EP0375571B1 - Process for the preparation by spray deposits of aluminium alloys of the 7000 series, and discontinuously reinforced composite materials having these high strength, highly ductile alloys as a matrix - Google Patents

Abstract

The invention relates to a process for obtaining an Al alloy of the 7000 series (Al-Zn-Cu-Mg) of high mechanical strength and good ductility by spray deposition; the process is aimed at obtaining Al alloys having a breaking load of >/= 800 MPa and an elongation greater than or equal to 5%, or obtaining these same alloys reinforced with ceramic particles. <??>The invention accordingly consists in: 1. forming, by spray deposition, a massive alloy of the following composition by weight: Zn from 8.5 to 15%; Mg from 2.0 to 4.0%; Cu from 0.5 to 2.0%; at least one of the following 3 elements: Zr from 0.05 to 0.8%; Mn from 0.05 to 1.0%; Cr from 0.05 to 0.8%, with Zr + Mn + Cr </= 1.4%; Fe up to 0.5%; Si up to 0.5%; other elements </= 0.05% each, </= 0.15% in total; remainder Al. 2. hot transforming of the body thus obtained at between 300 and 450 DEG C and optionally in the cold and 3. treating the product thus obtained by dissolution, quenching and annealing.

Description

The invention relates to a method for obtaining an Al alloy of the 7000 series (Al-Zn-Mg-Cu) with high mechanical strength and good ductility by "spray-deposition" (spray deposition). More specifically, the method aims to obtain Al alloys which have in the treated state (T6) a breaking load ≧ 800 MPa with an elongation, at least in the long direction, greater than or equal to 5%.

The invention also relates to obtaining composite materials with very high strength, high rigidity and good ductility having as matrix the 7000 alloys described above with a particulate reinforcement of ceramics and obtained directly by "spray-deposition".

Many works have already been carried out on the alloys of the 7000 series, loaded with alloying elements with a view to obtaining high mechanical strengths associated with good ductility, either by conventional metallurgy, or by powder metallurgy.

Thus, in the first case, we know the French patents FR 2517702 or FR 2457908 in which are presented alloys of the 7000 series not exceeding a breaking load of 650-700 MPa approximately, with an elongation of the order of 8 -9% (in the long sense).

Attempts have also been made to obtain alloys of the 7000 series with high resistance by powder metallurgy, that is to say by a process comprising the formation of particles (powders, flakes, ground ribbon, etc.) which are then consolidated in massive form by various methods (cold, hot, isostatic compressions, spinning, etc.).

However, these alloys although reaching high or very high mechanical strengths, have very low elongations, which prohibit any industrial use.

Thus HAAR reports in Alcoa Report n ° 13-65-AP59-S- Contract n ° DA-360-034-ORD-3559 RD (Frankfort Arsenal), May 1966, breaking loads exceeding 800 MPa but with extensions of the order of 1%. Likewise, BOWER et al- Met. Trans. Flight. 1, January 1970, p.191 - reports, on alloys of the same family, produced by "splat cooling" (hammer and anvil technique) breaking loads of 800 MPa, but with elongations of 2%.

The patents US 3563814 and US 4732610 relate to alloys of the same family obtained by powder metallurgy but whose mechanical characteristics are clearly lower than the targeted objectives (breaking load of the order of 500 MPa to 600 MPa).

• 1. à former par pulvérisation-dépôt un alliage massif de composition pondérale suivante :

  Zn

  8,5 à 15,0 %

  Mg

  2,0 à 4,0 %

  Cu

  0,5 à 2,0 %

  au moins un des 3 éléments suivants :

  Zr

  de 0,05 à 0,8 %

  Mn

  de 0,05 à 1,0 %

  Cr

  de 0,05 à 0,8 %

     avec Zr + Mn + Cr ≦ 1,4%

  Fe

  jusqu'à 0,5 %

  Si

  jusqu'à 0,5 %

  Autres (impuretés)

  ≦0,05 % chacune
  ≦0,15 % au total

     reste Al.
• 2. à transformer à chaud le corps ainsi obtenu entre 300 et 450°C et éventuellement à froid.
• 3. à traiter thermiquement le produit obtenu par mise en solution, trempe et revenu.

