DK158317B - PROCEDURE FOR MANUFACTURING HEAT EXTRADED PRODUCTS OF AL-ZN-MG-CU ALLOYS WITH HIGH STRENGTH AND INCREASED TRANSPARENCY - Google Patents

Abstract

1. A method of producing hot extruded products of the type Al-Zn-Mg-Cu, which, in the treated state, has improved transverse characteristics, characterised by casting an alloy of the following composition (% by weight) : Si =< 0.08 Cu 1.0 to 2.0 Mg 2.1 to 3.5 Zn 7.2 to 9.5 Cr 0.07 to 0.17 Mn 0.15 to 0.25 Zr 0.08 to 0.14 Ti =< 0.10 Others each =< 0.05 Others total =< 0.15 Balance = Al and iron homogenizing the cast product in the range of temperatures of from 460 degrees C to the initial melting temperature of the alloy, hot extruding the product at a temperature of the order of 400 degrees C, optionally hot drawing the hot extruded product, putting the product into solution in the range of temperatures of from 460 to 490 degrees C, quenching the product in cold water (omicron =< 40 degrees C), cold working with a level of deformation (S - s/s) =< 10%, and a tempering operation : type T6 : that is to say, from 6 to 50 hours at from 115 to 150 degrees C, or type T7 : that is to say, from 3 to 24 hours at from 100 to 120 degrees C + 8 to 20 hours at from 150 to 170 degrees C, the longest periods of time generally being associated with the lowest temperatures.

Description

DK 158317 B

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for the production of high-strength aluminum alloys of the type Al-Zn-Mg-Cu of high strength, which products in the treated state (type T6 or T7) exhibit increased ductility and toughness, particularly in the transverse , as well as good resistance to stress corrosion.

High extruded heat extruded products are known which exhibit good longitudinal and ductility and longitudinal characteristics (see, for example, French Patent Specification No. 2,457,908). These are products made by a process in which the curing is followed directly by a deposit, whereby a complementary cold deformation step between the curing and the annealing is compulsory. This operation substantially improves the mechanical properties in terms of resilience while maintaining the increased toughness.

For some applications, especially in such areas where the materials are subjected to a very high load and must exhibit high reliability and use: safety (e.g. in aviation, military and the like), the properties are in the transverse direction. however, insufficient, especially as regards the parts which are only slightly welded to one another.

It has now been found that these disadvantages can be remedied by precisely the method disclosed herein.

In the process according to the invention, an alloy is cast, the composition of which is as follows (in weight? 0): 2

DK 158317B

Si £ 0.08 Cu in .0 - 2.0 Mg 2.1 - 3.5 Zn 7.2 - 9.5 Cr0.07-0.17

Mn 0.15 - 0.25 Zr 0.08 - 0.14 Ti £ 0.10 other metals each 5 0.05 other metals total ύ 0.15 residue = Al and Fe, then homogenize the molded product at a temperature at between 460 ° C and the temperature at which the alloy begins to melt, the product extrudes at a temperature of the order of 400 ° C, 20 if desired extends the heat extruded product at a temperature of the order of 380 ° C, the product dissolves at a temperature of between 460 and 480 ° C, 25% quench the product in cold water (Θ 4.40 C) and make a stir. This annealing is done under the following conditions: 30 in [Type T6: between 6 and 50 hours at a temperature of 115-150 ° C or in type T7: between 3 and 24 hours at a temperature of 100-120 ° C + 8-20 hours at a temperature between 150 and 35 170 ° C.

Third

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Generally, the longest times are associated with the lowest temperatures.

The process according to the invention is characterized in that the content of Fe is limited to a maximum of 0.10% by weight and that a cold deformation of the product with a degree of deformation (<10%) is made between the quenching and the annealing.

