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
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent

Definitions

• the present invention relates to a highly stable aluminum alloy' of the AlZnMgCu type, and to its use in the production of recrystallization hardened, semi-finished materials, products or articles which are resistant to stress corrosion, such as die-pressed components, e.g. castings, or extrusion profiles.
• Aluminum alloys of the AlZnMgCu type are known to be highly stable.
• Aluminum alloys of this type used hitherto are preferably produced with a nondeformable and stabilized substructure, which substructure is retained aftersolution treatment and has a molecular structure which is denoted by press effect. This press-effect results from texture, subgrain structure, grainflow in the forming and direction.
• the use of such alloys in a recrystallized state is, however, also possible provided such molecular structure is obtained during sheet metal production.
• the use of alloy is generally limited to workpieces having a wall thickness of less than mm. Due to the differing stoichiometric recrystallization hardening on the aluminum, the addition of chromium, manganese, vanadium and zirconium mainly intended to prevent the recrystallization phenomena and stress corrosion, tends to act differently on the strength properties of the semi-finished products made of highly stable aluminum alloys and finished by heat treatment. In addition, the morphological effects of such primary separations and the crystallographically conditioned changing cycle of crystal structure faults and separations have to be considered. Including electro-chemical operations, these complex influences determine the static and dynamic characteristics, as well as the characteristic values important in technical designs of fracture tenacity, residual strength and progressive rupture rate of each particular alloy.
• chromium shows the highest negative influence followed -by vanadium and zirconium, provided the amounts of the said elements added is so adjusted that they have the equivalent effect on the prevention of recrystallization.
• typical individual ingredients can be incorporated in AlZnMgOu alloys, depending upon the solubility thereof in the solid state: Approximately 0.18% chromium, approximately 0.52% manganese, approximately 0.19% vanadium, ap: proximately 0.21% zirconium.
• Zirconium-containing aluminum alloys 0.5 to 1.8% copper, 0.08 to 0.20% iron, 2.20 to 2.94% magnesium, 0.05 to 0.51% manganese, 0.04 to 0.20% silicon, 5.64 to 6.9% zinc, 0.05 to 0.1% titanium, 0.1 to 0.25% zirconium, 0.05 to 0.5% vanadium.
• Zirconiumand chromium-containing aluminum a1- loys to 1.0% copper, 1.5 to 7% magnesium, 1.5 to 13.5% zinc, 0.05 to 0.5% chromium, 0.05 to 0.5% zirconium.
• a substantial improvement in the so-called stress corrosion resistant alloys is obtained by the addition of silver, particularly if special heat treatments are employed. More especially, the age-hardening relative to silver-free AlZnMgCu alloys is associated with a slight reduction in strength properties.
• Zirconium and silver 0.9 to 1.73% copper, 0.08 to 0.25% iron, 2.12 to 2.67% magnesium, 0 to 0.11 manganese, 0.05 to 0.09% silicon, 5.60 to 6.35% zinc, 0 to 0.01% chromium, 0.03 to 0.4% titanium, 0.28 to 0.35% silver, 0.07 to 0.19% zirconium.
• Chromium, manganese, vanadium and silver 0.1 to 1.5% copper, 0 to 0.4% iron, 1.5 to 6.0% magnesium, 0.1 to 1.5% manganese, 0 to 0.4% silicon, 4 to 12% zinc, 0.1 to 0.06% chromium, 0 to 0.2% titanium, 0.02 to 0.05% boron, 0.1 to 1.0% silver, 0 to 0.15% vanadium.
• alloy for forgings and extrusion profiles was developed, preferably of the following manganeseand vanadium-free compositions: 0.9 to 1.2% copper, 0 to 0.25% iron, 2.3 to 2.6% magnesium, 0 to 0.1% manganese, 0 to 0.3% silicon, 5.6 to 6.0% zinc, 0.15 to 0.20% chromium, 0.03 to 0.05% titanium, 0.002 to 0.005% boron, 0.25 to 0.40% silver the remainder being aluminum together with conventional impurities.
• AlZnMgCu alloys containing zirconium as compared with similar alloys containing chromium, have the advantage of a substantially improved penetration hardening. If one compares the highly stable aluminum alloys varyingly modified by the incorporation of chromium and zirconium after the complete heat treatment, inclusive of single or multi-stage heat hardening on workpieces of identical wall thickness, then the zirconium-containing alloys have the advantage over chromium-containing alloys in that they can be treated with very low cooling speeds after the solution treatment in order to obtain the usual strength values. Resulting therefrom are very low, natural stress states which, in turn, mean that during the subsequent processing of the semi-finished products distortion or delay can be avoided.
• AlZnMgCu alloys which were alloyed with zirconium only, relative to chromiumcontaining alloys, have the disadvantage of a reduction in the resistance relative to stress corrosion.
• the addition of silver to chromium-containing alloys reduces the resistance thereof to stress corrosion accordingly, the favorable results obtainable with the individual use of chromium or a combination of chromium and silver do not extend to an improvement in stress corrosion.
• a high strength aluminum alloy of the AlZnMgCu type comprising 1.1 to 3.0% copper, 2.0 to 3.5% magnesium, 5.0 to 7.5 zinc, 0 to 0.4% titanium, 0 to 0.006% boron and 0.04 to 0.1% chromium in combination with 0.08 to 0.3% zirconium, the remainder being aluminum together with the usual impurities.
• the alloys of the present invention are particularly useful for producing hardened semi-finished products which are resistant to stress corrosion, and is applicable to products having both considerable and thin wall thicknesses, which products, after the solution treatment are subjected to low cooling off speeds.
