85 2.0 1.62 0.08 0.087 0.08 0.057 - <0.002 - <0.002 - <0.002 rest rest

2177 nominal actual

61.3 61.68 2.0 1.67 0.08 0.084 0.05 0.049 - <0.002 - <0.002 - <0.002 rest rest

2178 nominal actual

61.2 61.51 2.0 1.83 0.08 0.090 0.08 0.065 - <0.002 0.03 0.005 - <0.002 rest rest

2179 nominal actual

61.2 61.40 2.0 1.71 0.08 0.088 0.08 0.069 - <0.002 0.06 0.025 - <0.002 rest rest

2180 nominal actual

61.3 61.42 2.0 1.98 0.05 0.058 0.03 0.021 - <0.002 - <0.002 - <0.002 rest rest

2181 nominal actual

61.3 61.52 2.0 1.85 0.05 0.047 0.06 0.050 - <0.002 - <0.002 - <0.002 rest rest

2182 nominal actual

62.8 62.87 2.0 1.73 0.05 0.056 0.2 0.13 0.2 0.19 - <0.002 0.3 0.31 rest rest

2183 nominal actual

62.75 62.72 2.0 1.84 0.05 0.059 0.2 0.13 0.2 0.19 0.03 0.027 0.3 0.32 rest rest

2184 nominal actual

62.7 62.70 2.0 1.70 0.05 0.058 0.2 0.11 0.2 0.19 0.06 0.051 0.3 0.32 rest rest

Actual nominal 2185

62.6 62.35 2.0 2.01 0.05 0.053 0.2 0.13 0.2 0.19 0.1 0.032 0.3 0.32 rest rest

2186 nominal actual

61.3 61.35 2.0 2.0 0.05 0.059 0.06 0.048 0.01 0.010 - <0.003 - <0.002 rest rest

Actual nominal 2187

61.2 61.32 2.0 1.99 0.05 0.059 0.01 0.072 0.01 0.009 - <0.003 - <0.002 rest rest

Table 1: Nominal and real compositions of test alloys in% by weight

5 The following tests were carried out with regard to the optimization of the composition:

Trial 1:

For each of the test alloys set forth in Table 1, a degalvanization test according to ISO 6509 was carried out. In this case, the degree of degalvanization of the respective alloy was determined according to

10 a previously defined embodiment of the test in corrosive liquids by measuring a maximum depth of degalvanization in µm. The maximum depth of de-galvanization determined in this way is a measure of the susceptibility to the de-galvanization of the investigated test alloy. The larger the maximum depth of degalvanization of the respective test alloy, the greater its susceptibility to degalvanization.

15 The maximum depths of de-galvanization determined in each case according to ISO 6509 are reproduced in Table 2 for the test alloys.

Trial 2:

20 The test according to ISO 6509 for the verification of stability against degalvanization works with a very aggressive electrolytic solution with regard to degalvanization, which is not suitable for the determination of the IK, which should be attributed to very fine potential differences between grain boundaries and grain surface.

25 For this reason, all test alloys were subjected to those test conditions, of which it is known that they lead to intercrystalline corrosion. For this purpose, for example, tests were carried out with solutions containing ammonium chloride under defined conditions. The degree of intercrystalline corrosion was related to the degree of intercrystalline corrosion of an alloy of CuZn36Pb2As, whose known intercrystalline corrosion was established as 100%. The result of these investigations is set out in

30 column 2 of Table 2.

Alloy No.

Susceptibility to IK compared to CuZn36Pb2As in% Maximum degalvanization depth according to ISO 6509 in µm

2088

19 13

2089

46 12

2090

100 fifteen

2094

30 6

2102

8 0

2106

24 12

2131

91 0

2132

25 0

2133

10 0

2134

10 0

2135

65 0

2136

27 0

2156

5 212

2157

7 18

2158

7 0

2159

100 0

2160

100 0

2161

17 0

2162

13 0

2163

10 0

2164

8 0

2165

2. 3 0

2166

fifteen 0

2167

18 0

2168

18 0

2169

17 0

2170

48 0

2171

100 0

2172

10 0

2173

eleven 0

2174

10 0

2175

88 fifty

2176

96 46

2177

100 75

2178

100 Four. Five

2179

83 60

2180

42 80

2181

42 95

2182

33 40

2183

58 3. 4

2184

42 38

2185

46 54

2186

twenty-one 62

2187

33 108

Table 2: Susceptibility to IK of test alloys and maximum depth of degalvanization 5 (according to ISO 6509)

Trial 3:

Based on NSF 61, 1994 (Drinking Water Systems Components-Health Effects; NSF International Standard 61, section 9, March 1994), lead delivery was investigated to drinking water. In this case, as an embodiment of the invention, a brass alloy was compared with a weight ratio of 64.05% copper, 2.7% lead, 0.1% iron, 0.3% aluminum, 0 , 2% silicon and 0.05% arsenic as well as the zinc moiety, with an alloy of CuZn36Pb2,7As0,14 and with an alloy of CuZn39Pb2,7 according to the state of the art. The three alloys coincide in their proportion of lead of 2.7% by weight. The new alloy is stable against the

15 Degalvanization and intercrystalline corrosion. The CuZn36Pb2,7As0,14 alloy constitutes a state of the art and has a small degalvanization, but has a less high stability against intercrystalline corrosion. The CuZn39Pb2.7 alloy is recognizably susceptible to degalvanization.

Trial 4:

A sample of an alloy of CuZn36Pb2As with a diameter of 27 mm, after an annealing of 500 or respectively of 600 ° C, in each case was warmed once in a water bath and cooled once in an oven. The proportion of the IK was measured. It was shown that by an active cooling the susceptibility to IK can be reduced by 27 to 60%.

Results of tests 1 to 3:

Figure 1 shows the susceptibility to intercrystalline corrosion in% corresponding to column 3 of Table 2 for test alloys No. 2088, 2089, 2090, 2131 and 2132. These alloys differ in their arsenic content. with an otherwise essentially equal composition. The respective arsenic content in% by weight is recorded in the abscissa in Figure 1. The test alloys represented have only a negligible proportion or have no proportion of iron, silicon, manganese and aluminum at all.

It is shown that for a copper and zinc alloy with an increased arsenic content, the susceptibility to intercrystalline corrosion increases. In the case of an arsenic content of 0.14% by weight, the susceptibility to the IK of the comparative alloy corresponding to Table 2 is achieved. However, the susceptibility to the IK decreases considerably for small arsenic contents.

However, for an arsenic-free alloy, such as, for example, No. 2156, a very high maximum depth of degalvanization can be observed. If, therefore, a brass alloy must be stable against degalvanization, then a certain arsenic content must be present. From this point of view, a necessary arsenic content between 0.01 and 0.1% by weight is established from Figure 1 for a brass alloy with a small degalvanization that is stable against IK. Above an arsenic ratio of 0.1% by weight, no protection against IK is guaranteed. If the arsenic content is reduced to below 0.08% by weight, then the susceptibility to intercrystalline corrosion is only less than 60%.

Test alloys No. 2180 and 2181, in regard to their arsenic content, have a non-critical value of 0.05% by weight with respect to IK. Additionally, these test alloys show, however, a small proportion of iron of 0.03% by weight or respectively of 0.06% by weight. A comparison with iron-free test alloys No. 2088 and 2089 shows that the critical upper limit for arsenic content is evidently reduced by the addition of iron. Within the error tolerances the susceptibility to intercrystalline corrosion increases. Also, the susceptibility to degalvanization increases with the addition of iron. If test alloy No. 2159, which has an iron content of 0.082% by weight, is taken into account, then its susceptibility to intercrystalline corrosion can be clearly observed. Test alloy No. 2159 shows, in a manner corresponding to Table 2, a susceptibility to IK of 100%, while test alloys No. 2088 and No. 2089 only show a susceptibility of 19% or respectively of 46%.

If the arsenic content is increased, then the addition of iron no longer essentially worsens susceptibility to intercrystalline corrosion. This fact is observable by comparing test alloys No. 2175 to 2178, which, with an arsenic content of 0.08% by weight, have an increasing iron content, with comparison alloys No. 2089 on 2090

By means of small additions of iron, the critical upper limit for arsenic is therefore reduced, so that after all, through the influence of iron, even in the case of "safe" arsenic contents, intercrystalline corrosion can occur . Iron is therefore a critical element. According to this, iron is unwanted, but for reasons of cost it cannot be avoided, since in the case of using a cheap brass scrap it will be reintroduced as an impurity in the production process. The production of an iron-free brass alloy based on pure or respectively iron-free starting substances is considerably more expensive.

However, it has been surprisingly shown that by the addition of silicon the iron can be evidently fixed, and thus its harmful influence on the corrosion resistance of a brass alloy can be suppressed. This is observable from alloys No. 2094, 2102 and 2106. These alloys have, in the case of arsenic content of 0.07% by weight, iron proportions of 0.14% by weight, 0 , 1% by weight or respectively 0.2% by weight. At the same time, these test alloys contain silicon in proportions of 0.08% by weight and 0.2% by weight. A look at Table 2 confirms that silicon can suppress the harmful effects of iron. The susceptibility to intercrystalline corrosion decreases. Also, these test alloys generally have a small degalvanization.

