EP0823489B2 - AlMgMn alloy product for welded structures with improved corrosion resistance - Google Patents

Description

Technical area

The invention relates to the field of rolled or extruded products, such as sheets, strips, tubes, bars, wires or profiles, made of aluminum alloy of the AlMgMn type with Mg> 5% by weight, intended for welded constructions requiring, in particular more than one high elastic limit, good fatigue resistance and good toughness, good corrosion resistance for structural applications, such as boats, offshore constructions or industrial vehicles.

State of the art

It is well known that the use of AlMg alloys of the 5000 series according to the nomenclature of the Aluminum Association in the hardened state (state H according to NF EN 515), either completely hardened (state H1), or partially softened (state H2) or stabilized (state H3), makes it possible to obtain good mechanical characteristics and a good resistance to corrosion. For example, alloys 5083 and 5086 are widely used in the field of mechanical construction, welded or not, for applications that require proper corrosion resistance.

However, after welding, the thermally affected zone around the weld joint is in the annealed state (state O), with less mechanical characteristics, which does not allow to exploit fully, in welded constructions, the mechanical characteristics. of the material. Indeed, the certification and control bodies generally recommend that only the mechanical characteristics in state O be taken into account when sizing a structure.

It is well known that the use of magnesium and manganese-loaded alloys makes it possible to increase the mechanical characteristics in the O-state. However, this is generally done to the detriment of the resistance to corrosion and fatigue. , and increases the speed of propagation of cracks.
It is for this reason that there exists in the standard NF EN 515 a specific metallurgical state (H116) for the 5000 series alloys containing at least 4% magnesium, to which mechanical properties limits and a resistance are attached. Exfoliating corrosion specified.

This is another reason why some mechanical design codes limit the use of 5000 series alloys containing more than 4% magnesium in a corrosive environment, if the temperature of the part in use is likely to exceed a certain temperature. specified between 65 and 80 ° C. Indeed, it is well known that these alloys are susceptible to thermal sensitization to corrosion, a cumulative effect that is manifested by the intergranular precipitation of Al ₃ Mg ₂ , thus reducing the cohesion of the grains. It is linked to the fact that, starting from a magnesium content higher than 3%, a significant fraction of the magnesium is in supersaturated solution and can precipitate during the reheating of the wrought metal (see: D. Altenpohl, "Aluminum und Aluminumlegierungen Berlin / Göttingen 1965, pp. 654 and 675). This effect known for a long time appears to be inevitable and ultimately limits, through the magnesium content, the mechanical characteristics of the wrought products AlMgMn alloys for mechanical construction and more particularly for welded mechanical construction. For this reason, it is considered that the AlMg and AlMgMn wrought alloys with a magnesium content greater than 5.6% are of no interest (cf. Aluminumtaschenbuch, 14th edition, Düsseldorf 1983, p. 44 ).

In order to improve the mechanical characteristics, the research work focused mainly on two aspects: the conduct of the welding operation itself, in order to improve the mechanical characteristics of the welded joint, and in particular its resistance to fatigue; and thermomechanical treatments, in order to improve the corrosion resistance of the part. However, there is a practical limit to these attempts to improve AlMgMn alloys, since any progress in this field can only be made in industrial practice if it is possible to avoid expensive and complex thermomechanical treatments and to drive to a manufacturing range ensuring reliable production. This last condition means that a small variation of a production parameter, for example the temperature of the metal at the output of the hot rolling mill, must not cause a significant variation on the properties of the final product.

This is how requests for Japanese Patent JP 06-212373 and JP 06-93365 , concerning AlMgMn alloys processed in complex ranges and difficult to make reliable, do not meet the objective.

Similarly, the request for European patent EP 0385257 (Sumitomo Light Metal Industries Ltd.) claims the application of a complex and unreliable thermomechanical treatment method to an alloy containing, inter alia, 4.0 to 6.0% magnesium and 0.1 to 1.0 % of manganese. The intended application is not that of mechanical engineering, but that of the lid for boxes; the technical characteristics (in particular the resistance to pitting corrosion) of this product compare favorably with those of the products known for this application, but do not meet the requirements of the welded mechanical construction.

