EP1319093B1 - Electroplating solutions for the preparation of ternary tin zinc cobalt alloy layers - Google Patents

Description

The invention relates to galvanic electrolyte baths and their use.

It is known that iron materials by coatings with zinc and subsequent passivation, such as by a chromating (based Cr ⁶⁺ ) or chromite (based Cr ³⁺ ), which is recognizable by a yellow, blue, black or olive green color of the surface , can be protected from corrosion. With these measures, protection times for the salt spray test (DIN 50021-SS) of 200 to 600 hours can be achieved until the first occurrence of red rust (corrosion protection through coatings and coatings, D. Grimme and J. Krüger, Weka Fachverlag für technische Führungskräfte, Augsburg) ,

Higher requirements, such as resistance to salt spray testing up to the first occurrence of red rust of up to 1000 hours, may be met by coating with zinc alloys containing nickel, cobalt or iron as the alloying component followed by chromating. The proportion of alloying elements may be less than 1% by weight, for example 0.4-0.6% by weight of Fe in the ZnFe system, up to 15% by weight, for example 12-15% by weight of Ni in the ZnNi system ( Zinc alloy process: properties and applications in the art , Dr. A. Jiménez, B. Kerle and H. Schmidt, Galvanotechnik 89 (1998) 4 ).

Tin-zinc alloy layers can also be used as anti-corrosion layers for iron. In the salt spray test, values of up to 1000 hours are achieved with chromated SnZn layers until the first appearance of red rust. The most favorable alloy composition is 70% by weight of Sn and 30% by weight of Zn. The disadvantage seen is the low hardness of SnZn layers of only about 50 HV ( Tin-Zinc-Plating, E. Budmann and D. Stevens, Trans. IMF 76 (1998) 3 ).

The observation of developments in the field of corrosion protection of ferrous materials, such as in the automotive industry, reveals that in future higher demands are placed on corrosion protection systems that can not be met with the known methods. Such increased demands on the resistances in the salt spray test can be more than 3000 hours. In addition, such anticorrosive layers should have the highest possible hardness, be resistant to abrasion and in particular should also be solderable as possible.

The invention therefore an object of the invention to find galvanic electrolyte baths for the deposition of alloy systems with particularly high corrosion resistance, which meet the future requirements in terms of corrosion protection.

• 10 - 40 g/l Zinn als Sulfat, Natrium- oder Kaliumstannat,
• 0,5 - 10 g/l Zink als Sulfat, Chlorid, Hydroxid oder Oxid,
• 0,1 - 10 g/l Kobalt als Sulfat, Chlorid, Hydroxid oder Oxid,
• 50 - 200 g/l Tetranatriumpyrophosphat,
• 1 - 20 g/l Kalium- oder Natriumhydroxid,
• 10 - 200 g/l Komplexbildner,
• 0,1 - 10 g/l Netzmittel, und
• 0,1 - 5 g/l Glanzbildner.

The invention relates to a neutral electrolyte bath with a pH of 6 to 10, which has the following composition:

• 10 - 40 g / l tin as sulfate, sodium or potassium stannate,
• 0.5 - 10 g / l zinc as sulfate, chloride, hydroxide or oxide,
• 0.1-10 g / l cobalt as sulfate, chloride, hydroxide or oxide,
• 50-200 g / l tetrasodium pyrophosphate,
• 1 - 20 g / l potassium or sodium hydroxide,
• 10-200 g / l complexing agent,
• 0.1-10 g / l wetting agent, and
• 0.1-5 g / l brightener.

• 10 - 50 g/l Zinn als Sulfat, Chlorid, Natrium- oder Kaliumstannat,
• 1 - 10 g/l Zink als Sulfat, Chlorid, Hydroxid oder Oxid,
• 0,1 -10 g/l Kobalt als Sulfat,
• 1 - 20 g/l Kalium- oder Natriumhydroxid,
• 10 - 200 g/l Komplexbildner,
• 0,1 - 10 g/l Netzmittel, und
• 0,1 - 5 g/l Glanzbildner.

