KR880002516B1 - Zinc-aluminium alloys and coatings - Google Patents

Abstract

A protective metal coating alloy especially for steel sheet contains 85-97 wt.% of Zn, 3-15 wt.% of Al and 5 wt.ppm-1.0 wt.% of a rare metal containing alloy, especially including 0.01-0.1 wt.% of mischmetal. The alloy can be hot dip coated onto substrates and gives a good continuous coating without the need for extensive surface preparation.

Description

Zinc-Aluminum Plating Material and Plating Method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to zinc-aluminum plated bodies and plating methods thereof for plating a plated body such as sheet steel.

The use of zinc as a protective plate has been known for a long time and the continuous or batch hot dip galvanizing method using zinc has been used for a long time to prevent corrosion of various kinds of steel products. There is a bar.

Enhanced corrosion resistance and other advantages [eg, sacrificial protecrtion of enhanced steel; In order to obtain enhanced moldability, weldability and colorability, efforts have been made in the field of zinc plating to develop new zinc alloys for application to the plated body by continuous or batch plating. This work led to the development of new platings such as alloy Zn-55 Al-1.5 Si and other zinc alloys containing less (ie less than 15%) Al-1.5 Si components. Zn-55 Al alloy plating plate developed by Bethlehem Steel Company (see US Pat. Nos. 3,343,930 and 3,393,089) has excellent corrosion resistance but satisfactory sacrificial protection against steel plated materials in view of high aluminum content. It does not provide action.

Subsequent studies attempted to modify and adjust the composition of the molten metal bath in order to perform plating (by the plating method) with improved corrosion resistance to withstand under various atmospheric conditions. One aspect of this study was the effect of the condition of the surface to be plated on the quality of the product obtained later. As a result of this study, in order to achieve better plating with some of the previously developed alloy plating materials, it is known that an uneconomical surface pretreatment such as using a very expensive device is required. For example, in the case of a zinc plated body, it typically contains about 5% of Al and other components such as Sb, Pb + Mg and Pb + Mg + Cu developed by Inland Steel. (See US Pat. Nos. 4,152,472 to Inland Steel Corporation and US Pat. Nos. 4,029,478 and 4,056,366 to Nippon Steel Corporation). This type of composition has confirmed that even with very careful surface treatment, bare spots and similar defects are formed.

In view of the above results, a molten metal bath in which the surface of the plated body does not need to be treated by a special method or an expensive device, and in which the bare portion or other defects are not substantially formed on the formed protective plate. Needed.

Accordingly, the present invention provides a hot dip metal bath containing zinc which forms a very excellent protective plate without defects such as bare portions. In general, the metal bath composition and the plated body thereby have a superior point as compared to the conventional plated bath and plated body additionally containing a mixture of rare earth elements. In particular, the present invention relates to zinc-aluminum compositions or zinc-aluminum alloys which are added by adding a rare earth element in the form of a mischmetal. Zinc-aluminum alloys herein refer to low aluminum zinc alloys, which are generally known to contain about 3% to 15% aluminum.

The molten plated metal bath according to the present invention may be varied in various ways, such as a known zinc-aluminum plating bath, and the plated body obtained by such a metal bath may also vary in various ways. In either case, however, it is essential that sufficient amounts of micrometal alloys be added to these plating baths to achieve the effect as described herein.

It is preferred to add about 5 PPM to 1.0%, or preferably about 0.01% to 0.1%, of the micrometals by weight to the zinc-aluminum bath. At this time, when the micrometal is added below 5 PPM, the effect of the micrometal is reduced, and when the micrometal is added more than 1.0%, the micrometal precipitate is formed in the plating bath, resulting in contaminating the product. It is desirable to.

As will be appreciated by those skilled in the art, the term micrometals refers to several types of rare earth alloys that are already known. For example, two typical cerium micrometals have the following composition (in weight percent):

(1) Ce 45-60; Other gray metal 35-50; Residue containing Fe, Mg, Al, Si and impurities.

(2) Ce 52.7 other rare earth metals 48.5, Fe 0.04, Mg 0.28 Al 0.08, Si 0.27 and residual impurities.

A typical tantalum micrometal can be of the following composition (in weight percent):

(1) La 60-90; Ce 8.5; Nd 6.5; Pr 2; Anticipated impurities and residues containing Fe, Mg, Al and Si.

(2) La 83, Ce 8.5, Nd 6.5, Pr 2, Fe 0.2, Mg 0.03 Al 0.18, Si 0.43 and residual impurities.