The request for German patent DE 2443443 (Siemens AG) claims a weldable aluminum alloy machine component containing, inter alia, 3.5 to 4.9% Mg and 0.5 to 1.5% Mn. No information is given the mechanical characteristics or the corrosion resistance of this product.

The request for European patent EP 0507411 (Hoogovens Aluminum) describes the application of a complex thermomechanical treatment range to an AlMgMn alloy containing, inter alia, 0.8 to 5.6% Mg, up to 1% Mn and some other elements such as Fe , Ni, Co, Cu, Cr and Zn. The product thus obtained is characterized by good formability, including good elongation at break, and the absence of Lüders lines. It does not meet the needs of welded construction resistant to corrosion.

The European patent EP 0015799 (Ateliers et Chantiers de Bretagne) discloses a weldable alloy containing among others 3.5 to 4.5% magnesium and 0.2 to 0.7% manganese for the manufacture of tubes for cryogenic application. This application does not pose the problem of thermal sensitization to corrosion, and the document does not mention the mechanical characteristics or other properties of use of the product.

The US patent US 4043840 (Swiss Aluminum Ltd) describes a manganese-free AlMg alloy containing, inter alia, 2.0 to 6.0% magnesium and 0.03 to 0.20% vanadium. Vanadium reduces the intrinsic electrical conductivity of the metal and increases the contact resistance of the sheet, making it particularly suitable for spot welding. The product is intended for automotive body reinforcements; characteristics relevant for structural application are not described.

The US patent US 3502448 (Aluminum Company of America) discloses an alloy containing, inter alia, 4 to 5.5% magnesium, 0.2 to 0.7% manganese, which conducts, by cold rolling, to thin sheets and thin strips to the manufacture of beverage can lids, provided that the relationship between the contents of Mg and Mn is consistent with a certain algebraic relationship. This patent does not concern the field of welded mechanical engineering either.

The US Patent 4108688 (Kaiser Aluminum & Chemical) describes the use of very thick plates (> 150 mm) for the manufacture of equatorial flanges of LNG carriers, AlMg alloy of composition (% by weight): Mg: 3.8 - 6.0 Mn < 1 Si: 0.05 - 5 Fe <0.5 Cu <0.3 Cr <0.4 Zn <0.4. These sheets are homogenized for at least 12 hours between 549 and 577 ° C to transform the eutectic Mg ₂ Si coarse particles into finer particles with a maximum size of less than 25 μm. A welded joint with no microcracks in the thermally affected zone is obtained at welding. No indication is given of the number or density of these particles.

The article The effect of Fe and Si on the microstructure and properties of AA 5182 alloy sheet by GJ Marshall et al., Published in Light Metals 1996, p.257-267 , describes the quantitative microstructure of the Mg ₂ Si phases in an AA 5S182 alloy with 4.5% Mg and 0.3% Mn.

Recently, the applicant, in two French patent applications, presented a new approach to the improvement of AlMgMn products for structural applications, based on the development of new compositions of the alloy.

The request for French patent 95-12065 relates to a particular alloy composition, subsequently registered with the Aluminum Association under the designation 5383, containing inter alia 3 to 5% magnesium and 0.5 to 1% manganese, in which the sum of the contents (in% weight) Mn + 2Zn is> 0.75. This composition makes it possible to obtain rolled or spun products having a significantly better fatigue strength and a significantly smaller crack propagation rate than the known products intended for the same application. However, the cited patent application gives no indication of the corrosion resistance of the product. The alloy was presented in a communication titled GM RAYNAUD's New Aluminum Products for High-Speed Light Crafts at the Second International Forum on Aluminum Ships in Melbourne 22-23 November 1995 .

The request for French patent 95-12466 claims a very narrow composition, within the composition ranges of alloys 5083 and 5086, containing among others 4.3 to 4.8% magnesium and less than 0.5% manganese, to obtain good characteristics during large deformations. This application does not mention either the corrosion resistance.

