EP2652163B1 - 7xxx alloy thick products and their process of manufacture - Google Patents

Description

Field of the invention

The present invention generally relates to aluminum alloy products and, more particularly, to such thick 7xxx alloy products, their methods of manufacture and use.

State of the art

In the field of plastics obtained by injection, there is a growing demand for large products. In order to produce the molds making it possible to manufacture these large products, it is necessary to use thick blocks, that is to say ones whose thickness is greater than 350 mm, and preferably greater than 450 mm or even greater than 550 mm. By block, we mean a massive product, essentially parallelepiped shape.

Thick aluminum blocks are also useful in the field of mechanical engineering.

The characteristics required for the thick aluminum blocks for the manufacture of molds are static mechanical characteristics, such as the yield strength or the breaking strength, high as well as a good notch resistance, these properties being in good condition. general antinomies. Thus notch resistance is an important property of use for these products and it can be characterized for example by the NSR, which is the ratio between the elastic limit and the mechanical strength in the presence of a notch (" Sharp-Notch Strength-to-Yield Strength Ratio ") measured according to ASTM-E602. For thick products, these properties must in particular be obtained at quarter and / or at mid-thickness and the products must therefore have a low sensitivity to quenching. A product is said to be quench sensitive if its static mechanical characteristics, such as its yield strength, decrease as the quenching rate decreases. The quenching rate is the average cooling rate of the product during quenching.

The thick blocks should also preferably have low residual stresses. Indeed, the residual stresses cause deformations during the machining which affect the geometry of the mold. The residual stresses can be measured for example by the method described in the patent application WO 2004/053180 . By low residual stresses we typically mean a W _Tbar value of less than 4 kJ / m ³ , and in general of the order of 2 kJ / m ³

Finally, the thick blocks must be obtained with a process as fast and economical as possible.

The patent EP1587965 (Alcan) discloses an alloy useful for the manufacture of thick blocks, composition (in% by weight) 4.6-5.2% Zn; 2.6-3.0% Mg; 0.1-0.2% Cu; 0.05-0.2% Zr; not more than 0.05% Mn; not more than 0.05% Cr; not more than 0.15% Fe; not more than 0.15% Si; not more than 0.10% Ti and a method of manufacturing these blocks, in which the ingot obtained by continuous casting is used directly as a block.

International demand WO 2008/005852 (Alcan) discloses an alloy useful for very thick products comprising (in% by weight) 6 to 8% of zinc, 1 to 2% of magnesium, dispersoid-forming elements such as Zr, Mn, Cr, Ti and / or sc.

• l'alliage 7003 qui a la composition suivante:
  5,0 % - 6,5 % Zn; 0,50-1,0 % Mg; 0.05-0,25 % Zr; 0-0,20 % Cu; 0-0,35 % Fe; 0-0,30 % Si; 0-0,30% Mn; 0-0,20% Cr; 0-0,20 % Ti; balance Al avec impuretés inévitables <0,05 %, total <0,15%
• l'alliage 7021 qui a la composition suivante:
  5,0 % - 6,0 % Zn; 1,2-1,8 % Mg; 0.08-0,18 % Zr; 0-0,25 % Cu; 0-0,40 % Fe; 0-0,25 % Si; 0-0,10% Mn; 0-0,05% Cr; 0-0,10 % Ti; balance Al avec impuretés inévitables <0,05 %, total <0,15%

Alloys of similar composition are also known for other applications. For example, they are registered with the Aluminum Association:

• the alloy 7003 which has the following composition:
  5.0% - 6.5% Zn; 0.50-1.0% Mg; 0.05-0.25% Zr; 0-0.20% Cu; 0-0.35% Fe; 0-0.30% Si; 0-0.30% Mn; 0-0.20% Cr; 0-0.20% Ti; Al balance with unavoidable impurities <0.05%, total <0.15%
• alloy 7021 which has the following composition:
  5.0% - 6.0% Zn; 1.2-1.8% Mg; 0.08-0.18% Zr; 0-0.25% Cu; 0-0.40% Fe; 0-0.25% Si; 0-0.10% Mn; 0-0.05% Cr; 0-0.10% Ti; Al balance with unavoidable impurities <0.05%, total <0.15%

The patent US 3,852,122 (Ardal) describes an alloy of composition (in% by weight) 4.5 - 5.8% Zn, 1.0 - 1.8% Mg, 0.10 - 0.30% Zr, 0-0.30% Fe, 0- 0.15% Si, 0-0.25% Mn intended to produce long products usable for the manufacture of bumpers, structural parts and also parts used for the manufacture, storage and transport of gases in the condensed state.