The invention therefore consists:

• 1. to form by spray-deposition a solid alloy of the following weight composition:

  Zn

  8.5 to 15.0%

  Mg

  2.0 to 4.0%

  Cu

  0.5 to 2.0%

  at least one of the following 3 elements:

  Zr

  from 0.05 to 0.8%

  Mn

  0.05 to 1.0%

  Cr

  from 0.05 to 0.8%

  with Zr + Mn + Cr ≦ 1.4%

  Fe

  up to 0.5%

  Yes

  up to 0.5%

  Others (impurities)

  ≦ 0.05% each
  ≦ 0.15% in total

  remains Al.
• 2. to transform the body thus obtained to hot between 300 and 450 ° C and possibly cold.
• 3. heat treating the product obtained by dissolving, quenching and tempering.

By spray-deposition is meant a process in which the metal is molten, atomized by a jet of gas at high pressure in the form of fine liquid droplets which are then directed and agglomerated on a substrate so as to form a massive and coherent deposit, containing a low closed porosity. This deposit can be in the form of billets, tubes or plates whose geometry is controlled. A technique of this type is known as "Spray Deposition" by the Anglo-Saxons and is also called "OSPREY process".
This latter process is mainly described in the following patent applications (or patents): GB-B-1379261; GB-B-1472939; GB-B-1548616; GB-B-1599392; GB-A-2172827; EP-A-225080; EP-A-225732; WO-A-87-03012.

The best mechanical characteristics (Rm ≧ 800 MPa, A ≧ 5%) are obtained for the composition given above.

If Zn ≦ 8.5% by weight, the volume fraction of precipitates at the base of the structural hardening of the alloy (essentially of the type η -Mg Zn₂ or η '- (Mg, Zn, Al, Cu)) becomes insufficient and it is no longer possible to obtain the levels of high mechanical characteristics (such as breaking load ≧ 800 MPa) which are the objective of the present invention.

Similarly, if the Zn content exceeds 15% by weight, the volume fraction of the second phase is too high and leads to a brittle material, with very low elongations at break, which prohibits its industrial use.

Within the range 8 to 15% by weight of zinc, the copper and magnesium contents must be in proportions close to the stoichiometry of the hardening precipitates. In practice, it is found that when Mg <2% or Cu <0.5%, the nature and the volume fraction of the precipitates formed are insufficient to achieve the targeted mechanical characteristics. When, on the contrary, Mg is ≧ 4% or Cu ≧ 2.0%, these elements are present in excess in the alloy and weaken it considerably.
The presence of Cr, Zr, Mn, alone or in combination, provides additional hardening either by fiberizing effect by preventing or limiting the recrystallization which may occur during the heat treatment according to transformation operations by wrought, either by a dispersion hardening mechanism, since these elements form in combination with aluminum thin and well distributed dispersed phases (for example Al₃Zr, Al₆Mn, or ternary phases Al₁₈Cr₂Mg₃ and (Al, Cr , Mn) .However, their content must be limited to 0.8% for Cr and Zr and to 1.0% for Mn and their overall content (Zr + Cr + Mn) ≦ 1.4% because beyond, the the dispersed phases formed are too numerous and too coarse and consequently weaken the material. In addition, Cr, Zr and Mn contents greater than the limits indicated above lead to high liquidus temperatures of the alloys, which poses problems of development linked in particular to the sublimation of zinc or magnesium The iron and silicon contents are limited to more than 0.5%, because beyond that coarse intermetallic compounds are formed which harm the ductility of the alloy.

Zn

de 8,7 à 13,7%

Mg

de 2,2 à 3,8%

Cu

de 0,6 à 1,6%

au moins un des 3 éléments suivants :

Zr

de 0,05 à 0,5%

Mn

de 0,05 à 0,8%

Cr

de 0,05 à 0,5%

   avec Zr + Mn + Cr ≦ 1,2%

Fe

jusqu'à 0,3%

Si

jusqu'à 0,2%

autres (impuretés)

≦ 0,05% chacun
≦ 0,15% total

   reste Al.The preferred composition is:

Zn

from 8.7 to 13.7%

Mg

2.2 to 3.8%

Cu

0.6 to 1.6%

at least one of the following 3 elements:

Zr

from 0.05 to 0.5%

Mn

from 0.05 to 0.8%

Cr

from 0.05 to 0.5%

with Zr + Mn + Cr ≦ 1.2%

Fe

up to 0.3%

Yes

up to 0.2%

other (impurities)

≦ 0.05% each
≦ 0.15% total

remains Al.