The optimum properties are obtained by combining the following conditions:

Analysis F e £ 0.10 (wt SS) Si <0.08

Cu: 1.35 - 1.85 Mg: 2.4 - 3.0

Zn: 7.6 - 8.9 Cr: 0.10 - 0.17 Mn: 0.15 - 0.25! Zr: 0.08 - 0.14 20 Ti ^ 0.10 other metals each ^ 0.05 other metals total £ 0.15 residue = Al 25 Homogenization at 470 ° C - 5 ° C Solution at 465 to 480 ° C Cold deformation ~ ---) between 1.5 and 5%

S

Inlet type T6: 25-35 hours at 115-130 ° C

or type T7: 5-10 hours at 100-110 ° C

5o + 8-12 hours at 155-165 ° C

4

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It should be noted that the contents of the individual main alloying elements must be sufficient to achieve the desired mechanical properties, but at the same time they must be sufficiently limited so that the final products are not too fragile. The ductility in the transverse direction is thus strongly influenced by the contents of Fe and Si, which should therefore preferably be kept as low as possible, more specifically within the following limits: 10 Fe ^ 0.05 / ¾

Si ^ 0.05¾

Fe + Si at 0.06¾.

The following examples illustrate the properties obtained for an extruded hollow blank and for an extruded rod.

FIG. 1 shows in detail how the tests are carried out, and fig. 2 shows the design of a test body for determining the factor K (see appendix). The dimensions are stated in mm.

20 25

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5

Example 1

Two alloys A and B were cast, the compositions of which are set forth below, alloy A which is not in accordance with the invention served as a control.

5 Weight- »A B

Fe 0.14 0.05

They 0.06 0.04

Cu 1.63 1.60

Zn 8.13 8.00 10 Mg 2.69 2.46

Mn 0.18 0.20

Cr 0.13 0.12

Zr 0.11 0.13

Ti <0.05 <0.05 15

The alloy A, which was cast semi-continuously in the form of burrs having a diameter of 170 mm, was subjected to a homogenization treatment for 24 hours at a temperature of 460 ° C and then heat extruded by reverse extraction at a temperature of 400 ° C. - 10 ° C to form hollow workpieces with dimensions 0 107 x 141 mm. These hollow blanks were extracted in hot state at a temperature of 380 ° C - 20 ° C to dimensions 0 105.5 x 132 mm and machined by turning to a diameter of 127.2 mm.

Subsequently, the blanks were purified, subjected to a solution treatment at a temperature of 460 ° C, quenched in cold water, subjected to a cold state extraction with a degree of cold deformation (-) of 4S and finally annealed for 30 hours at 120 ° C.

30

The alloy B, which was in accordance with the invention, became. divided into four portions: B1, B2, B3 and B4:

The portion B1 was transformed in a manner identical to the transformation of alloy A, though the degree

6 DK 158317 B

of cold deformation (---) was 10 ° instead of 4%.

p

The portion B2 was transformed in the same way as alloy A.

5

The portion B3 was transformed in a manner identical to B2, except that the homogenization treatment was carried out at a temperature of 470 ° C (instead of 460 ° C) and the solution treatment was carried out at a temperature 10 of 470 ° C (instead for 460 ° C). The portion B3 thus corresponds to a preferred area of the invention.

The portion B4 was transformed in the same manner as portion B2 except that the final annealing was carried out as follows: 6 hours at 105 ° C + 10 hours at 150 ° C, 155 ° C, 160 ° C and 165 ° C (respectively). B41, B42, B43 and B44) or at a temperature of 120 ° C for 30 hours (B40).

From the hollow blanks obtained, the following were prepared (see FIG.

1): (a) smooth test pieces (1) for tensile testing, which are either taken from the body of the hollow workpiece, distinguishing between the longitudinal direction (L) and the transverse direction (the tangential direction T), or from the bottom of the hollow workpiece in the transverse direction; (T) (tangential direction). Through the tensile test, the test pieces were used to determine conventional mechanical characteristics, namely: 30 elastic limit RO, 2 breaking strength Rm breaking extensions? Measured over a usable initial length of 5, 6, vi:, where So is the cross section of sample 35 before stretching.

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7 b) tensile test specimens with incisions (2) with a coefficient of stress concentration K-j. = 6.5 (radius at the base of the incision: 0.025 mm) which was taken longitudinally of the body part of the hollow workpiece. The test pieces were broken at 5 tensile stresses which made it possible to determine their breaking strength Re. The ratio Re / R0.2, which indicates the ratio between the fracture strength of a specimen with incisions and the elastic limit of a smooth specimen, was used as the evaluation criterion.