Additionally, from the alloys n ° s 2160 - 2167 the influence of silicon on the corrosion resistance of the test alloys is observable. In the case of otherwise equal proportions of lead, arsenic and iron, silicon content is increased from test alloy No. 2160 to test alloy No. 2167. While overall corrosion stability remains equally good, it can be seen again that an addition of silicon in small amounts can avoid the harmful effects of small amounts of iron. From approximately 0.3% by weight, however, a susceptibility to intercrystalline corrosion appears again and again. If, therefore, in a brass alloy, small proportions of iron must be tolerated in order to obtain low production costs, then they can be made harmless by adding small amounts of silicon. In the case of tolerable proportions of iron of up to 0.3% by weight, a silicon content between 0.03 and 0.3% by weight should therefore be present.

From alloys No. 2135 and 2136, which have a silicon content of approximately 2% by weight, it can be seen that they are again susceptible to intercrystalline corrosion.

Figure 2 shows the susceptibility to intercrystalline corrosion according to the results in Table 2 for test alloys No. 2168 to 2171. These alloys differ in their composition in terms of their content. manganese, which increases from test alloy No. 2168 to test alloy 2171 from 0.006% by weight to 0.055% by weight. It is shown that manganese is a very critical element when it comes to intercrystalline corrosion, and that it cannot be neutralized by a certain proportion of silicon either. All test alloys No. 2168 to 2171 have a silicon content of approximately 0.2% by weight.

Permissible tolerances for manganese must therefore remain low. Below a proportion of 0.04% by weight, the susceptibility to intercrystalline corrosion is below 50%.

If the silicon is contained in a brass alloy, it has also been shown that the shell can be easily detached from these brass. This results in the installations being impurified by means of the fluttering shell. This problem can be solved by adding aluminum. Annealing tests (duration: 2 hours, temperature: 750 degrees Celsius) in test alloy No. 2102, which is stable against intercrystalline corrosion, confirm that its shell layer is easily detached. By adding an aluminum in a proportion of approximately 0.2% by weight, it was possible to improve the adhesion of the shell layer.

In Figure 3, for a test alloy with a weight ratio of 64.05% copper, 2.7% lead, 0.1% iron, 0.3% aluminum, 0.2% silicon and 0.05% of arsenic as well as the zinc residue (symbol *), for an alloy of CuZn36Pb2,7As0,14 (symbol O) and for an alloy of CuZn36Pb2,7 (symbol represents the delivery of lead to drinking water based on NSF 61, 1994. The delivery of lead is represented in µg per liter over time.

Surprisingly it has been shown that a stable alloy against intercrystalline corrosion, namely the test alloy, shows a lower lead delivery than the stable brass alloy against the CuZn35Pb2,7As0,14 degalvanization according to the state of the technique.

Claims (6)

one.

 Copper and zinc alloy stable against degalvanization, in particular for use in the health sector, characterized because she understands 50 to 80% by weight of Cu, from 0 to 5% by weight of Pb, from 0.01 to 0.10% by weight of As, from 0.03 to less than 0.3% by weight of Si, from 0 to 0.3% by weight of Fe, from 0 to 0.04% by weight of Mn, and optionally from 0.15 to 0.3% by weight of Al Zn remainder as well as the inevitable impurities, and because the equivalent of effective Cu is 60 to 70% in weight.

2.

 Copper and zinc alloy according to claim 1 or 2, characterized in that it is contained from 0 to 0.02% by weight of Mn.

3.

 Copper and zinc alloy according to one of the preceding claims, characterized in that it is content of 0.02 to 0.08 of As.

Four.

 Copper and zinc alloy according to one of the preceding claims, characterized in that it is content up to 0.2% by weight of Fe and from 0.15 to 0.25% by weight of Si.

5.

 Process for the production of a copper and zinc alloy according to one of the claims precedents, in which the starting materials are mixed in the indicated weight ratio, melted, and cast by casting to give a metal alloy, and the metal alloy is annealed for the formation of the α phase at 500 - 650 ° C, characterized in that the annealed metal alloy is actively cooled by agents refrigerants

6.

 Method according to claim 6, characterized in that the metal alloy, after a Subsequent treatment by cold forming at 250 to 600 ° C, is subjected for 10 min and 2 h to a Annealing with stress removal.

Figure 1 Figure 2 Figure 3