In order to obtain better results, the content of main elements preferably obeys the following relationship, $$\text{5.5 ≦ Mg + Cu +}\frac{\text{Zn}}{\text{6}}\text{≦ 6.5}$$

It is indeed in this area of composition that the volume fraction of the hardening phases is maximum while allowing complete dissolution of the addition elements during the heat treatment.

Thus, a very high level of mechanical strength can be achieved while retaining good ductility.
With regard to the effect of the dispersoid forming elements (Zr, Cr, Mn), it was realized that it was preferable to use them all 3 in combination rather than one or the other separately. Indeed, for a given overall content of Zr + Cr + Mn, we obtain a distribution of finer and better distributed dispersoids when the 3 elements are present simultaneously rather than only 1 or 2 of 3. When the 3 elements are associated, we however, has an interest in limiting their overall content to 1.2%. More precisely, we note that for an identical content, Zr leads to the formation of dispersoids (Al₃Zr) finer and better distributed than those formed from Cr or Mn; one is therefore led, when the ductility and the toughness of the alloy must be maximized to limit the Mn + Cr content to 0.6% maximum.

The hot transformation of the solid alloy obtained by spray-deposition generally takes place between 300 and 450 ° C, preferably by spinning, forging or rolling, in one or more successive operations; these operations can optionally be combined, for example spinning + rolling or spinning + forging / stamping.
The hot transformation operations can be supplemented by cold operations such as rolling, drawing, etc.
The solution is carried out between 440 and 520 ° C, between 2 and 8 hours depending on the size of the products; quenching is followed by tempering between 2 and 25 h between 90 and 150 ° C in one or more stages, the longest times being generally associated with the lowest temperatures (and vice-versa).
The product obtained by a spray-deposition process can optionally be homogenized before hot transformation between 450 and 520 ° C for 2 to 50 hours in one or more stages.

The invention also consists, using the alloys and the method described above, in obtaining composite materials with very high resistance (Rm ≧ 800 MPa), high Young modulus (E ≧ 80 GPa), with acceptable ductility by users (A ≧ 3%), as well as good resistance to wear and friction. These materials are characterized by an alloy matrix of the 7xxx series of composition indicated above and a dispersion of ceramic particles of SiC, Al₂O₃ or B₄C type (these examples not being limiting) and are obtained directly by the spray-deposition technique.

• 1/ A fondre et à pulvériser un alliage 7000 de composition décrite ci-dessus
• 2/ A coinjecter, dans le jet de gouttelettes métalliques atomisées des particules céramiques de type SiC, Al₂O₃, B₄C ou autres carbures, nitrures ou oxydes ou combinaison de ceux-ci, de forme sensiblement équiaxe et de taille comprise entre 1 µm et 50 µm et en fraction volumique, relative au métal, comprise entre 3 et 28%. Par taille on entend la dimension hors tout maximale de la particule.
• 3/ A agglomérer le jet de particules métalliques et céramiques sous la forme d'un métal massif par la technique de pulvérisation-dépôt.
• 4/ A transformer et traiter thermiquement le dépôt ainsi obtenu par une procédure analogue à celle décrite pour les alliages 7000 ci-dessus non renforcés.

The invention therefore consists:

• 1 / To melt and spray an alloy 7000 of the composition described above
• 2 / To co-inject, in the jet of atomized metal droplets, ceramic particles of the SiC, Al nitrO₃, B₄C or other carbides, nitrides or oxides type or combination thereof, of substantially equiaxial shape and of size between 1 μm and 50 μm and in volume fraction, relating to the metal, between 3 and 28%. By size is meant the maximum overall dimension of the particle.
• 3 / To agglomerate the jet of metallic and ceramic particles in the form of a solid metal by the spray-deposition technique.
• 4 / To transform and heat treat the deposit thus obtained by a procedure similar to that described for the 7000 alloys above not reinforced.

The invention will be better understood using the following examples:

EXAMPLE 1

• température de coulée: 750°C
• distance atomiseur-dépôt: 600 mm, maintenue sensiblement constante pendant l'essai
• collecteur en acier inxoydable animé d'un mouvement de rotation.
• oscillation de l'atomiseur par rapport a l'axe de rotation du collecteur

