Substrate with a corrosion resistant coating and method of production thereof

Abstract

The invention relates to a substrate with a corrosion resistant coating comprising at least one nickel layer and at least one chromium layer as finish. Between these layers, at least one tin-nickel alloy layer is deposited for suppression of corrosion reactions determined by CASS and Russian mud tests. The invention relates also to a method for producing such substrates with corrosion resistant coating.

Claims

1. A substrate with a corrosion-resistant coating, the corrosion-resistant coating comprising at least one nickel layer, a chromium layer as an outermost metal finish layer, and at least one tin-nickel alloy layer deposited between the at least one nickel layer and the chromium finish layer for suppression of corrosion reactions, wherein the chromium finish layer comprises chromium and from 1 to 25 wt. % carbon, from 1 to 30 wt. % oxygen, from 0 to 10 wt. % sulfur, from 0 to 10 wt. % nitrogen, and from 0 to 30 wt. % iron, wherein the at least one tin-nickel alloy layer is produced by deposition from an electrolyte having a temperature of from 40 C. to 60 C., and wherein the produced substrate passes a corrosion test according to UNI EN ISO 9227 CASS standard procedure for a test duration of at least 96 hours.

2. The substrate according to claim 1, wherein the at least one tin-nickel alloy layer comprises 55 to 75 weight-% tin and 25 to 45 weight % nickel.

3. The substrate according to claim 1, wherein the at least one tin-nickel alloy layer has a thickness of 0.1 to 10 m.

4. The substrate according to claim 1, wherein the at least one nickel layer has a thickness of 1 to 50 m.

5. The substrate according to claim 1, wherein the chromium finish layer has a thickness of 0.05 to 2 m.

6. The substrate according to claim 1, wherein the corrosion-resistant coating comprises a bright nickel layer or a further metallic layer deposited on the substrate.

7. The substrate according to claim 6, wherein the further metallic layer consists essentially of copper.

8. The substrate according to claim 6, further comprising a semi-bright nickel layer arranged between the bright nickel layer and the substrate or the further metallic layer.

9. The substrate according to claim 1, wherein the substrate comprises a metal, a metal alloy, or a plastic.

10. The substrate according to claim 1, wherein the produced substrate passes a corrosion test according to Volkswagen VW PV1067 standard procedure for a test duration of at least 48 hours.

11. A method for producing a corrosion resistant coating for a substrate, the method comprising: a) electroplating at least one nickel layer on the substrate, b) electroplating at least one tin-nickel alloy layer from an electrolyte having a temperature of from 40 C. to 60 C., and c) electroplating a chromium layer as an outermost metal finish layer, wherein electroplating the chromium layer comprises electro-plating chromium that includes from 1 to 25 wt. % carbon, from 1 to 30 wt. % oxygen, from 0 to 10 wt. % sulfur, from 0 to 10 wt. % nitrogen, and from 0 to 30 wt. % iron, so that the at least one tin-nickel alloy layer is deposited between the at least one nickel layer and the at least one chromium finish layer, wherein corrosion reactions are suppressed by the tin-nickel alloy layer such that the produced substrate passes a corrosion test according to UNI EN ISO 9227 CASS standard procedure for a test duration of at least 96 hours.

12. The method according to claim 11, wherein electroplating the at least one tin-nickel alloy layer comprises electroplating the at least one tin-nickel alloy layer from an acidic aqueous electrolyte with a pH in the range of 2 to 6, wherein the electrolyte comprises additives comprising at least one of chlorides, fluorides, fluoroborates apart from at least one tin salt and at least one nickel salt.

13. The method according to claim 12, wherein the electrolyte comprises second additives selected from the group consisting of complexing agents; wetting agents; and mixtures thereof.

14. The method according to claim 11, wherein electroplating the at least one tin-nickel alloy layer comprises electroplating the at least one tin-nickel alloy layer from an alkaline aqueous electrolyte, wherein the electrolyte comprises at least one tin salt and at least one nickel salt, wherein the salts are selected from the group consisting of sulfates, sulfamates, phosphates, pyrophosphates, glycine, and mixtures thereof.

15. The method according to claim 11, wherein electroplating the at least one tin-nickel alloy layer comprises electroplating the at least one tin-nickel alloy layer from a cyanide-containing aqueous electrolyte, wherein the electrolyte comprises at least one tin salt and at least one nickel salt, wherein the salts are selected from the group consisting of sulfates, sulfamates, phosphates, pyrophosphates, glycine, and mixtures thereof.

16. The method according to claim 11, wherein electroplating the at least one tin-nickel alloy layer comprises electroplating the at least one tin-nickel alloy layer from a neutral or weakly alkaline aqueous electrolyte with a pH in the range of 6 to 10, wherein the electrolyte comprises at least one tin salt and at least one nickel salt, wherein the salts are selected from the group consisting of sulfates, sulfamates, phosphates, pyrophosphates, glycine, and mixtures thereof.