In another embodiment of the invention, it relates to an alkaline electrolyte bath having a pH greater than 10 and having the following composition:

• 10 - 50 g / l tin as sulfate, chloride, sodium or potassium stannate,
• 1-10 g / l zinc as sulfate, chloride, hydroxide or oxide,
• 0.1-10 g / l cobalt as sulfate,
• 1 - 20 g / l potassium or sodium hydroxide,
• 10-200 g / l complexing agent,
• 0.1-10 g / l wetting agent, and
• 0.1-5 g / l brightener.

The above electrolytic baths can be used for electroplating a ternary tin-zinc-cobalt alloy layer consisting of 30 to 65% by weight of tin, 30 to 65% by weight of zinc and 0.1 to 15% by weight of cobalt. Preferably, the alloy layer consists of 40 to 55 wt.% Tin, 45 to 55 wt.% Zinc and 1 to 5 wt.% Cobalt. The alloy layer can serve as a corrosion protection layer, as a solderable layer or as a decorative final layer. Furthermore, it can be used with a subsequent passivation as a corrosion protection layer on a ferrous material.

It has now been found that the ternary tin-zinc alloys according to the invention, which consist of 30 to 65 wt.% Tin, 30 to 65 wt.% Zinc and 0.1 to 15 wt.% Cobalt, as a third alloy component, the requirements meet with regard to corrosion resistance excellent.

The alloy layers are produced by electroplating, namely by electrolytic deposition from aqueous electrolytic electrolyte baths containing the alloy components in dissolved form. The tin-zinc ternary alloys can be deposited on substrates from alkaline or neutral galvanic electrolyte baths. An alkaline electrolyte is understood here to mean an electrolyte having a pH greater than 10. The neutral electrolyte is an electrolyte with a pH of 6 - 10.

The alloy components are added to the aqueous electrolyte bath in the form of their respective medium soluble ionic compounds. Tin is preferably used as sulfate, chloride, sulfonate, oxalate or in the form of sodium or potassium stannate. Zinc is preferably added as sulfate, chloride, hydroxide, sulfonate or oxide. The As the third alloying component, cobalt is preferably added as each of sulfate, chloride, hydroxide or carbonate.

The galvanic electrolytes according to the invention for the production of ternary tin-zinc alloy layers may further contain customary and known additives and auxiliaries in electroplating. These may be alkalis for pH adjustment, such as sodium, potassium or ammonium hydroxide, or inorganic acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, alkali metal salts of these acids as buffer and / or conductive salts, organic acids such as hydroxycarboxylic acids and / or salts thereof, for example citric acid, complexing agents such as EDTA, wetting agents, brighteners, etc. Those skilled in the art, the criteria for the qualitative and quantitative selection of such additives and auxiliaries and their function in electroplating baths familiar.

The ratio of the metals in the electrodeposited alloy layer can be influenced in a known manner by the ratio of the metals in the bath composition, by the nature and amount of the other bath components and by the deposition parameters.

For the electrolytic deposition of the ternary tin-zinc alloys, the substrate to be coated, for example a component to be protected from corrosion from an iron material, is immersed in a corresponding galvanic bath and wired as a cathode. Anodes can be used as counterelectrodes of insoluble or, preferably in the case of neutral electrolytes, soluble materials. Insoluble anodes are usually made of graphite or platinized titanium. Soluble anodes suitably consist of the metals of the alloy layer to be deposited, preferably in the desired composition.

As a framework for the deposition of the ternary tin-zinc alloys from the electrolytes of the invention, a temperature of about 20 - 70 ° C and a current density of about 0.1 - 5 A / dm ^{2 are} considered, with deposition rates of about 0, 05 - 1 μm / minute.

• 10 - 50 g/l Zinn als Sulfat, Chlorid, Natrium- oder Kaliumstannat,
• 1 - 10 g/l Zink als Sulfat, Chlorid, Hydroxid oder Oxid,
• 0,1 - 10 g/l Kobalt als Sulfat,
• 1 - 20 g/l Kalium- oder Natriumhydroxid,
• 10 - 200 g/l Komplexbildner,
• 0,1 - 10 g/l Netzmittel, und
• 0,1 - 5 g/l Glanzbildner.