The patent application FR 2,341,661 (VMRBA) describes a composition alloy (in% by weight) 4.0-6.2% Zn, 0.8-3.0% Mg, 0-1.5% Cu, 0.05 - 0.30% Zr, 0 - 0.20% Fe, 0-0.15% Si, 0-0.25% Mn, 0-0.10% Ti intended to be forged or kneaded by hot deformation and to be used for construction vehicles, machinery, equipment tanks and tools.

The patent application JP81144031 (Furukawa) discloses an alloy composition (in% by weight) 4.0-6.5% Zn, 0.4-1.8% Mg, 0.1-0.5% Cu, 0.1-0.5% Zr, and additionally 0.05-0.20% Mn and / or 0.05-0.20% Cr, for the production of tubes.

The problem solved by the present invention is to obtain thick aluminum blocks having an improved property compromise between the static mechanical characteristics and the notch resistance, having a low level of residual stresses, by a rapid process. and economic.

Object of the invention

• (b) optionnellement, homogénéisation à une température comprise entre 450 et 550 °C pendant une durée de 10 minutes à 30 heures et/ou détente à une température comprise entre 300 et 400 °C pendant une durée de 10 minutes à 30 heures suivi d'un refroidissement jusqu'à une température inférieure à 100 °C;
• (c) mise en solution dudit bloc coulé à une température de 500 à 560°C pendant 10 mn à 20 heures,
• (d) refroidissement dudit bloc mis en solution jusqu'à une température inférieure à 100 °C réalisé avec une vitesse de refroidissement au moins égale à 800 °C/h puis détensionnement du bloc ainsi mis en solution et refroidi par une compression contrôlée avec une déformation permanente comprise entre 1% et 5%;
• (e) revenu dudit bloc mis en solution et refroidi, par chauffage à 120 à 170°C pendant 4 à 48 heures,

dans lequel aucune des dimensions dudit bloc coulé ne subit de déformation d'au moins 10% par corroyage entre les étapes de coulée et de revenu.The object of the invention is a method of manufacturing an aluminum block having a thickness greater than 350 mm comprising the steps of: (a) casting a thick aluminum alloy block comprising (in % by weight): Zn: 5.4-5.8%, Mg: 0.8-1.8%, Cu: <0.2%, Zr: 0.05-0.08%, Ti: <0 , 15%, Mn: <0.1%, Cr: <0.1%, Si: <0.15%, Fe: <0.20%, impurities with an individual content <0.05% each and <0 15% in total remains aluminum;

• (b) optionally, homogenizing at a temperature between 450 and 550 ° C for a period of 10 minutes to 30 hours and / or expansion at a temperature between 300 and 400 ° C for a period of 10 minutes to 30 hours followed by cooling to a temperature below 100 ° C;
• (c) dissolving said cast block at a temperature of 500 to 560 ° C for 10 minutes to 20 hours,
• (d) cooling said block in solution to a temperature below 100 ° C achieved with a cooling rate of at least 800 ° C / h and then stress relieving the block so dissolved and cooled by a controlled compression with a permanent deformation of between 1% and 5%;
• (e) returning said block dissolved and cooled, by heating at 120 to 170 ° C for 4 to 48 hours,

wherein none of the dimensions of said cast block undergo deformation of at least 10% by wrought between casting and tempering steps.

et

• R_p0,2 > 320 MPa, de préférence 330 MPa
  et/ou
• NSR > 0,8, de préférence 1,0.

Another object of the invention is a thick block of aluminum obtainable by the process according to the invention, characterized in that, at ¼ thickness in the direction TL, the elastic limit R _P0,2 and the NSR report between the notched specimen mechanical strength and the elastic limit R _P0.2 measured according to ASTM E602-03, paragraph 9.2 are such that: $$\mathrm{NSR}>-\mathrm{0,017}*{\mathrm{R}}_{\mathrm{p}0.2}+6.7$$

and

• R _p0.2 > 320 MPa, preferably 330 MPa
  and or
• NSR> 0.8, preferably 1.0.

Yet another object of the invention is the use of a thick block according to the invention for the manufacture of mold for injection of plastics.