17. The method according to claim 11, wherein the tin salt is selected from the group consisting of chlorides, fluorides, fluoroborates, sulfates, methane sulfonates and mixtures thereof, and the nickel salt is selected from the group consisting of chlorides, fluorides, fluoroborates, sulfates, sulfamates, pyrophosphates, methane sulfonates, and mixtures thereof.

18. The method according to claim 11, wherein electroplating the chromium finish layer comprises electroplating the chromium layer from an acidic aqueous electrolyte, wherein the electrolyte comprises at least one chromium(VI)-salt.

19. The method according to claim 11, wherein electroplating the chromium finish layer comprises electroplating the chromium layer from an acidic aqueous electrolyte with a pH in the range of 2 to 6, wherein the electrolyte comprises at least one chromium(III)-salt.

20. The method according to claim 19, wherein the electrolyte comprises additives selected from the group consisting of: organic acids or salts thereof; inorganic acids or salts thereof; conducting salts; blackening agents; and wetting agents.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) With reference to the following figures and subsequent examples, the subject matter according to the invention is intended to be explained in more detail without restricting said subject to the special embodiments shown therein.

(2) FIG. 1 shows different combinations of the inventive substrate coating.

(3) FIG. 2 shows a 100-fold magnification of a microscopic image of the surface produced according to example C (as it is known from the prior art) before carrying out the CASS test. Micropores are recognizable herein which are attributed to the nickel layer having micro-scale disruptions.

(4) FIG. 3 shows a 100-fold magnification of a microscopic image of an inventive surface produced according to example D before performing the CASS test.

(5) FIG. 4 shows a 100-fold magnification of a microscopic image of an inventive surface produced according to example C after 96 hours in the CASS test. The surface according to example C has strongly changed its appearance compared to the surface shown in FIG. 2, which indicates increased corrosion.

(6) FIG. 5 shows a 100-fold magnification of a microscopic image of an inventive surface produced according to example D after 96 hours in the CASS test. The surface according to example D has changed its appearance only marginal in contrast to the surface produced according to example C which illustrates the drastically improved corrosion resistance of the inventive coatings compared to the coatings known in the prior art.

DETAILED DESCRIPTION

Examples

(7) Formed parts of acrylonitrile-butadienestyrene (ABS) with a size of 5 to 7 cm were initially subjected to a preliminary processing to render the surface conductive for galvanic deposition.

(8) Subsequently, a nickel layer having micro-scale disruptions was deposited according to the prior art (as it is known from U.S. Pat. No. 3,268,424) with the following composition and following parameters:

(9) TABLE-US-00001 NiSO.sub.4*6H.sub.2O 200-300 g/l NiCl.sub.2*6H.sub.2O 20-80 g/l H.sub.3BO.sub.3 30-80 g/l kaolin (fine powder) 0.1-1.5 g/l pH 3-5 temperature 40-60 C.

(10) These nickel-coated parts were used as comparison for the coatings according to the invention.

(11) The coatings according to the invention were deposited from an electrolyte with the following composition and parameters:

(12) TABLE-US-00002 NiCl.sub.2*6H.sub.2O 200-300 g/l NH.sub.4HF.sub.2 30-80 g/l SnCl.sub.2*2H.sub.20 20-60 g/l pH 2-5 temperature 40-60 C.

(13) In a further inventive embodiment, the coating was deposited from an electrolyte with the following composition and parameters:

(14) TABLE-US-00003 NiCl.sub.2*6H.sub.2O 200-300 g/l NH.sub.4HF.sub.2 30-80 g/l SnCl.sub.2*2H.sub.20 20-60 g/l Diethylenetriamine 20-100 g/l pH 3.8-5.5 Temperature 40-60 C.

(15) Subsequently, the chromium finish was deposited.

(16) An electrolyte with the following composition and parameters was used for the deposition of a chromium(VI)-layer:

(17) TABLE-US-00004 CrO.sub.3 200-300 g/l H.sub.2SO.sub.4 0.5-2 g/l F.sup. 1-2 g/l temperature 30-40 C.

(18) Four different electrolytes were used for the deposition of a chromium(III)-layer. These electrolytes are distributed under the names TRISTAR 300, TRISTAR 300 AF, TRISTAR 700 and TRISTAR 720 by the company Coventya.

(19) The TRISTAR 300 process is a chloride-based process and provides a white chromium layer wherein the electrolyte has the following composition and parameters:

(20) TABLE-US-00005 Cr.sup.3+ 15-25 g/l organic acid 25-250 g/l Conducting salts 150-300 g/l pH 2-6 temperature 25-35 C.

(21) The TRISTAR 700 process is comparable with the process described before wherein a chromium layer with a darker coloration results. The electrolyte used herein has the following composition and parameters:

(22) TABLE-US-00006 Cr.sup.3+ 15-25 g/l organic acid 25-50 g/l conducting salts 150-300 g/l blackening agent 1-10 g/l pH 2-3 temperature 25-35 C.