The problem to which the present invention attempts to respond is therefore to provide rolled, drawn or drawn AlMgMn alloy products having, after welding, improved corrosion resistance and better resistance to the sensitizing effect of exposure to temperature. , while retaining good mechanical properties after welding, good resistance to fatigue and can be developed at the lowest cost.

Object of the invention

The Applicant has found that AlMgMn alloys can be made more resistant to the sensitizing effect of temperature exposure when they have a particular and well defined microstructure, which results from a set of parameters of the manufacturing process.

The subject of the invention is thus an AlMgMn alloy product for welded mechanical construction of composition (% by weight):
5.0 <Mg <6.5 0.2 <Mn <1.0 Fe <0.8 0.05 <Si <0.6 0.2 ≤ Zn <1.3
optionally Cr at a content <0.15 and / or one or more of the elements Cu, Ti, Ag, Zr, V, at a content <0.3 each, the unavoidable impurities <0.05 each and <0.15 at total, remains aluminum, wherein the number of Mg ₂ Si particles of size between 0.5 and 5μm is between 150 and 2000 per mm ² , and preferably between 300 and 1500 per mm ² .

Description of the invention

The applicant has found, surprisingly, that in order to obtain the targeted properties, the microstructure has a predominant influence. More particularly, in the high magnesium content range, that is to say above about 5%, the thermal sensitivity of the material to corrosion is considerably reduced. This improved corrosion resistance makes it possible to incorporate more magnesium to achieve mechanical characteristics equivalent to those of AlMgMn alloys known but unsuitable for use in a corrosive environment.

More precisely, there are four types of phases which influence the properties concerned: the eutectic phases Mg ₂ Si, the eutectic phases AlFeMnSi, the eutectic phases Al ₆ (Mn, Fe) and AlFeCr, and the manganese dispersoids, of sub-micron size, which are found in the grain.

C'est ce paramètre qu'on désignera par la suite par taille des particules.
Il est bien connu que les phases Mg₂Si contiennent la plus grande partie du silicium présent dans ces alliages, et que ces phases sont, en particulier dans les alliages dépassant 3 à 4 % de Mg, pratiquement insolubles (voir L.F. Mondolfo, « Aluminium Alloys, Structure and Properties», London 1976, p. 807). Par conséquent, leur nombre et leur taille sont déterminés lors de la coulée et n'évoluent pratiquement pas au cours du traitement thermomécanique du produit, à condition que l'on n'atteigne pas la température de fusion (brûlure) de ces phases qui constituent l'eutectique le plus fusible. La teneur en silicium correspond au niveau d'impureté du métal de base.The particular microstructure according to the invention is characterized by a new distribution in size and quantity of these known phases. This microstructure has been characterized in the following manner, well known in micrography. A polished cut of the metal is prepared and is observed by optical microscopy or scanning electron microscopy. Optical microscopy makes it easy to identify Mg ₂ Si phases compared to other phases present. Scanning electron microscopy lends itself better to the characterization of phases smaller than 0.5 μm in size; using the backscattered electron mode, it also makes it possible to distinguish the Mg ₂ Si phases.
In order to determine the size of the particles, it is evaluated, by numerical analysis of the micrographs, their area A from which the size parameter d according to the formula is calculated. $\mathrm{d}=\sqrt{4\mathrm{AT}/\mathrm{\pi }}\mathrm{.}$

It is this parameter that will be designated later by particle size.
It is well known that the Mg ₂ Si phases contain most of the silicon present in these alloys, and that these phases are, in particular in alloys exceeding 3 to 4% Mg, practically insoluble (see LF Mondolfo, "Aluminum Alloys, Structure and Properties, London 1976, 807). Therefore, their number and size are determined during casting and do not change substantially during the thermomechanical treatment of the product, provided that one does not reach the melting temperature (burn) of these phases which constitute the most fuse eutectic. The silicon content corresponds to the impurity level of the base metal.