Thus, the term micrometallic as used herein refers to the compositions described above as well as other micrometallic compositions that are apparent to those skilled in the art. As described above, preferred alloys for the addition of micrometals are zinc-aluminum alloys containing from about 3% to about 15% of aluminum, which typically contains about 5% of aluminum. On the other hand, these alloys may contain components such as Fe, Pb, Sb, Mg, Sn, Cu, and Si in addition to the micrometals. Such additives, in particular Pb, Sb and Sn, generally do not improve the quality of the plated body but may actually reduce the quality of the plated body.

Therefore, it is desirable to produce this alloy limited to substantially pure Zn, Al and micrometals. In other words, the content of Sb, Pb and Sn should not be an amount that would lower the purity limit required for the next starting material.

Zn-exceptionally high purity (99.99%)

Al-commercial purity (99.9%)

Purity with micrometals-iron (total rare earth metals -96%, Fe-4%)

Thus, one form of the present invention comprises a low aluminum (ie 3-15%) zinc bath containing Pb or Sn as well as micrometals. Pb and Sn are known as additives used in zinc plating baths to control the fluidity of the spangles and liquid metals of solidified plated bodies. Since lead causes corrosion between the particles of the plate, a method of adding Sb to the galvanizing bath to enhance the plating ability of the Zn-Al plated body in a similar manner without such harmful effects is described in US Pat. No. 4,056,366. . Therefore, the present invention contemplated the method of adding Sb to the composition containing the micrometal. Moreover, the Zn-Al composition containing Pb and Sb together was also included in the scope of the present invention. Typical compositions in this case contain 3-15% Al, 0.03-0.15% Sb, less than 0.02% Pb and added balance Zn of micrometals.

Zinc-aluminum alloys containing Pb, Mg and Cu have been reported to have grain boundary corrosion resistance. In this type of alloy plating, the addition of micrometals has distinct advantages in terms of integrity and uniformity. Therefore, Zn-Al alloys containing Mg, Pb, Cu and micrometals are included in the scope of the present invention. Typical compositions in this case contain balanced zinc with 3-15% Al, 0.02-0.15% Mg, 0.02-0.15% Pb possible 0.1-0.3% Cu and micrometals added.

In the present invention, various micrometals can be advantageously used by adding a micrometal mixture to a single zinc bath or plated body. For example, the same amount of La-micrometal can be added so that the concentration of total micrometal is about 5 ppm-about 1.0% (preferably about 0.01% -0.1% by weight).

In order to easily add the micrometal to the galvanizing bath, a master alloy was first prepared and then added to the zinc bath to the desired micrometal concentration. This master alloy contains 20% Zn and 80% micrometals or 85-95% Al and 15-5% micrometals.

Example 1

1. A rimming steel sheet specimen measured at 68 × 0.7 mm was hot-dipped galvanized in a device made of a plating bath when continuous melting. This is first pre-heated at intervals of 1-10 minutes at different temperatures in the range of 750-800 ° C. in an atmosphere containing 95% N ₂ -5% H ₂ , and then the specimen is moved in the hot part of the furnace. After cooling to about 430 ° C., it was placed in a zinc alloy bath maintained at 430 ° C. and protected under 95% N ₂ -5% H ₂ atmosphere. It was kept in a zinc bath for 5-60 seconds and then taken out and cooled in a 95% N ₂ -5% H ₂ gas jet. The same experiment was carried out in galvanizing baths of different composition types. Inspecting whether the integrity of the plated body, in particular bare and unplated areas, occurred from the hot dip galvanized specimens. When molten in a galvanized bath containing only 5-8% Al without any other metals, the plated specimens have a high ratio of bare and unplated sites, in this case the longest time at the highest temperature in a reducing atmosphere. It also appeared in samples that had been previously annealed. The addition of 0.15% Sb to the Zn-5% Al bath reduced the bare portions of the specimens relative to the proportion of the bare portions, but there were still 33% of the bare zinc plated surfaces. In the third bath containing 0.02% Ce added with 5% Al and Ce-micrometals, the hot dip galvanized specimen was 100% well plated under heat treatment conditions. Samples galvanized in a bath containing 0.03% La and 0.025% Ce added with Zn-5% Al, La and Ce-micrometals were well plated 100% even when preheated at temperatures as low as 750 ° C. .

