FI98468C - Galvanizing process and zinc alloy for use therewith - Google Patents

Description

98468

Electroplating method and zinc alloy used in it

The present invention relates to a process for hot-dip galvanizing a series of individual steel pieces, according to which a zinc bath containing silicon is used in a concentration which can reach saturation.

Such a method is known from DE-A-3 734 203. This publication essentially relates to hot-dip galvanizing of steel pieces containing more than 10 0.02% (by weight) of silicon. According to said publication, the electroplating of such steel poses serious problems when using the classical electroplating process, i.e. when using a bath consisting essentially of zinc. In fact, the resulting zinc coatings are thus both too thick and too brittle, and in addition have a greyish appearance. This is due to the fact that the iron-zinc alloy layer formed on the surface of the steel when the latter is in contact with the classical electroplating bath increases linearly over time throughout the immersion period when the steel contains more than 0.02% silicon. This does not happen with steels containing less silicon, as the growth rate in this case is proportional to the square root of the immersion time.

According to the above-mentioned publication, it has been found that the linear growth of 25 iron-zinc alloy layers with steels containing more than 0.02% silicon is due to the crystal lattice disturbances of the alloys forming the layer due to the silicon propagated from the steel layer. · · .. ·, said disturbance facilitating the diffusion of the iron contained in the steel through said layer.

Thus, said publication proposes that the diffusion of silicon contained in steel into the bed is prevented by increasing the activity of the silicon in the bath.

For this purpose, a zinc bath containing silicon is used, preferably a zinc bath impregnated with silicon, not only when the silicon content of all the parts to be galvanized is higher than 0.02%, but also when the silicon content of at least one piece to be galvanized is such, i.e. when it cannot be ruled out that there are some of the parts to be galvanized with a silicon content not exceeding 0,02%, it has been found that the electroplating of steels with a silicon content not exceeding 0,02% in such a bath produces very good results that are completely comparable to those obtained with this type of steel in a classic-10 sa bath.

The applicant has found that the disadvantage of this method is that it does not adequately meet the current needs of electroplators.

It is an object of the present invention to provide a method as defined above, but which avoids said disadvantage.

For this purpose, according to the invention (a) either the series is formed in such a way that all Kap-20 pieces have a silicon content of less than or equal to 0.02%, and in this first case the bath contains at least 0.005% silicon and optionally one or more of the following of the elements: lead in a concentration that can reach saturation, 0.001 to 0.015% of aluminum and 0.002 to 0.1% of calcium, the remainder being zinc. and unavoidable contaminants; • · · (b) or a series is formed such that at least one «IV’. ' the pieces are made of steel with a higher silicon content • · * ..! than 0.02%, and in this second case the bath contains at least 0.005% silicon as well as either 0.02 to 0.06% aluminum and 0.002 to 0.1% silicon. ** Siium and optionally lead in a concentration that can cause saturation, ____ or 0.05 to 0.12% nickel and optionally one, ··. 35 or more of the following elements: lead at a concentration that can reach saturation, 0.001 to 0.015% aluminum and 0.002 to 0.1% calcium, with the remainder being zinc and unavoidable impurities.

5 As regards the hot-dip galvanizing of steels which do not contain more than 0.02% silicon, that is to say, silicon-free or low-silicon steels, the applicant has found that, contrary to the proposals in DE-A-3 734 203, cited above, silicon the addition to a class 10 galvanizing bath, i.e. a bath consisting essentially of zinc, produces coatings that are significantly thinner than "classical" coatings, i.e. coatings obtained with steels with a silicon content not higher than 0.02%, in a classical galvanizing bath.

Thus, for example, a coating formed on silicon-free steel immersed for 5 minutes in a classical bath at 450 ° C has a "classical" thickness of 66, while the same steel and under the same conditions give a coating thickness of only 37. after adding 0.03% silicon to the bath. Needless to say, zinc consumption is reduced to the same extent as the thickness of the coating. The reduction in thickness is considerable even when the addition of silicon to the bath is 0.005%.

It should be noted here that the "classical" thickness, i.e. 25 to about 70 pm, has come in many technical fields. less and less necessary. For car manufacturers, for example, ·. For example, a coating thickness of about 40 [mu] m would be sufficient in many applications.

; *:

Thus, part (a) of the method «· · * · * * 30 of the present invention is particularly interesting when a series of steel pieces with a low silicon content (up to 0.02%) or no silicon are to be galvanized. not at all, and when v is desired a coating having a thickness less than the classical thickness, in particular a thickness less than · <·. 35 50 pm.