Les débits gaz d'atomisation et débit métal utilisés pour chaque composition sont également indiqués au tableau 1.
Après écroûtage à 140 mm, les billettes sont homogénéisées pendant 8 h à la température indiquée au tableau 1.
Les ébauches sont ensuite filées à chaud à 400°C dans une presse dont le conteneur a un diamètre de 143 mm sous forme de méplats de section 50 x 22 mm, soit un rapport de filage de 14,6.
Les méplats ainsi obtenus sont ensuite mis en solution à la température indiquée dans le tableau 1 pendant 2 h, trempés à l'eau froide puis revenus pendant 24 h à 120°C.
Les caractéristiques mécaniques de traction en sens long, moyenne de 3 essais, sont reportées dans le tableau 2 (Ro,₂: limite élastique à 0,2% de déformation résiduelle, Rm: charge de rupture; A%: allongement de rupture).Different alloys marked 1 to 7, the compositions of which are given in table 1, were melted and produced by spray-deposition (OSPREY process) in the form of cylindrical billets 150 mm in diameter under the following conditions:

• casting temperature: 750 ° C
• atomizer-deposit distance: 600 mm, kept approximately constant during the test
• stainless steel manifold driven by a rotational movement.
• oscillation of the atomizer relative to the axis of rotation of the collector

The atomization gas and metal flow rates used for each composition are also indicated in Table 1.
After peeling at 140 mm, the billets are homogenized for 8 h at the temperature indicated in Table 1.
The blanks are then hot-spun at 400 ° C in a press, the container of which has a diameter of 143 mm in the form of flats with a section of 50 x 22 mm, ie a spinning ratio of 14.6.
The flats thus obtained are then dissolved at the temperature indicated in Table 1 for 2 h, soaked in cold water and then returned for 24 h at 120 ° C.
The mechanical tensile characteristics in the long direction, average of 3 tests, are given in Table 2 (Ro, ₂: elastic limit at 0.2% residual deformation, Rm: breaking load; A%: elongation at break).

It can be seen that the alloys n ° 1 to 4 according to the invention have a very high level of mechanical characteristics, with in particular a breaking load ≧ 800 MPa as well as a correct level of ductility, with elongations at break ≧ 5% .

Alloy 5, outside the analytical limits of the invention (Zn content too low) has much weaker mechanical characteristics than the alloys of the invention.

The alloy 6, also outside the limits of the invention because of its too high Zn content, has a very low ductility (A%) and a plastic difference (Rm-R 0.2).

The alloy 7 is also outside the scope of the invention because of the overall Zr + Cr + Mn content which is too high. This is reflected, despite the good level of mechanical characteristics, by a very low ductility (elongation at break = 2%).
It is therefore clear that a significantly higher set of properties is obtained in the analytical framework of the invention for alloys produced by the spray-deposition technique.

Alloy 8 is an alloy whose composition falls within the analytical field of the alloys of the invention but which has been developed according to a powder metallurgy process described below: the alloy is melted and then atomized with nitrogen in the form powders; these are collected and sieved to 100 µm. Powders smaller than 100 µm are put in 140 mm diameter aluminum containers fitted with an orifice tube and are then degassed hot under secondary vacuum (by pumping through the tube) at a temperature of 460 ° C for 100 h. The powder containers thus degassed are sealed and then hot pressed in a blind die spinning press in a 143 mm diameter container at 450 ° C so as to reach the theoretical density of the material. The billets thus obtained are then machined in order to remove the material from the container and then spun under the same conditions as the billets of the previous examples. The product obtained is heat treated according to a similar procedure (see solution temperature in Table 1) and is characterized under the same conditions.
The results reported in Table 1 show that the product obtained has very low ductility and plastic deviation despite a relatively high level of resistance.

The case of the last alloy illustrates well the superiority of the method of the invention for obtaining alloys having both very high strengths and good ductility.

EXAMPLE 2

An alloy of composition Al:
Al: 10% Zn; 3.0% Mg; 1.0% Cu; 0.1% Zr; 0.15% Cr; 0.15% Mn, rest Al
was melted at 750 ° C and produced by spray-deposition in the form of 150 mm diameter billets with simultaneous coinjection of SiC particles of average size 10 μm, with a volume fraction of 15%.

• débit métal : 5,8 kg/min.
• débit gaz : 15 Nm3/min.
• distance atomiseur-dépôt: 620 mm, maintenue sensiblement constante pendant l'essai
• collecteur en acier inox animé d'un mouvement de rotation
• oscillation de l'atomiseur par rapport à l'axe de rotation du collecteur

The spray-deposit conditions were as follows:

• metal flow: 5.8 kg / min.
• gas flow: 15 Nm3 / min.
• atomizer-deposit distance: 620 mm, kept approximately constant during the test
• stainless steel collector with rotational movement
• oscillation of the atomizer relative to the axis of rotation of the collector

The billets thus obtained are then peeled to Ø 140 mm, homogenized for 8 hours at 470 ° C, hot-spun at 400 ° C in the form of flats of section 50 x 22 mm (spinning ratio 14.6).

