EP4209613A2 - Method for improved zinc plating of components - Google Patents

Abstract

The present invention relates to a method, a pretreatment agent and their use for improved galvanizing of ferrous components.

Description

Summary of the Invention

The present invention relates to a method, a pretreatment agent and their use for improved galvanizing of components, in particular metallic components, and a component produced therewith.

Processes for galvanizing or galvanizing containing aluminum should result in a smooth, trouble-free surface and preferably also a relatively small thickness of the galvanizing layer on the metallic components to be treated.

Some methods for this are known from the prior art. For example, in the DE 10 2019 108 033 A1 described that the surface roughness of the iron-based component is increased by subjecting it to a mechanical treatment, such as a blasting process, which is intended to achieve a lower galvanizing layer thickness in the aluminum-alloyed zinc melt.

In hot-dip or piece galvanizing or hot-dip galvanizing, some processes are also known, such as that in EP 3 445 889 A1 described method in which the surface preparation for producing a uniform zinc coating on the metallic component is to be achieved by an improved sequence of process steps and/or the flux composition.

In the known methods, the component is degreased, pickled and fluxed in preparation for galvanizing, with rinsing baths being able to be interposed between the steps. During degreasing, the component surface is freed from grease and oil and during pickling, it is freed from inherent impurities such as scale and rust. In so-called fluxing, the component is immersed in a flux with different compositions. This final cleaning step of the component is intended to briefly prevent renewed oxidation and rust film formation on the way to the galvanizing furnace and is used for fine cleaning of the surface of the component, with residual impurities being removed during the immersion process in the Zinc or ZnAl5 melt can be dissolved and removed by the resulting fine pickling effect.

The disadvantage of the known methods is that they do not produce a perfect surface for all metallic components, in particular components made of steel, which may have a more complex design, i.e. narrow spaces, edges or other difficult-to-reach places. However, even with simple components, the surface of the component is not perfect after the treatment and in many cases shows pimples, streaks, shells, scales and/or other irregularities.

Although a large number of possible components, concentrations, process steps, compositions and/or conditions are listed in some of the applications, checking the various combinations of the listings involves considerable effort and usually does not produce flawless surfaces, which, for example, in the architectural field, where aesthetic surfaces, i.e. surfaces without irregularities, could find application.

The object of the present invention is therefore to provide a method which generates a flawless galvanizing surface on the components to be treated, regardless of whether they have a complex or simple structure.

The present invention therefore relates to a method, a pretreatment agent and their use, which contribute to improved galvanizing of metallic components, in particular iron-based components, with a component surface being generated without irregularities. The process can also be used for thin-layer galvanizing with an aluminum-zinc melt (ZnAl5) and for batch galvanizing according to DIN EN ISO 1461, i.e. discontinuous hot-dip galvanizing of components.

In the process for galvanizing metallic components, in particular ferrous components, in thin-layer galvanizing and/or discontinuous piece galvanizing, at least one pretreatment of the at least one component is carried out prior to galvanizing, which comprises treating the component with at least one process liquid with a pH value below 2, using at least one tin(II) compound and at least one bismuth compound, with a deposit of metallic tin and bismuth is effected on the component surface of the component.

1. a) in einem ersten Vorbehandlungsschritt das Bauteil mit Zinn(II)-haltiger Prozessflüssigkeit behandelt wird und in einem zweiten Vorbehandlungsschritt das mindestens mit Zinn(II) vorbehandelte Bauteil mit einer Bismut-haltigen Prozessflüssigkeit behandelt wird;

oder
b) in einem ersten Vorbehandlungsschritt das Bauteil mit Bismut-haltiger Prozessflüssigkeit behandelt wird und in einem zweiten Vorbehandlungsschritt das mindestens eine Bauteil mit einer Bismutabscheidung auf der Bauteiloberfläche mit einer Zinn(II)-haltiger Prozessflüssigkeit behandelt wird.In one embodiment, the pretreatment of the at least one component includes separate steps of tin and bismuth application, wherein

1. a) in a first pretreatment step, the component is treated with a process liquid containing tin(II) and in a second pretreatment step, the component pretreated at least with tin(II) is treated with a process liquid containing bismuth;

or
b) in a first pretreatment step the component is treated with a bismuth-containing process liquid and in a second pretreatment step the at least one component with a bismuth deposit on the component surface is treated with a tin(II)-containing process liquid.

Alternatively or additionally, the at least one component is pretreated in a combined process liquid that has at least one tin(II) compound and one bismuth compound.

The tin(II) compound is preferably tin chloride (SnCl ₂ ). Bismuth chloride (BiCl ₃ ), bismuth oxide (Bi ₂ O ₃ ), bismuth subcarbonate ((BiO) ₂ CO ₃ ) and/or bismuth granules (metal basis) are preferably used for the bismuth compound.

In a preferred aspect, the tin(II) compound-containing process solution has an acidic pH of ≦0.5. The concentration of the tin(II) ions within the process liquid is preferably 0.1 g/l to 30 g/l. The residence time or treatment time of the process liquid comprising at least one component in the tin(II) compound is preferably between 10 seconds (sec) and 30 minutes (min).

In a preferred aspect, the bismuth compound-containing process solution has an acidic pH value ≦0.5, with a bismuth concentration or bismuth ion concentration of between 0.1 g/l and 10 g/l, preferably at 2 g/l, being particularly preferred. is included in the process liquid. The dwell time or treatment time of the component in the process liquid containing the bismuth compound is between 10 seconds (sec) and 15 minutes (min), preferably 60 seconds.

In a further aspect of the present invention, the pretreated component is pretreated in a further or third step before it is subjected to drying and galvanizing.

1. a) mit einer Flussmittelzusammensetzung umfassend
   1. i) ZnCl₂ (Zinkchlorid) im Bereich von 25 g/l bis 350 g/I; und
   2. ii) NH₄Cl (Ammoniumchlorid) im Bereich von 25 g/l bis 350 g/l,
   wobei der Gesamtsalzgehalt zwischen 200 g/l und 600 g/l liegt und einen pH-Wert von 0,5 bis pH 6, besonders bevorzugt von 4 aufweist;
2. b) mit einer Vorbehandlungsflüssigkeit umfassend NH₄Cl (Ammoniumchlorid) im Bereich von 100 g/l bis 400 g/l, vorzugsweise 200 g/l, und einem pH-Wert von 0,5 bis pH 6, besonders bevorzugt von 4; oder
3. c) mit einer Vorbehandlungsflüssigkeit umfassend ZnCl₂ (Zinkchlorid) im Bereich von 200 g/l bis 600 g/l und einem pH-Wert von 0,5 bis pH 6, besonders bevorzugt von 4.

The third or further step involves treatment

1. a) comprising with a flux composition
   1. i) ZnCl ₂ (zinc chloride) in the range of 25 g/l to 350 g/l; and
   2. ii) NH ₄ Cl (ammonium chloride) in the range of 25 g/l to 350 g/l,
   wherein the total salt content is between 200 g/l and 600 g/l and has a pH of 0.5 to pH 6, particularly preferably 4;
2. b) with a pretreatment liquid comprising NH ₄ Cl (ammonium chloride) in the range of 100 g/l to 400 g/l, preferably 200 g/l, and a pH value of 0.5 to pH 6, particularly preferably 4; or
3. c) with a pretreatment liquid comprising ZnCl ₂ (zinc chloride) in the range of 200 g/l to 600 g/l and a pH value of 0.5 to pH 6, particularly preferably 4.