«I · · 98468 4

With regard to the hot-dip galvanizing of steels containing more than 0.02% silicon, the applicant has found, also contrary to the proposals of the above-mentioned DE-A-3 734 203, that the addition of silicon to a zinc bath is not sufficient to solve the problem of excessive coating growth, but that it is necessary to add, in addition to 0.005% or more of silicon, either 0.02 to 0.06% of aluminum and 0.002 to 0.1% of calcium or 0.05 to 0.12% of nickel.

The minimum concentrations for aluminum (0.02%) and nickel-10 (0.05%) are required to significantly reduce the thickness of the coating. A minimum silicon content (0.005%) is necessary to enhance the inhibitory effect of aluminum and nickel on the growth rate of the coating, especially when the galvanized steel contains up to 0.20% silicon, and to avoid the formation of nickel-iron-metal stones in the bath. A minimum calcium content (0.002%) is necessary to obtain a coating with no, or virtually no, continuity defects. Avoiding such errors proved difficult, even in the presence of calcium, when the aluminum content is higher than 0.06%. A nickel content higher than 0.12% leads to the formation of undesired Ni-Zn metal compounds. Calcium added at concentrations above 0.1% has no effect.

In view of the above, it is clear that the f · · galvanizing bath according to part (b) of the method according to the present invention is of particular interest, not only when the series of galvanized steel pieces * · * ..! consists entirely of bodies with a silicon content of more than 0,02% t · · 30, but also when galvanized is a mixed series consisting partly of pieces which do not contain silicon or which have a silicon content • · · is low (up to 0,02%), and partly from pieces .... with a higher silicon content, and thus when ··. 35 a series of steel pieces with a composition »· · 5 98468 is unknown, which is often the case for customers when electroplating.

It should be noted here that the use of an electroplating bath consisting of 0.1% silicon, 0.2% aluminum, 0.1% nickel, 0.1% tin and balancing zinc is already known from CN -A-85 109 366. This must be a bath impregnated with silicon because the solubility of silicon in zinc at 450 ° C, which is the temperature normally used in electroplating, rises to only about 10 0.03%. The exact type of steel this bath is intended for is not mentioned. It is also not specified whether the bath is intended for continuous galvanizing or for galvanizing individual pieces. However, the Applicant has found that such a bath 15 is not suitable for galvanizing individual pieces, as it certainly adds many continuity errors in the coating, whatever the silicon content of the pieces to be galvanized.

The applicant has also found that the presence of silicon in the bath at a concentration of at least 0.005% prevents the formation of base metal stones (iron-zinc metal stones) at any silicon content of the galvanized steel, which makes the method according to the invention even more attractive.

It is desirable for the bath to contain at least 0.01% silicon in both cases, on the one hand, and a coating «· r, · on the other hand. to achieve a significant reduction in thickness, in particular with steels containing 0 to 0.20% silicon, + ('., 1 and, on the other hand, to prevent the formation of base metal stones with certainty.

It is also desirable that the bath contain, in some cases, lead in a concentration that can reach * ♦ »; saturation, for example 0.1 to 1.2%, with a view to reducing the surface tension of the bath. It is further desirable that the bath in the first case contain 0.001 to 0.015% aluminum and / or 0.002 to 0.1% calcium, to protect the zinc from oxidation; otherwise, a yellowish film forms on the surface of the bath, messing up the galvanized pieces. For the same reason, it is preferred that the Nikke-5 lipitic bath used in the second case also contain 0.001 to 0.015% aluminum and / or 0.002 to 0.1% calcium.

The preferred calcium content is 0.005 to 0.05%.

It is clear that the composition of the bath changes during the operations because the wear rates of the components, zinc and additives, by oxidation and other reactions, at the operating temperature (normally about 450 ° C) and in the presence of flow (ZnCl 2 and NH 4 Cl) are different, and in practice, the larger the more oxidizable metal. The lack of additives due to oxidation mainly affects silicon and calcium and also aluminum in the absence of calcium.

The applicant has now found that it is possible to maintain the composition of the bath during the electroplating operation by compensating for the bath consumption by adding to the bath a zinc-based alloy-20 ring containing: (a) in the first case 0.1 to 1.5% silicon and optionally one or more of the following elements: , 1 to 1.2% lead, 0.01 to 0.8% aluminum and 0.02 to 1% calcium; .. 'i 25 and ·: * (b) in the second case 0.1 to 1.5% of silicon in the same way as · * either 0.1 to 0.8% of aluminum and 0.02 to 1% of calcium • · · And optionally 0.1 to 1.2% lead, .. 30 or 0.05 to 0.12% nickel and optionally one or more of the following elements: 0.1 to 1.2% lead, • · · '· * * 0.01 to 0.8% aluminum and 0.02 to 1% calcium.