Description of figures

Figure 1 : Compromise obtained between the elastic limit R _P.0,2 and the parameter called NSR ("Sharp-Notch Strength-to-Yield Strength Ratio"), which is the ratio of the notched specimen mechanical strength and the elastic limit R _P0,2 .

Unless stated otherwise, all the information concerning the chemical composition of the alloys is expressed as a percentage by weight based on the total weight of the alloy. The designation of alloys is in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The definitions of the metallurgical states are given in the European standard EN 515.

Unless otherwise stated, the static mechanical characteristics, in other words the ultimate ultimate tensile strength R _m , the tensile yield strength R _p0,2 and the elongation at break A, are determined by a tensile test. according to standard EN 10002-1 or NF EN ISO 6892-1, the location to which the parts are taken and their meaning being defined by the EN 485-1 standard. The notched specimen mechanical strength is obtained in accordance with ASTM E602-03. In accordance with E602-03, paragraph 9.2, the so-called NSR ratio between notched specimen strength and yield strength R _P0.2 ("Sharp-Notch Strength-to-Yield Strength Ratio") is calculated. report gives an indication of the notch resistance of the sample.

$$\mathrm{Mg}:\mathrm{0,8}-\mathrm{1,8}\%$$

$$\mathrm{Cu}:<\mathrm{0,2}\%,$$

$$\mathrm{Zr}:\mathrm{0,05}-\mathrm{0,08}\%,$$

$$\mathrm{Ti}<\mathrm{0,15}\mathrm{}\%,$$

$$\mathrm{Mn}<\mathrm{0,1}\mathrm{}\%,$$

$$\mathrm{Cr}<\mathrm{0,1}\%,$$

$$\mathrm{Si}<\mathrm{0,15}\mathrm{}\%,$$

$$\mathrm{Fe}<\mathrm{0,20}\mathrm{}\%,$$

impuretés ayant une teneur individuelle < 0,05 % chacune et < 0,15% au total, reste aluminium.The problem is solved by an alloy comprising (in% by weight); $$\mathrm{Zn}:5.4-5.8\%,$$

$$\mathrm{mg}:0.8-1.8\%$$

$$\mathrm{Cu}:<0.2\%,$$

$$\mathrm{Zr}:0.05-0.08\%,$$

$$\mathrm{Ti}<0.15\mathrm{}\%,$$

$$\mathrm{mn}<0.1\mathrm{}\%,$$

$$\mathrm{Cr}<0.1\%,$$

$$\mathrm{Yes}<0.15\mathrm{}\%,$$

$$\mathrm{Fe}<0.20\mathrm{}\%,$$

impurities with an individual content <0.05% each and <0.15% in total, remains aluminum.

The combination of the zinc content of 5.4 - 5.8% by weight, the magnesium content of 0.8 to 1.8% and the copper content of less than 0.2% by weight makes it possible to achieve an improved compromise between mechanical strength and notch resistance. The preferred magnesium content is 1.0 to 1.4% by weight or even 1.1 to 1.3% by weight. The preferred copper content is less than 0.05% by weight or even less than 0.04% by weight.

The zirconium content is 0.05 to 0.08% by weight, so as to further reduce the quenching sensitivity of the thick aluminum blocks.

The titanium content is less than 0.15% by weight. Advantageously, an amount of titanium of between 0.01 and 0.05% by weight and preferably between 0.02 and 0.04% by weight is added in order to refine the grain size during casting.

The Cr content and the Mn content are less than 0.1%. Preferably, the Cr content is less than 0.05% by weight or even less than 0.03% by weight, and / or the Mn content is less than 0.05% by weight or even less than 0, 03% by weight, which allows in particular to further reduce the sensitivity to quenching thick aluminum blocks.

Si and Fe are unavoidable impurities whose content is to be minimized so as in particular to improve the mechanical strength on the notched specimen. The Fe content is less than 0.20% by weight and preferably less than 0.15% by weight. The Si content is less than 0.15% by weight and preferably less than 0.10% by weight.