The Applicant has found that the increase in the number of small Mg ₂ Si particles (0.5 to 5 μm size) results in an unexpected improvement in the corrosion resistance of both the welded structures and the raw sheets. This effect is particularly pronounced when the number of Mg ₂ Si particles is between 150 and 2000 particles / mm ² and, preferably, between 300 and 1500 per mm ² . Above 2000 particles per mm ² , no further effect on the corrosion resistance is observed; in some cases there is even a drop in the yield point after welding. Moreover, she has found that by decreasing the size of the Mg ₂ Si particles, the fatigue strength of the welded joints is improved. Thus, the number of "large" particles (size> 5 μm) should represent only a small part of the total particles (size> 0.5 μm), typically less than 25%, and preferably , less than 20%. Finally, the surface fraction of Mg ₂ Si particles, also measured by image analysis from optical microscopy, must be less than 1%, and preferably 0.8%.

It is well known that the eutectic phases AlFeMnSi, Al ₆ (Mn, Fe) and AlFeCr (size> 0.5 μm) contain part of the Mn, Si and Cr present in the alloy and do not participate in the hardening of the alloy. alloy nor its resistance to corrosion. They trap part of Mn, Cr and Si. It is known that these phases are insoluble and their size, number and morphology are determined during casting.

The Applicant has found that reducing the size and the number of these phases, improves the fatigue strength and the mechanical properties of the metal. The number of particles of this type size> 0.5 μm, must be less than 5000 per mm ² , and preferably, 2500 per mm ² . The surface fraction of particles of size> 0.5 μm must be <3%, and preferably 2%, knowing that the number of large particles larger than 5 μm must not represent more than 25% (preferentially 20%). %) of all particles of size> 0.5 μm. In addition, a decrease in the volume fraction of these eutectic phases results in an improvement in the corrosion resistance.

It is well known that dispersoids (Al, Mn, Fe, Cu) less than 0.2 microns in size improve the mechanical characteristics of the product, and in particular the elastic limit of the welded joint. The Applicant has observed a strong effect of the dispersoid fraction on the corrosion resistance: the sensitizing effect of exposure to the temperature is greatly reduced when the surface fraction of dispersoids exceeds 0.5%, and preferably 1%.

The invention can be applied to a fairly broad composition domain, and the composition limits used can be explained as follows:

It is well known that magnesium provides good mechanical strength. Below 3.5%, and more particularly below 3.0%, the alloy is generally free of corrosion problems and the present invention is of little interest. Above 6.5%, the problem of the thermal sensitization to corrosion becomes so strong that even the implementation of the present invention no longer makes it possible to obtain products that can be used in a corrosive medium.

Manganese improves the tensile strength and decreases the tendency of the metal to recrystallize, which is known to those skilled in the art. Below 0.2%, the present invention is of no industrial interest because the resistance to the pull is too weak. Above 1%, elongation at break, tenacity and fatigue resistance become too low for the intended applications.

Zinc, in the presence of manganese, improves the breaking strength, but beyond 0.5 to 0.7%, the applicant has observed, by studying the corrosion behavior, especially in the marine environment, the welded joint after aging, some cases of failure. For zinc contents greater than 0.5%, it therefore appears necessary to protect the welded joint from contact with the corrosive medium, for example by painting or metallization. It has been found that the presence of 0.2 to 0.3% of zinc makes it possible to increase the magnesium content without increasing the thermal sensitivity of the material to exfoliating corrosion.

Copper and chromium also have a favorable effect on the yield point, but the chromium content must imperatively be limited to 0.15% to maintain good fatigue resistance. The copper content is strictly limited to 0.30% and preferably should not exceed 0.18% to avoid the occurrence of corrosive corrosion pitting.

The iron content does not have much influence in the context of the present invention; it should be less than 0.8% to avoid the formation of primary phases during casting, while for high manganese contents, it is preferable that it does not exceed 0.4%.

The silicon content must be sufficient to ensure the formation of silicon phases such as Mg ₂ Si, and at least 0.05%, but must not exceed 0.6%. The alloy may also contain, for certain applications, titanium, silver, zirconium or vanadium in an amount of less than 0.3%.

