EP0602265A1 - Procédé de revêtement d'alliage du zinc-aluminium par immersion à chaud - Google Patents

Procédé de revêtement d'alliage du zinc-aluminium par immersion à chaud Download PDF

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Publication number
EP0602265A1
EP0602265A1 EP92121339A EP92121339A EP0602265A1 EP 0602265 A1 EP0602265 A1 EP 0602265A1 EP 92121339 A EP92121339 A EP 92121339A EP 92121339 A EP92121339 A EP 92121339A EP 0602265 A1 EP0602265 A1 EP 0602265A1
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EP
European Patent Office
Prior art keywords
zinc
aluminum alloy
coating
bath
coated layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP92121339A
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German (de)
English (en)
Inventor
Seii C/O Mitsui Mining & Smelting Sugimoto
Koichi C/O Mitsui Mining & Smelting Sato
Junshi C/O Mitsui Mining & Smelting Yoshioka
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mitsui Mining and Smelting Co Ltd
Original Assignee
Mitsui Mining and Smelting Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to JP03267006A priority Critical patent/JP3009269B2/ja
Priority claimed from JP03267006A external-priority patent/JP3009269B2/ja
Application filed by Mitsui Mining and Smelting Co Ltd filed Critical Mitsui Mining and Smelting Co Ltd
Priority to EP92121339A priority patent/EP0602265A1/fr
Publication of EP0602265A1 publication Critical patent/EP0602265A1/fr
Withdrawn legal-status Critical Current