(23) The TRISTAR 300 AF process is a sulfate-based process and results in a chromium layer with white color. The electrolyte comprises the following composition and parameters:

(24) TABLE-US-00007 Cr.sup.3+ 5-15 g/l organic acid 5-20 g/l conducting salts 150-300 g/l pH 3-4 temperature 45-65 C.

(25) The TRISTAR 720 process is comparable to the TRISTAR 300 AF process, but results in a chromium layer with darker coloration. The electrolyte comprises the following composition and parameters:

(26) TABLE-US-00008 Cr.sup.3+ 5-15 g/l organic acid 5-20 g/l conducting salts 150-300 g/l blackening agent 2-10 g/l pH 3-4 temperature 45-65 C.

(27) A first corrosion test according to UNI EN ISO 9227 CASS was carried out with such produced samples. The duration of the test was 24, 48, 72, 96 and 120 hours.

(28) As a second corrosion test, the standard procedure VW PV1067 of Volkswagen AG and NES M4063 of Nissan, respectively, was applied. A muddy corrosion accelerator was produced including a mixture of a solution of 3 g Kaolin and 5 ml of an aqueous solution saturated with calcium chloride. Subsequently, a certain amount of mud was evenly distributed on the surface of the individual samples. The test samples were stored in a chamber at constant temperature and humidity (60 C. and 23% rel. air humidity). The duration of the test was 48 hours.

(29) The evaluation of the above-described corrosion tests was carried out with an evaluation method which is similar to the evaluation method of ISO 10289 and performs an evaluation based on the size of the defective areas. This is illustrated in Table 1.

(30) TABLE-US-00009 TABLE 1 Defective areas A(%) Quotation no defects 10 0 < A 0.1 9 0.1 < A 0.25 8 0.25 < A 0.5 7 0.5 < A 1.0 6 1.0 < A 2.5 5 2.5 < A 5 4 5 < A 10 3 10 < A 25 2 25 < A 50 1 50 < A 0

(31) In the first corrosion tests (CASS test), the respective samples were investigated after 24 hours of testing phase. They were cleaned and dried during each inspection without damaging the surface to ensure a correct evaluation. In this way, any changes to the appearance of the surface during the test, like e.g. spots, mattness, flaking, rust, or pitting, could be monitored.

(32) The samples were evaluated during the second corrosion test with calcium chloride at the end of the test (after 48 hours). The samples were cleaned and dried without damaging the surface. Any change of the surface could be also monitored exactly.

(33) In table 2, the individual samples are illustrated together with the test results. The samples A, C, E, G and I are those which represent the prior art. These samples comprise a nickel layer with micro-scale disruptions as intermediate layer between the bright nickel layer and the chromium finish.

(34) Examples B, D and D, F, F, H, L and L are coatings according to the invention and comprise a tin-nickel alloy layer between the bright nickel layer and the chromium finish.

(35) As can be seen from table 2, sample B demonstrates a better corrosion resistance compared to sample A both in CASS test and CaCl2 test. Sample D and D demonstrates a better corrosion resistance compared to sample C both in CASS test and CaCl2 test. Sample F and F demonstrates a better corrosion resistance compared to sample E both in CASS test and CaCl2 test. Sample H demonstrates a better corrosion resistance compared to sample G both in CASS test and CaCl2 test. Sample L and L demonstrates a better corrosion resistance compared to sample I both in CASS test and CaCl2 test.

(36) Particularly the samples D, D, F and F demonstrate excellent results and pass both the 96-hours CASS-test and the 48-hours VW PV1067 standard test. More particularly the sample D, F showed the best corrosion resistance to CASS test passing both the 120 h.

(37) TABLE-US-00010 TABLE 2 micro- discontinuous Samples noble Nickel Tin-Nickel Chromium 24 h 48 h 72 h 96 h 120 h CaCl.sub.2 TEST A 2-5 m Hexavalent 10 10 8 7 4 5 Chromium B 0.1-1.0 m Hexavalent 10 10 9 8 7 6 Sn65Ni35 Chromium C 2-5 m TRISTAR 300 4 3 3 2 2 9 D 0.1-1.0 m TRISTAR 300 10 10 10 10 8 10 Sn65Ni35 D 2.0-5.0 m TRISTAR 300 10 10 10 10 10 10 Sn65Ni35 E 2-5 m TRISTAR 700 9 9 8 7 6 9 F 0.1-1.0 m TRISTAR 700 10 10 9 8 8 10 Sn65Ni35 F 2.0-5.0 m TRISTAR 700 10 10 10 10 9 10 Sn65Ni35 G 2-5 m TRISTAR 300 10 9 8 8 6 5 AF H 0.1-1.0 m TRISTAR 300 10 10 10 9 8 6 Sn65Ni35 AF I 2-5 m TRISTAR 720 9 9 8 7 5 5 L 0.1-1.0 m TRISTAR 720 10 10 9 8 8 6 Sn65Ni35 L 2.0-5.0 m TRISTAR 720 10 10 10 10 8 6 Sn65Ni35