The applicant has not been able to note a significant influence of the other impurities limited to 0.05% per element, their sum not exceeding 0.15%.

Another object of the invention relates to the manufacture of products having the microstructure previously described in the form of wide strips hot-rolled, of width greater than 2500 mm, preferably of width greater than 3300 mm. Such a width implies that the cold rolling is abandoned because the cold rolling mills are not designed to allow rolling at such a width. This means that one obtains the strip or the sheet having all the characteristics described directly by hot rolling, which is possible with the invention.

The use of the products thus obtained for mechanical engineering, welded preferably, such as for example shipbuilding, offshore construction or the construction of industrial vehicles, is another object of the present invention.

The products according to the invention have a high yield strength after welding, which of course depends on the Mg content, and which is higher (in MPa) than 40 + 20% Mg. The fatigue strength after welding, measured bending plane with R = 0.1, is greater than 140 MPa at 10 ⁷ cycles. The deformation at the cutting of the sheets, measured in the H22 state after planing and pulling, is less than 3 mm; without traction, that is to say only after leveling, it is less than 5 mm.

Examples

Four-alloy industrial plates of the composition shown in Table 1 were produced by vertical semi-continuous casting. Table 1 No. mg Yes Fe mn Cr 1 5.2 0.10 0.18 0.80 0.12 2 4.4 0.15 0.25 0.50 0.10 3 4.0 0.20 0.27 0.30 0.05 4 4.7 0.04 0.12 0.60 0.10

Casting parameters for 10 examples are shown in Table 2 Table 2 ex. Casting temperature in ° C Casting speed in mm / min Refining used in kg / t refining AT5B 1 695 50 1 2 685 42 1.5 3 675 30 2 4 695 50 1 5 685 42 1.5 6 675 30 2 7 695 50 1 8 685 42 1.5 9 675 30 2 10 695 50 1

The homogenization of the plates was carried out as follows:

• . Montée avec une vitesse de 30 °C / h jusqu'à 440 °C,
• . Maintien pendant 5 h à 440 °C,
• . Montée à une vitesse de 20 °C / h jusqu'à 510 °C,
• . Maintien pendant 2 h à 510 °C
• . descente à une vitesse de 20 °C / h jusqu'à 490 °C,
• . puis laminage à chaud.

For examples 1, 2, 4, 5, 7, 8 and 10:

• . Raised with a speed of 30 ° C / h up to 440 ° C,
• . Hold for 5 hours at 440 ° C,
• . Mounted at a speed of 20 ° C / h up to 510 ° C,
• . Hold for 2 hours at 510 ° C
• . descent at a rate of 20 ° C / h to 490 ° C,
• . then hot rolling.

• . Montée avec une vitesse de 30 °C / h jusqu'à 535 °C,
• . Maintien pendant 12 h à 535 °C,
• . descente à une vitesse de 20 °C / h jusqu'à 490 °C,
• . puis laminage à chaud.

For examples 3, 6 and 9:

• . Raised at a speed of 30 ° C / h up to 535 ° C,
• . Hold for 12 hours at 535 ° C,
• . descent at a rate of 20 ° C / h to 490 ° C,
• . then hot rolling.

Examples 1 and 2, and Example 3 (resulting in a microstructure outside the invention) correspond to composition 1.

Examples 4 and 5, and Example 6 (resulting in a microstructure outside the invention) correspond to composition 2.

Examples 7 and 8, and Example 9 (resulting in a microstructure outside the invention) correspond to composition 3.

Example 10 (resulting in a microstructure outside the invention) corresponds to composition 4 which is outside the scope of the invention.

After reheating for 20 hours at a temperature above 500 ° C, the plates were hot rolled to a final thickness of 14 mm.

The laminated sheet samples were characterized by techniques known to those skilled in the art. The tensile strength R _m and the yield strength R _0.2 were measured on these sheets. These measurements make it possible to globally evaluate a first aspect of the suitability of the product for the intended use, the present invention not however concerned with an improvement of the static mechanical characteristics.

