Aqueous, alkaline electrolyte for depositing zinc-containing layers onto surfaces of metal piece goods

Abstract

The invention relates to an aqueous, alkaline electrolyte for electrochemically depositing a zinc-, iron-, manganese-containing layer onto surfaces of metal piece goods, in particular piece goods made of iron and/or steel, characterized in that the electrolyte contains: zinc ions in an amount of 4-60 g/L; iron ions in an amount of 0.5-30 g/L; manganese ions in an amount of 0.1-15 g/L. The invention also relates to a method for electrochemically depositing a zinc-, iron-, manganese-containing layer onto one or more surfaces of a metal piece good. The invention also relates to a metal piece good comprising a zinc-, iron, manganese-containing layer electrochemically deposited onto a surface of the metal piece good in accordance with the inventive method.

Claims

1. An aqueous, alkaline electrolyte for electrochemically depositing a zinc-, iron-, manganese-containing layer onto surfaces of metal piece goods, wherein the electrolyte contains: zinc ions in an amount of 4-60 g/L; iron ions in an amount of 0.5-30 g/L; and manganese ions in an amount of 0.2-5 g/L.

2. The aqueous, alkaline electrolyte according to claim 1, comprising manganese ions in an amount of 0.3-1 g/L.

3. The aqueous, alkaline electrolyte according to claim 2, comprising zinc ions in an amount of 4-45 g/L.

4. The aqueous, alkaline electrolyte according to claim 2, comprising iron ions in an amount of 0.5-25 g/L.

5. The aqueous, alkaline electrolyte according to claim 1, comprising: zinc ions in an amount of 7-10 g/L; iron ions in an amount of 1-3 g/L; and manganese ions in an amount of 0.3-1 g/L.

6. The aqueous, alkaline electrolyte according to claim 1, wherein the zinc ions comprise zincate ions, and the electrolyte further comprises conducting salts and at least one complexing agent.

7. The aqueous, alkaline electrolyte according to claim 1, wherein the aqueous, alkaline electrolyte does not contain nickel.

8. The aqueous, alkaline electrolyte according to claim 1, wherein the metal piece goods comprise iron and/or steel.

9. A method for electrochemically depositing a zinc-, iron-, manganese-containing layer onto surfaces of metal piece goods, the method comprising introducing the metal piece goods into the aqueous, alkaline electrolyte according to claim 1 and electrochemically depositing the zinc-, iron-, manganese-containing layer onto the metal piece goods.

10. The method according to claim 9, wherein the zinc-, iron-, manganese-containing layer comprises: zinc in an amount of 40 wt. % to 96 wt. %; iron in an amount of 4 wt. % to 50 wt. %; and manganese in an amount of 0.05 wt. % to 10 wt. %, based on total weight of zinc, iron, and manganese, as measured by energy-dispersive X-ray spectroscopy at an excitation voltage of 20 kV.

11. The method according to claim 10, wherein: the zinc is present in an amount of 65 wt. % to 92 wt. %; the iron is present in an amount of 8 wt. % to 30 wt. %; and the manganese is present in an amount of 0.1 wt. % to 5 wt. %.

12. The method according to claim 10, wherein: the zinc is present in an amount of 77 wt. % to 89 wt. %; the iron is present in an amount of 10 wt. % to 20 wt. %; and the manganese is present in an amount of 0.5 wt. % to 3 wt. %.

13. The method according to claim 10, wherein: the iron is present in an amount of 4 wt. % to 30 wt. %; the manganese is present in an amount of 0.1 wt. % to 5 wt. %; and remainder zinc.

14. The method according to claim 9, wherein the electrochemically deposited zinc-, iron-, manganese-containing layer has a thickness of 3 μm to 30 μm.

15. The method according to claim 9, wherein the electrochemically deposited zinc-, iron-, manganese-containing layer further comprises adapted passivation, and when the zinc-, iron-, manganese-containing layer comprising adapted passivation is subjected to a salt spray test according to ISO 9227 and/or ASTM B117-73, corrosion protection until initial attack of more than 400 hours is observed, wherein the corrosion protection is measured according to DIN 50961 Chapter 10.

16. The method according to claim 9, wherein the metal piece goods comprise iron and/or steel.

17. A method of protecting a metal piece good against corrosion comprising electrochemically depositing a zinc-, iron-, manganese-containing layer onto surfaces of the metal piece good, wherein the zinc-, iron-, manganese-containing layer is electrochemically deposited from the aqueous, alkaline electrolyte according to claim 1.