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    • 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 relates to a hot dip zinc-aluminum alloy coating process on a steel or iron materials as the base. More particularly, this invention relates to a hot dip zinc-aluminum alloy coating process obtained by forming a thick coated layer having a good appearance and high corrosion resistance.
  • Zinc-aluminum alloy coating is recently attracting attention because it offers higher corrosion resistance as compared with zinc coating, and has come to be used extensively in outdoor applications such as building materials, support lines for electric or telephone, and metal parts over-head fittings and fasteners for transmission lines or electric powerlines.
  • This coating is regarded as an anti-corrosive measure for steel materials to be used in severe corrosive environments including the marine, sea coast regions, and hot-spring areas and for steel materials required to be maintenance-free.
  • a steel material as a base is degreased or annealed and subjected to pickling or reduction thereby to clean the surface, and the cleaned steel material is then immersed in or passed through a molten zinc-aluminum alloy bath either after flux treatment is conducted or while the reducing atmosphere is maintained.
  • Techniques for immersing the bases in molten zinc-aluminum alloy baths can be roughly divided into the following two groups; (1) the direct immersion method in which the base is immersed directly in a molten zinc-aluminum alloy bath, and (2) the indirect immersion method in which the base is first subjected to zinc coating (by either hot dipping or electroplating) or to metal coating and is then immersed in a molten zinc-aluminum alloy bath.
  • the thickness of a coated layer formed by galvanizing or zinc-aluminum alloy coating is usually in proportion to corrosion resistance. That is, the larger the thickness of a coated layer, the higher the corrosion resistance.
  • the corrosion resistance of a zinc-aluminum alloy coated layer is three times that of a zinc coated layer of the same thickness, the alloy coated layer comes to have the same corrosion resistance as the zinc coated layer if the thickness of the former is only 1/3rd of that of the latter. Accordingly, in order to enable the zinc-aluminum alloy coated layer to exhibit high corrosion resistance, the zinc-aluminum alloy coated layer is required to have the same thickness as the zinc coated layer.
  • the factors which determine coating thickness are the wet adhesion and viscosity of the coating bath, the thickness of an intermetallic compound layer (alloy layer) such as Fe-Zn, Fe-Al, or Fe-Al-Zn formed at the steel-coated layer interface, the drawing-up speed of the coated steel leaving the molten zinc or zinc-aluminum alloy bath, wiping conditions of molten coated layer, and cooling conditions.
  • an intermetallic compound layer such as Fe-Zn, Fe-Al, or Fe-Al-Zn formed at the steel-coated layer interface
  • the thickness of a coated layer can be increased to some degree by heightening the drawing-up speed of the coated steel leaving the molten zinc or zinc-aluminum alloy bath (e.g., increasing the line speed), a vibration may be caused, resulting in difficulties in obtaining uniformity of thickness.
  • the drawing-up speed can be changed with ease in the case of continuous coating of a continuous material such as steel sheet or steel wire, but cannot be changed easily in batch type coating.
  • the coating thickness as a whole is generally being controlled by adjusting the thickness of an alloy layer formed at the interface between the steel and the coated layer.
  • an Fe-Zn alloy layer is formed at the interface in galvanizing.
  • the thickness of this alloy layer is determined mostly by the kind of steel (i.e., steel composition), the bath temperature, and the time period over which the steel material is immersed in the bath (i.e., dipping time).
  • the alloy layer thickness can be increased by either heightening the bath temperature or lengthening the immersion time (dipping time). It is, therefore, possible in hot dip galvanizing to easily obtain a thick coated layer of 30 ⁇ m or more. In the case where hot dip galvanizing is used in applications where processability is required, such as galvanized steel sheet, it is necessary to restrain the growth of an Fe-Zn alloy layer.
  • aluminum is added in the galvanizing bath in an amount of about from 0.1 to 0.5% by weight thereby to regulate the thickness in the range of from 10 to 30 ⁇ m by taking advantage of the aluminum's function of inhibiting an Fe-Zn alloy-forming reaction.
  • the behavior of the alloy layer varies greatly depending on the concentration of Al in the bath.
  • an aluminum concentration of about from 3 to 7% by weight which is ordinarily used frequently, the growth of an Fe-Zn alloy layer is restrained due to the aforementioned aluminum's function of inhibiting an Fe-Zn alloy-forming reaction to give a thin coated layer having a thickness below 30 ⁇ m, under such most common conditions that the bath temperature is from 430 to 460°C which is relatively low and the immersion time (dipping time) is 3 minutes or less which also is relatively short.
  • this coating method is modified by raising the bath temperature to higher than 460°C or lengthening the immersion time (dipping time), the result is the rapid growth of an Fe-Al alloy layer and the thus-formed layer, if it is thick, has poor appearances such as gray spot, rough surface, and peeling and is of no commercial value.
  • the bath In the case of an aluminum concentration of from 7 to 60% by weight, the bath also gives a deposit having no commercial value due to the abnormal growth of an Fe-Al alloy layer.
  • the Fe-Al alloy layer growth can be inhibited by silicon addition into the bath in an amount of from 3 to 5% by weight based on the amount of the aluminum contained in the bath. This inhibiting effect of silicon is produced also at an aluminum concentration of from 3 to 7% by weight. However, because of this inhibiting effect, an Fe-Al alloy layer grows little and a thin coated layer having a thickness below 30 ⁇ m results.
  • the indirect immersion method necessitates more than one bath and the process is complicated. For example, it is necessary to take a measure to cope with changes of the aluminum concentration in the zinc-aluminum alloy bath and with fluctuations of the bath level. It is also necessary to take a measure to avoid inclusion of aluminum into the zinc bath. Because of the above, there is a strong desire for a technique for obtaining, by a simple and economical direct immersion method, a zinc-aluminum alloy coated layer having a thickness of 30 ⁇ m or more and also having a good appearance and high commercial value.