According to the method explained above, the number, the surface fraction and the size distribution of eutectic precipitates Mg ₂ Si and AlFeMnSi were measured by image analysis. For post weld characterization, samples were prepared by an automatic continuous butt MIG welding shipyard company, with a 45 ° symmetrical chamfer with respect to the vertical to a thickness of 6 mm, with wire alloying 5183. The welding was carried out parallel to the rolling direction.

The corrosion resistance was measured by weight loss after immersion and by measuring the depth of intergranular corrosion. The immersion was carried out in the bath "inter-acid" described in the Official Journal of the European Community of September 13, 1974 (No. C 10484). It is an immersion for 24 hours in a bath composed of NaCl (30 g / l), HCl (5 g / l) and distilled water, at a temperature of 23 ° C ± 0.5 ° C, the volume of liquid being greater than 10 ml per cm ² of sample surface. Before immersion, the samples were subjected to thermal sensitization by heating at 100 ° C. for a variable duration between 1 and 30 days.

The deformation at cutting has been measured as follows:
From a sheet with a width of 2000 mm and a length of 2500 mm in the H22 state, sawing is done in the middle parallel to its length, a band of width 130 mm. This band is placed on a marble, and the deformation of the raised ends expressed by the gap between the edge of the band and the surface of the marble is measured.

Table 3 shows the observed microstructure, and Table 4 summarizes the results of the other characterizations performed. Table 3 ex. Mg ₂ Si phase number of 0.5-5 μm % Mg ₂ Si phases of size> 5 μm fraction surfac. Mg ₂ Si% nb.part. AlFeMn CrSi 0.5-5 μm % go. AlFeMn CrSi 0.5-5 μm fr. surf. AlFeMn CrSi% fr. surf. dispersoids% 1 416 16 0.24 1510 18 1.8 1.6 2 222 21 0.21 2088 20 2.3 1.4 3 140 28 0.19 2800 32 2.8 1.0 4 812 14 0.53 1422 15 1.7 1.0 5 548 20 0.46 1950 17 2.3 0.9 6 152 30 0.40 2002 28 2.5 0.5 7 1024 10 0.76 859 15 0.8 0.7 8 408 18 0.68 1035 18 1.0 0.6 9 160 38 0.62 1264 22 1.2 0.2 10 145 10 0.09 1390 17 1.8 1.2 ex. Depth of pitting after 10-day sensitization at 120 ° C Depth of pitting after a 40 day sensitization at 120 ° C Elastic limit of welded joint MPa 1 135 250 155 2 170 280 152 3 400 650 145 4 110 200 137 5 160 240 135 6 320 540 130 7 80 150 125 8 150 220 120 9 280 450 118 10 400 680 145

It can be seen that Examples 1, 2, 4, 5, 7 and 8 are distinguished by a particularly low pitting depth compared with Examples 3, 6 and 9 corresponding to the prior art, and with respect to Example 10 which gives the bad result that is expected for a high magnesium AlMgMn alloy produced according to the prior art.

The elastic limit of the welded joint is very good for Examples 1, 2, 3 and 10, and quite good for Examples 7, 8 and 9, which are less rich in magnesium. However, Example 10 is unusable because of its low corrosion resistance. On the other hand, the very good strength of the sheet of Example 7 may allow it to be used in welded construction intended for a very corrosive environment and constitutes an improvement over the prior art represented by Example 9.

Surprisingly, the best compromise between the elastic limit of the welded joint and the corrosion resistance is obtained for composition 1, the richest in magnesium, provided that the specific microstructure is obtained (Examples 1 and 2). Same for composition 2, corresponding to the traditionally used alloy 5083 in this area, there is a notable improvement in the corrosion resistance associated with the specific microstructure (Examples 4 and 5).