• mise en solution 2 h à 470°C
• trempe à l'eau froide
• revenu 24 h à 120°C

These flats are heat treated under the following conditions:

• solution solution 2 h at 470 ° C
• cold water quenching
• 24 hour heat recovery at 120 ° C

The tensile characteristics as well as the Young's modulus (E) were measured long-term. The results obtained, average of 3 tests, are given below:
Ro, ₂ = 798 MPa, Rm = 820 MPa, A = 4%, E = 95 GPa

• on évite les opérations longues et coûteuses de dégazage et de compactage
• la méthode est plus sûre, car il n'y a pas de manipulation de poudres réactives.

The spray-deposition process according to the invention, in addition to the best compromise of mechanical characteristics obtained, has the following advantages over conventional powder metallurgy:

• long and costly degassing and compaction operations are avoided
• the method is safer because there is no handling of reactive powders.

Claims (11)

1. A method of producing alloys of Al of the series 7000 with a high level of strength and good ductility characterised in that:

   a) a solid alloy of the following composition by weight is formed by spray deposition:

   Zn   from 8.5 to 15.0%

   Mg   from 2.0 to 4.0%

   Cu   from 0.5 to 2.0%

   at least one of the following 3 elements:

   Zr   from 0.05 to 0.8%

   Mn   from 0.05 to 1.0%

   Cr   from 0.05 to 0.8%

      with Zr + Mn + Cr ≦ 1.4%

   Fe   up to 0.5%

   Si   up to 0.5%

   others (impurities)   ≦ 0.05% each
   ≦ 0.15% total

   balance Al.

   b) the body obtained in that way is subjected to transformation in the hot condition at between 300 and 450°C and then possibly in the cold condition, and

   c) the product obtained is subjected to heat treatment by solution treatment, quenching and ageing.
2. A method according to claim 1 characterised in that the chemical composition is as follows:

   Zn   from 8.7 to 13.7%

   Mg   from 2.2 to 3.8%

   Cu   from 0.6 to 1.6%

   at least one of the following 3 elements:

   Zr   from 0.05 to 0.5%

   Mn   from 0.05 to 0.8%

   Cr   from 0.05 to 0.5%

      with Zr + Mn + Cr ≦ 1.2%

   Fe   up to 0.3%

   Si   up to 0.2%

   others (impurities)   ≦ 0.05% each
   ≦ 0.15% total

   balance Al.
3. A method according to claims 1 and 2 characterised in that the amounts of Mg, Cu and Zn expressed in percentages by weight comply with the following relationship: $$\text{5.5 ≦ Mg + Cu +}\frac{\text{Zn}}{\text{6}}\text{≦ 6.5}$$

   
4. A method according to claim 1, claim 2 or claim 3 characterised in that Cr, Zr and Mn are present simultaneously in the composition of the alloy, with: $$\text{Cr ≧ 0.05\%, Mn ≧ 0.05\%, Zr ≧ 0.05\%}$$

   

   and $$\text{Mn+Cr+Zr≦1.2\%.}$$

   
5. A method according to claim 4 characterised in that the composition of the alloy is such that: $$\text{Mn+Cr≦0.6\%.}$$

   
6. A method according to one of claims 1 to 5 characterised in that a homogenisation operation at between 450 and 520°C for a period of 2 to 50 hours is carried out between steps a) and b).
7. A method according to one of claims 1 to 6 characterised in that the hot transformation operation is effected by extrusion, rolling or forging or a combination of those operations.
8. A method according to claim 7 characterised in that the hot transformation operation is completed by a cold transformation operation.
9. A method according to one of claims 1 to 8 characterised in that the solution treatment is effected at between 440 and 520°C for a period of from 2 to 8 hours.
10. A method according to one of claims 1 to 9 characterised in that the ageing operation is effected at between 90 and 150°C for a period of from 2 to 25 hours.
11. A method for the production of composite materials with a metallic matrix wherein a solid alloy is produced in accordance with one of claims 1 to 10 characterised in that during the spray deposition operation ceramic particles of substantially equiaxis shape, of a size of between 1 and 50 µm, and in a fraction by volume (relative to the metal) of between 3 and 28%, are co-injected.