1. a) NH₄Cl (Ammoniumchlorid) im Bereich von 100 g/l bis 400 g/l, vorzugsweise 200 g/l umfassen; oder
2. b) ZnCl₂ (Zinkchlorid) im Bereich von 200 g/l bis 600 g/l umfassen,

wobei die Prozessflüssigkeit einen pH-Wert ≤ 2, besonders bevorzugt ≤ 0,5 aufweist.In one embodiment, the process liquid may further comprise a tin(II) compound and/or a bismuth compound

1. a) NH ₄ Cl (ammonium chloride) in the range of 100 g/l to 400 g/l, preferably 200 g/l; or
2. b) ZnCl ₂ (zinc chloride) in the range from 200 g/l to 600 g/l,

wherein the process liquid has a pH of ≦2, particularly preferably ≦0.5.

In one embodiment, one or more rinsing baths can be interposed between the individual pretreatment steps in order to reduce or avoid carry-over of the chemicals or other deposits.

In a further aspect, the component is dried after the pre-treatment. In one embodiment, the drying process takes place at a maximum temperature of 150.degree. Following the pre-treatment and/or drying, the component can be immersed in the galvanizing bath and galvanized.

In a preferred embodiment, the component is degreased and pickled before the pretreatment, wherein preferably at least one rinsing bath can be installed before, between and/or after the steps of degreasing and pickling.

In a preferred aspect of the invention, the pretreatment method described above leads to the formation of an incompletely closed metallic layer of metallic tin and bismuth on the component surface. The metallic tin formed on the component surface as a result of the pre-treatment leads to a reduction in the layer thickness of the zinc layer in the discontinuous galvanizing. In thin-layer galvanizing, the metallic layer of tin and bismuth leads to an improved surface structure.

1. a) eine Zinn(II)-Verbindung, vorzugsweise Zinnchlorid (SnCl₂), in verdünnter Salzsäure (HCl) mit einem pH-Wert von ≤ 2, vorzugsweise ≤ 0,5 und einer Konzentration der Zinn(II)-lonen von zwischen 0,1 g/l bis 30 g/I;
2. b) eine Bismut-Verbindung, vorzugsweise Bismutchlorid (BiCl₃), in verdünnter Salzsäure (HCl) mit einem pH-Wert von ≤ 2, vorzugsweise ≤ 0,5 und einer Bismutkonzentration von 0,1 g/l bis 10 g/l, vorzugsweise 2 g/I; und/oder
3. c) NH₄Cl (Ammoniumchlorid) im Bereich von 100 g/l bis 400 g/l, vorzugsweise 200 g/l, und einem pH-Wert ≤ 6, vorzugsweise ≤ 4.

The present invention also relates to a pretreatment agent for galvanizing metallic components, in particular ferrous components, in thin-layer galvanizing and/or discontinuous batch galvanizing, comprising:

1. a) a tin(II) compound, preferably tin chloride (SnCl ₂ ), in dilute hydrochloric acid (HCl) with a pH of ≤ 2, preferably ≤ 0.5 and a concentration of the tin(II) ions of between 0 .1 g/l to 30 g/l;
2. b) a bismuth compound, preferably bismuth chloride (BiCl ₃ ), in dilute hydrochloric acid (HCl) with a pH of ≦2, preferably ≦0.5 and a bismuth concentration of 0.1 g/l to 10 g/l, preferably 2 g/l; and or
3. c) NH ₄ Cl (ammonium chloride) in the range from 100 g/l to 400 g/l, preferably 200 g/l, and a pH ≤ 6, preferably ≤ 4.

In one embodiment, the pretreatment agent can also contain ZnCl ₂ (zinc chloride) in the range of 25 g/l to 350 g/l, the total salt content in the process liquid being between 200 g/l and 600 g/l and a pH value of ≤ 6 , preferably ≤ 4.

In addition, the present invention also relates to a component which has been produced according to the method described above and/or has been treated with the pretreatment agent.

The present invention is characterized by the embodiments in the claims and described in more detail by the statements in the following description, the examples and the drawings.

Description of the drawings

1

Schematic representation of a method according to the invention with a pretreatment bath which has a tin(II) compound with a subsequent flux bath which includes a bismuth compound and NH ₄ Cl. Rinse (I), pretreatment bath with a stannous compound (II), flux bath with bismuth compound and ammonium chloride (NH ₄ Cl) (III), drying oven (IV); Fe ⁰ /Fe ²⁺ (black circles), Sn ⁰ /Sn ²⁺ (dotted circles); NH ₄ Cl (checkered circles), Bi ⁰ /Bi ³⁺ (striped circles), iron-based component surface (1), metallically deposited Sn-Bi layer (2), dried salt layer (3).

2

Representation of the surface structure of a galvanized component after the ZnAl5 melt (thin-layer galvanizing). Surface of a component which has been subjected to a flux treatment comprising bismuth chloride and ammonium chloride (a); Surface of a component that has been treated with tin chloride, bismuth chloride and ammonium chloride (b).

3

Representation of a layer structure in discontinuous batch galvanizing according to DIN EN ISO 1461 in the sebisty steel area, comprising delta, zeta and eta phase and an additional tin-zinc-iron phase due to the tin-bismuth treatment according to the invention.

Detailed description of the invention

The present invention relates to a method, a pretreatment agent and their use for improved galvanizing of metallic components, in particular ferrous components, whereby these are used in thin-layer galvanizing with an aluminum-zinc melt (ZnAl5) and batch galvanizing according to DIN EN ISO 1461, i.e. discontinuous hot-dip galvanizing of components or assemblies of parts.

Hereinafter, as used herein, the article "a" and all derivatives thereof should be understood generally as "one or more" unless otherwise indicated or clear from the context as a singular form.

To the extent that the terms "includes," "has," "possesses," and the like are used in the specification or claims, such terms should be construed in the same way as the term "comprising" or "comprising", i.e., not exhaustive, unless it is explicitly stated.

The method according to the invention described here relates in particular to the pretreatment of a component within an immersion bath, in which a deposit of a metallic layer is preferably produced. The term “bath” or “baths” used below generally refers to basins that can be filled with liquid, preferably process liquid, and into which a component can be let. For this reason, the pools or baths are mostly open at the top. In principle, several baths are mentioned, but it can also be a basin or bath that is divided into individual sections that contain the respective process liquid. In such a case, the individual sections would each correspond to a bath.

The term "component(s)" refers to metallic components of any kind, preferably components made of ferrous or iron-based material, in particular components made of steel, such as blanks, sections, structures and/or finished workpieces. The term "component" also includes groups and / or combinations of components of different or the same type and / or different or the same material that a common treatment in one or several process baths and/or steps. In some cases, these groupings can also be put together using suitable aids such as traverses, goods carriers or similar devices. Complex components or components with a complex design designate components or objects that have one or more narrow spaces, edges or other difficult-to-reach places.

The terms "pre-treatment" or "pre-treatment agent" include any process that the component undergoes prior to treatment in the zinc bath or compositions used to pre-treat the component prior to zinc smelting. The pretreatment or pretreatment agent may also include, but is not limited to, a flux treatment or flux commonly used in thin-film galvanizing or batch galvanizing. However, in the present invention the term "pre-treatment" mainly means the treatment of a component in which at least one metallic layer is deposited on the component, the pre-treatment preferably being carried out before a fluxing treatment and/or the galvanizing process, unless otherwise specified.

In the present description, the term "deposit" includes all deposits, deposits, layer formations, secretions, precipitation reactions and similar reactions on the component surface. In particular, deposits in the present invention are metallic deposits due to redox reactions on the component surface within a pretreatment bath.

