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 Al-Mg type with high mechanical strength, and more particularly alloys for welded constructions such as automobile bodies, industrial vehicles and fixed or mobile tanks.
• the parameters that govern the user's choice are essentially the static mechanical characteristics: the tensile strength R m , the elastic limit R p0 , 2 , and the elongation at break A.
• Other parameters that come into play, depending on the specific needs of the intended application, are the mechanical characteristics of the welded joint, the corrosion resistance of the sheet and the welded joint, the fatigue strength of the sheet and of the welded joint, resistance to crack propagation, toughness, bendability, weldability, propensity for the formation of residual stresses under conditions of manufacture and use of the specified sheets, and the ease of producing regular quality sheet metal with a production cost as low as possible.
• the state of the art offers several ways to improve the mechanical characteristics of Al-Mg type alloys.
• EP 769 564 A1 discloses an alloy of composition (in percent by mass): Mg 4.2 - 4.8 Mn ⁇ 0.5 Zn ⁇ 0.4 Fe ⁇ 0.45 If ⁇ 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 low-wrought state a value of R m > 275 MPa, a value of A> 17.5% and a product R m ⁇ A>6500; a better controlled composition makes it possible to bring this product R m x A to a value greater than 7000 and even greater than 7500. Alloys of this type are used under the designation 5186 in construction of welded road tanks.
• the product R m x A is used as a parameter to estimate the behavior of the structures under a large plastic deformation, for example in case of damage.
• the person skilled in the art knows how to increase in one of the known Al-Mg 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 particular microstructure.
• the sheets 5186 alloy are characterized not only by a product R m x A high, but also by a high value of A, which promotes the folding of said sheets and facilitated their use in mechanical engineering.
• compositional products 3.0 ⁇ Mg ⁇ 6.5 0.2 ⁇ Mn ⁇ 1.0 Fe ⁇ 0.8 0.05 ⁇ Si ⁇ 0.6 Zn ⁇ 1.3 may also contain some other elements, and characterized by a very particular microstructure; these products have not been designed for use in the construction of tanks but for welded constructions used in contact with seawater or in the maritime environment.
• the problem addressed by the present invention 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 hazardous materials, while 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 percents) Mw 4.85 - 5.35 Mn 0.20 - 0.50 Zn 0.20 - 0.45 If ⁇ 0.20 Fe ⁇ 0.30 Cu ⁇ 0.25 Cr ⁇ 0.15 Ti ⁇ 0.15 Zr ⁇ 0.15 the rest of the aluminum with its inevitable impurities.
• Another subject of the invention is a road or rail tank made at least partially with sheet metal (in percent by mass) Mg 4.90 - 5.35 Mn 0.20 - 0.50 Zn 0.25 - 0.45 If 0.05 - 0.20 Fe 0.10 - 0.30 Cu ⁇ 0.25 Cr ⁇ 0.15 Ti ⁇ 0.15 Zr ⁇ 0.10 the rest of the aluminum with its inevitable impurities, said sheets having a product R m (TL) x A (TL) of at least 8500, and preferably at least 9000.
• the designation of the alloys follows the rules of The Aluminum Association. Unless otherwise stated, the chemical compositions are indicated in percent by weight.
• the Applicant has surprisingly found that in order to solve the problem, it is necessary to select a very narrow Al-Mg-Mn-Zn composition range which is distinctly different from that of alloy 5186. In particular, it is necessary to increase the content of magnesium, add a small amount of zinc, and reduce the levels of minor addition elements, Fe, Si, and Mn, while keeping them above a minimum level.
• magnesium is well known to increase the mechanical characteristics (R 0 , 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 requirements. However, beyond 5.35% magnesium, the corrosion resistance begins to degrade; a maximum value of 5.30% is preferred.
• the addition of zinc in sufficient quantity is found to have a beneficial effect on the mechanical characteristics of the sheets and on the limit of elasticity at the welded joints. Moreover, it improves the resistance to corrosion. In the context of the present invention, 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 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 from 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 behavior.
• the applicant has found that it is preferable to maintain the copper content below 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 the usual impurities of 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 a too high content of these elements limits the recrystallization and leads to a fall in the value of A.