An alkaline electrolyte according to the invention has the following framework composition:

• 10 - 50 g / l tin as sulfate, chloride, sodium or potassium stannate,
• 1-10 g / l zinc as sulfate, chloride, hydroxide or oxide,
• 0.1-10 g / l cobalt as sulfate,
• 1 - 20 g / l potassium or sodium hydroxide,
• 10-200 g / l complexing agent,
• 0.1-10 g / l wetting agent, and
• 0.1-5 g / l brightener.

The galvanic deposition of the alloy takes place at temperatures between 40-70 ° C at current densities of 1 - 5 A / dm ² with deposition rates of 0.15 - 0.3 microns / minute. As anodes graphite or platinized titanium can be used.

As complexing agents, organic acids and their salts, phosphonic acids, phosphonates, gluconates, glucoheptonic acids, glucoheptonates and ethylenediaminetetraacetic acid can be used. Suitable wetting agents and brighteners can be used in the appropriate media resistant surfactants, polyhydric alcohols and betaines.

By changing the ratio of the individual components in the bath, the alloy composition of the layer can be varied. Thus, an increase in the hydroxide content causes a reduction in the tin content and a corresponding increase in the other two metals in the layer. An increase in the amount of complexing agent causes a decrease in the zinc content and an increase in the tin content in the layer. On the third alloy metal, these changes have virtually no influence.

• 10 - 40 g/l Zinn als Sulfat, Natrium- oder Kaliumstannat,
• 0,5 - 10 g/l Zink als Sulfat, Chlorid, Hydroxid oder Oxid,
• 0,1 - 10 g/l Kobalt als Sulfat,
• Chlorid, Hydroxid oder Oxid,
• 50 - 200 g/l Tetranatriumpyrophosphat,
• 1 - 20 g/l Kalium- oder Natriumhydroxid,
• 10 - 200 g/l Komplexbildner,
• 0,1 - 10 g/l Netzmittel, und
• 0,1 - 5 g/l Glanzbildner.

A neutral electrolyte according to the invention may have the following typical framework composition:

• 10 - 40 g / l tin as sulfate, sodium or potassium stannate,
• 0.5 - 10 g / l zinc as sulfate, chloride, hydroxide or oxide,
• 0.1-10 g / l cobalt as sulfate,
• Chloride, hydroxide or oxide,
• 50-200 g / l tetrasodium pyrophosphate,
• 1 - 20 g / l potassium or sodium hydroxide,
• 10-200 g / l complexing agent,
• 0.1-10 g / l wetting agent, and
• 0.1-5 g / l brightener.

The galvanic deposition of the alloy is carried out at temperatures between 40-70 ° C at current densities of 0.5 - 3 A / dm ² with deposition rates of 0.05 - 0.3 microns / minute. As anodes graphite or platinized titanium can be used. The use of soluble anodes is also possible.

The ratio of the alloy composition can be varied by varying the coating parameters.

The ternary tin-zinc alloys have very advantageous material properties, due to which they can be used both as an independent material, and in particular in the form of coatings on substrates in different ways.

In general, the ternary tin-zinc alloys have a particularly high corrosion resistance. Therefore, these alloys are particularly suitable as corrosion protection coatings on iron materials. Accordingly, the corresponding galvanic electrolytes can preferably be used to produce corrosion protection coatings on iron materials. Thus coated iron sheets in combination with the usual passivation by chromating or chromitization readily achieve a resistance to the occurrence of red rust of over 3000 hours.

Other properties can be controlled by the choice of the respective third alloying element. The properties of the ternary tin-zinc alloy layers can be optimized depending on the choice of the third alloy element. Table 1 gives an overview of the influence of the third alloying element when either good corrosion resistance, hardness, abrasion or solderability are desired. Here, the nickel and iron alloys are given as comparative examples. <b><u> Table 1 </ u></b> corrosion hardness abrasion solderability SnZnNi + - + - SnZnFe - + - + SnZnCo + + - +

Among the three alloy systems, the SnZnFe and SnZnCo alloy layers achieve the highest hardness values. The highest abrasion resistance is exhibited by SnZnNi layers. Such alloy layers can therefore be used advantageously as wear protection layers under mechanical stress. SnZnFe and SnZnCo layers are particularly easy to solder and are therefore excellently suited in electronics as solderable layers and as contact surfaces. Table 2 shows the corresponding data for exemplarily selected alloy systems. <b><u> Table 2 </ u></b> layer SnZnNi SnZnFe SnZnCo composition Sn 44% Sn 52% Sn 46% Zn 56% Zn 44% Zn 51% Ni 0.2% Fe 4% Co 3% hardness 50 165 179 (HV 0.025) abrasion 4.9 9.1 7.2 (mg weight loss / 1000 strokes after Bosch-Weinmann) solderability 0.3-0.4 0.8-1.2 0.3 - 0.6 (ZCT in seconds)

