Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C18/00—Alloys based on zinc
  • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
  • C23C2/06—Zinc or cadmium or alloys based thereon

Definitions

• the present invention is directed to the appli- cation of zinc coatings to a substrate - commonly sheet steel.
• hot dip galva ⁇ nizing either continuous or batch type, has long been used for a variety of steel products to protect the products from corrosion.
• 3,343,930 and 3,393,089) reportedly exhibits a good corrosion resistance but, in view of its high aluminum content does not provide a satis ⁇ factory sacrificial protection of the steel substrate, Subsequent-s-fcudies have been aimed at modifying the composition of molten metal baths in order to form (by hot-dipping) a coating which improves corrosion resistance even in the most varied environ ⁇ ments.
• One of the aspects of these studies was the influence of the preparation of the surface to be coated on the quality of the product obtained. It thus appears that in order to ensure a quality coating, some of the alloy coatings previously developed required expensive preliminary surface treatments involving expensive equipment.
• the bath compositions and resultant coatings constitute improvements over known alloy " batha.-and coatings in that they contain additionally mixtures of rare earth elements.
• the present invention is directed to zinc-aluminu ⁇ compositions or alloys which have added thereto rare earths in the form of mischmetal.
• the zinc-aluminum alloys be what are commonly referred to as low aluminum zinc alloys which are generally recognized to contain from about 3% to about 15% aluminum.
• the hot-dip metal baths according to the present invention may vary considerably just as known zinc-aluminum baths and coatings may vary. In each instance, however, it is essential that the bath have added thereto a mischmetal alloy in an amount sufficient to yield the improved results observed and described herein.
• mischmetal refers to a variety of knovm rare earth alloys.
• two typical cerium mischmetals might have the following compositions (in weight %) :
• Ce 45-60 other rare earths 35-50, the balance comprising Fe, Mg, Al, Si and impurities.
• Typical Lanthanum mischmetals can be defined by the following (in weight %) :
• mischmetal refers to the above compositions as well as other mischmetal compositions readily apparent to those skilled in the art.
• the preferred alloy to which mischmetal is to be added is a zinc-aluminum alloy containing from about 3% to about 15% aluminum. Such alloys typically contain about 5% aluminum. These alloys may contain constituents in addition to mischmetal such as Fe, Pb, Sb, Mg, Sn, Cu and Si.
• one embodiment of the invention comprises a low aluminum (i.e., 3-15%) zinc bath containing Pb or Sn as well as mischmetal.
• Pb and Sn are known additives to galvanizing baths for modifying the fluidity of the liquid metal or the spangle of the solidified coating.
• Zinc-aluminum alloys containing lead and also Mg and Cu are reported to be immune to grain boundary corrosion.
• mischmetal additions have been shown to exhibit a pronounced beneficial effect as regards soundness and uniformity.
• a Zn-Al alloy containing Mg, Pb, Cu and misch- metal is encompassed by the present invention.
• a typical composition might contain 3-15% Al, 0.02- 0.15% Mg, 0.02-0.15% Pb and possibly 0.1-0.3% Cu, the balance being Zn with mischmetal additions.
• mischmetals may be advantageously used according to the invention, including mixtures of mischmetals in a single zinc bath or coating.
• a La-mischmetal and a Ce-misch ⁇ ietal may be added simultaneously, preferably in an amount such that the total mischmetal concentration is within the ranges described above, i.e. from about 5 ppm to about 1.0% and preferably from about 0.01 to 0.1% by weight.
• a master alloy may be first prepared and then added to the zinc bath so as to yield the desired mischmetal concentration.
• Such master alloys might be comprised of 20% Zn and 80% mischmetal or 85-95% Al and 15-5% mischmetal.