For some samples, the deformation at the cutting of sheets in state H22 (designation according to EN 515) was evaluated. Table 5 ex. Deformation at cutting after roller planing, in mm Cutting deformation after roller planing and pulling, in mm 6 5.0 3.0 4 1.5 0.5 5 2.5 1.0

Claims (17)

1. An AlMgMn aluminium alloy product for welded mechanical construction with the composition (% by weight) :
   5.0<Mg<6.5, 0.2<Mn<1.0, Fe<0.8, 0.05<Si<0.6, 0.2≤Zn<1.3
   possibly Cr<0.15 and/or one or more of the elements Cu, Ti, Ag, Zr, V, each with a content of <0. 30, and the unavoidable impurities, <0.05 each and <0.15 total, remainder aluminium,
   characterised in that the number of Mg₂Si particles between 0.5 µm and 5 µm in size is between 150 and 2000 per mm², and preferably between 300 and 1500 per mm².
2. A product according to claim 1, wherein Zn≤0.5.
3. A product according to any of claims 1 or 2, characterised in that the number of Mg₂Si particles having a size greater than 5 µm is less than 25%, and preferably less than 20%, of the number of all Mg₂Si particles having a size greater than 0.5 µm.
4. A product according to any of claims 1 through 3, characterised in that the surface fraction of the Mg₂Si particles is <1%, and preferably <0.8%.
5. A product according to any of claims 1 through 4, characterised in that the number of AlFeMnSi, Al₆(Mn,Fe) and AlFeCr particles having a size greater than 0.5 µm is less than 5000 per mm², and preferably less than 2500 per mm².
6. A product according to claim 5, characterised in that the surface fraction of the AlFeMnSi, Al₆(Mn,Fe) and AlFeCr phases having a size greater than 0.5 µm is less than 3% and preferably less than 2.5%.
7. A product according to any of claims 5 or 6, characterised in that the number per mm² of the AlFeMnSi, Al₆(Mn,Fe) and AlFeCr phases having a size greater than 0.5 µm represents less than 25% and preferably less than 20% of all of the phases having a size greater than 0.5 µm.
8. A product according to any of claims 1 through 7, characterised in that the surface fraction of the manganese dispersoids having a size less than 0.2 µm is greater than 0.5%, and preferably greater than 1.0%.
9. A product according to any of claims 1 through 8, characterised in that the depth of intergranular corrosion of metal sheets aged for 10 days at 120ºC, after immersion for 24 hrs. at 23ºC, in a bath composed of 30 g/l NaCl, 5 g/l HCl and distilled water, is less than 400 µm, and preferably less than 200 µm.
10. A product according to any of claims 1 through 9, characterised in that it shows a yield strength after welding, expressed in MPa, greater than (40 + 20 x %Mg).
11. A sheet or plate according to any of claims 1 through 10, characterised in that the cutting deformation, measured at the H22 temper after levelling and stretching, is less than 3 mm.
12. A sheet or plate according to any of claims 1 through 11, characterised in that the cutting deformation, measured at the H22 temper after levelling, is less than 5 mm.
13. A hot-rolled strip made from an Al-Mg-Mn aluminium alloy with the composition
    5.0<Mg<6.5, 0.2<Mn<1.0, Fe<0.4, 0.05<Si<0.6, 0.2≤zn<1.3
    possibly Cr<0.15 and one or more of the elements Cu, Ti, Ag, Zr, V, each with a content <0. 30, and the unavoidable impurities, <0.05 each and <0.15 total, remainder aluminium,
    having a width of at least 2500 mm, preferably at least 3300 mm, characterised in that the number of Mg2Si particles having a size of between 0.5 µm and 5 µm, is between 150 and 2000 per mm², and preferably between 300 and 1500 per mm².
14. A strip according to claim 13, in which Zn≤0.5.
15. The utilization of a product according to any of claims 1 through 14, with a zinc content less than or equal to 0.5%, in shipbuilding.
16. The utilization of a product according to any of claims 1 or 3 through 13, with a zinc content greater than 0.5% and a protective coating of the welded zone, for shipbuilding.
17. The utilization of a product according to any of claims 1 through 13, for the construction of industrial vehicles.