MXPA99006234A

MXPA99006234A - Zinc alloys yielding anticorrosive coatings on ferrous materials

Info

Publication number: MXPA99006234A
Application number: MXPA/A/1999/006234A
Authority: MX
Inventors: Bernal Ferrero Manuel
Original assignee: Industrial Galvanizadora Sa
Priority date: 1997-01-02
Filing date: 1999-07-01
Publication date: 2000-05-01

Abstract

The present invention relates to a zinc alloy yielding anti-corrosive coatings on ferrous materials;characterized as consisting of zinc plus its usual impurities and possibly aluminium and/or lead as well as alloying metals consisting of between x and y%of nickel together with between v and w%of at least one of the metal:vanadium and chrome wherein:x is equal to or higher than 0.001, preferably higher than 0.04, y is lower than or equal to 0.6, preferably lower than 0.2, v is equal to or higher than 0.001, preferably higher than 0.03, w is lower than or equal to 0.6, preferably lower than 0.04.

Description

ZINC ALLOYS TO PRODUCE ANTICORROSIVE COATINGS IN FERROUS MATERIALS FIELD OF THE INVENTION The present invention relates to zinc alloys for producing anticorrosive coatings in ferrous materials, consisting of zinc, plus their usual impurities and possibly aluminum or lead together with alloy metals: nickel, as well as vanadium and / or chromium.

BACKGROUND OF THE INVENTION Corrosion is a frequent but undesirable process in certain metals. To prevent corrosion, metals are usually coated with a layer of zinc. There are different methods known and used to coat steel and other metals with zinc and zinc alloys, such as: hot dip galvanization, zinc spraying, etc. One of the oldest methods that are still used for economic and technical reasons is the so-mentioned process of hot dip galvanization. Hot dip galvanization basically consists of the immersion, for a few minutes, of ferrous materials in a zinc melt bath at a temperature between 430 and 560 ° C.

Hot immersion produces a physicochemical mechanism by means of which a diffusion process is carried out between the base iron of the parts and the zinc. The zinc coating provides the good corrosion resistance needed for ferrous metals. In general, a zinc coating obtained by means of hot-dip galvanization consists of several layers: an internal alloy of iron and zinc that adheres to the surface of the ferrous material and an outer layer, consisting almost entirely of pure zinc , according to the composition of the bath, which is called Eta phase. In the inner layer, formed by the diffusion of zinc in the ferrous material, you can distinguish up to three zones or sublayers, identified by their different iron contents. The sublayer closest to the base material is called the Gamma phase and contains 21 to 28% iron. Next, there is the Delta phase, which contains 6 to 11% iron and, finally, the Zeta phase containing approximately 6% iron. Depending on the composition of the ferrous material of the part to be coated, the Zeta phase varies greatly in thickness and often tends to pass through the outer layer consisting mainly of pure zinc. When, for example, the structural steel is galvanized in a conventional zinc bath, without additional alloy metals, a galvanized coating with a relatively thin Delta phase and a layer is produced Zeta The Zeta layer consists of large column crystals and reaches very close to the surface of the coating, while the Eta layer of pure zinc is almost nonexistent. The resulting coating layer exhibits a very low adhesion due to the iron-rich thick Zeta phase.

PREVIOUS TECHNIQUE PATENT ABSTRACTS OF JAPAN, vol. 096, no. 007, of 31 July 1996 and JP 08 060329 A (KOBE STEEL LTD) refer to the production of a galvannealed steel sheet in a continuous hot dip process where the zinc coating bath contains Al, as well as Ni, Co and / or Ti. PATENT ABSTRACTS OF JAPAN, vol. 018, no. 052 (C-1158), of the January 27, 1994 and JP 05 271892 A (NISSHIN STEEL CO. LTD), describe a method to control the galvanization bath. The objective of this invention is to reduce the influence of aluminum in the zinc bath in the hot dip galvanization of the steel sheet by adding Ni. The coating bath contains Zn, Al and Ni. PATENT ABSTRACTS OF JAPAN, vol. 017, no. 345 (C-1077), of June 30, 1993 and JP 05 044006 A (NIPPON STEEL CORP) refer to the production of a hot dip galvanized alloy steel sheet that has excellent functionality and corrosion resistance . The galvanization bath contains Al and V.