1. (a) coulée d'un bloc épais en alliage d'aluminium comprenant (en % en poids) :Zn: 5,4-5,8%,Mg: 0,8 - 1,8 %,Cu : < 0,2 %,Zr : 0,05 - 0,08 %,Ti: < 0,15 %,Mn: < 0,1 %,Cr: < 0,1 %,Si: < 0,15 %,Fe: < 0,20 %, impuretés ayant une teneur individuelle < 0,05 % chacune et < 0,15% au total, reste aluminium ;
2. (b) optionnellement, homogénéisation à une température comprise entre 450 et 550 °C pendant une durée de 10 minutes à 30 heures et/ou détente à une température comprise entre 300 et 400 °C pendant une durée de 10 minutes à 30 heures suivi d'un refroidissement jusqu'à une température inférieure à 100 °C;
3. (c) mise en solution dudit bloc coulé à une température de 500 à 560°C pendant 10 mn à 20 heures,
4. (d) refroidissement dudit bloc mis en solution jusqu'à une température inférieure à 100 °C, réalisé avec une vitesse de refroidissement au moins égale à 800 °C/h puis détensionnement du bloc ainsi mis en solution et refroidi par une compression contrôlée avec une déformation permanente comprise entre 1% et 5%;
5. (e) revenu dudit bloc mis en solution et refroidi, par chauffage à 120 à 170°C pendant 4 à 48 heures, dans lequel aucune des dimensions dudit bloc coulé ne subit de déformation d'au moins 10% par corroyage entre les étapes de coulée et de revenu.

A suitable method for making thick alloy blocks according to the invention comprises the steps of

1. (a) casting of a thick block of aluminum alloy comprising (in% by weight): Zn: 5.4-5.8%, Mg: 0.8 - 1.8%, Cu: <0.2 %, Zr: 0.05 - 0.08%, Ti: <0.15%, Mn: <0.1%, Cr: <0.1%, Si: <0.15%, Fe: <0, 20%, impurities with an individual content <0.05% each and <0.15% in total, remains aluminum;
2. (b) optionally, homogenizing at a temperature between 450 and 550 ° C for a period of 10 minutes to 30 hours and / or expansion at a temperature between 300 and 400 ° C for a period of 10 minutes to 30 hours followed by cooling to a temperature below 100 ° C;
3. (c) dissolving said cast block at a temperature of 500 to 560 ° C for 10 minutes to 20 hours,
4. (d) cooling said block dissolved in a temperature of less than 100 ° C., carried out with a cooling rate of at least 800 ° C./h, and then relieving the block thus put into solution and cooled by a controlled compression with permanent deformation of between 1% and 5%;
5. (e) returning said block dissolved and cooled, by heating at 120 to 170 ° C for 4 to 48 hours, wherein none of the dimensions of said cast block undergoes deformation of at least 10% by wrought between the steps of casting and income.

The casting of the thick block is preferably carried out by semi-continuous casting with direct cooling ("Direct Chill Casting"). The thick block has a thickness greater than 350 mm, and preferably greater than 450 mm or even greater than 550 mm. The block is essentially parallelepipedal in shape, it generally has a larger dimension (length), a second larger dimension (width) and a smaller dimension (thickness).

The block may optionally then be homogenized, typically by a heat treatment at a temperature between 450 and 550 ° C for a period of 10 minutes to 30 hours and / or undergo a flash treatment at a temperature between 300 and 400 ° C for a period of 10 minutes to 30 hours followed by cooling to a temperature below 100 ° C.

The block is then put into solution, that is to say heat-treated so that the block temperature reaches 500 to 560 ° C for a period of between 10 minutes and 5 hours, or even 20 hours. This heat treatment can be carried out at a constant temperature or in several stages.

After dissolution, the block is cooled to a temperature below 100 ° C, preferably to room temperature. The cooling rate is at least 800 ° C / h. Such a cooling rate can be obtained by spraying or immersion in water. Since a cooling rate that is too high can generate excessive residual stresses in the blocks, water is preferably used at a temperature of at least 50.degree. C. and preferably at least 70.degree. C. for cooling. In this second embodiment, the block thus hardened is stripped, preferably by cold compression with a permanent deformation rate of between 1% and 5% and preferably between 2 and 4%. The stress relieving allows to reduce the residual stresses in the metal and to avoid the deformations during the machining.

Finally, one realizes the income of the block thus put in solution and cooled. The income is made so that the block reaches a temperature of 120 and 170 ° C and preferably between 130 and 160 ° C for a period of 4 to 48 hours and preferably between 8 and 24 hours. Advantageously, an income is achieved to reach the T6 or T652 state, corresponding to the peak of the static mechanical properties (Rm and Rp0,2).