In addition to these functional applications, the ternary tin-zinc alloys can also be used as decorative end layers. Thus, the three alloy systems, depending on the choice of the third alloy element, interesting and appealing, lying in the blue range colors.

EXAMPLES example 1

• 30 g/l Zinn als Natriumstannat
• 2,4 g/l Zink als Zinkoxid
• 1 g/l Kobalt als Kobaltsulfat
• 8 g/l Kaliumhydroxid
• 50 g/l Natriumcitrat
• 100 ml/l Natriumphosphonat
• 2,5 ml/l anionisches Tensid
• 1 g/l Butindiol

An alkaline electrolyte for depositing an alloy consisting of 45 wt.% Sn, 52 wt.% Zn and 3 wt.% Cobalt has the following composition:

• 30 g / l tin as sodium stannate
• 2.4 g / l zinc as zinc oxide
• 1 g / l cobalt as cobalt sulfate
• 8 g / l potassium hydroxide
• 50 g / l sodium citrate
• 100 ml / l sodium phosphonate
• 2.5 ml / l anionic surfactant
• 1 g / l butynediol

It turns a pH of 11. The above-mentioned layer composition can be obtained with this electrolyte at a temperature of 60 ° C and current densities of 1-2 A / dm ² . In this case, about 0.2 microns alloy layer are built up per minute. The density of the alloy layer is 7.27 g / cm ³ .

• Erstes Auftreten von Weißrost in der Zeitperiode 1800 - 3000 Stunden.
• Nach 3000 Stunden wurde die Prüfung abgebrochen, da bis 3000 Stunden kein Rotrost aufgetreten ist.

A coating of iron sheets with this alloy in a thickness of 8 microns with chromating (based Cr ⁶⁺ ) showed the following resistance in the salt spray test according to DIN 50021 - SS:

• First occurrence of white rust in the time period 1800 - 3000 hours.
• After 3000 hours, the test was aborted because no red rust occurred up to 3000 hours.

Example 2

• 25 g/l Zinn als Zinnsulfat
• 2,4 g/l Zink als Zinkoxid
• 1 g/l Kobalt als Kobaltsulfat
• 130 g/l Tetranatriumpyrophosphat
• 2,5 ml/l anionisches Tensid
• 1g/l Butindiol

A neutral electrolyte for depositing an alloy consisting of 48% by weight of Sn, 49% by weight of Zn and 3% by weight of cobalt has the following composition:

• 25 g / l tin as tin sulfate
• 2.4 g / l zinc as zinc oxide
• 1 g / l cobalt as cobalt sulfate
• 130 g / l tetrasodium pyrophosphate
• 2.5 ml / l anionic surfactant
• 1 g / l butynediol

It turns to a pH of 8.5. The above-mentioned layer composition can be obtained with this electrolyte at a temperature of 60 ° C and current densities of 0.5 - 1 A / dm ² . 0.15 μm layer is built up per minute. The density of the alloy layer is 7.27 g / cm ³ .

Example 3 (comparative example )

• 5 g/l Zinn als Zinnsulfat
• 6,8 g/l Zink als Zinksulfat
• 12 g/l Nickel als Nickelsulfat
• 80 g/l Natriumcitrat
• 25 g/l Borsäure
• 10 ml/l anionisches Tensid
• 1 ml/l Beta-Naphtolethoxylat

A weakly acidic electrolyte for depositing an alloy consisting of 49.2% by weight Sn, 50.5% by weight Zn and 0.3% by weight nickel has the following composition:

• 5 g / l tin as tin sulfate
• 6.8 g / l zinc as zinc sulfate
• 12 g / l nickel as nickel sulfate
• 80 g / l sodium citrate
• 25 g / l boric acid
• 10 ml / l anionic surfactant
• 1 ml / l beta-naphthol ethoxylate

It turns a pH of 4.5. The above-mentioned layer composition can be obtained with this electrolyte at a temperature of 40 ° C and current densities of 1.5 A / dm ² . In this case, about 0.4 microns alloy layer are built up per minute. The density of the alloy layer is 7.2 g / cm ³ .

