LU86738A1 - PROCESS FOR IMPROVING THE PROPERTIES OF A SUBSTRATE PROVIDED WITH A ZINC COATING - Google Patents

Description

% * i ‘,: ~ 7 Λ GRAND-DUCHÉ DE LUXEMBOURG BL-3986 / vdw! Patent N '' * 1 0 / J C,.

Minister of January 16, 1987 · of the Economy and Movennes Classes „, Intellectual Property Service

Tl, redd, Vre ............-........................... SSf LUXEMBOURG

^ .7.8 "· ^ 'Ài ^ ,. Invention Patent Application 7 -----------------------------------------, - ----------------------- c î) I. Request RESEARCH CENTER ... METALLURGICAL., CEN3RUM ... V00R RESEARCH .IN ·. DE METALLUR ^ ’as a non-profit association, verenieing zonder winstoogmerk ____________________________________ 47 rue Mont.py er .....-...... 1040 Bruxelles, _______ represented by Freyling ex Er ne s t T.

& M eyer $ ....... Ern is ,. _i ng. c ο n s. as a private road, 46 rue d u ...... Cemetery / 3)

Luxembourg, acting, as agents _____________________________________ deposits (s) this_______s eize „j anvier mille neuf. hundred quatr.e-v.ing t-.s ep t_____ (4) to. 15.00 hours, at the Ministry of the Economy and the Middle Classes, in Luxembourg: 1. this request for the obtaining of a patent for invention concerning:

Process .for improvement i nrsr Ip.s properties of a substrate_____________________ (5) ... provided with a coating i zinc core___________________________________________________________________ 2. description in language ............... .......... F r ances ai ........................ of the invention in triplicate; 3 ............................... / .. / .............. ................. drawing boards, in triplicate; 4. the receipt of taxes paid to the Luxembourg Registration Office on ..... 16 ri-19 87_____________; 5. the delegation of power, dated from ............ Bruxel l es .......................... ......... on .............. 14-1-19 87_________; 6. the successor document (authorization); declares (s) assuming responsibility for this declaration, that the inventor (s) is (are): (6) r Armand DAV.IN., 1.6 rue des_Peupliex.5., B _4.2.Q ..8 ..._ Bonc.ell.as ______________________ r ...... Dimitri ....... COSTS0UDARIS, ..... 1 Q ./ .. 0 ... 7..1 ... .... quai ...... Orban, B. - 4020 Liege________________ claims) for the above patent application the priority of one (s) application (s) of (7) ........ ........................................ / .. / ...... .................................................. .................................................. .. filed in (8) ........................................ .................................................. ............

on (9) ........................................ U ..... .................................................. .................................................. ..................-............................... .............................................. .... ..... — ____________________________________ under N ° (10) ..................... / ... / .......... .................................................. .................................................. _................................................. .................................................. .................................................. ....

on behalf of (11) ................................ / .. / ........ .................................................. .................................................. .................................................. .................................................. .............................................

elect (elect) domicile for him / her and, if designated, for his / her representative, in Luxembourg___________________________________________ 46 ....... ru e ....... du ....... C.ime. .ti.àr.a __________________________________________________________________________________________________________________________________________________ (12) request (s) the grant of a patent for the invention for the subject described and represented in the abovementioned appendices, with postponement of this grant to ____________ .. ^^^ ALd ^ x-hui t ................................................. ......................month. (13) / authorized representative: '"' r * ......--------------------------------- ---------------------------------------------------------- ---------------------------------------------------------- (14) MEYERS Ernest11 · Statement of Deposit

The aforesaid patent application has been filed with the Ministry of the Economy and the Middle Classes, Intellectual Property Service in * Luxembourg, dated: 16-1-1987 // | [t / ’” - ··. .ÿ \. Pr. The Minister of Economy and the Middle Classes, at 3:00 p.m. r:: Jp. to / \ V 'f. The head of the department ^ Oe Intellectual property, A 68007 - "SÄ- ·· / EXPLANATIONS RELATING TO THE DEPOSIT FORM.

it "if necessary" Request for certificate of addition to the main patent, to main patent application No ............ of ........... . ** - (2) enter the surname, first name, profession.

- address of the applicant, when the applicant is an individual or corporate name, legal form, address of the head office, when the applicant is a legal person - (3) enter the name. first name, address of professional representative, industrial property attorney, with a special power. if applicable: "represented by ........... acting as an agent" [i 't I. · * I Bï.-3986 / vdt? MEMORY DgSClStTlg deposited in support of a

^ BVEHTIOSI PATENT APPLICATION

au î.uiiQDfeoui * 3 C 2384/8701.

METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder uiinstoogmerk in BRUXELLES, (Belgium).

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Method for improving the properties of a substrate provided with a zinc-based coating.

The present invention relates to a method for improving the properties, in particular the corrosion resistance, of a substrate provided with a zinc-based coating.