  • An object of the present invention is to provide a process for preparing a highly corrosion-resistant hot dip zinc-aluminum alloy-coated material obtained by a direct immersion method which is simple and economical and by which a zinc-aluminum alloy coated layer having a thickness of 30 ⁇ m or more and also having a good appearance and high commercial value can be obtained by hot dipping and the drawbacks of the currently-employed indirect immersion methods are overcome, such zinc-aluminum alloy coated layer being unable to be obtained by any conventional direct immersion method.
  • a hot dip zinc-aluminum alloy coating process which comprises the step of coating a steel by adding into a molten coating bath comprising 0.10 to 10 % by weight of aluminum, 1.5 to 10 % by weight of copper and the remainder consisting essentially of zinc.
  • Fig. 1 is a photomicrograph showing a copper-free thin normal coated layer at a magnification of 400 diameters.
  • Fig. 2 is a photomicrograph showing a copper-free thick abnormal coated layer at a magnification of 400 diameters.
  • Fig. 3 is a photomicrograph showing a copper-containing thick normal coated layer according to the present invention at a magnification of 400 diameters.
  • the present invention having such a constitution has been accomplished as a result of intensive studies in which various additive elements were added into a bath comprising a zinc-aluminum alloy containing from 0.10 to 10% by weight of aluminum with the remainder consisting of zinc exclusive of unavoidable impurities in order to obtain a zinc-aluminum alloy coated layer having a thickness of 30 ⁇ m or more by a direct immersion method using the bath, and in which the effect of the addition of these elements on coated layer's thickness and on alloy-forming reactions occurring at the steel base interface were investigated. It has been found from the studies that addition of copper into the above-described bath in an amount of from 1.5 to 10% by weight is extremely effective in obtaining a thick coated layer having a uniform thickness of 30 ⁇ m or more and a good appearance.
  • the amount of copper is below 1.5% by weight, the growth of an Fe-Al alloy layer cannot be controlled because the copper produces no effects, resulting in a thin coated layer having a thickness below 30 ⁇ m or in a defective thick coated layer in which an Fe-Al alloy layer has grown abnormally.
  • copper amounts exceeding 10% by weight are uneconomical in that because the alloy comes to have a heightened melting point, the bath should be kept at a higher temperature, leading to higher cost.
  • the material to be coated in the process of the present invention is not particularly limited as long as it is a steel material commonly used as a material in zinc-aluminum alloy coating. However, since coated layer's thickness varies depending on the kind of steel, it is necessary to fix beforehand coating conditions suited for the kind of the particular steel.
  • the steel material may be pretreated by a known method. In the case where the coating is to be conducted in the atmospheric condition, flux treatment is necessary.
  • the flux for use in this case should be one for use in zinc-aluminum alloy coating, such as that shown in JP-B-64-5110. (The term "JP-B" as used herein means an "examined Japanese patent publication".) If a flux for ordinary zinc coating is used, the flux-treated steel material shows poor wettability during coating and may remain uncoated.
  • the coating bath is not particularly limited as long as it has the composition as specified above, and any method may be used for preparing the bath.
  • zinc may be mixed with aluminum and copper.
  • a zinc-aluminum alloy may be used with either copper or a zinc-copper alloy.
  • other element generally added in zinc-aluminum alloy coating i.e., magnesium, sodium, a misch metal, lanthanum, or cerium, may be further added.
  • the bath temperature desirably is in the range of from a temperature 20°C higher than the melting point of the coating material to one 50°C higher than that, although the preferred bath temperature cannot be specified unconditionally because the melting point of the coating bath composition varies.
  • the immersion time may be the same as that in ordinary hot dipping. Since coated layer's thickness is determined by a combination of bath temperature and immersion time (dipping time), it is necessary to fix beforehand the bath temperature and immersion time (dipping time) so as to give the desired coated layer's thickness. Further, drawing-up and cooling after coating may be conducted by a known method.
  • the bath comes to have a higher melting point and the coating should be conducted at a higher temperature, resulting in a lessened practical utilization value, although the Fe-Al alloy layer-controlling effect of copper is observed.
  • the upper limit of aluminum concentration has been fixed at 10% by weight. It is, however, possible to apply the present invention even at an Al concentration of more than 10% by weight.
  • bath temperature and immersion time (dipping time) used in the Example of the present invention were selected based on the kind, shape, number, and industrial value of the materials to be coated, so that higher temperature or a reduction or prolongation of the immersion time (dipping time) is a factor which is suitably varied according to the kind, shape, and number of the materials to be coated.
  • bath temperature and immersion time (dipping time) are not conditions which limit the scope of the present invention.
  • a zinc-aluminum alloy coated layer which is free from non-uniformity or any appearance defect and retains good coated layer quality such as corrosion resistance can be obtained using a single coating bath (direct immersion method) as in hot dip galvanizing, by only performing compositional control of the coating bath and fixing the bath temperature and the immersion time (dipping time) at constant values, without the necessity of conducting a high level of operation or a special operation. Furthermore, since a uniform and thick zinc-aluminum coated layer is thus obtained according to the present invention, high corrosion resistance can be obtained stably due to the increase in thickness in addition to the effect of aluminum.
  • a rolled steel (SS 400 in JIS) for use as general-purpose structural material which had dimensions of 50W x 100L x 3.2T mm and a low-carbon SPCC cold rolled steel sheet having a thickness of 0.3 mm.
  • each coated layer was measured with a magnetic thickness tester and by microscopic examination of a section of the coated layer. Further, the appearance of each coated layer was evaluated with the naked eye in three grades as follows.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Coating With Molten Metal (AREA)
EP92121339A 1991-08-22 1992-12-15 Procédé de revêtement d'alliage du zinc-aluminium par immersion à chaud Withdrawn EP0602265A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP03267006A JP3009269B2 (ja) 1991-08-22 1991-09-19 溶融亜鉛合金めっき被覆物
EP92121339A EP0602265A1 (fr) 1991-08-22 1992-12-15 Procédé de revêtement d'alliage du zinc-aluminium par immersion à chaud