Example 2

This example relates to tests conducted using a continuous annealing and hot dip galvanizing apparatus for testing. In this test, 800 kg of reaming steel coil, 150 mm wide and 0.25 mm thick, was first treated with a temperature of 680-860 ° C. in a Selas type furnace. The treated plate was cooled in an atmosphere controlled at about 430 ° C. and then placed in a 7 ton zinc bath. The steel sheet was washed with nitrogen gas and cooled in a nozzle and wound up. Depending on the experimental conditions, the processing speed of the steel sheet varied from 10-30 m / min. Several coils were galvanized in a bath containing Zn-5% Al and 0.05% -0.001% cerium micrometals. The cerium content varied from 0.04-0.0008% and the La content varied from 0.02% -0.0002%. The final plated material varied in particle size from 1-5mm depending on cooling conditions, and varied in thickness from 5-35m depending on gas washing conditions. The plating state was uniformly plated without bare portions, unplated portions and other disadvantages. An-5% Al baths containing 0.05% or more of cerium micrometals and 0.13% Sn were also used in pilot galvanizing lines for testing. The resulting plated body had similar characteristics to those described above, but had a slightly less gloss due to different spangles. In addition, an auxiliary bath containing Zn, 5% Al, 0.13% Sn, 0.05% Pb and about 0.05% Ce + La (with Ce micrometals or La micrometals added; or about 20% Zn and A master alloy containing 80% La or Ce micrometals or a master alloy containing about 90% Al and 10% La or Ce micrometals) was used for the test hot dip galvanizing line. The plated bodies showed various thicknesses and uniform plating states, and there were no bare and unplated portions. The experimental conditions for the test were as described in the examples, and the continuous annealing regarding the shape of the furnace, the composition of the gas, the speed, the cleaning method, and other effective conditions in the galvanized wire were the advantages of the zinc bath with the composition according to the present invention. Can be used as The bath and plating compositions described herein may also be used in non-continuous (eg, batch) galvanizing methods.

Example 3

Various tests were conducted to evaluate the formability and adhesion, corrosion resistance in various environments, electrochemical corrosion resistance and microstructure of the samples obtained from the test production. Formability and adhesion were evaluated by the swelling test and the Erichsen test. For both plates obtained from the hot dip galvanizing bath containing micrometals, the adhesion and formability equivalent to those of the standard galvanized plated body were obtained. And moldability appeared. For example, cracks did not occur when the sheet was bent at 180 ° C. in the expansion test, and a 0.25 mm thick plate was formed at a depth of 9 mm in the Ericsson test. In the salt spray test, the corrosion resistance of the Zn-Al plated body containing the micrometal was more than twice that of the standard zinc plated body of deep thickness. For example, when plating with a plated body according to the present invention, the first time of melting was about 900 hours, whereas the time of melting was 350 hours after plating with a standard galvanized body of the same thickness. In addition, the corrosion resistance in the atmosphere containing 10 ppm of So ₂ was at least 50% higher than that of a conventional galvanized body. In addition, the electrochemical corrosion resistance of Zn-Al micrometallic plated body was examined by exposing the scratches on the specimen in the atmosphere containing So ₂ to observe the corrosion process. The electrochemical corrosion resistance of Zn-5% Al plated containing micrometals was equivalent to that of pure galvanized and much better than that containing Zn-55 Al-1.5 Si.

Claims (13)

A protective metal plate adhered to a plated body comprising about 85% to about 97% Zn, about 3% to 15% Al, and at least 5 ppm to about 1.0% of a rare earth-containing alloy. The plated body of claim 1, wherein the rare earth-containing alloy is a micrometal. 3. The plated body of claim 2 containing from about 0.01 to 0.1% micrometals. 3. A plated body according to claim 2, wherein the micrometal is Ce-micrometal or La-micrometal. The plating according to claim 3, wherein the micrometal is Ce-micrometal or La-micrometal. 5. The plated material of claim 4, wherein the micrometal is Ce-micrometal comprising about 45-60% Ce, about 35-50% other rare earth metals and a residue consisting of Fe, Mg, Al, Si and impurities. 5. The method of claim 4, wherein the micrometals comprise 99.3% rare earth metals (the rare earths comprise 52.7% Ce and 47.3% of other rare earth metals), Fe 0.04%, Mg 0.28%, Al 0.08%, Si 0.27% and residual impurities. Plating body which is Ce-micro metal containing. The micrometals of claim 4, wherein the micrometals comprise 60-90% La, up to 8.5% Ce, up to 6.5% Nd, up to 2% Pr and residues consisting of Fe, Mg, Al, Si and impurities Plating material which is La-micro metal. The method of claim 8, wherein the micrometal comprises 98% rare earth metal consisting of 83% La, 8.5% Ce, 6.5% Nd, 2% Pr, and also 0.2% Fe, 0.03% Mg, 0.18% Al, 0.43 Plated material comprising% Si and residual impurities. Immersing the plated body in a molten zinc alloy comprising zinc, aluminum and micrometals, wherein the bath systemized to produce the plating is about 85% -97% Zn, about 3% A method of plating a protective metal plated body against a plated body comprising -15Al and at least about 5 ppm or more of micrometals. 12. The method of claim 10, wherein the micrometal is added as an alloy of a master alloy type. 12. The method of claim 10, wherein the master alloy comprises 20% Zn and 80% micrometals. 12. The method of claim 10, wherein the master alloy comprises about 85-95% Al and 5-15% micrometals.