The zinc-based alloy to be used, preferably in the form of ingots, may contain, as the case may be: <7 98468 either 0.1 to 1.5% Si and 0.1 to 1.2% Pbr; or 0.1 to 1.5% Sir and 0.02 to 1% Ca; or 0.1-1.5% Si, 0.01-0.8% Aira and 0.02-1% Cara; 5 or 0.1 to 1.5% Sir, 0.01 to 0.8% Air and 0.1 to 1.2% Pbr; or 0.1 to 1.5% Sir, 0.02 to 1% Cara and 0.1 to 1.2% Pbr; or 0.1 to 1.5% Sir, 0.01 to 0.8% Air, 0.02 to 10 1% Cara and 0.1 to 1.2% Pbr; or 0.1 to 1.5% Sir, 0.1 to 0.8% Aira and 0.02 to 1% Cara; or 0.1 to 1.5% Sirt, 0.1 to 0.8% Aira, 0.02 to 1%

Cara and 0.1-1.2% Pbrä; 15 or 0.1 to 1.5% Sirt and 0.05 to 0.12% Nir; or 0.1 to 1.5% Sir, 0.05 to 0.12% Nir and 0.1 to 1.2% Pbr; or 0.1 to 1.5% Sira, 0.05 to 0.12% Nira and 0.01-0.8% Aira; 20 or 0.1 to 1.5% Sirt, 0.05 to 0.12% Nira, 0.01 to 0.8% Aira and 0.1 to 1.2% Pbrä; or 0.1 to 1.5% Sir, 0.05 to 0.12% Nira and 0.02 -1% Cara; or 0.1 to 1.5% Sir, 0.05 to 0.12% Nira, 0.02 to 25% Cara and 0.1 to 1.2% Pbr; .J · or 0.1 to 1.5% Sirt, 0.05 to 0.12% Nira, 0.01 to 0.8% Aira and 0.02 to 1% Cara; «» Or 0.1 to 1.5% Sirt, 0.05 to 0.12% Nira, 0.01 to 0.8% Aira, 0.02 to 1% Cara and 0.1 to 1.2% Pbrä ,; ·. The rest of the 30 is zinc and impurities that cannot be • · · ”* ... avoided.

• · · • · · *. It will be appreciated that the zinc-based alloy may be replaced by an equivalent of at least one pre-alloy form and zinc, or at least one pre-alloy form and alloy containing fewer additives than the alloy to be replaced.

Thus, for example, it is possible to replace 100 kg of zinc alloy containing 1% Si and 0.1% Aira 5 (first case) with the following equivalent: either 10 kg of pre-alloy with 10% Si and 1% Aira (prepared powder metallurgy) and 90 kg Znr, or 10 kg pre-alloy with 10% Sirte (already from 10 hemetallurgy), 1 kg pre-alloy with 10% Aira and 89 kg Znr, or 1 kg pre-alloy with 10% Aira and 99 kg of alloy with 1.01% Sirte.

The zinc-based alloy 15 defined hereinabove may be used in applications other than those described herein.

In the former, all percentages are by weight.

Example 1 This example relates to the electroplating of steel having the following composition in weight percent: 0.050 C, 0.28 Mn, 0.012 Si, 0.009 S, 0.014 P, 0.020 Al, 0.020 Ni, 0.020 Cr and 0.025 Cu.

In the first test a zinc bath is used and in the second test t 1 1 v a zinc bath with 0,029% Sirt.

·· · 25 In both cases the bath temperature is 450 ° C and the immersion time is 5 minutes.

·· ♦ • V The thickness of the coating obtained in the first test • ··:,:: is 66 pmr, while in the second test it is only 39 pmr.

: *. 30 Example 2 • ··. ·; ·. This example relates to the electroplating of steel having the following composition in weight percent: 0.144 C, 0.920 Mn, 0.092 Si, 0.010 S, 0.014 P, 0.048 Al, 0.020 Ni, 0.020 Cr and 0.025 Cu.

• · 9 98468

The first test uses a zinc bath with 0.029% Si, the second test uses a zinc bath with 0.10% Ni, and the third test uses a zinc bath with 0.10% Ni and 0.029% Si. In these three cases, the bath temperature is 450 ° C and the immersion time is 5 minutes.

The coating obtained in the first test has a thickness of 200 μm, in the second test it has a thickness of 69 μm and in the third test it has a thickness of only 50 μm.