18. The method according to claim 17, wherein the metal piece good comprises iron and/or steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached figures which illustrate the following:

(2) FIG. 1 depicts the results of the coating corrosion in the neutral salt spray test up to 1608 h as described in the Examples.

(3) FIG. 2 depicts coating corrosion and incipient red rust at 1032 h NSS as described in the Examples.

(4) FIG. 3 depicts coating and base metal corrosion at 384 h NSS as described in the Examples.

DETAILED DESCRIPTION OF THE INVENTION

(5) In an embodiment, the present invention provides an aqueous, alkaline electrolyte. In yet another embodiment, the present invention provides a method for depositing zinc-containing layers onto surfaces of metal piece goods.

(6) In embodiments, the present invention provides an aqueous, alkaline electrolyte and a method for depositing zinc-containing layers onto surfaces of piece goods, in which the piece goods are introduced into the aqueous, alkaline electrolyte.

(7) In an embodiment, the invention further provides a piece good provided with a zinc-containing layer, and to the use of the zinc-containing layer as corrosion protection on metallic piece goods, in particular those made of iron and steel.

(8) An object of the present invention is to provide a zinc-containing layer which, even without nickel, has the highest possible corrosion protection without losing its properties as a sacrificial anode. Furthermore, it is the object of the present invention to be heat-resistant in the sense of the use of the component, and to provide good protection against contact corrosion with aluminum alloys. In particular, the necessarily resulting corrosion products should be as inconspicuous as possible, especially not white and voluminous like typical zinc corrosion products.

(9) In an embodiment, the present invention provides an aqueous, alkaline electrolyte for electrochemically depositing a zinc-, iron-, manganese-containing layer onto surfaces of metal piece goods, in particular piece goods made of iron and/or steel, characterized in that the electrolyte contains: a. zinc ions in an amount from 4-60 g/l, preferably from 4-45 g/l, more preferably from 4-30 g/l, more preferably from 5-20 g/l, in particular from 7-10 g/l; b. iron ions in an amount from 0.5-30 g/l, preferably from 0.5-25 g/l, more preferably from 0.6-25 g/l, more preferably from 0.7-10 g/l, in particular from 1-3 g/l; c. manganese ions in an amount from 0.1-15 g/l, preferably from 0.1-10 g/l, more preferably from 0.2-8 g/l, more preferably from 0.2-5 g/l, in particular from 0.3 to 1 g/l.

(10) Furthermore, the following are preferably contained: 1. Sufficient sodium hydroxide or potassium hydroxide to produce soluble zincate ions, 2. anions such as acetate, carbonate, chloride, silicate, sulfate, as counterions to the aforementioned cations and—together with the sodium ions and potassium ions—as conducting salts, and/or 3. organic additives for stabilizing soluble complexes, for uniform deposition, for improved metal distribution, and to adjust the desired gloss level.

(11) Surprisingly, it has been found that a zinc layer with a higher iron content and at the same time a certain manganese content not only avoids the aforementioned disadvantages, but is moreover able to exceed the already outstanding corrosion protection values of zinc/nickel. This layer can be passivated in trivalent or chromium-free conversion layers, and can moreover also be provided with organic or inorganic topcoats.

(12) The electrolyte according to the invention thereby has the following economic and ecological advantages:

(13) The electrolyte according to the invention manages without nickel, which as a strong allergen would happily be avoided for safety reasons. However, the corrosion protection which can be produced with this electrolyte can be measured with the zinc/nickel layers according to the prior art, and thus represents a substantially better compatible alternative. Zinc, iron, and manganese are essential for humans and are generally well tolerated. The electrolyte according to the invention is alkaline, preferably highly alkaline, having a pH value of more than 13, preferably 13.5-14.5, especially approximately 14. In addition, however, it is not the source of any special hazards. Despite the increase in alloy partners from one to two, and the complexity incurred by this, the electrolyte according to the invention can be operated with the same economic efficiency as an alkaline zinc/nickel bath.

(14) Suitable sources of zinc ions can be soluble zinc compounds such as zinc chloride, zinc sulfate, or else organic zinc compounds such as zinc methanesulfonate, for example. Zinc oxide, or also metallic zinc, is usually dissolved in the highly alkaline electrolyte, and the necessary zincate ions are thus produced.

(15) Suitable sources of iron ions can be soluble iron compounds such as iron chloride, iron sulfate, iron carbonate, or else organic iron compounds such as iron acetate, for example.

(16) Suitable sources of manganese ions can be soluble manganese compounds such as manganese chloride, manganese sulfate, manganese carbonate, or also potassium permanganate. The latter would preferably be reduced with a little methanol to a soluble manganese compound in a solution preparation.

