Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
  • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent

Definitions

• the present invention relates to alloys of the Al-Mg type with high mechanical strength, and more particularly the alloys intended for welded constructions such as automobile bodies, industrial vehicles and fixed or mobile tanks.
• the parameters which govern the choice of the user are essentially the static mechanical characteristics: the tensile strength R m , the elastic limit R p o, 2 , and the elongation at break A
• Other parameters that come into play, depending on the specific needs of the targeted application, are the mechanical characteristics of the welded joint, the corrosion resistance of the sheet and welded joint, the fatigue resistance of the sheet and of the welded joint, the resistance to crack propagation, the toughness, the bendability, the weldability, the propensity for the formation of residual stresses under conditions of manufacture and use of determined sheets, and the ease of producing regular quality sheets with the lowest possible production cost.
• Mg 4.2 - 4.8 Mn ⁇ 0.5 Zn ⁇ 0.4 Fe ⁇ 0.45 Si ⁇ 0.30 with Mn + Zn ⁇ 0.7 and Fe> 0.5 Mn which may also contain certain other elements, which makes it possible to manufacture sheets having in a slightly hardened state a value of R m > 275 MPa, a value of A> 17.5% and a product R m x A>6500; a better controlled composition allows this product R m x A to be brought to a value greater than 7000 and even greater than 7500. Alloys of this type are used under the designation 5186 in the construction of welded road tanks.
• the product R m x A is used as a parameter to estimate the behavior of structures under large plastic deformation, for example in the event of damage.
• Those skilled in the art know how to increase in one of the known Al-Mg type alloys one of the two parameters R m and A to the detriment of the other; said patent application teaches that sheets with a better compromise between these two parameters can be obtained if the sheet has a very specific microstructure.
• the 5186 alloy sheets are not only characterized by a high product R m x A, but also have a high A value, which favors the folding of said sheets and facilitates their use in mechanical construction.
• Mg 2 - 6 Mn 0.05 - 1.0 Cr 0.03 - 0.3 Zr 0.03 - 0.3 V 0.03 - 0.3 which may additionally contain Cu 0.05 - 2.0 and / or Zn 0.1 - 2.0 produced by continuous casting and whose size of intermetallic particles is less than or equal to 5 ⁇ m.
• These alloys would be suitable for the manufacture of sheets for automobile bodywork, because they would make it possible, by means of very specific thermo-mechanical treatment ranges, sheets with a thickness of 1 mm which do not show L ⁇ ders lines. .
• Patent EP 823 489 B1 discloses products of composition 3.0 ⁇ Mg ⁇ 6.5 0.2 ⁇ Mn ⁇ 1.0 0.0 Fe ⁇ 0.8 0.05 ⁇ Si ⁇ 0.6 Zn ⁇ l , 3 may also contain certain other elements, and characterized by a very particular microstructure; these products were not designed to be used for the construction of tanks but for welded constructions used in contact with sea water or in the maritime environment.
• the problem to which the present invention attempts to respond is to improve the mechanical characteristics of Al-Mg alloy products, in particular with a view to their use for producing welded constructions, such as tanks for road or rail transport of dangerous materials, all keeping the other characteristics of the material at a level at least comparable to that of existing materials.
• the object of the invention is a wrought product of Al-Mg alloy, characterized in that it contains (in mass percentages)
• Another object of the invention is a road or rail tank made at least partially with composition sheets (in percent by mass) Mg 4.90 - 5.35 Mn 0.20 - 0.50 Zn 0.25 - 0.45
• alloys follows the rules of The Aluminum Association. Unless otherwise stated, the chemical compositions are indicated in percent by mass.
• the Applicant has surprisingly found that in order to solve the problem posed, it is necessary to select a very narrow Al-Mg-Mn-Zn composition domain which is clearly distinguished from that of the 5186 alloy.
• the content of magnesium add a small amount of zinc, and reduce the contents of minor additives, Fe, Si, and Mn, while keeping them above a minimum level.
• magnesium is well known for increasing the mechanical characteristics (Ro, 2 and R m ) of certain types of aluminum alloys; the Applicant has found that a magnesium content of at least 4.85%, preferably greater than 4.90% and even more preferably greater than 4.95% or even 5.00% makes it possible to obtain the level of characteristics mechanical required.
• a magnesium content of at least 4.85%, preferably greater than 4.90% and even more preferably greater than 4.95% or even 5.00% makes it possible to obtain the level of characteristics mechanical required.
