HK1054576B

HK1054576B - Electroplating solutions for the preparation of ternary tin zinc cobalt alloy layers

Info

Publication number: HK1054576B
Application number: HK03106913.8A
Authority: HK
Inventors: Klaus Leyendecker; Günter Wirth; Klaus Reissmüller; Steffen Dumke
Original assignee: Degussa Galvanotechnik Gmbh
Priority date: 2000-09-16
Filing date: 2001-08-16
Publication date: 2009-07-17

Description

The invention relates to galvanic electrolyte baths and their use.

It is known that ironworking materials can be protected against corrosion by coating them with zinc and then passivation, for example by chromation (based on Cr6+) or chromitation (based on Cr3+), which is characterized by a yellow, blue, black or olive green colouration of the surface.

Higher requirements, such as resistance to salt fog testing up to the first appearance of red rust of up to 1000 hours, can be met by coating with zinc alloys containing nickel, cobalt or iron as an alloying component and then chromating.

The most favourable alloying composition is 70% by weight Sn and 30% by weight Zn. The low hardness of SnZn layers is seen as a disadvantage of only about 50 HV (Tin-Zinc Plating, E. Budmann and D. Stevens, IMF Trans 76 (1998) 3).

The observation of developments in the field of corrosion protection of iron materials, for example in the automotive industry, shows that in future higher requirements will be placed on corrosion protection systems which cannot be met by the known methods.

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

The invention relates to a neutral electrolyte bath with a pH of 6 to 10 and having the following composition: 10 - 40 g/l tin as sulphate, sodium or potassium stanate, 0.5 - 10 g/l zinc as sulphate, chloride, hydroxide or oxide, 0,1 - 10 g/l cobalt as sulphate, chloride, hydroxide or oxide, 50 - 200 g/l tetrasodium pyrophosphate,1 - 20 g/l potassium or sodium hydroxide,10 - 200 g/l complex formers, 0,1 - 10 g/l net formers, and 0,1 - 5 g/l gloss formers.

In another embodiment of the invention, it refers to an alkaline electrolyte bath with a pH greater than 10 and having the following composition: 10 - 50 g/l tin as sulphate, chloride, sodium or potassium stanate,1 - 10 g/l zinc as sulphate, chloride, hydroxide or oxide,0,1 - 10 g/l cobalt as sulphate,1 - 20 g/l potassium or sodium hydroxide,10 - 200 g/l complex formers,0,1 - 10 g/l net agents, and0,1 - 5 g/l gloss formers.

The above electrolyte baths can be used to galvanize 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% by weight of tin, 45 to 55% by weight of zinc and 1 to 5% by weight of cobalt. The alloy layer can be used as a corrosion protection layer, as a soldable layer or as a decorative finish layer. It can also be used as a corrosion protection layer on a ferrous material with subsequent passivation.

It has now been found that ternary tin-zinc alloys, 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, produced in accordance with the invention, are the third alloying component which satisfies the requirements for corrosion resistance.

The alloy layers are produced by galvanic means, namely by electrolytic deposition from aqueous galvanic electrolyte baths containing the alloy components in dissolved form. The ternary tin-zinc alloys can be deposited from alkaline or neutral galvanic electrolyte baths on substrates.

The alloying components are added to the aqueous electrolyte bath in the form of their ionogenic compounds soluble in the respective medium. Tin is preferably used as a sulfate, chloride, sulfonate, oxalate or in the form of sodium or potassium stanate. Zinc is preferably added as a sulfate, chloride, hydroxide, sulfonate or oxide. The third alloying element, cobalt, is preferably added as a sulfate, chloride, hydroxide or carbonate.

The galvanic electrolytes of the invention for the production of ternary tin-zinc alloy layers may still contain additives and auxiliaries common and known in galvanic engineering, such as alkalies for pH adjustment, such as sodium, potassium or ammonium hydroxide, or inorganic acids such as hydrochloric acid, sulphuric acid, phosphoric acid, boric acid, alkaline salts of these acids as buffer and/or lead salts, organic acids such as hydroxycarbon acids and/or their salts, such as citric acid, complexes such as EDTA, net agents, glossers, etc. The qualitative criteria for the quantitative selection of the additives and their function and function in the bath are valid.

The ratio of metals in the galvanically deposited alloy layer can be known to be affected by the ratio of metals in the bath composition, by the type and quantity of other bath components and by the deposition parameters.

The electrolytic separation of ternary tin-zinc alloys involves the substrate to be coated, such as a corrosion-protective component made of an iron material, being immersed in a suitable galvanic bath and turned into a cathode. Anodes made of insoluble or, preferably, soluble materials, preferably neutral electrolytes, can be used as counter electrodes. Insoluble anodes are usually composed of graphite or plated titanium.

The conditions for the separation of the ternary tin-zinc alloys from the electrolytes of the invention can be regarded as a temperature of about 20 to 70 °C and a current density of about 0.1 to 5 A/dm2, resulting in separation rates of about 0.05 to 1 μm/minute.

An alkaline electrolyte of the invention has the following framework composition: 10 - 50 g/l tin as sulphate, chloride, sodium or potassium stanate,1 - 10 g/l zinc as sulphate, chloride, hydroxide or oxide,0,1 - 10 g/l cobalt as sulphate,1 - 20 g/l potassium or sodium hydroxide,10 - 200 g/l complex formers,0,1 - 10 g/l net agents, and0,1 - 5 g/l gloss formers.

The galvanic deposition of the alloy takes place at temperatures between 40 and 70 °C at current densities of 1 to 5 A/dm2 with deposition rates of 0.15 to 0.3 μm/min. Graphite or plated titanium can be used as anodes.