10 (c) specimens with incisions (3) of the type Charpy V for impact testing (45 ° V-shaped incisions, 2 mm in depth, with a radius at the bottom of the incision of 0.25 mm). The test pieces were taken longitudinally of the body part of the hollow 15 workpieces so that the rupture crack propagates in the direction of the thickness of the body part of the hollow part (normalized direction L-R '. The workpieces were used to determine the following characteristics: pre-cracked specimen) and Eco (fractional energy for a specimen previously cracked by fatigue treatment on a Physmet apparatus).

d) specimens (4) for measuring the toughness factor K; the conditions for determining this factor K are described in the following appendix.

e) specimens for corrosion tests in the form of C-rings taken from the body part and with a width of 40 mm. - Oisse specimens were tested for stress corrosion in accordance with the standard AFN0R A 05-301.

The results (averages) are given in Table I of the appendix below.

With respect to the items A1, B1, B2 and B3, which are treated according to the T6 regulation, it is noted that the portions B1, B2 and S3 according to the invention exhibit fracture extensions, in cross-sections.

8 DK 158317B

the direction in the part of the bottom, which is relatively easily processed, which is substantially higher than the corresponding values of the reference mixture A1. In addition, the mixture BZ, which was subjected to cold deformation after quenching and pre-tempering, exhibits in the preferred range of the invention (> 1.5% and - 5%) a number of tensile strength characteristics corresponding to a higher performance than the mixture B1 in which the degree of cold deformation was 10%.

In addition, the mixture B3, for which the conditions of homogenization, solution treatment and cold deformation between quenching and annealing are within the preferred range of the invention, provides a particularly high degree of performance, especially with respect to the elongation at break of the bottom of it. hollow blank, which is more than four times the corresponding value of the reference mixture A.

Finally, mixtures B4x show that, for a two stage T7 treatment 20, it is possible for the alloys of the invention to achieve a particularly high level of resistance to stress corrosion.

Example 2 25

Three alloys · C, D and E with the compositions given below were cast semi-continuously in the form of 200 mm diameter bars:

30% by weight C D E

Fe 0.16 0.09 0.02

Si 0.10 0.05 0.02

Cu 1.45 1.45 1.45

Mg 2.65 2.65 2.65 Zn 8.10 8.10 8.10

Mn 0.22 0.21 0.22

Cr 0.15 0.10 0.16

Zr 0.11 0.12 0.11

Ti 0.05 0.05 0.05

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9

The alloy C, which is not in accordance with the invention, served as a reference.

Each of the alloys was homogenized for a period of 5 hours at 475 ° C, then a surface layer was removed to obtain a diameter of 170 mm. Without inverse heat extrusion, the alloys, at a temperature of 350-400 ° C, were transformed into bars with a diameter of 50 mm.

The rods were dissolved for 1 hour at 478 ° C, quenched in cold water and annealed for 24 hours at 120 ° C.

The following samples were taken from the bars for experimental purposes: 15 a) Smooth samples for longitudinal tensile testing and the transverse direction for measuring the values of RO, 2,

Rm and k ° / a (above 5.65 VTo).

b) tensile test specimens with incisions and with a coefficient of 20 the concentration of 8 in the transverse direction to measure Re and determine the ratio Re / R0.2.

(c) Tensile test specimens (format: 30 x 31.25, thickness: 12.5 mm) in directions L-R and C-R (ASTM indication).

The test conditions corresponding to the specification ASTM E399 made it possible to determine the voltage concentration factor K,.

Ic

The results (averages) are given in the following Table 2.

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TABLE 2

Direction * Alloy C Alloy D Alloy E

L 690 690 685 RO, 2 (MPa) T 545 540 540 5 L 715 720 705

Rm (MPa) T 605 610 610 L 5 5.5 5.5 A (%) T / o / -c c. C 10 T 4.9 6.5 6.6 R e / R 0.2 T 0, 90 1.20 1.30, / ru \ LR 32 35 38 K- (Mpaym) CR 22 24 29 15 K 2 (Ic j (m) L 0.215 0.255 0.310 ^ R0.2 2 T 0.163 0.198 0.290 20 * L: longitudinal direction T: transverse direction C: circumferential R: radial

Particularly noteworthy is the improvement of the properties in the transverse direction, in particular the plasticity (Α? Ί) and the toughness (Re / R0.2 and Kjc) of the alloys D and E according to the invention. The alloy E corresponds to the preferred composition range of the invention and exhibits the best results in this regard. It should be noted that the value of the ratio (^ Ic), which is representative of the critical \ p 2 / ke length of a crack which gives rise to a catastrophic fracture of the corresponding item, is almost the same in the transverse and longitudinal direction of the latter alloy.