• a maximum value of 5.30% is preferred.
• the addition of zinc in sufficient quantity appears to have a beneficial effect on the mechanical characteristics of the sheets and on the limit d elasticity at welded joints. In addition, it improves corrosion resistance.
• it is preferred not to exceed a content of 0.45%.
• a content of between 0.25% and 0.40% is preferred.
• the Applicant has found that a minimum content of 0.20% of manganese must be maintained to control the granular structure, but that it must remain below 0.50% and preferably 0.40%, in order to avoid the formation of coarse intermetallic phases and to facilitate recrystallization in the final state.
• the preferred range is 0.25 to 0.35%.
• the presence of manganese in sufficient quantity also contributes to obtaining the mechanical characteristics.
• copper is known to degrade the general corrosion resistance.
• the Applicant has found that it is preferable to keep the copper content less than 0.25%; a content of less than 0.20%, less than 0.15% or even less than 0.10% is preferred.
• Iron and silicon are common impurities in aluminum.
• the iron content must not exceed 0.30% and the silicon content 0.20%.
• the Applicant has surprisingly found that the presence of a certain amount of iron and silicon contributes to achieving the objective of the present invention: by way of example, a content of at least 0.05% of silicon promotes a finely recrystallized granular microstructure.
• a content of at least 0.10% is preferred.
• the product according to the invention may contain a small amount of chromium, titanium and zirconium.
• the content of each of these elements must not exceed 0.15%, and more preferably 0.10%, because too high a content of these elements limits recrystallization and leads to a decrease in the value of A.
• the products according to the invention are always produced by semi-continuous casting, followed by the processing steps which correspond to the desired product form: spinning for spun or drawn products (bars, tubes, profiles, wires); rolling for rolled products (sheets, strips, thick sheets). In the case of rolled products, the rolling plates produced by semi-continuous casting are hot rolled, then optionally cold. The strips are then planed and cut into sheets.
• the exit temperature of the hot rolling mill and the winding temperature as well as the rate of work hardening which influence the mechanical characteristics of the product must be carefully adjusted.
• the preferred final thickness is between 3 and 12 mm.
• the sheet is obtained directly at the final thickness by hot rolling.
• an exit temperature from the hot rolling mill will advantageously be chosen between 260 ° C. and 330 ° C., and preferably between 290 ° C. and 330 ° C. Below 260 ° C, the microstructure obtained is not well suited to the intended application, and above 330 ° C, there is sometimes a magnification of the grain which degrades the desired mechanical characteristics.
• This particular embodiment of the invention namely the direct production of sheets at the final thickness not hot rolling, also facilitates the manufacture of sheets of very large width, for example greater than 3000 mm, and preferably greater at 3300 mm and even more preferably greater than 3500 mm.
• the product according to the invention is characterized by an elongation at break A of at least 24%, and preferably at least 27%. This characteristic facilitates the implementation of the product. By way of example, it gives laminated sheets an excellent ability to bend and shape.
• a product which has a yield strength R PO, 2 (TL) of at least 145 MPa, preferably of at least 150 MPa and even more preferably of at least 170 MPa, a breaking strength R m (TL) of at least 290 MPa and preferably at least 300 MPa, and an elongation at break A (TL) of at least 24% and preferably at least 27%.
• Mn 0.20 - 0.40 Zn> 0.25 and preferably> 0.30, an iron content of at least 0.10% iron, and a content of at least 0.10% silicon.
• an attempt is essentially made to optimize the product R m (TL) x A ( TL>
• a product having a product R m is obtained.
• (TL) x A ( TL ) in which R m (TL) is expressed in MPa and A (TL) in percent, measured on test specimens taken in the sense TL, is greater than 8200, preferentially greater than 8500 and even more preferentially greater than 9000, while keeping a sufficient level of R PO, 2 ( TL ) •
• This product in particular in the form of sheets, is particularly suitable for the manufacture of tanks, in particular for the transport by road or rail of dangerous materials.
• the products according to the invention show a corrosion resistance at least as good as the products in comparable Al-Mg alloys which are known, despite a significantly higher magnesium content.
• this corrosion resistance is preferably characterized, either by the loss of mass and by the maximum depth of metal having defects due to intergranular corrosion after an intergranular corrosion test (Journal Officiel des European Communities, 19/11/1984, N ° L300-35 to 43), either by a stress corrosion test carried out according to standard ASTM G 30, G39, G44 and G49.