• the invention also includes alloys in which the chromium content is replaced by from 0.05 to 0.20% vanadium.
• the incorporation of vanadium renders the alloy in accordance with the present invention further insensitive to quenching.
• the alloys in accordance with the invention are subjected to a two-stage heat treatment, the first stage at a temperature in the region of between and 0., preferably serving a preform of most finely distributed separated material of the type 1 '-MgZn whilst the second heat treatment stage leads to the production of n-MgZnand stable, superhardened T-phase, which acts as nucleus forming agents and can build up on the separated material of the first heat treatment stage. This leads to an improved degree of dispersion and hence also increases the strength values of the final alloy.
• the present invention also relates to the further treatment of workpieces made of the said alloys, after solution treatment, to quenching in boiling water, metal melts or molten salts.
• This moderate cooling ofl after solution treatment presupposes that in the center of the workpieces, a cooling off speed of approximately 2 C./sec. is achieved.
• the cooling off speed can be controlled by the temperature of the quenching bath with the object being to attain a natural stress freedom as high as possible, so that a minimum delay is involved in the subsequent shaping of the semi-finished products.
• the impurities originating from crude aluminum were 0.08 to 0.13% iron and 0.08 to 0.16% silicon. All charges were refined with a titanium-boronprealloy, so that amounts of titanium of from 0.02 to 0.04% were obtained in the final alloy.
• Table 1 sets out the mechanical properties for two different cooling off speeds, the characteristic values of the active state having been taken into account. The values obtained for the stability to stress corrosion refer to test workpieces of short width. All remaining values bars were utilized as test material:
• AlZnMgCuAg Cr 0.18 std. 160 C. 0.45 1.34 3.85 46.3 57.0 60.5 10 32 43 AlZnMgCuAg Mn 0.88 15 std. 160 C. 1. 81 3. 03 11. 32.0 57. 5 60.9 8 '18 38 AlZnMgCuAg Zr 0.13 15 std. 160 C. 0.85 1. 70 4.36 44. 7 54.7 59. 0 12 27 36 AbZnMgCuAg Cr 0.05 Zr 15 std. 160 C 0. 85 1. 37 4. 43 42. 5 57. 8 62. 1 12 I 30 38 AlZnMgCuAg Cr (105+ 15 std. 160 C 1. 01 2. 15 0. 10 40. 6 53. 5 57. 9 10 21 38 (quenched in boiling water) 50 C./ see. between 465 and AlZnMgCuAg Or 018 > 24 std. 120 C. 0.72 2.21 5.37 39.6 45. 0 51. 1 11.5 15
• the alloy AlZnMgCuAgCrZr after quenching with water of 25 C., and subjecting to a heat recrystallization hardening of 15 hours at 160 C., enables the comparison of maximum values shown herein to be obtained.
• the maganese-containing material yields low fracture toughness and relatively low K -values. For these reasons, the use of manganese, either alone or in combination, was not considered further.
• the alloy of the type AlZnMgCuAgCr appears to show maximum results with regard to a compromise with reference to the strength properties exhibited and the resultant steep drop of these properties, after a complete heat treatment with quenching in boiling water, which drop is noticably high. 'It all the properties mentioned are considered then the alloy TABLE 2 Durability in days (quenched in boiling Water) Additional element (percent by weight) Basic alloy The results shown in Table 2, in correlation to Table 1, clearly show the superiority of the combination of chromium and zirconium in such alloys.
• the following alloy of the AlZnMgCu with more finely adapted tolerances has proved to be particularly favor able in its strength properties: 1.1 to 1.3% copper, 2.3 to 2.7% magnesium, 5.7 to 7.1% zinc, 0.02 to 0.05% titanium, 0.002 to 0.006% boron, 0.04 to 0.08% chromium in combination with 0.10 to 0.16% zirconium, the remainder being aluminum together with the usual impurities.
• the impurities of iron and silicon should preferably be below 0.1%.
• the special refining with titanium and/or boron may be dispensed with, since the nucleus formation occurring due to the titanium compounds in a molten state enables a suiiiciently fine crystalline primary setting to be obtained.
• a method of using a highly stable aluminum alloy of the AlZnMgCu type consisting essentially of 1.1 to 1.3% copper, 2.3 to 2.7% magnesium, 5.7 to 7.1% zinc, 0.2 to 0.5% silver, 0 to 0.09% manganese, 0.02 to 0.05% titanium, 0.002 to 0.006% boron, and 0.04 to 0.08% chromium in combination with 0.10 to 0.16% zirconium, the remainder being aluminum together with the usual impurities, as material for producing recrystallizationhardened semi-finished products which are resistant to stress corrosion, comprising the steps of subjecting the alloy to a solution treatment, and thereafter to low-rate cooling.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Conductive Materials (AREA)
• Continuous Casting (AREA)
• Adornments (AREA)
• Forging (AREA)
• Extrusion Of Metal (AREA)
• Prevention Of Electric Corrosion (AREA)

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Cited By (18)

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• 1970
  • 1970-10-23 DE DE2052000A patent/DE2052000C3/de not_active Expired
• 1971
  • 1971-10-05 GB GB4619071A patent/GB1319754A/en not_active Expired
  • 1971-10-21 US US00191517A patent/US3794531A/en not_active Expired - Lifetime
  • 1971-10-21 ES ES396253A patent/ES396253A1/es not_active Expired
  • 1971-10-21 FR FR7137791A patent/FR2113037A5/fr not_active Expired
  • 1971-10-23 IT IT30235/71A patent/IT960529B/it active

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