·· · • ··· ·· ·: *: • · • ·· «· ♦ • · ·« · • * ·· ♦ ·· ·

Claims (7)

1. A method of hot-dip galvanizing a series of individual articles of steel, using a zinc bath 5 containing rinsing in a concentrate capable of obtaining saturation, characterized in that: whose silicon content is lower or equal to 0.02%, and in this first case the zinc bath contains at least 0.005% silicon and optionally one or more of the following elements: lead at a concentration which can reach saturation, 0.001 - 0.015% aluminum and 0.002 - 0.1% calcium, the remainder consisting of zinc and inevitable impurities; B) or the series is formed in such a way that at least one of the articles is of silicon content greater than 0.02%, and in this second case the zinc bath contains at least 0.005% silicon and either 0.02-0. 06% aluminum and 0.002 - 0.1% calcium and optionally lead in a concentration which can be saturated, or 0.05 - 0.12% nickel and optionally one or more of the following elements; lead in a concentration that can be saturated, 0.001 - 0.015% aluminum and 0.002 - 0.1% calcium, and the ether balance consists of zinc and inevitable contaminants: 1 '9ar. 2. A method according to claim 1, characterized in that the bath contains at least 0.01% silicon in each case. ; ·. 3. A method according to claim 1 or 2, characterized in that the bath contains 0.1 - 1.2% *. lead. 4. A process according to any of claims 1-3, characterized in that the bath in the second 98468 case contains 0.02 - 0.06% aluminum and 0.005 - 0.05% calcium. 5. A method according to any of claims 1-4, characterized in that the bath composition is maintained during the galvanizing process by compensating the bath consumption through the abi: % klsel and optionally one or more of the following elements; 0.1 - 1.2% lead, 0.01 - 0.8% aluminum and 0.02 - 1% calcium; and (b) in the second case, 0.1 to 1.5% contains clay and contains 0.1 to 0.8% aluminum and 0.02 to 1% calcium and optionally 0.1 to 1.2% lead, or 0.05 - 0.12 nickel and optionally one or more of the following elements: 0.1 - 1.2% lead, 0.01 - 0.8% aluminum and 0.02 - 1% calcium, or an equivalent thereof. said alloy in the form of at least one alloy and pure zinc or in the form of at least one alloy and a zinc base alloy containing less additives than said alloy. Grate of zinc base alloy, especially for use in the process of claim 5, characterized in that it contains either 0.1-1.5% Si and 0.02-1% Ca; ·; ·; or 0.1 - 1.5% Si, 0.01 - 0.8% Al and 0.02 - V 1% Ca; Or 0.1 - 1.5% Si and 0.1 - 1.2% Pb; or 0.1 - 1.5% Si, 0.01 - 0.8% Al and 0.1 - µl. 1.2% Pb; or 0.1-1.5% Si, 0.02-1% Ca and 0.1-1.2% Pb; or 0.1 - 1.5% Si, 0.01 - 0.8% Al, 0.02 - 1%! Ca and 0.1 - 1.2% Pb; 98468 or 0.1 - 1.5% Si, 0.1 - 0.8% Al and 0.02 - 1% Ca; or 0.1 - 1.5% Si, 0.1 - 0.8% Al, 0.02 - 1% Ca and 0.1 - 1.2% Pb; 5 or 0.1 - 1.5% Si and 0.05 - 0.12% Ni; or 0.1 - 1.5% Si, 0.05 - 0.12% Ni and 0.1 - 1.2% Pb; or 0.1 - 1.5% Si, 0.05 - 0.12% Ni and 0.01 - 0.8% Al; Or 0.1 - 1.5% Si, 0.05 - 0.12% Ni, 0.01 - 0.8% Al and 0.1 - 1.2% Pb; or 0.1 - 1.5% Si, 0.05 - 0.12% Ni and 0.02 - 1. Ca; or 0.1 - 1.5% Si, 0.05 - 0.12% Ni, 0.02 - 1% Ca and 0.1 - 1.2% Pb; or 0.1 - 1.5% Si, 0.05 - 0.12% Ni, 0.01 - 0.8% Al and 0.02 - 1% Ca; or 0.1 - 1.5% Si, 0.05 - 0.12% Ni, 0.01 - 0.8% Al, 0.02 - 1% Ca and 0.1 - 1.2% Pb. Wherein the ether is zinc and inevitable impurities. • 1 ·. · ♦ · 1 * · »« · 1 * · • »• · 1 t 1 1 • · · 4« i • · 4 «” «· 1 ft · · • · ·%