In addition to the sequence of the process steps, the pre-treatment of the component before it is placed in the flux bath and the zinc bath has proven to be particularly effective for the even coating of the component surface with zinc or zinc containing aluminum and the final galvanizing result.

The component to be treated is first freed from fats and oils in the degreasing process using the known methods. Further deposits such as rust and/or scale are then removed in the pickle. In order to avoid carry-over of chemicals between the individual baths, between the individual steps as well one or more rinsing baths upstream, intermediate and/or downstream. This pre-cleaned component is then treated further.

In contrast to the usual, well-known process steps, the component in the present invention is not treated directly in a flux bath, which according to the prior art contains at least the components zinc chloride and ammonium chloride, but undergoes at least one pretreatment before fine cleaning takes place in the flux bath. This at least one pre-treatment can be carried out both in thin-layer galvanizing with aluminum-containing zinc (ZnAl5) and in normal hot-dip galvanizing according to the DIN EN ISO 1461 standard, i.e. when hot-dip galvanizing manufactured components in a discontinuous process.

The component is pretreated with tin (Sn) and bismuth (Bi) compounds, whereby the treatment with one of the two components can also be part of the flux bath.

The pretreatment of the component with tin (Sn) and/or bismuth (Bi) compounds is based on the vapor deposition, an ion exchange process based on a redox reaction. In this process, electrons are transferred from a baser metal (reducing agent) to a more noble metal (oxidizing agent), with the degree of willingness to accept or release electrons depending on the redox potential of the corresponding metals.

In the present method, the pre-cleaned component, which usually consists of iron or steel, is treated with at least one process liquid that includes a tin (Sn) and/or bismuth (Bi) compound. The treatment preferably takes place in an immersion process, in which the at least one component is immersed in a basin filled with process liquid. However, with some components or methods it can also be provided that the process liquid is also applied to the component surface in some other way, such as by means of a spraying method.

During investigations into the mode of action of the tin (Sn) and bismuth (Bi) compound on the component surface made of steel, several possible applications were identified appraised. The results of all of these showed an improved effect on the component surface with the effect of an improved coating with zinc and zinc containing aluminum (ZnAl5) compared to the known flux compositions. In the following, therefore, the possible pre-treatment steps are shown in detail.

In a first aspect of the present invention, the component is treated in a process liquid containing tin(II) in a first pretreatment step. In addition to the tin(II) compound in an acidic solution, this process liquid preferably contains no further components. The component, which is usually iron-based, has a lower redox potential compared to the tin(II)-containing process liquid and therefore acts as a reducing agent, which donates electrons to the tin(II) compound (oxidizing agent), such as the 1 can be seen. Consequently, the elemental iron (E ⁰ = - 0.44 V) on the surface of the component changes to its oxidized 2-valent form in the acidic medium and into solution (Fe ²⁺ ). The more noble (E ⁰ = - 0.14 V) and divalent tin (here Sn ²⁺ ) present in the process solution, on the other hand, absorbs the deposited electrons of the iron and changes into its elementary form and separates metallically on the component surface off, see 1 Clause IIa and IIb.

Attempts to treat ferrous components with a tin(II) compound have shown that if only tin(II) compound is present in the process solution and a preferably diluted solution containing hydrochloric acid (approx. 10-20 g/l HCl) with a acidic pH value (pH ≤ 0.5), the metallic tin is deposited on the component surface at certain points, but covering the entire component, which means that no closed tin layer is formed on the component surface. Consequently, the component surface still has "reactive, free" iron atoms on the component surface, which could react with other compounds.

The deposition of tin on the component surface can be increased by the tin(II) concentration and/or the dwell time of the component in the process liquid, whereby a more cohesive deposition of tin on the component surface can be achieved. However, experiments have shown that even the selective deposition of tin on the component surface with a subsequent further treatment with a bismuth compound entailed better coatings with zinc or aluminium-containing zinc than known processes in the prior art. The concentration of the tin(II) ions should therefore be between 5 g/l to 30 g/l, preferably 10 g/l, when used in batch galvanizing according to DIN EN ISO 1461 in one embodiment. The dwell time of the component in the process liquid should also be between 10 seconds (sec) and 30 minutes (min), preferably 15 min. When used in the field of thin-layer galvanizing, for example in a ZnAl5 melt, the tin ion concentration is preferably reduced to ≦10 g/l and the residence time to preferably 60 seconds. The different handling within the two processes of thin-layer galvanizing and discontinuous batch galvanizing (hot-dip galvanizing) with regard to the tin component results from the different modes of action and effects of the tin within the respective zinc melts. In discontinuous piece galvanizing, the use of tin improves the quality of the subsequent zinc coating and reduces the layer thickness. This requires a higher proportion of the metallically deposited tin on the surface of the component in the pre-treatment than in thin-layer galvanizing. In the case of thin-layer galvanizing, on the other hand, preliminary results show that the tin only leads to a qualitatively better coating with zinc after the melt, but no reduction in the thickness of the zinc layer was found. Consequently, with such a method of thin-layer galvanizing, for example in an aluminum-containing zinc melt, the concentration of tin and the residence time can be reduced.

Tin(II) chloride (SnCl ₂ ) is preferably used as the tin(II) compound.

Subsequent to the treatment of the component in the tin(II)-containing process liquid, the component is treated again with another process liquid, which applies a further metal deposition or vapor deposition to the component surface. In this second treatment step, the component with the tin deposit is treated with a bismuth-containing process liquid, such as in 1 Figure II shown. In this case, too, the process liquid preferably contains no further compounds in addition to a bismuth compound in an acidic solution components. The bismuth used or a compound thereof (oxidizing agent) has a redox potential of +0.308 V, with tin and iron representing the reducing agent.

Tests have shown that treating the tin-containing component surface with bismuth or a bismuth compound leads to little or no detachment of the previously deposited tin on the iron-based component, which means that the number or amount of metallically deposited tin (Sn) is almost constant compared to the previous one Treatment step remains because, as described above, Fe with E ⁰ = - 0.44 V compared to Sn with E ⁰ = - 0.14 V is electrochemically the less noble metal and thus the preferred reaction partner.

Analogously to the treatment step with the tin(II) compound, the iron on the component surface is oxidized in the bismuth-containing process liquid and the bismuth itself is reduced, as a result of which it is metallically deposited on the ferrous component surface, such as the 1 Items III a and III b can be found. In this method step, too, the concentration of bismuth-containing compounds and/or the dwell time of the component in the process liquid can be varied in order to adjust the number or the amount of metallically deposited bismuth on the component surface.

In principle, one or more rinsing processes can be interposed between the two process baths, but the test series have shown that the tin deposited on the component surface undergoes little or no change in the bismuth-containing process bath. Any tin(II) compounds (Sn ²⁺ compounds) and/or iron compounds that were entrained from the previous process step also did not have any negative effects on the component and/or the coating of this with bismuth.

The bismuth (Bi) is preferably used in the process liquid of the at least one process bath in the form of bismuth chloride (BiCl ₃ ), bismuth oxide (Bi ₂ O ₃ ), bismuth subcarbonate ((BiO) ₂ CO ₃ ) and/or bismuth granules (metal basis).

This time, too, the process solution is preferably an acidic process solution, which particularly preferably has 10-20 g/l HCl and a pH ≦0.5. The concentration of the bismuth or the bismuth ions within the process bath is preferably between 0.1 g/l and 10 g/l, preferably 2 g/l. The dwell time of the component in the process liquid should also be between 10 seconds (sec) and 15 minutes (min), preferably 60 seconds.