(17) The electrolyte may also contain complexing agents, in particular amines, polyalkyleneimines, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, further chelating ligands such as acetylacetone, urea, urea derivatives, and further complex ligands in which the complexing functional group contains nitrogen, phosphorus, or sulfur. Further optional components of the electrolyte are additives selected from the group consisting of gloss agents, wetting agents, and mixtures thereof. These preferably include benzylpyridinium carboxylate, nicotinic acid, N-methylpyridinium carboxylate, and aldehydes.

(18) The anode is preferably comprised of steel, nickel, nickel-plated steel, platinum-plated titanium or another platinum-plated inert metal, or titanium coated with mixed oxides or another inert metal coated with mixed oxides.

(19) The metallic workpieces, connected as a cathode, are attached to the gantry or coated in a drum or another plant suitable for bulk workpieces.

(20) According to the invention, a method is also provided for electrochemically depositing zinc-containing layers onto surfaces of piece goods, in which method the piece goods are introduced into an electrolyte as has been described above, and zinc-containing layers are electrodeposited onto the piece goods.

(21) The deposition preferably takes place at a temperature of 20 to 40° C., particularly preferably at a temperature of 25° C. The current density during the deposition is preferably in a range from 0.1 to 20 A/dm<2>, in particular from 0.5 to 3 A/dm<2>.

(22) A further subject matter of the present invention is a zinc-containing layer produced by a method as described above.

(23) In one embodiment of the invention, the layer containing zinc, iron, and manganese contains metallic zinc and iron as well as metallic and/or oxidic manganese. The weight fractions of the elements can be measured by means of energy-dispersive X-ray spectroscopy, EDX.

(24) In practical tests, it has been found that the weight fraction of the elements in a zinc-, iron-, manganese-containing layer deposited with the method according to the invention, measured via energy-dispersive X-ray spectroscopy (EDX) at an excitation voltage of 20 kV, is usually within the following ranges: zinc is usually in the range from 40% by weight to 96% by weight, preferably from 65% by weight to 92% by weight, even more preferably from 77% by weight to 89% by weight, respectively relative to the total weight of zinc, iron, manganese.

(25) The weight fraction of iron is usually in the range from 4% by weight to 50% by weight, preferably from 8% by weight to 30% by weight, more preferably from 10% by weight to 20% by weight, respectively relative to the total weight of zinc, iron, manganese.

(26) The weight fraction of manganese is usually in the range from 0.05% by weight to 10% by weight, preferably from 0.1% by weight to 5% by weight, more preferably from 0.5% by weight to 3% by weight, respectively relative to the total weight of zinc, iron, manganese.

(27) For example, the thickness of the zinc-containing layer may vary depending on the desired corrosion protection properties. For most application purposes, it has proven to be advantageous to set the zinc-containing layer with an average layer thickness from 3 to 30 μm, preferably from 5 to 20 μm, and especially from 7 to 15 μm. The layer thickness can hereby be determined magneto-inductively, by means of X-ray fluorescence on copper parts, or by measuring a fracture in a scanning electron microscope.

(28) According to a preferred embodiment of the invention, the zinc-, iron-, manganese-containing layer with adapted passivation, for example SurTec 680 Chromiting, imparts to an object a corrosion protection in the salt spray test according to ISO 9227 and/or ASTM B 117-73 without or with heat load, for example of 120° C. for 24 hours, until initial attack according to DIN 50961 Chapter 10, of more than 400 hours, preferably of more than 500 hours, and especially of more than 600 hours.

(29) Objects or articles having a layer containing zinc, iron, manganese according to the invention can consequently be protected against corrosion permanently, and thus particularly advantageously. Objects or articles which have a zinc-containing layer according to the invention are also the subject matter of the present invention.

(30) The subject matter of the present invention is also the use of a zinc-, iron-, manganese-containing layer, made from an aqueous, alkaline electrolyte according to claim 1, as corrosion protection on a metallic piece good, in particular a such a piece good made of iron and steel.

Examples

(31) The invention is explained in more detail below with reference to several non-limiting examples.