PATENT ABSTRACTS OF JAPAN, vol. 017, no. 678 (C-1141), of December 13, 1993 and JP 05 222502 A (KAWASAKI STEEL CORP) refer to the manufacture of Zn-Cr-AI series of galvanized steel by hot dip excellent in terms of resistance to corrosion and shedding The objective of this invention is to obtain hot dipped galvanized steel using a Zn-Cr-AI alloy with excellent resistance to corrosion and shedding. A substance containing phosphorus is deposited on the surface of the steel to be galvanized. PATENT ABSTRACTS OF JAPAN, vol. 016, no. 168 (C-0932), dated April 22, 1992 and JP 04 013856 A (NIPPON STEEL CORP) describe the production of a galvannealed steel sheet that has superior resistance to corrosion in a continuous hot dip. The galvanization bath consists of an alloy of Zn-AI-Cr and includes a subsequent heat treatment at approximately 510 ° C. PATENT ABSTRACTS OF JAPAN, vol. 018, no. 114 (C-1171), of the February 24, 1994 and JP 05 306445 A (NIPPON STEEL CORP) refer to the fabrication of a sheet of high strength galvannealed annealed steel containing P. The phosphorus content is 0.01-0.2% and the composition of the bath is zinc, aluminum and one or two of the following elements: Mn, Mg, Ca, Ti, V, Cr, Co and Ce. GB 1 493 224 A (ITALSIDER SPA) refers to a zinc base alloy for a continuous coating of wire and steel sheet using the Sendzimir technique. The coating bath consists of Zn, Al, Mg, Cr, Ti. EP 0 042 636 A (CENTER RECHERCHE METALLURGIQUE) refers to a process characterized by the use of a coating bath containing zinc in addition to one or two of the following elements Al, Be, Ce, Cr, La, Mg, Mn, Pb, Sb, Si, Sn, Ta, Ti, Te and Th to obtain on the first coating an additional protective layer formed by stable compounds. None of these documents suggests the use of nickel together with vanadium and / or chromium as alloy metals for zinc.

OBJECTIVES OF THE INVENTION The objects of the invention are to provide improved zinc-based alloys which are used to coat parts made of ferrous materials which have superior resistance to corrosion. Surprisingly, it was discovered that these targets could be achieved by means of specific alloy metals, most particularly by means of a zinc alloy to produce corrosion-resistant coatings in ferrous materials characterized in that they consist of zinc plus their usual impurities and possibly aluminum and / or lead , as well as alloying metals consisting of between x and y% of nickel together with between v and w% of at least one of the metals: vanadium and chromium, wherein: x is equal to or greater than 0.001, preferably greater than 0.04, and is less that or equal to 0.6, preferably less than 0.2, v is equal to or greater than 0.001, preferably greater than 0.03, w is less than or equal to 0.6, preferably less than 0.04. All the indicated percentages are expressed as% p / p in the specification and in the claims. Without being limited to the explanations that have been provided, applicants have observed that the use of these alloys produces a much thinner Zeta layer, resulting in an improvement in their mechanical strength, and a relatively thicker Eta layer, than it results in a significant increase in the corrosion resistance of the coating. Generally, vanadium is preferred, which generally gives better results than chromium. Preferably, the zinc content of the alloy is at least 90% and most preferably at least 95% and the aluminum content is equal to or less than 0.25%, and most preferably between 0.001 and 0.25%, while the content of lead is between 0 and 2% and usually below 1.2%. The most common "impurity" in the zinc bath is iron, and the iron may be present in amounts up to the solubility limit of Fe in the zinc bath at different operating temperatures. When the ferrous material is galvanized in a zinc alloy according to the invention, the structure of the coating is very different from that obtained when galvanizing without said alloy metals. The Delta phase is very similar in appearance, but the Zeta layer, usually consists of large column crystals, which have been transformed into a relatively thin layer of crystals as a result of the inhibiting (leveling) action of alloy metals, nickel , vanadium and / or chromium. In addition a thick layer of zinc appears (Eta phase) which, otherwise, is thinner when galvanized without said alloy metals. The new galvanized structure, with relatively thin layers Delta and Zeta, increases the ductility and the adhesion of the coating, as well as the resistance to corrosion due to the relatively greater thickness of the external layer of zinc. The alloys according to the invention can be used with different types of steel, especially those that have a high content of Si and / or P and / or Al, since they reduce the radioactivity of these; besides promoting the corrosion resistance. The galvanization of the ferrous material using the alloys of the invention is typically carried out with hot-dip galvanization processes in batches, although the use of a continuous hot dip galvanization process is also contemplated.

EXAMPLES Test series were made on sheets of steel whose dimensions are 200 x 100 x 3.5 mm, with the following coatings: - Galvanized samples by hot immersion in a bath whose composition was: 0.005% Al, 0.150% Ni, 0.045% V and the rest of Zn. The samples are called "A-1" or "A-10". The method of work and the characteristics of the galvanization tests are given here later in table 1. - Hot-dip galvanized samples in a bath with the following composition: 0.004% Al and the rest Zn. These samples are referred to as: "B-1" or "B-10". The working method and the galvanization test characteristics are given here later in Table II. All corrosion tests were performed in accordance with ASTM-B-117-90. The results of table I and table II are shown in figure 1.

Working method 1. Degreasing: 6% Galva Zn-96 aqueous solution, for 20 minutes. 2. Chemical bath: 50% hydrochloric acid, until it is completely clean. 3. Rinse: in water (pH = 7) 4. Fluidification: 1 minute at 80 ° C. 5. Drying: Electric oven: 5 minutes at 120 ° C. 6. Galvanization:: Consult the tables. For all immersion / extraction tests V inside / outside = 2/2 m / minute. 7. Cooling:: In the air.