Both of the aforementioned process steps are preferably carried out at room temperature. However, to speed up the reactions, the temperature can also be increased up to 60°C.

After the two treatment steps with tin/bismuth, the component has a thin, porous layer of tin and bismuth deposited on its surface. A thickness of ≦1 μm was determined here.

1. i) ZnCl₂ (Zinkchlorid) im Bereich von 25 g/l bis 350 g/I; und
2. ii) NH₄Cl (Ammoniumchlorid) im Bereich von 25 g/l bis 350 g/l,

wobei der Gesamtsalzgehalt von 200 g/l bis 600 g/l nicht überstiegen werden sollte. Ferner weist die Flussmittelzusammensetzung einen pH-Wert von 0,5 bis pH 6, besonders bevorzugt bei einem pH-Wert von 4 auf.In the following third process step, the component is now subjected to the actual flux treatment. In principle, the flux bath can have any known flux composition. A flux composition comprises

1. i) ZnCl ₂ (zinc chloride) in the range of 25 g/l to 350 g/l; and
2. ii) NH ₄ Cl (ammonium chloride) in the range of 25 g/l to 350 g/l,

the total salt content should not exceed 200 g/l to 600 g/l. Furthermore, the flux composition has a pH of 0.5 to pH 6, particularly preferably at a pH of 4.

Furthermore, in connection with the two pre-treatment steps, a flux composition consisting only of NH ₄ Cl (ammonium chloride) in the range of 100 g/l to 400 g/l, preferably 200 g/l, without the use of ZnCl ₂ (zinc chloride), surprisingly showed a particular good coating of the component surface with zinc or zinc containing aluminum after the zinc bath. Here, too, the pH value was preferably around 4.

In one aspect of the present invention, a flux composition comprising ZnCl ₂ (zinc chloride) alone in the range of 200 g/l to 600 g/l can also be used.

With regard to the flux, the temperature during treatment in the flux bath is between 30°C and 60°C, preferably between 40°C and 50°C, particularly preferably 45°C. In addition, a pretreatment time in the flux bath of preferably 10 seconds (sec) to 5 minutes (min), particularly preferably 60 seconds, is provided.

1. 1. Getrennte Vorbehandlungen mit Zinn, Bismut und Flussmittel
   1. a) Zinnbehandlung, Bismutbehandlung, Flussmittelbehandlung
      1. i) Erster Behandlungsschritt - Zinn(II)Verbindung
         Hierbei weist das Prozessbad eine Zinn(II)-Verbindung auf, die als Oxidationsmittel in Bezug auf das eisenhaltige Bauteil agiert (wie zuvor beschrieben). Das Prozessbad weist im Wesentlichen eine saure Lösung mit einer Zinn(II)Verbindung auf und nur geringe Anteile anderer Stoffe. Die Prozessflüssigkeit im Zinn(II)-Bad enthält neben der Zinn(II)-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten;
      2. ii) Zweiter Behandlungsschritt - Bismutbehandlung
         Das im Zinn(II)-Bad behandelte Bauteil wird in einer Prozessflüssigkeit mit Bismut behandelt, welches als Oxidationsmittel in Bezug auf das eisenhaltige Bauteil agiert. Die Prozessflüssigkeit im Bismut-Bad enthält neben der Bismut-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten;
      3. iii) Dritter Behandlungsschritt - Flussmittelbehandlung Das Bauteil wird in bekannten oder vorzugsweise den zuvor beschriebenen Flussmitteln behandelt.
   2. b) Bismutbehandlung, Zinnbehandlung, Flussmittelbehandlung
      1. i) Erster Behandlungsschritt - Bismutbehandlung
         Das Bauteil wird in einer Bismut-haltigen-Prozessflüssigkeit, die vorzugsweise keine weiteren Bestandteile neben einer Bismutverbindung, Eisen und Salzsäure umfasst, behandelt. Das Bismut scheidet sich hierbei auf der aus Eisen bestehenden Bauteiloberfläche ab und bildet eine Beschichtung. Die Prozessflüssigkeit im Bismut-Bad enthält neben der Bismut-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten;
      2. ii) Zweiter Behandlungsschritt - Zinn(II)Verbindung Das mit Bismut behandelte und überzogene Bauteil wird in einem Zinn(II) enthaltenem Prozessbad behandelt, wobei eine Zinn-Schicht auf das Bauteil aufgebracht wird. Die Prozessflüssigkeit im Zinn(II)-Bad enthält neben der Zinn(II)-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten.;
      3. iii) Dritter Behandlungsschritt - Flussmittelbehandlung Das Bauteil wird in bekannten oder vorzugsweise den zuvor beschriebenen Flussmitteln behandelt.
2. 2. Teilkombinierte Vorbehandlung (Fig. 1)
   1. a) Zinnbehandlung, kombinierte Bismut-Flussmittelbehandlung
      1. i) Erster Behandlungsschritt - Zinn(II)Verbindung
         Wie zuvor beschrieben wird hierbei eine Zinnschicht auf die eisenhaltige Bauteiloberfläche durch das Oxidationsmittel Zinn(II)Verbindung aufgebracht. Die Prozessflüssigkeit im Zinn(II)-Bad enthält neben der Zinn(II)-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten;
      2. ii) Zweiter Behandlungsschritt - Bismut-Flussmittelbehandlung Neben der Feinreinigung durch das Flussmittel wird eine Bismutschicht auf das Bauteil aufgebracht. Hierbei ist darauf zu achten, dass anderes als bei den üblichen Flussmitteln, der pH-Wert unter 2, vorzugsweise ≤ 0,5, liegt.
   2. b) Bismutbehandlung, kombinierte Zinn(II)-Flussmittelbehandlung
      1. i) Erster Behandlungsschritt - Bismutbehandlung
         Bei dieser Behandlung wird nach den zuvor beschriebenen Bedingungen eine Bismutschicht auf die eisenhaltige Bauteiloberfläche mittels Redoxreaktion aufgebracht. Die Prozessflüssigkeit im Bismut-Bad enthält neben der Bismut-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten;
      2. ii) Zweiter Behandlungsschritt - Zinn(II)-Flussmittelbehandlung Neben der Feinreinigung durch das Flussmittel wird eine Zinnschicht auf das Bauteil durch die Zinn(II)-Verbindung als Oxidationsmittel aufgebracht. Hierbei ist darauf zu achten, dass anderes als bei den üblichen Flussmitteln (pH-Wert 4-6), der pH-Wert unter 2, vorzugsweise ≤ 0,5, liegt.
   3. c) Kombinierte Zinn-/Bismutbehandlung, Flussmittelbehandlung
      1. i) Erster Behandlungsschritt - Zinn(II)-Bismutbehandlung
         In dieser Prozessflüssigkeit liegen Bismut-Verbindungen und Zinn(II)-Verbindungen als Oxidationsmittel vor, wodurch gleichzeitig Bismut und Zinn auf die Bauteiloberfläche abgelagert wir. Die Prozessflüssigkeit im Zinn(II)/Bismut-Bad enthält neben einer Zinn(II)-Verbindung und einer Bismut-Verbindung in einer sauren Lösung vorzugsweise keine weiteren Komponenten d;
      2. ii) Zweiter Behandlungsschritt -Flussmittelbehandlung
         Das Bauteil wird in bekannten oder vorzugsweise den zuvor beschriebenen Flussmitteln behandelt.
3. 3. Kombinierte Zinn-/Bismut-/Flussmittelbehandlung ohne ZnCl₂
   • Nur ein Behandlungsschritt - kombinierte Zinn(II)-Bismut-Flussmittelbehandlung
   • Neben der Feinreinigung durch das Flussmittel, das kein ZnCl₂, sondern lediglich NH₄Cl enthält, wird eine Zinn- und Bismutschicht parallel/gleichzeitig auf das Bauteil durch die Zinn(II)-Bismut-Komponenten als Oxidationsmittel aufgebracht. Hierbei ist darauf zu achten, dass anderes als bei den üblichen Flussmitteln (pH-Wert 4-6), der pH-Wert unter 2, vorzugsweise ≤ 0,5, liegt.