Example 4 (Comparative Example )

• 5 g/l Zinn als Zinnsulfat
• 6,8 g/l Zink als Zinksulfat
• 10 g/l Eisen als Eisensulfat
• 80 g/l Natriumcitrat
• 25 g/l Borsäure
• 10 ml/l anionisches Tensid
• 1 ml/l Beta-Naphtolethoxylat

A weakly acidic electrolyte for depositing an alloy consisting of 52 wt.% Sn, 44 wt.% Zn and 4 wt.% Iron has the following composition:

• 5 g / l tin as tin sulfate
• 6.8 g / l zinc as zinc sulfate
• 10 g / l iron as iron sulfate
• 80 g / l sodium citrate
• 25 g / l boric acid
• 10 ml / l anionic surfactant
• 1 ml / l beta-naphthol ethoxylate

It adjusts to a pH of 4.4. The above-mentioned layer composition can be obtained with this electrolyte at a temperature of 40 ° C and current densities of 1.5 A / dm ² . In this case, about 0.4 microns alloy layer are built up per minute. The density of the alloy layer is 7.25 g / cm ³ .

Claims (8)

1. Neutral electrolyte bath having a pH from 6 to 10 and the following composition:

   10 - 40 g/l tin as the sulphate, or as sodium or potassium stannate,

   0.5 - 10 g/l zinc as the sulphate, chloride, hydroxide or oxide,

   0.1 - 10 g/l cobalt as the sulphate, chloride, hydroxide or oxide,

   50 - 200 g/l tetrasodium pyrophosphate,

   1 - 20 g/l potassium hydroxide or sodium hydroxide,

   10 - 200 g/l complexing agent,

   0.1 - 10 g/l wetting agent, and

   0.1 - 5 g/l brightener.
2. Alkaline electrolyte bath having a pH greater than 10 and the following composition:

   10 - 50 g/l tin as the sulphate, chloride, or as sodium or potassium stannate,

   1 - 10 g/l zinc as the sulphate, chloride, hydroxide or oxide,

   0.1 - 10 g/l cobalt as the sulphate,

   1 - 20 g/l potassium hydroxide or sodium hydroxide,

   10 - 200 g/l complexing agent,

   0.1 - 10 g/l wetting agent, and

   0.1 - 5 g/l brightener.
3. Use of an electrolyte bath according to Claim 1 or 2 for galvanic production of a ternary tin-zinc-cobalt alloy layer consisting of 30 to 65% by weight tin, 30 to 65% by weight zinc and 0.1 to 15% by weight cobalt.
4. Use according to Claim 3, wherein the alloy layer consists of 40 to 55% by weight tin, 45 to 55% by weight zinc and 1 to 5% by weight cobalt.
5. Use of an electrolyte bath according to Claim 1 or 2 for galvanic production of a ternary tin-zinc-cobalt anticorrosion layer consisting of 30 to 65% by weight tin, 30 to 65% by weight zinc and 0.1 to 15% by weight cobalt.
6. Use of an electrolyte bath according to Claim 1 or 2 for galvanic production of a ternary tin-zinc-cobalt alloy layer consisting of 30 to 65% by weight tin, 30 to 65% by weight zinc and 0.1 to 15% by weight cobalt, wherein the alloy layer with subsequent passivation is an anticorrosion layer on a ferrous material.
7. Use of an electrolyte bath according to Claim 1 or 2 for galvanic production of a ternary tin-zinc-cobalt alloy layer consisting of 30 to 65% by weight tin, 30 to 65% by weight zinc and 0.1 to 15% by weight cobalt, wherein the alloy layer is a solderable layer.
8. Use of an electrolyte bath according to Claim 1 or 2 for galvanic production of a ternary tin-zinc-cobalt alloy layer consisting of 30 to 65% by weight tin, 30 to 65% by weight zinc and 0.1 to 15% by weight cobalt, wherein the alloy layer is a final decorative layer.