• the products according to the invention are always produced by semi-continuous casting, followed by the conversion steps which correspond to the desired product shape: spinning for spun or drawn products (bars, tubes, profiles, wires); rolling for rolled products (sheets, strips, thick plates).
• the rolling plates produced by semi-continuous casting are hot-rolled, then possibly cold-rolled.
• the strips are then glued and cut into sheets.
• the hot mill outlet temperature and the winding temperature as well as the rate of work hardening which affect 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. In this case, an outlet temperature of the hot rolling mill of between 260 ° C.
• This particular embodiment of the invention namely the direct obtaining of the 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 higher at 3300 mm and even more preferably above 3500 mm.
• the product according to the invention is characterized by an elongation at rupture A of at least 24%, and preferably at least 27%. This feature facilitates the implementation of the product. For example, it gives the rolled sheets an excellent ability to bend and shape.
• a product which has a yield strength R p0 , 2 (TL) of at least 145 MPa, preferably at least 150 MPa and even more preferably 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 silicon of at least 0.10%.
• R m (TL) x A (TL) it is sought essentially to optimize the product R m (TL) x A (TL) .
• This product, especially in the form of sheets, is particularly suitable for the manufacture of tanks, particularly for the road or rail transport of hazardous materials.
• the products according to the invention show a corrosion resistance at least as good as the comparable Al-Mg alloy products which are known, and this, 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 ( Official Journal of the European Communities, 19/11/1984, N ° L300-35 to 43 ), or by a stress corrosion test performed according to ASTM G 30, G39, G44 and G49.
• the stress corrosion test can advantageously be carried out with reference to the ASTM G 129 standard, the applicant having established in the past the good correlation between these standards and ASTM G 129 (cf. R.
• the selected intergranular corrosion test is considered representative of a natural exposure in a marine atmosphere ( R.Dif et al., Proceedings of the EUROCORR Conference, 1999, Aachen, Germany ).
• the corrosion behavior is evaluated in the initial state but also after artificial aging treatments whose conditions may vary.
• a treatment of 7 days at 100 ° C is conventionally used on the alloys of the 5xxx series in order to reproduce the natural aging at room temperature during about twenty years ( EHDix et al., Proceedings of the 4th 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 duration of exposure, a certain sensitivity to corrosion.
• sensitization phenomenon it is advisable to carry out thermal treatments more advanced than 7 days at 100 ° C.
• the concept of equivalent time is usually used to limit the number and duration of treatments to be performed.
• Q represents the thermal activation energy of the magnesium diffusion (in J / mol).
• R is the constant of perfect gases.
• the value of the report Q R from the literature is of the order of 10,000K to 13,500K.
• the products according to the invention show, during the intergranular test, an intergranular corrosion resistance which is characterized by at least a loss of mass of less than 20 mg / cm 2 after an aging of 7. days at 100 ° C., and with a maximum attack depth of less than 130 ⁇ m, and preferably less than 70 ⁇ m.
• said products also show, after aging for 20 days at 100 ° C., a mass loss of less than 50 mg / cm 2 and preferably less than 30 mg / cm 2 , and a maximum attack depth of less 250 microns, and preferably less than 100 microns.
• the most preferred products in the context of the present invention show, after an aging of 20 days at 120 ° C., a loss of mass of less than 95 mg / cm 2 , and preferably less than 80 mg / cm 2 , and even more preferentially less at 60 mg / cm 2 , with a maximum attack depth of less than 450 ⁇ m and preferentially less than 400 ⁇ m, it being understood that this characteristic is added to at least one of the characteristics mentioned above, namely after aging for 20 days at 100 ° C or 20 days at 120 ° C.
• These products, if they possess in addition to excellent mechanical characteristics for example a product R m x A of at least 8500 or even 9000 are particularly suitable for the manufacture of welded constructions, such as road or rail tanks, as explained below.
• the Applicant prefers the Slow Strain Rate Testing method described for example in the ASTM G129 standard. This test is faster and has been shown to be more discriminating than the conventional methods of determining the non-breaking stress stress corrosion stress, provided that the experimental conditions are well controlled.
• the principle of the slow tensile 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 features of the most sensitive tensile test are elongation at break A and maximum stress (at necking) R m .