As shown above, other sequences of the three pretreatment steps described above and variations of the bath ingredients also showed improved coatings with zinc or zinc-aluminum compared to the previously known processes in the tests carried out. The following possible separations of the pre-treatments and/or merging were therefore examined and showed improved coating results:

1. 1. Separate pre-treatments with tin, bismuth and flux
   1. a) Tin treatment, bismuth treatment, flux treatment
      1. i) First treatment step - stannous compound
         Here, the process bath contains a tin(II) compound that acts as an oxidizing agent in relation to the ferrous component (as previously described). The process bath essentially has an acidic solution with a tin(II) compound and only small amounts of other substances. The process liquid in the tin(II) bath preferably contains no other components apart from the tin(II) compound in an acidic solution;
      2. ii) Second treatment step - bismuth treatment
         The component treated in the tin(II) bath is treated in a process liquid containing bismuth, which acts as an oxidizing agent with respect to the ferrous component. The process liquid in the bismuth bath also contains the bismuth compound preferably no other components in an acidic solution;
      3. iii) Third treatment step - flux treatment The component is treated in known or preferably the previously described fluxes.
   2. b) bismuth treatment, tin treatment, flux treatment
      1. i) First treatment step - bismuth treatment
         The component is treated in a bismuth-containing process liquid, which preferably does not include any other components apart from a bismuth compound, iron and hydrochloric acid. The bismuth is deposited on the iron component surface and forms a coating. The process liquid in the bismuth bath preferably contains no other components apart from the bismuth compound in an acidic solution;
      2. ii) Second treatment step - tin(II) compound The component treated and coated with bismuth is treated in a process bath containing tin(II), whereby a layer of tin is applied to the component. The process liquid in the tin(II) bath preferably contains no other components apart from the tin(II) compound in an acidic solution.;
      3. iii) Third treatment step - flux treatment The component is treated in known or preferably the previously described fluxes.
2. 2. Partially combined pretreatment ( 1 )
   1. a) Tin treatment, combined bismuth flux treatment
      1. i) First treatment step - stannous compound
         As previously described, a tin layer is applied to the iron-containing component surface using the oxidizing agent tin(II) compound. The process liquid in the tin(II) bath preferably contains no other components apart from the tin(II) compound in an acidic solution;
      2. ii) Second treatment step - bismuth flux treatment In addition to fine cleaning with the flux, a layer of bismuth is applied to the component. Here it is important to ensure that, unlike the usual fluxes, the pH value is below 2, preferably ≤ 0.5.
   2. b) Bismuth treatment, combined stannous flux treatment
      1. i) First treatment step - bismuth treatment
         In this treatment, a layer of bismuth is applied to the ferrous component surface by means of a redox reaction according to the conditions described above. The process liquid in the bismuth bath preferably contains no other components apart from the bismuth compound in an acidic solution;
      2. ii) Second treatment step - tin(II) flux treatment In addition to fine cleaning with the flux, a layer of tin is applied to the component using the tin(II) compound as an oxidizing agent. It is important to ensure that the pH value is below 2, preferably ≤ 0.5, in contrast to the usual fluxes (pH value 4-6).
   3. c) Combined tin/bismuth treatment, flux treatment
      1. i) First treatment step - stannous bismuth treatment
         Bismuth compounds and tin(II) compounds are present in this process liquid as oxidizing agents, which means that bismuth and tin are deposited on the component surface at the same time. In addition to a tin(II) compound and a bismuth compound in an acidic solution, the process liquid in the tin(II)/bismuth bath preferably contains no further components d;
      2. ii) Second treatment step - fluxing
         The component is treated in known fluxes or, preferably, in the fluxes described above.
3. 3. Combined tin/bismuth/flux treatment without ZnCl ₂
   • Only one treatment step - combined tin(II) bismuth flux treatment
   • In addition to fine cleaning with the flux, which does not contain ZnCl ₂ but only NH ₄ Cl, a tin and bismuth layer is applied in parallel/simultaneously to the component using the tin(II) bismuth components as an oxidizing agent. It is important to ensure that the pH value is below 2, preferably ≤ 0.5, in contrast to the usual fluxes (pH value 4-6).

Tin(II) chloride (SnCl ₂ ) is particularly advantageous as a tin(II) compound, since this can be dissolved very easily and its addition causes a pH value drop to approx. 2.0 at 10 g/l Sn . At a pH value of 2, the tin(II) compound is not yet completely in solution and causes a milky process liquid. Complete tin(II) chloride dissolution occurs analogously to bismuth chloride (BiCl ₃ ) dissolution at a pH value of ≤ 0.5, which means that there is a very good agreement, miscibility and compatibility of the two components. As can be seen from the examples, no interaction between the two components was observed either.

The components are then further treated in the usual process steps, i.e. dried and then galvanized.

The tests carried out in normal galvanizing, which are listed among other things in example 1, showed that an improved coating quality of the zinc layer could be generated with the separate processes under number 1 above in comparison to the known process steps in hot-dip galvanizing. In the tests, the separate pre-treatment with the sequence bismuth treatment-tin treatment-flux treatment, see number 1.b, yielded the qualitatively best results with the thinnest layer of zinc layer, as can be seen in example 1. Here, a significant layer thickness reduction of the zinc layer of > 20% was achieved compared to the sole flux treatment from the prior art in the normal melt. The separate pre-treatment with the process steps of number 1 b), ie the bismuth treatment, tin treatment and flux treatment delivered improved results in Surface coating, ie layer thickness and corrosion resistance, as well as met the increasing visual demands, such as no or few pimples, streaks, linkers, cracks, shells, scales and/or other irregularities. Further details can be found in Example 1 below.

In the thin-layer galvanizing, which includes an aluminum-containing zinc melt and is shown in example 2, no significant layer thickness differences were found in the sequence of the process steps in the preliminary test series. However, the application of a tin-containing compound in combination with a bismuth-containing compound resulted in a smoother surface without irregularities, compared to which a pretreatment without the stannous compound resulted in pitting or at least other irregularities in the surface structure. The tin deposition on the component surface in the pre-treatment had a positive influence on the viscosity of the ZnAl5 shell close to the component, which minimized the formation of irregularities on the component surface. In addition, the formation of pronounced spangles on the surface of the components after galvanizing could be observed during use.

In one embodiment of the present invention, only ammonium chloride (NH ₄ Cl) was used as the flux component. The advantage of using this alone instead of in combination with zinc chloride (ZnCl ₂ ) is that the pre-treatment is significantly cheaper, since the zinc chloride and the processing of the corresponding bath are relatively expensive compared to the component ammonium chloride (NH ₄ Cl). In addition, the use of ZnCl ₂ is also questionable from the point of view of impurities and the environment. With the help of ammonium chloride (NH ₄ Cl), a fine pickling effect is achieved without removing the previously or parallel applied Sn/Bi layer on the component surface. During the drying process, the ammonium chloride (NH ₄ Cl) forms a layer of salt on the surface of the component. In the normal zinc as well as in the ZnAl5 melt, the ammonium chloride (NH ₄ Cl) is heated by the hot melt. This sublimes at approx. 340 °C, ie the salt immediately changes from its solid to its gaseous state, releasing hydrochloric acid which triggers a fine pickling effect on the surface of the component.