• EXAMPLES 1 Specimens of rimming steel sheet measuring 68 x 120 x 0.7 mm were galvanized in a device simulating a continuous galvanizing bath. They were first pre ⁇ heated in an atmosphere containing 95% N 2 - 5% H 2 at different temperatures from 750 to 800°C for times ranging from 1 to 10 minutes. After this heating stage the specimens were transferred from the hot zone of the furnace, cooled down to about 430°C and then introduced into a zinc alloy bath maintained at 430°C and protected by the 95% 2 - 5% H 2 atmosphere. They were maintained in the zinc bath for periods ranging from 5 to 60 seconds and then removed from the bath and cooled in a jet of 95% l ⁇ - - 5% H 2 gas.
• This example relates to trials carried out with a pilot continuous annealing and galvanizing plant.
• 800 kg coils of rimming steel sheet 150 mm wide and 0.25 mm thick were first treated in a Selas type furnace at temperatures ranging from 680 to 860°C.
• the sheet was then cooled in a controlled atmosphere to about 430°C and then introduced into a seven-ton zinc bath.
• the sheet was then nitrogen-gas wiped at the exit, jet cooled and finally coiled.
• the speed of the sheet varied in the range 10 to 30 m/min.
• the coating was uniform and free of bare spots, uncoated areas or other defects.
• a Zn - 5% Al bath containing 0.13% Sn and as above 0.05% of cerium mischmetal was also used in the pilot galvanizing line.
• the coatings obtained had characteristics similar to those described above with a coating somewhat less bright due to a different spangle behavior.
• An additional bath containing Zn, 5% Al, 0.13% Sn, 0.05% Pb and about 0.05% Ce + La (added as Ce mischmetal or La mischmetal; or added as a master alloy containing about 20% Zn and 80% La and/or Ce mischmetals; or added as a master alloy containing about 90% Al and 10% La and/or Ce misch ⁇ metal) was also used in the pilot galvanizing line.
• the coatings obtained showed a wide range of thickness, were uniform and again were free of bare spots and uncoated areas.
• pilot plant conditions are mentioned as examples only and that other condi- tions prevailing in continuous annealing and galva ⁇ nizing lines as regards furnace type, composition of gas, speeds, wiping methods, etc., can be used with advantage with the zinc bath composition according to the invention.
• bath and coating co posi- tions as described herein may be used in non- continuous (e.g. batch) galvanizing methods.
• the formabili-fc'y and adherence was evaluated by means of bulge tests and Erichsen tests.
• the coatings obtained with the isch- metal-containing bath exhibited an adherence and formability equivalent to that of standard galvanized coatings.
• a 180° bending gave rise to no cracking and in the Erichsen test a depth of 9 mm was made on 0.25 mm thick sheets without peeling of the coating.
• the corrosion resistance, in a salt spray test, of the Zn-Al coatings containing mischmetal was more than twice that of a standard galvanized coating of the same thickness.
• the time to first rusting was about 900 hours instead of 350 hours with a conventional galvanized coating of the same thickness.
• the corrosion resistance in an environment containing 10 ppm S0 2 was shown to be at least 50% greater than that of a conventional- galvanized coating.
• the galvanic protection of the Zn-Al mischmetal coating was also determined by examining the progress of corrosion around scratches machined on specimens exposed to a S0 2 -containing environment.
• the galvanic protection of the mischmetal-containing Zn - 5% Al coating was equal to that of a pure zinc coating and far superior to that of a coating containing Zn-55Al-1.5Si.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Coating With Molten Metal (AREA)

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Cited By (8)

Citations (11)

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• 1981
  • 1981-03-18 EP EP19810901054 patent/EP0048270B1/en not_active Expired
  • 1981-03-18 JP JP56501400A patent/JPH0124221B2/ja not_active Expired
  • 1981-03-18 WO PCT/US1981/000347 patent/WO1981002748A1/en active IP Right Grant
  • 1981-03-18 BR BR8107944A patent/BR8107944A/pt not_active IP Right Cessation
  • 1981-03-24 CA CA000373746A patent/CA1175686A/en not_active Expired
  • 1981-12-21 IN IN1437/CAL/81A patent/IN156009B/en unknown

Patent Citations (11)

Non-Patent Citations (1)

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