• the Applicant has found that the elongation at break is a parameter much more discriminating than the maximum stress. It is necessary to ensure that the reduction of the static mechanical characteristics corresponds effectively to stress corrosion, defined as synergistic and simultaneous action of the mechanical stress and the environment.
• the critical aspects of the slow tensile test are the selection of the tensile specimen, the rate of deformation and the corrosive solution.
• the Applicant has used a specimen (taken in the Travers-Long direction), having an indented shape with a radius of curvature of 100 mm, which makes it possible to locate the deformation and make the test even more severe. Concerning the speed of stress, too fast a speed does not allow the phenomena of stress corrosion to develop, but a speed too slow mask the corrosion under stress.
• the Applicant has used a deformation speed of 5.10 -5 s -1 (corresponding to a traverse displacement speed of 4.5 ⁇ 10 -2 mm / min) which makes it possible to maximize the effects of stress corrosion cracking ( R.Dif et al., Proceedings of the 6th International Conference on Aluminum Alloys, 1998, Toyohashi, Japan, pp. 1615-1620 ).
• the products according to the invention can advantageously be used for welded constructions, 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, especially as reinforcements. They show good fitness skills.
• the products according to the invention are used in the form of rolled sheets in a slightly hardened metallurgical state, such as the O state or the H111 state, with a thickness of 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 (TL) x A (TL) greater than 8200, preferably greater than 8500 and even more preferably greater than 9000 and good corrosion resistance.
• a slightly hardened metallurgical state such as the O state or the H111 state
• the weight loss during an intergranular corrosion resistance test is less than 30 mg / cm 2 after aging for 20 days at 100 ° C.
• the CSC index in Slow traction is less than 50% after 20 days aging at 100 ° C.
• the products according to the invention can be welded by all the welding processes 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 were carried out in the Travers-Long direction on H111 butt-welded metal plates with a V-chamfer by semi-automatic smooth-flow MIG welding with a 5183 alloy filler wire.
• the rolling plates were heated and then hot rolled.
• the plate corresponding to Example H1 was heated 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 of inlet at 490 ° C and a winding temperature of 310 ° C.
• the heating was done in two stages (21h at 510 ° C + 2h at 490 ° C), the rolling inlet temperatures were 477 respectively.
• 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. The properties of the sheets made from these alloys are shown in Table 2. The sheets bear the same reference letter as the alloy in which they were made.
• test piece was taken in the long direction through the welded joint so that the seal is in the middle. With the cord trimmed symmetrically, we found a value of R m of 285 MPa, and with an unstressed cord a value of 311 MPa.
• LDH Limit Dome Height
• LDH is a peripherally locked blank coining test ( R. Thompson, "The LDH test to evaluate the sheet metal formability-Final report of the LDH Committee of the North American Deep Drawing Research Group, SAE Conference, Detroit, 1993, SAE Paper No. 93-0815 ).
• the blank size 490 mm x 490 mm is solicited in equiaxed bi-expansion. Lubrication between the punch (diameter 250 mm) and the sheet is ensured by a plastic film and grease.
• the value LDH is the displacement of the punch at break, the limit depth of the stamping.
• a value of 101 mm is obtained for the sheet H1, and a value of 94.1 mm for the sheet H2.
• an alloy of the prior art with a comparable thickness had obtained the LDH value of 94.3 mm (cf. L. Cottignies et al., "AA 5186: a new aluminum alloy for welded constructions", Journal of Light Metal Welding and Construction, 1999 ).
• the alloy according to the invention has a better resistance to corrosion under stress after aging, especially for intermediate levels of aging, despite a higher magnesium content.
• the alloy according to the invention has a level of resistance to intergranular corrosion comparable to or better than that of the prior art.
• a rolling plate with a composition of: Mg 5.0%, Zn 0.30%, Mn 0.35%, Si 0.01%, Fe 0.15%, Cu 0.03% was produced by semi-continuous casting. , 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 slight leveling, the sheets were annealed with a rise in temperature at 378 ° C for 8 h, followed by a hold for 30 minutes at a temperature between 378 ° C and 390 ° C.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Metal Rolling (AREA)
• Prevention Of Electric Corrosion (AREA)
• Heat Treatment Of Steel (AREA)
• Arc Welding In General (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Powder Metallurgy (AREA)
• Laminated Bodies (AREA)

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• 2002
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• 2003
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