Composition of steel 0.075% C, 0.320% Mn, 0.020% Si, 0.012% S, 0.013% P, 0.040% AL, 0.020% Cr, 0.020% Ni, 0.035% Cu. The microstructure of the coatings was examined under an optical microscope, using a light field and polarized light techniques in samples together with 2% nital (2% nitric acid in ethanol) and under scanning electron microscopy (SEM) in polished sections. The distribution and analysis of the elements was determined by means of X-ray spectrometry (EDS) and a luminescent discharge optical spectroscope (GDOS). With the two techniques, EDS and GDOS, it was possible to observe that nickel and vanadium alloy metals are located mainly between the Delta and Zeta phases of the coating, restricting the growth of both intermetallic phases. This results in a more homogeneous coating with a thinner intermetallic layer, which provides great adhesion and ductility, increasing the mechanical strength of the coating. It also produces an outer zinc layer that is thicker and more compact, therefore, significantly improving the corrosion resistance. To estimate the adhesion of the coating, which is reflected in its mechanical strength, the standard hammer test ASTM A-123 was used. The results of these tests show the strong adhesion of the coatings obtained using the inventions. The coating did not fracture between the two hammer blows, while the zinc coating without the alloy metals fractured under the same conditions. To compare the corrosion resistance of conventionally galvanized coatings with those obtained using the protocols of the invention, accelerated corrosion tests were carried out. The results will be found in Figure 1. The graph shows the initial thickness of the coating required to resist corrosion in a salt spray chamber, in accordance with ASTM B-1 17-90, for as long as showed along the X axis. The results on the left side (which represent substantially a parabolic curve) are the resistance values of an unalloyed galvanized zinc product found in Table II. The results on the right side (representing substantially a straight line) are the values given by a galvanized product using the alloy shown in Table I. The graph shows that for the minimum thickness accepted as an industrial standard, 40 μm, the Conventionally galvanized product resists for 400 hours, while the galvanized product with alloys, subject of the invention, resists corrosion for 1300 hours. 70 μm of a conventional galvanized product resists for some 600 hours, while a product coated in accordance with the invention resists corrosion for more than 2300 hours. With conventional galvanization, increasing the coating to a thickness above 140 μm does not improve the resistance to more than 900 hours, while galvanizing with the subject alloy of the invention, a corrosion resistance greater than 2400 hours can be obtained, with a thickness increased to slightly more than 70 μm.

With a minimum thickness of 40 μm, the invention offers a level of corrosion resistance that would need a much greater thickness of 160 μm if It is conventionally galvanized. This clearly shows that the invention not only improves the mechanical strength and the corrosion resistance in a remarkable way, but also allows a saving in zinc consumption of more than 75%. Subsequent comparisons of a composition according to the invention and the other compositions have been conducted under operating conditions as mentioned below: 1. Degreasing: Cetenal 70 and 9590 2. Rinsing: in water (pH = 7) 3. Chemical Bath : until it is clean. 4. Rinse: in water (pH = 7) 5. Fluidification: 1 minute, G105 200 g / l T = cold. 6. Drying: On top of the bath until it dries. 7. Galvanization: T = 440 ° C, ^ m = varies v. inside / outside = at 10/10 m / min The other operating conditions and results are mentioned in table III below. Having described in detail the nature of the invention, and having given practical examples of its use, it should be noted that modifications can be made, as long as they do not represent a substantial change to the characteristics claimed below.

TABLE I (INVENTION) TABLE II (Conventional) TABLE (CONVENTIONAL)

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - Zinc alloy for anticorrosive coatings in ferrous materials, consisting of 0-0.25% aluminum, 0-1.2% lead, 0.001-0.6% nickel 0.001-0.6% vanadium, the rest being zinc and usual impurities.

2. The zinc alloy according to claim 1, further characterized in that the nickel content is 0.04-0.2%.

3. The zinc alloy according to claim 1 or 2, further characterized in that the vanadium content is 0.03-0.04%.

4. The zinc alloy according to any of claims 1 to 3, further characterized in that the zinc content is at least 90%.

5. The zinc alloy according to any of claims 1 to 4, wherein the zinc content is at least 95%.

6. The zinc alloy according to any of claims 1 to 5, further characterized in that the aluminum content is 0.001-0.25%.

7. The zinc alloy according to any of claims 1 to 6, wherein the content of lead is 0-1.2%.

8. - Process for producing anticorrosive coatings in ferrous materials, wherein the alloy according to claims 1 to 7 is applied in a batch process of hot dip galvanization.

9. Process for producing anticorrosive coatings in ferrous materials, wherein the alloys according to any of claims 1 to 7 are applied in a continuous process of hot dip galvanization.