Organic acids and their salts, phosphoric acids, phosphonates, gluconates, glucoheptonic acids, glucoheptonates and ethylene diamine triacetic acid may be used as complexes, and persistent surfactants, multi-value alcohols and betaines may be used as net agents and glossers in the corresponding media.

Changes in the ratio of the individual components in the bath can vary the alloying composition of the layer. For example, an increase in the hydroxide content causes a decrease in the zinc content and a corresponding increase in the other two metals in the layer. An increase in the amount of complexes causes a decrease in the zinc content and an increase in the tin content in the layer.

A neutral electrolyte of the invention may have the following typical framework composition: 10 - 40 g/l tin as sulphate, sodium or potassium stanate, 0.5 - 10 g/l zinc as sulphate, chloride, hydroxide or oxide, 0,1 - 10 g/l cobalt as sulphate, chloride, hydroxide or oxide, 50 - 200 g/l tetrasodium pyrophosphate,1 - 20 g/l potassium or sodium hydroxide,10 - 200 g/l complex formers, 0,1 - 10 g/l net formers, and 0,1 - 5 g/l gloss formers.

The galvanic deposition of the alloy takes place at temperatures between 40 and 70 °C at current densities of 0.5 to 3 A/dm2 with deposition rates of 0.05 to 0.3 μm/min. Graphite or plated titanium can be used as anodes.

The ratio of alloy composition may be varied by variation of coating parameters.

The ternary tin-zinc alloys have very advantageous material properties which allow them to be used in various ways both as a stand-alone material and, in particular, as coatings on substrates.

In general, ternary tin-zinc alloys have a particularly high corrosion resistance. Therefore, these alloys are particularly suitable as corrosion protection layers on iron materials. The corresponding galvanic electrolytes can therefore be used preferably to generate corrosion protection layers on iron materials.

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 alloy element when either good corrosion resistance, hardness, abrasion or solubilty is desired. Other

	Korrosion	Härte	Abrieb	Lötbarkeit
SnZnNi	+	-	+	-
SnZnFe	-	+	-	+
SnZnCo	+	+	-	+

The three alloy systems have the highest hardness levels of SnZnFe and SnZnCo alloy layers. The most abrasion resistant are SnZnNi layers. These alloy layers can therefore be used as wear-resistant layers under mechanical stress. SnZnFe and SnZnCo layers are particularly soldable and are therefore particularly suitable in electronics as soldable layers and contact surfaces. Other


Sn 44 %	Sn 52 %	Sn 46 %
Zn 56 %	Zn 44 %	Zn 51 %
Ni 0,2 %	Fe 4 %	Co 3 %
50	165	179
50	165	179	(HV 0,025)
4,9	9,1	7,2
(mg Gewichtsverlust / 1000 Hübe nach Bosch-Weinmann)
0,3 - 0,4	0,8 - 1,2	0,3 - 0,6
(ZCT in sek)

In addition to these functional applications, the ternary tin-zinc alloys can also be used as decorative finishes, so that the three alloy systems have interesting and attractive colour schemes in the blue range, depending on the choice of the third alloy element.

The Commission Example 1

An alkaline electrolyte for the removal of an alloy consisting of 45% by weight of Sn, 52% by weight of Zn and 3% by weight of Cobalt has the following composition: 30 g/l Tin as sodium stannicate2,4 g/l Zinc as zinc oxide1 g/l Cobalt as cobalt sulphate8 g/l Potassium hydroxide50 g/l Sodium citrate100 ml/l Sodium phosphate2,5 ml/l Anionic surfactant1 g/l Butadiol

The above-mentioned layer composition can be obtained with this electrolyte at a temperature of 60 °C and current densities of 1-2 A/dm2.

Coating of iron sheets with this alloy in a thickness of 8 μm with chromation (Cr6+ base) showed the following resistance in the salt fog test according to DIN 50021 - SS: First appearance of white rust in the period 1800-3000 hours. After 3000 hours the test was cancelled as no red rust appeared until 3000 hours.

Example 2

A neutral electrolyte for the removal of an alloy consisting of 48 W/kg Sn, 49 W/kg Zn and 3 W/kg Cobalt has the following composition: 25 g/l tin as tin sulphate2,4 g/l zinc as zinc oxide1 g/l cobalt as cobalt sulphate130 g/l tetrasodium pyrophosphate2,5 ml/l anionic surfactant1 g/l butindiol

The pH value is 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/dm2.

Example 3 (comparative example)

A weak acid electrolyte for the removal of an alloy consisting of 49,2% by weight of Sn, 50,5% by weight of Zn and 0,3% by weight of Nickel has the following composition: 5 g/l tin as tin sulphate6,8 g/l zinc as zinc sulphate12 g/l nickel as nickel sulphate80 g/l sodium citrate25 g/l boric acid10 ml/l anionic surfactant1 ml/l beta-naphtoelethoxylate

The pH value is set to 4.5. The above layer composition can be obtained with this electrolyte at a temperature of 40 °C and current densities of 1.5 A/dm2.

Example 4 (comparative example)

A weak acid electrolyte for the separation of an alloy consisting of 52 W/kg Sn, 44 W/kg Zn and 4 W/kg Iron has the following composition: 5 g/l tin as tin sulphate6,8 g/l zinc as zinc sulphate10 g/l iron as iron sulphate80 g/l sodium citrate25 g/l boric acid10 ml/l anionic surfactant1 ml/l beta-naphtoelethoxylate

The pH value is set to 4.4 and the above layer composition can be obtained with this electrolyte at a temperature of 40 °C and a current density of 1.5 A/dm2.

Claims

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.
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.
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.
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.
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.
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.
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.
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.