Between each operation, it is possible to perform simple operations of sawing the block and / or machining surfaces.

typiquement inférieure à 0,135.On the other hand, said block does not undergo between the casting and the significant deformation step income by wrought. By "wrought" is typically meant rolling operations or hot forging. By "significant deformation" is meant that none of the dimensions of the cast block - which is a thick block of substantially parallelepiped shape (length L, width TL, thickness TC) - undergoes significant modification, that is to say typically at least about 10%, by heat treatment between casting and income. In other words, none of the dimensions of the cast block is subjected to a relative variation typically greater than 10% in absolute value by wrought, which means that said wrought-molding does not lead to permanent deformation in each direction L, TL, TC greater than a value close to Ln (1,1) = 0,095 and corresponds to a generalized plastic deformation $\left(\tilde{\epsilon }=\sqrt{\frac{2}{3}\left({\epsilon }_{\mathrm{The}}^2+{\epsilon }_{T\mathrm{The}}^2+{\epsilon }_{T\mathrm{VS}}^2\right)}\right)$

typically less than 0.135.

The thick blocks obtained by the process according to the invention have a compromise of advantageous properties, in particular between the elastic limit and the notch resistance, which are two antagonistic properties (the more important one is, the more other is weak). More specifically, the Applicant has found that for a thick block of an alloy having the composition according to the invention and having been obtained by following the claimed process steps until the income (casting, homogenization and stress relief optional, dissolution and quenching without significant wrought between the casting and the final step of income), regardless of the income treatment (mono- or multi-level) subsequently carried out to reach a given elastic limit Rp0.2, the NSR ("Sharp-Notch Strength-to-Yield Strength Ratio") parameter used to characterize the notch resistance of the block thus obtained, reaches a value that does not depend on the income treatment performed to obtain the targeted Rp02. For such thick blocks, a relationship between the RpO 2 and the NSR measured for example at ¼ of the thickness can therefore be established, and this relationship appears to be substantially linear.

Thus, the Applicant has been able to establish that the notch resistance, as evaluated at ¼ thickness in the TL direction by the NSR (measured according to ASTM E602-03, paragraph 9.2) is greater than: $$-\mathrm{0,017}*{\mathrm{R}}_{\mathrm{p}0.2}+\mathrm{6.7.}$$

Typically, the NSR is at least 0.8, preferably 1.0, and the yield strength is at least 320 MPa and preferably 330 MPa.

Obtaining both high mechanical strength and high notch resistance is a surprising result.

The thick blocks according to the invention are advantageously used for the manufacture of molds for injection of plastics

EXAMPLE

The example of the invention is referenced B. Examples A, C and D are presented for comparison. The chemical compositions of the various alloys tested in this example are provided in Table 1. <u> Table 1: Chemical composition (% by weight) </ u> Reference Yes Fe Cu mn mg Zn Zr Cr Ti AT 0.05 0.08 0.02 0.01 1.2 5.7 0.08 <0.01 0.04 B 0.05 0.08 0.03 <0.01 1.2 5.6 0.08 <0.01 0.04 VS 0.05 0.13 0.2 0.01 2.8 4.9 0.09 <0.01 0.03 D 0.08 0.04 0.6 <0.01 2.2 6.3 0.10 <0.01 0.03

Alloys A, B, C and D were cast as blocks of thickness 625 mm.

The blocks of alloys A and C were transformed as follows: the blocks were first homogenized at 10h 480 ° C. The blocks were then dissolved for 4 hours at 540 ° C. and air-cooled at approximately 40 ° C./h (from 540 ° C. to 410 ° C. in 2 hours and then from 410 ° C. to 90 ° C. in 9 hours). ). The blocks were then first treated at 105 ° C for about 12 hours and then at 160 ° C for about 16 hours.

The alloy blocks B and D were transformed as follows: the blocks first underwent a 2 hour expansion at 350 ° C. After being dissolved for 4 hours at 540 ° C. (Block B) or 10 hours at 475 ° C. (Block D), the blocks were cooled with water at 80 ° C. by immersion. The blocks then underwent compression straightening of 3%. The alloy blocks B were then tempered at 130 ° C for 24 h (block B1) or 150 ° C for 16 h (block B2). The alloy block D was first treated at 90 ° C for 8 to 12 hours and then at 160 ° C for 14 to 16 hours.