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11

APPENDIX

MEASUREMENT OF THE SAFETY FACTOR K

The test piece is shown in FIG. 2. It has the following dimensions: thickness: B = 8 mm width: W = 8 mm 5 length: 55 mm milled cut: a = 2 mm, diameter at the bottom of the cut —0.08

A fatigue crack is started in the above defined specimen, which is taken out in the body part in the direction LR under the conditions specified in the standard ASTM E399 (0.45 <a / W <0.55, propagation of the fatigue of at least 1 , 3 mm, load below 60% of Pq).

The specimen cracked as a result of fatigue is then subjected to an experiment involving a slow bending. in three places. During the experiment, a curve is drawn which indicates the force as a function of the speed of movement of the recording equipment's paper (constant speed).

20

The factor K is calculated according to the formula given in the standard ASTM E399 (Bend Specimen) and which is K = —-: -. f (a / W) 25 B. W3 / 2 (in MPa m) in which: P: maximum load measured on the graph in neu / ton, 30 S: distance between the supports in m, W: thickness of the sample in m a: length of crack in m

12 DK 158317 B

Measurement of crack length:

After the fracture, the specimen is projected onto a frosted glass plate using a profiloscope (g = 20).

5

The portion of the fracture corresponding to the initial crack caused by fatigue is then marked on transparent paper. The crack lengths are then measured at locations corresponding to one-quarter, one-half, and three-quarters of the thickness of the specimen.

The value of a used in the formula is the mean of the three measurements.

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DK 158317 B

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Claims (8)

14 DK 158317 B Patent claims: A process for the preparation of heat extruded 5 products of Al-Zn-Mg-Cu alloys which, in the treated state, have improved transverse properties and have the following composition (wt? £): Si £ 0.08 20 Cu 1.0 to 2.0 Mg 2.1 to 3.5 Zn 7.2 to 9.5 Cr 0.07 to 0.17 Mn 0.15 to 0.25 Zr 0.08 to 0.14 Ti 0.10 other metals each —0.05 other metals in total —0.15 residue = Al and Fe 20, thereby homogenizing the molded product at a temperature of between 460 ° C and the starting alloy melting temperature, the product undergoes heat extrusion at a temperature of about 400 ° C, optionally heat extracting the heat extruded product, dissolves the product at a temperature of between 460 and 480 ° C, quench the product in cold water (Θ <40 ° C) and make an inlet which is either of the type T6 corresponding to between 6 and 50 hours at a temperature between 115 and 150 ° C or of the type T7 corresponding to between 3 and 24 hours at a temperature of between 100 and 120 ° C followed by between 8 and 20 hours at a temperature between 150 and 170 ° C, the longest periods of time generally being associated with the lowest temperatures, characterized by the content of Fe being limited to a maximum of 0.10¾ after we gt and that a cold deformation of the product is carried out with a degree of deformation (__) “Sr 10¾ between S quenching and annealing. DK 158317 B Process according to claim 1, characterized in that the alloy has the following preferred composition (weight t -%): Fe 2: 0.10 Process according to claim 1 or 2, characterized in that the amounts of Fe and Si are limited to (weight-o): 20 Fe - 0.05 Si - 0.05 Fe + Si ir 0.06. Process according to any one of claims 1-3, characterized in that the homogenisation is carried out at a temperature between 465 and 475 ° C. Process according to any one of claims 1-4, characterized in that the solution treatment is carried out at between 465 and 480 ° C. Si -0.08 Cu 1.35 to 1.85 Mg 2.4 to 3.0 Zn 7.6 to 8.9 Cr 0.10 to 0.17 10 Mn 0.15 to 0.25 Zr 0, 08 to 0.14 Ti ^ 0.10 other metals each - 0.05 other metals in total —0.15 while the remainder is Al. A method according to any one of claims 1-5, characterized in that the degree of cold deformation 35 (-) is between 1.5 and 5%. s DK 158317 B Process according to any one of claims 1-6, characterized in that the annealing is carried out in a temperature range of between 115 and 130 ° C for a period of time between 25 and 35 hours. 5 Method according to any one of claims 1-6, characterized in that the annealing comprises a residence of between 5 and 10 hours at 100-110 ° C and a residence of between 6 and 12 hours at 155-165 ° C.