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP23371391 1991-08-22
JP03267006A JP3009269B2 (ja) 1991-08-22 1991-09-19 溶融亜鉛合金めっき被覆物
EP92121339A EP0602265A1 (fr) 1991-08-22 1992-12-15 Procédé de revêtement d'alliage du zinc-aluminium par immersion à chaud

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Publication Number Publication Date
EP0602265A1 true EP0602265A1 (fr) 1994-06-22

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1850031A1 (fr) * 2006-04-27 2007-10-31 Tsubakimoto Chain Co. Chaîne à rouleaux résistante à la corrosion
WO2011011383A1 (fr) * 2009-07-20 2011-01-27 Eastern Alloys, Inc. Alliage de zinc résistant au fluage, à résistance élevée
US9243315B2 (en) 2009-06-25 2016-01-26 Nippon Steel & Sumitomo Metal Corporation High-strength Zn—Al coated steel wire for bridges with excellent corrosion resistance and fatigue properties and method for manufacturing the same
EP3041971B2 (fr) † 2013-09-02 2022-07-27 Saint-Gobain Pam Canalisation Revetement exterieur pour element de tuyauterie enterre a base de fer, element de tuyauterie revetu et procede de depot du revetement

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2146376A1 (en) * 1970-09-17 1972-03-30 Fredericia Galvaniseringsansta Hot galvanising - iron and steel articles by immersion in zinc and then in zinc-aluminium alloys
JPS56105446A (en) * 1980-01-29 1981-08-21 Mitsubishi Metal Corp Zinc alloy for hot dipping
JPS5735672A (en) * 1980-08-11 1982-02-26 Nippon Mining Co Ltd Galvanizing method providing high corrosion resistance

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2146376A1 (en) * 1970-09-17 1972-03-30 Fredericia Galvaniseringsansta Hot galvanising - iron and steel articles by immersion in zinc and then in zinc-aluminium alloys
JPS56105446A (en) * 1980-01-29 1981-08-21 Mitsubishi Metal Corp Zinc alloy for hot dipping
JPS5735672A (en) * 1980-08-11 1982-02-26 Nippon Mining Co Ltd Galvanizing method providing high corrosion resistance

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 5, no. 180 (C-79)(852) 19 November 1981 & JP-A-56 105 446 ( MITSUBISHI KINZOKU ) 21 August 1981 *
PATENT ABSTRACTS OF JAPAN vol. 6, no. 106 (C-108)(984) 16 June 1982 & JP-A-57 35 672 ( NIPPON KOGYO ) 26 February 1982 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1850031A1 (fr) * 2006-04-27 2007-10-31 Tsubakimoto Chain Co. Chaîne à rouleaux résistante à la corrosion
US9243315B2 (en) 2009-06-25 2016-01-26 Nippon Steel & Sumitomo Metal Corporation High-strength Zn—Al coated steel wire for bridges with excellent corrosion resistance and fatigue properties and method for manufacturing the same
WO2011011383A1 (fr) * 2009-07-20 2011-01-27 Eastern Alloys, Inc. Alliage de zinc résistant au fluage, à résistance élevée
EP3041971B2 (fr) † 2013-09-02 2022-07-27 Saint-Gobain Pam Canalisation Revetement exterieur pour element de tuyauterie enterre a base de fer, element de tuyauterie revetu et procede de depot du revetement

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