The zinc-based coatings which are targeted in the context of the present invention are particularly the coatings deposited on ferrous products, whatever the method applied for depositing these coatings. It would not, however, depart from the scope of the invention to apply the present process to other types of products provided with a zinc-based coating.

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It has been known for a very long time that a zinc-based coating makes it possible to effectively protect a ferrous product against corrosion by various ambient media, notably by the atmosphere. This protection results from two well-known mechanisms. First, under the effect of atmospheric oxygen, the zinc coating is covered with an impermeable film of zinc oxide (ZnO) which forms a barrier between the atmosphere and the zinc and prevents the 'subsequent oxidation thereof. In addition, zinc continues to play a protective role even when the coating is damaged and atmospheric air can reach the surface of the ferrous product. Because of its favorable position, relative to that of iron, in the series of electrochemical tensions, zinc indeed causes the passivation of iron and consequently prevents corrosion of the ferrous product.

The presence of a zinc-based coating therefore preserves the integrity of the underlying ferrous product and prevents the formation of red rust which, for aesthetic reasons, is generally unacceptable.

Various processes for depositing zinc-based coatings are known and currently applied. Although they all pursue the same protection objective, certain processes are more widely applied than others, in particular because of their particular adaptation to more frequent types of products. In this regard, mention may be made first of all of the continuous processes of galvanizing by immersion in a bath of molten zinc or by electrolysis in various solutions, particularly suitable for coating filiform products such as wires or plates such as steel strips. . For products of any shape, the most widely used coating method is dip galvanization, that is, by immersion in a bath of molten zinc. The methods of electrolytic deposition or deposition by vacuum evaporation are also used to a lesser extent.

The zinc-based coatings deposited by the processes which have just been mentioned generally behave satisfactorily under the usual conditions of exposure to ambient media. However, it is becoming more and more frequent that the performance achieved by these coatings is no longer sufficient, due to the increase in the aggressiveness of certain atmospheres. In particular, very humid atmospheres cause the formation of white rust which deteriorates not only the appearance of the product, but also the integrity of the coating. Likewise, corrosive industrial atmospheres lead to very high corrosion rates and therefore reduce the service life of the products. Furthermore, the usual zinc-based coatings do not always offer sufficient adhesion to paints applied subsequently, since this adhesion is linked to the quality and composition of the surface of the zinc coating.

The objective of the present invention is to propose a process making it possible to economically improve the behavior of zinc-based coatings as regards both their resistance to particularly aggressive media and their final appearance.

The present invention is based on the observation of the surprising results obtained by the use of so-called physical methods of re-clothing in combination with the deposition of coatings based on zinc.

For the purposes of this patent application, the expression "a so-called physical method" should be understood to mean a method which, like vacuum evaporation or sputtering, only uses physical phenomena, the exclusion of any chemical reaction.

We can briefly recall the principle of two of the physical methods usable for the purposes of the present invention.

Vacuum evaporation consists of heating the material to be deposited under vacuum, to a temperature at which its vapor pressure becomes high enough for the material to vaporize. The vapor thus obtained is then deposited on a substrate, with a relatively high deposition rate.

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Sputtering consists in bombarding a source of metal to be deposited by means of inert gas atoms, projected at high speed and under reduced gas pressure, so as to extract from this source metal atoms which are then deposited on the substrate. to be coated.

These methods are in themselves well known and, moreover, already applied for the metallization of supports such as strips of paper, glass or plastic. However, they have never been used to deposit a thin layer of a metallic material, for example a metal or an oxide, on a metallic product, before or after the deposition of a zinc-based coating, to which they provide unexpectedly, a marked increase in corrosion resistance under severe conditions.

Under these conditions, the process which is the subject of the present invention, for improving the properties of a substrate provided with a zinc-based coating, is essentially characterized in that one deposits on the one hand by a physical method, a thin layer of metallic material, and secondly said zinc-based coating.

The present invention relates to the combination of a deposition by a physical method and a conventional coating based on zinc. The order of execution of these two operations is not imposed by the invention, but it depends on the type of substrate used and the application envisaged.

According to a first advantageous implementation of the process of the invention, a thin layer, with a maximum thickness of 5 μm, of at least one metal chosen from chromium, titanium, molybdenum and aluminum is deposited, on a galvanized steel substrate.

The steel substrate may have been galvanized by immersion in a zinc bath or electrolytically.

Tests have shown that a layer of one of the abovementioned metals, of a thickness not exceeding 1 μm, causes a considerable increase in the resistance to the formation of white rust. in a humid atmosphere, as well as corrosion resistance in an industrial atmosphere. In addition, the substrate thus treated continues to benefit from the electrochemical protection by passivation provided by the underlying zinc.

In the case of an aluminum deposit in particular, the resistance to corrosion in salt spray or in an atmosphere of SC ^ is much better than that which is obtained with conventional Zn-Al coatings.