The mechanical characteristics obtained, measured at ¼ thickness in the TL direction are presented in Table 2 <u> Table 2: Mechanical characteristics obtained at ¼ thickness in the TL direction </ u> Reference Returned Rm (MPa) Rp0.2 (MPa) A50 (%) NSR AT 105 ° C 10-15h + 160 ° C 16-17h 355 332 1.8 0.88 B1 T ° 1 (130 ° C / 24h) 407 359 3 0.7 B2 T ° 2 (150 ° C / 16h) 376 324 8 1.3 VS 105 ° C 10-15h + 160 ° C 16-17h 335 320 0.4 0.50 D 90 ° C 8-12h + 160 ° C 14-16h 401 335 2 0.87

The Figure 1 presents the compromise obtained between the elastic limit R _P0,2 and the report called "Sharp-Notch Strength-to-Yield Strength Ratio", known under the abbreviation "NSR" and commonly used to characterize the sensitivity to the effect notch of a material. As its full English name indicates, this parameter is the ratio between the mechanical strength measured on notched specimen and the elastic limit measured on non-notched specimen. The rationale for the use of this parameter and the experimental protocol for measuring it are described in ASTM E602-03, particularly in section 9.2.

Under identical transformation conditions, the alloy A allows, with respect to the alloy C, a simultaneous improvement in the yield strength and in the NSR ratio, and thus in the notch strength. The NSR report obtained is greater than
-0.017 R _p0.2 + 6.4.

The process for converting the alloy according to the invention makes it possible to further improve the NSR ratio. Thus, the alloy block B according to the invention has an NSR ratio greater than -0.017 * R _p0.2 + 6.7.

This ratio is not reached by alloy D under similar processing conditions.

Claims (6)

1. Method for manufacturing an aluminium block wherein the thickness is greater than 350 mm comprising steps for:

   (a) casting a thick aluminium alloy block comprising (as a % by weight): Zn: 5.4 - 5.8%, Mg: 0.8 - 1.8%, Cu: < 0.2%, Zr: 0.05 - 0.08%, Ti : < 0.15%, Mn : < 0.1%, Cr : < 0.1%, Si: < 0.15%, Fe : < 0.20%, impurities having an individual content < 0.05% each and < 0.15% in total, remainder aluminium;

   (b) optionally, homogenising at a temperature between 450 and 550°C for a period of 10 minutes to 30 hours and/or stress relief at a temperature between 300 and 400°C for a period of 10 minutes to 30 hours followed by cooling to a temperature less than 100°C;

   (c) solution heat treatment of said cast block at a temperature of 500 to 560°C for 10 min to 20 hours,

   (d) cooling of said solution-heat treated block to a temperature less than 100°C, carried out with a cooling rate at least equal to 800°C/hour followed by stress relief of the solution-heat treated and cooled block by controlled compression with a permanent set between 1% and 5%

   (e) aging of said solution-heat treated and cooled block, by heating at 120 to 170°C for 4 to 48 hours,

   wherein none of the dimensions of said cast block is subject to strain of at least 10% by working between the casting and aging steps.
2. Method according to claim 1 wherein the solution-heat treated and cooled block undergoes stress relief with a permanent set between 2 and 4%.
3. Method according to claim 2 wherein the cooling of step (d) is carried out by spraying with or immersing in water at a temperature of at least 50°C and preferably of at least 70°C.
4. Aluminium block wherein the thickness is greater than 350 mm suitable for being obtained using the method according to any one of claims 1 to 3,
   said block comprising (as a % by weight): Zn: 5.4 - 5.8%, Mg: 0.8 - 1.8%, Cu: < 0.2%, Zr: 0.05 - 0.08%, Ti: < 0.15%, Mn: < 0.1%, Cr: < 0.1%, Si: < 0.15%, Fe: < 0.20%, impurities having an individual content < 0.05% each and < 0.15% in total, remainder aluminium; and
   characterised in that, at ¼ thickness in the direction TL, the yield strength R_P0.2 expressed in MPa and the ratio referred to as NSR between the mechanical strength on a notched test piece and the yield strength R_P0.2 measured as per the standard ASTM E602-03, paragraph 9.2 are such that:

   - NSR > -0.017 * R_p0.2 + 6.7 and

   - R_p0.2 > 320 M Pa, preferably 330 MPa.
5. Aluminium block according to claim 4 characterised in that NSR > 0.8, preferably 1.0.
6. Use of a thick block according to any one of claims 4 to 5 for the manufacture of moulds for the injection of plastics.

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