In the case of the "pure" NH ₄ Cl component in the Sn-Bi flux bath, Bi-flux bath, Sn flux bath or sole flux bath, the drying oven temperature must be ≤ 150 °C in the drying process, unlike in the usual methods (200 to 230 °C). be limited. Tests showed that the ammonium chloride applied to the component surface would otherwise burn and the effect of this was ineffective in the subsequent zinc melt.

In thin-layer galvanizing (ZnAl5), the surface tension of the melt is increased by the high aluminum concentration. The advantage of the Sn-Bi pretreatment, preferably with a separate or combined flux bath comprising ammonium chloride (NH ₄ Cl), particularly preferably a separate flux bath, is that after the pretreatment a thin metallic layer of tin and bismuth and possibly ammonium chloride is present on the component surface is. As the experiments in the examples have shown, this layer of tin and bismuth is not completely closed, but rather forms layers and phases which lower the surface tension in the ZnAl5 melt and positively influence the viscosity of the melt by keeping it in the Make the part more flowable near it.

The parallel or subsequent treatment of the component with ammonium chloride (NH ₄ Cl), preferably a subsequent treatment, which is applied as a layer of salt on the two metallic layers, initially produces a fine pickling effect, which then leads to perfect wetting of the component by the metallic tin /bismuth (Sn/Bi) layer, since both of the above-mentioned elements are then present in parallel in relation to the compounds in the melt in excess in the boundary layer area between the component surface and the ZnAl5 melt, which leads to a high-quality thin-layer coating on the component, which leads to few to no irregularities.

In the normal galvanizing of individual parts in the discontinuous process according to DIN EN ISO 1461, the tin/bismuth pre-treatment has an additional or further advantage. As can be seen from the experiments in Example 1, similar modes of action and processes to thin-layer galvanizing (Example 2) were investigated, with the difference that the zinc melt has a zinc bath temperature of approx. 450 °C that is approx. 30 K higher and only small traces from 0.0019% by weight aluminum. As in the thin-layer process, when using ammonium chloride (NH ₄ Cl) a layer of salt is formed on the surface after drying, which causes a faster fine pickling effect in the zinc bath of hot-dip galvanizing. Here, too, the deposited tin and bismuth have positive effects, such as reducing the surface tension and lowering the viscosity in the vicinity of the component surface of a normal melt. However, the metallic tin deposit that has formed on the surface has another effect in galvanizing according to DIN EN ISO 1461 than the improved viscosity, namely on the layer thickness growth of the galvanizing layer. When using tin, this shows a reduction in the layer thickness of the zinc coating. The zinc coating usually includes different phases that depend on the material of the component, in particular its silicon content. Different phases usually form within the zinc coating, which include, for example, a delta, zeta and eta phase (pure zinc), see 3 . In the case of a component made from a Sebisty steel, the zeta phase causes this zeta layer to form very strongly from the component to the top layer, making the entire zinc coating relatively thick. However, the metallic tin, which has deposited on the surface of the component in the pretreatment of the present invention by means of vapor deposition, forms a diffusion barrier between the zeta phase and the eta phase, which inhibits the layer thickness growth of the zeta phase. Like in the 3 shown, a tin-iron-zinc phase forms between the zeta and the eta phase, resulting in a reduced overall layer thickness compared to a treatment without tin, in which the zinc coating consists almost exclusively of the zeta phase, which forms the thickness greater than or equal to the phases in 3 are shown. The metallurgical processes in the layer structure are therefore different in the two galvanizing processes. In contrast, a ZnAl5 melt causes an immediate formation of an Fe-Al boundary layer directly on the component surface, which prevents any further layer thickness growth. Here the tin only has a positive effect on the quality of the thin-layer galvanizing, but no effects that reduce layer thicknesses, as these are caused by the aluminum in the melt. Consequently, in contrast to the known galvanizing according to DIN EN ISO 1461 (hot-dip galvanizing), significantly thinner zinc layers can be used, especially with reactive steels with a Si content > 0.14% Si (silicon; 0.14-0.25% Si = Sebisty steel; > 0.25% Si = high silicon steel). With the improved process sequences and compositions, any further melting additives can be dispensed with in the molten bath (galvanizing bath) according to DIN EN ISO 1461, with the exception of small Al additions of the order of up to 0.005% by weight, although a component with an even galvanizing layer that is also possible corresponds to optical requirements, is provided by the local process with a significantly smaller zinc coating.

Consequently, in addition to the method for pretreating iron-based components, the invention also relates to a component itself that has been pretreated with such a method. In contrast to the component from the prior art, the pre-treated component has a significantly smoother galvanizing layer, which has fewer or no irregularities and in the case of normal hot-dip galvanizing (batch galvanizing) according to DIN EN ISO 1461, i.e. the hot-dip galvanizing of manufactured individual parts in a discontinuous process, has a significantly reduced zinc layer.

These and other embodiments of the present invention are disclosed in, and are encompassed by, the specification and examples. Additional literature on known materials, methods and uses that can be used in accordance with the present invention can be retrieved from public libraries and databases, for example using electronic devices. A more complete understanding of the invention can be obtained by reference to the following examples, which are provided for the purpose of illustration and are not intended to limit the scope of the invention.

examples Example 1: Tests on tin/bismuth treatment in normal hot-dip galvanizing according to DIN EN ISO 1461

In order to be able to examine the different galvanizing results of the various processes, identical square steel tubes in the Sebisty range with a length of around 10 cm and deep rust on the component surface (hereinafter "components") were used, which were degreased and pickled in identical processes.

During alkaline hot degreasing, the components were treated at 60°C for 10 minutes. In the subsequent iron pickling, these were then pickled at a temperature of 27°C for 60 minutes. Corresponding parameters for degreasing and iron pickling can, for example, EP3483304 B1 be removed.

The components were then pretreated in different ways, as shown in Table 1. Tab. 1 Test series - pre-treatment sample pre-treatment steps 1 2 3 1 (reference) Flux bath (state of the art) 2 Pre-treatment bath containing tin Pre-treatment bath containing bismuth flux bath 3 Pre-treatment bath containing bismuth Pre-treatment bath containing tin flux bath

1. i) 2,0 g/l Eisen(II)-Verbindungen
2. ii) 100 g/l ZnCl₂ (Zinkchlorid); und
3. iii) 250 g/l NH₄Cl (Ammoniumchlorid)

Ferner wies die Flussmittelzusammensetzung einen pH-Wert von 4 auf.The prior art flux (Sample 1) had the following composition:

1. i) 2.0 g/l iron (II) compounds
2. ii) 100 g/l ZnCl ₂ (zinc chloride); and
3. iii) 250 g/l NH ₄ Cl (ammonium chloride)

Furthermore, the flux composition had a pH of 4.

In addition, as an alternative flux bath (sample 2-3), a 300 g/l NH ₄ Cl (ammonium chloride) preconditioner was used without including ZnCl ₂ (zinc chloride). This flux was also used at a pH of 4.

The tin-containing treatment bath had a concentration of 10 g/l tin(II) ions at a pH of 0.4. Tin(II) chloride (SnCl ₂ ) was used here. The pretreatment in the tin bath was carried out at room temperature.