• the stress corrosion test can be carried out advantageously by referring to standard ASTM G 129, the applicant having established in the past the good correlation between these standards and standard ASTM G 129 (see R.
• the intergranular corrosion test chosen is deemed to represent a natural exposure in a marine atmosphere (R.Dif et al, Proceedings of the EUROCORR ConfInterconnection, 1999, Aachen, Germany).
• Corrosion behavior is evaluated in the initial state but also after artificial aging treatments, the conditions of which may vary.
• a 7-day treatment at 100 ° C. is conventionally used on the alloys of the 5xxx series in order to reproduce natural aging at room temperature for around twenty years (EHDix et al., Proceedings of the 4 th annual Conference of NACE, San Francisco, USA, 1958).
• the structures can be subjected to relatively high temperatures (above 60 ° C).
• temperatures above 60 ° C.
• certain alloys of the 5xxx series can develop, beyond a certain exposure time, a certain sensitivity to corrosion.
• sensitization it is advisable to practice heat treatments more advanced than 7 days at 100 ° C.
• equivalent time is usually used in order to limit the number and duration of the treatments to be carried out.
• a treatment of duration ti carried out at a temperature Ti will be equivalent to a treatment of duration t 2 carried out at a temperature T 2 , given by the equation (R.Dif et al., Proceedings of the 6 * International ConfInteron on Aluminum Alloys, 1998, Toyohashi, Japan, pp. 1489-1494):
• the value of the ratio - issue of the literature is of the order of 10,000K to 13,500K.
• the products according to the invention show, during the intergranular test, resistance to intergranular corrosion which is characterized at least by a loss of mass of less than 20 mg / cm 2 after aging of 7 days at 100 ° C, and by a maximum depth of attack of less than 130 ⁇ m, and preferably less than 70 ⁇ m.
• said products also show, after aging for 20 days at 100 ° C., a loss of mass of less than 50 mg / cm 2 and preferably less than 30 mg / cm 2 , and a maximum depth of attack of less of 250 ⁇ m, and preferably less than 100 ⁇ m.
• the most preferred products in the context of the present invention show, after aging for 20 days at 120 ° C., a mass loss of less than 95 mg / cm 2 , and preferably less than 80 mg / cm, and even more preferably less than 60 mg / cm, with a maximum depth of attack of less than 450 ⁇ m and preferably less than 400 ⁇ m, it being understood that this characteristic is added to at least one of the characteristics mentioned above, namely after aging of 20 days at 100 ° C or 20 days at 120 ° C.
• These products if they also have excellent mechanical characteristics (for example an R m x A product of at least 8,500 or even 9,000) lend themselves particularly well to the manufacture of welded constructions, such as road or rail tanks, as explained below.
• the principle of the slow traction test consists in comparing the tensile properties in an inert medium (laboratory air) and in an aggressive medium.
• the decrease in static mechanical properties in a corrosive environment corresponds to the sensitivity to stress corrosion.
• the most sensitive tensile test characteristics are the elongation at break A and the maximum stress (at necking) R m .
• the Applicant has found that the elongation at break is a significantly more discriminating parameter than the maximum stress. It is necessary to ensure that the reduction in static mechanical characteristics effectively corresponds to stress corrosion, defined as a synergistic and simultaneous action of mechanical stress and the environment.
• the Applicant has therefore also carried out tensile tests in an inert medium (laboratory air), after a prior pre-exposure of the test piece, without constraint, to the aggressive medium, for the same duration as the tensile test carried out in this middle. If the tensile characteristics obtained do not differ from those obtained in an inert medium, the sensitivity to stress corrosion can then be defined using an index I of “sensitivity to CCS” defined as: j _ - ⁇ / 0 M ⁇ l ⁇ euInerte ⁇ ' u MiheuAgressi 1 sunny.
• the critical aspects of the slow tensile test concern the choice of the tensile specimen, the strain rate and the corrosive solution.
• the Applicant has used a test piece (taken in the Travers-Long direction), having a notched shape with a radius of curvature of 100 mm, which makes it possible to locate the deformation and to make the test even more severe.
• the stressing speed too fast a speed does not allow stress corrosion phenomena to develop, but a too slow speed masks stress corrosion.