(32) Two electrolytes according to the invention were prepared as follows: I. Two zinc solutions were prepared as follows: 1. 35 kg NaOH were dissolved in approximately 50 kg of softened water. 4 kg of zinc oxide were then dissolved in the hot solution while stirring. Once it had completely dissolved, it was filled with softened water to 100 kg.=SODIUM ZINCATE SOLUTION To 500 ml/l of softened water and 225 ml/l of the sodium zincate solution was added 1.5 g/l iron (as a sulfate) with 0.66 g/l EDTA and 15 g/l triethanolamine as a complexing agent. 2 g/l potassium permanganate was then dissolved therein and reduced with 4 ml/l methanol. The resulting solution was filled with softened water just up to 1 liter of electrolyte. 2. 40 kg KOH were dissolved in approximately 50 kg of softened water. 3 kg of zinc oxide were then dissolved in the hot solution while stirring. Once it had completely dissolved, it was filled with softened water to 100 kg.=POTASSIUM ZINCATE SOLUTION. To 500 ml/l of softened water and 225 ml/l of the potassium zincate solution was added 1.5 g/l iron (as a sulfate) with 0.66 g/l EDTA and 15 g/l triethanolamine as a complexing agent. 2 g/l potassium permanganate were then dissolved therein and reduced with 4 ml/l methanol. The resulting solution was filled with softened water just up to 1 liter of electrolyte.

(33) Both electrolytes were adjusted to be semi-bright with commercially available base and gloss additives for alkaline galvanization, for example SurTec 704 I and II. Degreased and pickled steel plates were immersed in the respective electrolytes and coated at 23° C. with a current density of 2 A/dm.sup.2.

(34) The resulting approximately 6 μm thick layer was examined in EDX. The following values were measured:

(35) Potassium zincate electrolyte: iron: 11.8-12.5%, manganese: 0.2-2.0%, remainder zinc

(36) Sodium zincate electrolyte: iron: 11.9-12.5%, manganese: 0.2-2.0%, remainder zinc

(37) Both plates were passivated in SurTec 680 Chromiting and dried. The dried plates were annealed at 120° C. for 24 hours in order to weaken the corrosion protection according to the VDA requirements.

(38) In the neutral salt spray test, both plates achieved anticorrosion protection of >600 hours without discoloring or showing black dots. (Comparison: Unalloyed zinc from alkaline electrolytes would already have stronger corrosion under the same conditions, and zinc/nickel from alkaline electrolytes would have a more or less pronounced grey discoloration.) II. A further zinc solution according to the invention was prepared as follows: 1. To 500 ml/l softened water and 225 ml/l of the sodium zinc solution from Example 1.1 was added 1.5 g/l iron (as a chloride) and 12 g/l gluconic acid as a complexing agent. 2 g/l potassium permanganate was then dissolved therein and reduced with 4 ml/l methanol. The resulting solution was filled with softened water just up to 1 liter of electrolyte. III. Two zinc solutions NOT according to the invention were prepared as follows for comparison: 1. To 500 ml/l softened water and 225 ml/l of the sodium zinc solution from Example 1.1 was added 1.5 g/l iron (as a chloride) and 12 g/l gluconic acid as a complexing agent. The resulting solution was filled with softened water just up to 1 liter of electrolyte. 2. To 500 ml/l softened water and 225 ml/l of potassium zincate solution from Example 1.2 was added 1.5 g/l of iron (as a sulfate) and 12 g/l of gluconic acid as a complexing agent. The resulting solution was filled with softened water just up to 1 liter of electrolyte.

(39) For comparison, in Examples III.1 and III.2 the manganese addition was omitted.

(40) All three electrolytes were adjusted to be semi-bright with commercially available base and gloss additives for alkaline galvanization, for example SurTec 704 I and II. Degreased and pickled steel plates were immersed in the respective electrolytes and coated at 23° C. with a current density of 2 A/dm.sup.2.

(41) The resulting approximately 6 μm thick layers were examined in EDX. The following values were measured: II.1: iron: 11.8-12.5%, manganese 0.2-2.0%, remainder zinc III.1: iron: 11.9-12.5, remainder zinc III.2: iron: 11.9-12.5%, remainder zinc

(42) Plates from all three electrolytes were passivated in SurTec 675/551, a cobalt-free, silicate-containing middle layer passivation, and dried.

(43) Whereas the samples from Example II showed neither coating corrosion (“white corrosion”) nor red rust (FIG. 1) in the neutral salt spray test up to 1608 h, the samples from Examples 111.1 and 111.2 turned out distinctly worse.

(44) Sample III.1 (FIG. 2) showed voluminous coating corrosion and incipient red rust at 1032 h NSS. The corrosion test was terminated here.

(45) Sample III.2 (FIG. 3) already showed coating and base metal corrosion at 384 h NSS, the experiment was terminated at 768 h neutral salt spray test (NSS) with more base metal corrosion and voluminous coating corrosion.

(46) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

(47) The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.