The bismuth-containing pretreatment bath had a concentration of 2 g/l bismuth(III) ions, such as bismuth chloride (BiCl ₃ ), bismuth oxide (Bi ₂ O ₃ ), bismuth subcarbonate ((BiO) ₂ CO ₃ ), with bismuth subcarbonate ((BiO ) ₂ CO ₃ ) was used. The pH of the bath was 0.3. The pretreatment in the bath containing bismuth was carried out at room temperature.

The process liquids of the pre-treatment baths, i.e. tin(II) bath and/or bismuth bath, only had the two components in an acidic solution, i.e. preferably no other substances or components were present in the process liquid.

The surfaces of samples 2 and 3, which were treated with an additional pre-treatment using bismuth and/or tin, showed a deposition of the corresponding metal on the component surface after the corresponding treatment step, as can be seen in Table 2. Tab. 2 Surface after pre-treatment with bismuth and/or tin sample Results Surface finish after pre-treatment with bath containing bismuth and/or tin Process step 1 Process step 2 2 Component has a silvery-grey surface Component has a black coating 3 Component has a black coating The surface of the component becomes silvery/grey the longer it is immersed in the bath

After the pre-treatment of the components, they were air-dried for at least 30 minutes. Depending on the treatment, the surface of the component showed different deposits, which showed orange and grey/black areas in the pre-treatments containing bismuth and tin, as can be seen in Table 3. Tab. 3 Surface finish after drying sample Results Surface condition of the component after drying 1 (reference) Gray finish; NH ₄ Cl residues (white deposits); No re-oxidation and renewed flash rust formation 2 Dark orange and silvery-dark gray areas visible on the surface of the component; No re-oxidation and renewed flash rust formation 3 Light orange, silvery and gray areas visible on the surface of the component; No re-oxidation and renewed flash rust formation

• 0,1 Gew. % Bi
• 0,1 Gew. % Sn
• 0,049 Gew. % Ni
• 0,0019 Gew.% Al
• < 99,75 Gew. % Zn

After drying, the components were simultaneously treated in a zinc bath after hot-dip galvanizing in accordance with DIN EN ISO 1461 at 450 °C and an immersion time of 5 minutes. The zinc bath had the following parameters:

• 0.1 wt% Bi
• 0.1 wt% Sn
• 0.049 wt% Ni
• 0.0019 wt% Al
• <99.75 wt% Zn

Samples 2 and 3 showed an even and clean surface coating, which also showed a further optical and haptic improvement of the zinc layer compared to the reference sample through the use of the alternative flux comprising only ammonium chloride (NH ₄ Cl).

Although samples 2 and 3 had a more even surface with few to no irregularities, the layer thickness measurement of the galvanized layer showed that sample 3, which was first treated in a bath containing bismuth, then in a bath containing tin and finally with a flux , showed a layer thickness reduced by an average of > 20% compared to the reference sample.

The average layer thicknesses of the components are given in Table 4 below, which result from the layer thicknesses of the four outer sides of the square steel tubes as well as several independent test runs. Tab. 4 Layer thickness measurement of the galvanized layer sample Average layer thickness [µm] Increase + / Decrease - [%] 1 91.63 +/- 0.00 (= 100%) 2 80.50 - 12:15 3 72.79 - 20.56

Example 2: Tests on tin/bismuth treatment in thin-layer galvanizing using a ZnAl5 melt

In order to be able to examine the different galvanizing results of the various processes, identical square steel tubes in the Sebisty range with a length of approximately 10 cm and Deep rust on the component surface (hereinafter "components") used, which were degreased and pickled in identical processes.

The components were then pretreated as shown in Table 5 before they were dried and subjected to a zinc bath containing aluminum. Tab. 5 test series - pre-treatment sample pre-treatment steps 1 2 3 1 Bismuth flux bath 2 Pre-treatment bath containing tin Pre-treatment bath containing bismuth flux bath 3 Pre-treatment bath containing bismuth Pre-treatment bath containing tin flux bath 4 Pre-treatment bath containing tin and bismuth flux bath 5 Flux bath containing tin and bismuth

1. i) 0-350 g/l ZnCl₂ (Zinkchlorid);
2. ii) 25-350 g/l NH₄Cl (Ammoniumchlorid);

The flux (sample 2-4) had the following composition:

1. i) 0-350 g/l ZnCl ₂ (zinc chloride);
2. ii) 25-350 g/l NH ₄ Cl (ammonium chloride);

Furthermore, the flux composition had a pH of 4.0.

The tin-containing pretreatment baths and the tin-containing flux bath had a concentration of 10 g/l tin(II) at a pH of 0.3. Tin(II) chloride (SnCl ₂ ) was used here. The pretreatment in the tin bath (samples 2-3) was at room temperature and a residence time of 15 min, with the combined tin and bismuth bath (Sample 4) at room temperature and a residence time of 60 s to 15 min and the tin and bismuth flux bath (Sample 5) at 45 °C and a dwell time of 60 s to 15 min.

The bismuth-containing pretreatment baths and the bismuth-containing flux bath had a concentration of 2 g/l bismuth(III), such as bismuth chloride (BiCl ₃ ), bismuth oxide (Bi ₂ O ₃ ), bismuth subcarbonate ((BiO) ₂ CO ₃ ), with bismuth subcarbonate ( (BiO) ₂ CO ₃ ) was used. The pH of each bath was 0.3. The pretreatment in the bismuth flux bath (sample 1) was at 45 °C and a dwell time of 60 s, in the bismuth pretreatment bath (samples 2-3) at room temperature and a dwell time of 60 s, in the combined tin and bismuth bath (sample 4) at room temperature and a dwell time of 60 s to 15 min and for the tin and bismuth flux bath (sample 5) at 45 °C and a dwell time of 60 s to 15 min.

The metallic tin deposition by means of vapor deposition produced a silvery, gray matt surface on the components, which developed very slowly and increased over the course of the dwell time in the pre-treatment bath. The application of bismuth, on the other hand, produced an immediate black discoloration of the surface of the component within seconds, which intensified over the course of the dwell time in the pre-treatment bath.

After the pre-treatment, the samples were dried in the drying oven. However, the drying temperature of the samples was dependent on the flux composition used. In the case of fluxes without zinc chloride, the maximum drying temperature was limited to 150°C, since otherwise the NH ₄ Cl (ammonium chloride) deposited on the component would burn and disturb the subsequent galvanizing surface or not properly wet it. In the presence of increasing zinc chloride (ZnCl ₂ ) concentration in the flux, a usual temperature of 200-250 °C could be used.

This was followed by galvanizing in a zinc bath comprising 2% by weight to 10% by weight aluminum (Al) and 90% by weight to 98% by weight zinc (Zn), with preferably 5% by weight ± 1% by weight Al and 95 wt% ±1 wt% Zn were used. The The residence time of the components in the ZnAl5 melt, ie the galvanizing bath, was ≦10 min, preferably 5 min ±1 min, at a temperature of 420°C ±10°C.

After galvanizing, the layer thickness of the components was measured and the appearance of the galvanizing surface was examined. Here, as in Example 1, the layer thicknesses of the four outer sides of the square steel tubes were assessed from a number of measurements. Only slight differences in layer thickness were recorded within the test series, which means that the order of treatment with tin ²⁺ and/or bismuth ³⁺ and the flux bath in the ZnAl5 thin-layer galvanizing does not seem to be relevant.

In addition, components in which the length of the dwell time (60 seconds to 15 minutes) in the tin-containing bath or flux bath was varied showed no change in the layer thickness of the galvanizing layer and the thin-layer galvanizing quality in the thin-layer galvanizing in preliminary tests.