• the Applicant has used a deformation speed of 5.10 "5 s " 1 (corresponding to a displacement speed of the cross member of 4.5.10 "2 mm / min) which makes it possible to maximize the effects of corrosion under stress (R.Dif et al., Proceedings of the 6 th International ConfInter on Aluminum Alloys, 1998, Toyohashi, Japon, pp. 1615-1620).
• the same type of problem arises insofar as an environment which is too aggressive masks corrosion under stress, but where an environment which is too mild does not make it possible to demonstrate the phenomenon of corrosion.
• a solution of 3% NaCl + 0.3% H 2 O 2 has been used successfully in the context of the present invention.
• the products according to the invention can be advantageously used for welded construction, for the construction of road or rail tanks or for the construction of industrial vehicles. They can also be used for the construction of automobile bodies, in particular as reinforcing parts. They show a good aptitude for shaping.
• the products according to the invention are used in the form of sheets rolled in a slightly hardened metallurgical state, such as state O or state Hl ll, of thickness between 3 mm and 12 mm, and preferably between 4.5 mm and 10 mm, for the construction of road or rail tanks, said sheets being characterized by a product R m ( ⁇ L) A ( TL greater than 8200, preferably greater than 8500 and even more preferably greater than 9000, and by good corrosion resistance.
• the mass loss during an intergranular corrosion resistance test is less than 30 mg / cm 2 after aging for 20 days at 100 ° C, and the CSC index in slow traction is less than 50% after aging for 20 days at 100 ° C.
• the products according to the invention can be welded by any welding process that can be used for Al-Mg type alloys, such as MIG or TIG welding, friction welding, laser welding, electron beam welding. . More particularly, the Applicant has found that the MIG welding of the products according to the invention leads to welded joints characterized by a breaking limit at least as high as with known alloys such as 5186. These welding tests have been carried out in the transverse-long direction on sheets in the Hll l state welded end to end with a V-shaped chamfer by semi-automatic MIG welding in smooth current, with a filler wire of alloy 5183.
• Laminating plates of different alloys have been produced by semicontinuous casting. Their composition is indicated in Table 1.
• the chemical analysis of the elements was carried out by spark spectroscopy on a spectrometry pawn obtained from liquid metal taken from the pouring channel.
• the rolling plates were reheated and then hot rolled.
• the plate corresponding to example H1 was reheated in three stages: 10 h at 490 ° C, 10 h at 510 ° C, 3 h 45 min at 490 ° C and then hot rolled with a temperature d input of 490 ° C and a winding temperature of 310 ° C.
• the reheating was done in two stages (9 p.m.
• the entry temperatures for lamination were respectively 477 ° C, 480 ° C, 479 ° C, 474 ° C and 478 ° C while the winding temperatures were 290 ° C, 300 ° C, 270 ° C, 310 ° C and 300 ° C respectively. After winding, all the sheets were planed and cut.
• Alloys A, B, C, D, E and F are alloys according to the state of the art. Alloys
• G, H and I are alloys according to the invention.
• test piece was taken in the Long direction through the welded joint so that the joint is in the middle.
• a value of R m was found of 285 MPa, and with a non-leveled cord a value of 311 MPa.
• LDH Limit Dome Height
• a value of 101 mm is obtained for the sheet H1, and a value of 94.1 mm for the sheet H2.
• the LDH value of 94.3 mm was obtained for an alloy of the prior art with a comparable thickness (see L. Cottignies et al, “AA 5186: a new aluminum alloy for welded constructions”, Journal of Light Métal Welding and Construction, 1999).
• the alloy according to the invention has better corrosion resistance under stress after aging, in particular for intermediate aging levels, despite a higher magnesium content.
• the alloy according to the invention has a level of resistance to intergranular corrosion comparable to or even better than that of the prior art.
• a rolling plate of composition was produced by semi-continuous casting: Mg 5.0%, Zn 0.30%, Mn 0.35%, Si 0.01%, Fe 0.15%, Cu 0.03% , Zr 0.02%, Cr 0.03%, Ni ⁇ 0.01%, Ti 0.02%. After homogenization for 19 h at 505 ° C, the plate was hot rolled to a thickness of 7 mm. After a light leveling, the sheets were annealed with a temperature rise to 378 ° C for 8 h, followed by maintenance for 30 minutes at a temperature between 378 ° C and 390 ° C.
• the sheets thus obtained have the following average mechanical characteristics (direction T-L):

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