Such a deposit also makes it possible to impart an attractive metallic appearance to the substrate, corresponding for example to that of chromed steel or stainless steel products. This solution is also particularly advantageous, on the one hand because of its significantly lower cost than that of producing stainless steel articles, and on the other hand because of the passivation by zinc, than the 'we do not meet with simply chrome products.

According to another implementation of the invention, a thin layer, of a maximum thickness of 5 μm, of at least one oxide of a metal chosen from chromium, titanium and manganese is deposited on a substrate. in galvanized steel intended for painting.

This not only results in a marked improvement in the corrosion resistance of the painted product, but also a significant reduction in the tendency to blister formation, as well as the penetration of corrosion along the cut edges.

In this case also, the painted product can be given an appropriate metallic appearance while retaining the resistance properties inherent in the galvanized product.

According to yet another implementation of the invention, a thin layer, of a maximum thickness of 5 μm, of at least one metal chosen from iron, nickel and manganese is deposited on a substrate made of

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- 6 -: galvanized steel intended for phosphating.

It has been found that such a treatment, applied in particular to galvanized sheets with minimized flowering intended for the automobile body, makes it possible to improve the aptitude for phosphating, as well as the adhesion of the paint applied subsequently.

In the particular case where this paint is applied by the cataphoresis method, the aforementioned treatment makes it possible to avoid the phenomenon of crater formation, which causes surface defects in the paint due to the release of hydrogen.

Still according to the invention, the deposition of said thin layer can also be carried out before the deposition of the zinc-based coating.

An interesting application of the process of the invention is in the case of galvanized steels of the so-called "galvannealed" type, that is to say coated with zinc and then heated so as to form an Fe-Zn intermetallic layer. The formation of this layer is favored by a content as low as possible, preferably less than 0.1% by weight, of aluminum in the zinc bath.

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According to the implementation of the invention intended for this type of steel, a thin layer with a maximum thickness of 5 μm is deposited, of at least one metal chosen from iron, nickel and copper, before deposit the zinc coating.

It has been found that the presence of this thin layer facilitates the formation of the intermetallic compounds Fe-Zn and allows aluminum contents reaching up to 0.5% in the zinc bath.

This implementation has proved to be advantageous, because it makes it possible, using the same bath, to produce galvanized parts in a conventional or "galvannealed" manner, simply by applying or not applying the "galvannealing" heating.

- 7 - '»sf By way of illustration of the interest of the process of the invention, it will be noted that samples hot-dip galvanized and provided with a layer of chromium of 0.4 μm in thickness do not present any corrosion after three years exposure in an industrial atmosphere. An identical hot-galvanized steel control sample, but not coated with chromium undergoes, under the same exposure conditions, corrosion leading to a thickness reduction of 2 μm per year.

In another example of implementation, samples of hot-dip galvanized steel were coated, by cathode sputtering, with a layer of chromium oxide of 0.6 μm thick, then they were painted in the process (coil coated). It was found that the penetration of corrosion along the cut edges, after 1000 h of exposure to salt spray, did not even reach 0.5 mm, whereas it is 2 mm in the case of a steel. untreated galvanized.

Claims (8)

1. Method for improving the properties of a substrate provided with a zinc-based coating, characterized in that a thin layer of a metallic material is deposited on the substrate on the one hand, by a physical method , and secondly said coating based on zinc. 2. Method according to claim 1, characterized in that the physical method is vacuum evaporation. 3. Method according to claim 1, characterized in that the physical method is sputtering. 4. Method according to either of claims 1 to 3, for improving the corrosion resistance of a galvanized substrate, characterized in that a layer with a maximum thickness of 3 µm is deposited at least one metal chosen from chromium, titanium, molybdenum and aluminum, on the zinc-based coating. 5. Method according to either of claims 1 to 3, to improve the adhesion of paints applied continuously, on a galvanized substrate, characterized in that a layer with a maximum thickness of 5 is deposited ym, of at least one oxide of a metal chosen from chromium, titanium and manganese, on the zinc-based coating. 6. Method according to either of claims 1 to 3, for improving the ability to phosphatize a galvanized substrate, character. laughed in that a layer with a maximum thickness of 5 μm, of at least one metal chosen from iron, nickel and manganese, is deposited on the zinc-based coating. 7. Method according to either of claims 1 to 3, for improving the formation of an intermetallic layer, characterized in that a layer with a maximum thickness of 5 μm of at least one is deposited metal chosen from iron, nickel and copper on the substrate before depositing the zinc-based coating. "- · ίΐ.1% * ',? ; - 9 - 8. Method according to either of claims 1 to 3, to give an attractive metallic appearance to a galvanized or galvanized and painted substrate, characterized in that a layer of maximum thickness is deposited on said substrate of 5 iim> of at least one metal chosen from chromium, aluminum, copper or stainless steel. y