However, like him 2 As can be seen, compared to Sample 1, Samples 2-5, in which co- or subsequent sub-deposition by means of tin-containing compounds such as SnCl ₂ and bismuth-containing compounds as described above, had less unevenness on the surface of the component, such as for example pimples. In addition, the surface was smooth and shiny after the use of tin and bismuth, which means that the components pretreated in this way could also be used for optically demanding applications. In the Fig. 2 b) the increased and pronounced formation of so-called spangles can also be seen. As a rule, the application of an alloy layer during hot-dip galvanizing and thin-layer galvanizing serves to protect against corrosion. Optics and aesthetics play a relatively subordinate role in the applications, but this has become increasingly important for customers over the past decade. With the composition and the process sequences of the present invention, however, in addition to corrosion protection, surfaces can also be generated which can also be used for other applications due to their optically perfect design and make hot-dip or thin-layer galvanizing more varied.

• 0,1-10 g/l SnCl_2;
• 0,1-2,0 g/l BiCl₂; und
• 100-300 g/l NH₄Cl

bei einem pH-Wert ≤ 0,5 und einer Verweilzeit im Bad von 60 sek, wobei das Tauchbad eine Temperatur von 40-45 °C aufweist und der nachgeschaltete Trockenofen eine maximale Temperatur von 150 °C und mindestens 100°C aufweist.Since only minor changes in the galvanizing layer could be detected within the thin-layer galvanizing, the execution as a common bath, comprising a tin-containing compound, a bismuth-containing compound and a compound for the fine pickling effect, seems to be advantageous, since this one bath has the advantage that the Investment costs and space requirements are lower and higher productivity is achieved. In addition, only a one-time preparation is required. Consequently, pre-treating the component after degreasing and pickling with a bath containing the following components and concentrations seems to be most efficient:

• 0.1-10 g/l SnCl _2;
• 0.1-2.0 g/l BiCl ₂ ; and
• 100-300 g/l _NH4Cl

at a pH value ≤ 0.5 and a dwell time in the bath of 60 seconds, the immersion bath having a temperature of 40-45 °C and the downstream drying oven having a maximum temperature of 150 °C and at least 100 °C.

Claims (15)

Method for galvanizing metallic components, in particular ferrous components, in thin-layer galvanizing and/or discontinuous batch galvanizing, wherein at least one pretreatment for depositing a metallic layer on the at least one component is carried out before galvanizing, comprising treating the component with a process liquid a pH below 2, comprising at least one tin(II) compound and at least one bismuth compound, causing metallic tin and bismuth to be deposited on the component surface of the component. The method of claim 1, wherein the pre-treatment comprises treating the at least one component in separate steps of tin and bismuth deposition, wherein i) in a first pretreatment step the component is treated with a process liquid containing tin(II) and in a second pretreatment step the at least one component with a tin deposit on the component surface is treated with a process liquid containing bismuth; or ii) in a first pretreatment step the component is treated with a bismuth-containing process liquid and in a second pretreatment step the at least one component with a bismuth deposit on the component surface is treated with a tin(II)-containing process liquid. Method according to Claim 1, in which the pretreatment of the at least one component takes place in a process liquid which has at least one tin(II) compound and one bismuth compound. Process according to claim 1 to 3, wherein the stannous compound is tin chloride (SnCl ₂ ) and the bismuth compound is bismuth chloride (BiCl ₃ ), bismuth oxide (Bi ₂ O ₃ ), bismuth subcarbonate ((BiO) ₂ CO ₃ ) and/or bismuth granules (metal basis). A method according to any one of claims 1 to 4, wherein the pretreatment a) with a tin(II) compound i) a tin(II) compound-containing process solution having an acidic pH ≤ 0.5; ii) the process liquid has a concentration of stannous ions of between 0.1 g/l to 30 g/l in the process liquid; and iii) the dwell time of the component in the process liquid comprising stannous compound between 10 seconds (sec) and 30 minutes (min); and or b) with a bismuth compound i) a process solution containing a bismuth compound has an acidic pH value of ≦0.5; ii) the process liquid has a concentration of the bismuth compound of between 0.1 g/l to 10 g/l, preferably at 2 g/l in the process liquid; and or iii) the dwell time of the component in the process liquid comprising bismuth compound is between 10 seconds (sec) and 15 minutes (min), preferably 60 seconds. The method according to claim 1 to 5, wherein the pretreated component in a further or third step
comprising a flux composition i) ZnCl ₂ (zinc chloride) in the range of 25 g/l to 350 g/l; and ii) NH ₄ Cl (ammonium chloride) in the range of 25 g/l to 350 g/l, the total salt content being between 200 g/l and 600 g/l and a pH of 0.5 to pH 6 , more preferably 4; or Process according to Claims 1 to 5, in which the pretreated component is treated in a further or third step with a pretreatment liquid comprising NH ₄ Cl (ammonium chloride) in the range from 100 g/l to 400 g/l, preferably 200 g/l, and a pH Value from 0.5 to pH 6, particularly preferably from 4 is treated. The method according to any one of claims 1 to 7, wherein the process liquid further comprises a stannous compound and/or a bismuth compound a) ZnCl ₂ (zinc chloride) in the range from 25 g/l to 350 g/l and NH ₄ Cl (ammonium chloride) in the range from 25 g/l to 350 g/l, the total salt content being between 200 g/l and 600 g/l; or b) NH ₄ Cl (ammonium chloride) in the range from 100 g/l to 400 g/l, preferably 200 g/l, the pH being ≦2, preferably ≦0.5. A method according to any one of claims 1 to 8, wherein a) one or more rinsing baths are interposed between the individual pretreatment steps; b) the component is dried after the pre-treatment and then immersed in a galvanizing bath; c) the component is degreased and pickled prior to the pretreatment, with preferably at least one rinsing bath being upstream, intermediate and/or downstream between the steps of degreasing and pickling. Method according to one of Claims 1 to 9, in which a drying process takes place after the pretreatment at a maximum temperature of 150°C. Method according to one of Claims 1 to 10, in which, after the pretreatment, an incompletely closed metallic layer of metallic tin and bismuth is deposited on the component surface. Method according to one of Claims 1 to 11, in which the metallic tin formed on the component surface as a result of the pretreatment brings about a reduction in the layer thickness of the zinc layer in the discontinuous batch galvanizing (hot-dip galvanizing). Pretreatment agent for galvanizing metallic components, in particular ferrous components, in thin-layer galvanizing and/or discontinuous piece galvanizing, comprising: a) a tin(II) compound, preferably tin chloride (SnCl ₂ ), in dilute hydrochloric acid (HCl) with a pH of ≦2, preferably ≦0.5, with a tin(II) concentration of between 0, 1 g/l to 30 g/l; b) a bismuth compound, preferably bismuth chloride (BiCl ₃ ), in dilute hydrochloric acid (HCl) with a pH of ≦2, preferably ≦0.5, with a bismuth concentration of 0.1 g/l to 10 g /l, preferably at 2 g/l; and or c) NH ₄ Cl (ammonium chloride) in the range from 100 g/l to 400 g/l, preferably 200 g/l, and a pH of ≦6, preferably ≦4. A pretreatment composition according to claim 13, further comprising ZnCl ₂ (zinc chloride) in the range of 25 g/l to 350 g/l, the total salt content in the process liquid being between 200 g/l and 600 g/l and a pH ≤ 6 , preferably ≦4. Component produced by a method according to one of Claims 1 to 12 or treated with a pretreatment agent according to Claim 13 or 14.

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