GB2188334A

GB2188334A - Electrolyte for zinc alloy deposition

Info

Publication number: GB2188334A
Application number: GB08704939A
Authority: GB
Inventors: Brian D Bammel; Walter J Wieczerniak; Kenneth D Snell
Original assignee: OMI International Corp
Current assignee: OMI International Corp
Priority date: 1986-03-03
Filing date: 1987-03-03
Publication date: 1987-09-30
Anticipated expiration: 2007-03-03
Also published as: DE3705949A1; IT8747660A0; SE8700716L; SE8700716D0; FR2595102A1; GB8704939D0; ES2002580A6; IT1206252B; CA1314512C; FR2595102B1; GB2188334B; DE3705949C2

Abstract

An aqueous acidic electrolyte suitable for electrodepositing zinc alloys comprising a combination of zinc and at least one metal selected from the group consisting of nickel, cobalt, iron, and mixtures thereof incorporates an effective amount of an additive agent for providing improved grain-refinement and enhancing the adjustment of the codeposition of the alloying metals in the zinc alloy deposit, the additive agent comprising a bath soluble polyhydroxy compound having three or more hydroxyl groups eg. sorbitol, methyl glucose at least one of which is substituted with a polyoxyalkylene group. Other additives may also be present.

Description

SPECIFICATION Zinc alloy electrolytes The present invention broadly relates to an improved electrolyte and process for electrodespositing zinc alloys, and more particularly, to an improved aqueous acid zinc alloy electrolyte containing additive agents for providing improved grain-refinement, reduced dendrite formation, increased adhesion and ductility and an unexpected adjustment in the codeposition of one or more alloying metals in the zinc alloy deposit.

Electrolytes incorporating zinc ions in further combination with one our a combination of nickel, cobalt, iron or mixtures thereof have heretofore been used or proposed for use for depositing zinc alloy deposits of a decorative orfunctional type on a variety of conductive substrates such as iron and steel, for example, to provide for improved corrosion resistance, enhance appearance and/orto build up the surface of a worn part enabling refinishing thereof to restore its original operating dimensions.

Such zinc alloy electrolytes and processes are in widespread commercial use for industrial or functional plating including strip plating, conduit plating, wire plating, rod plating, tube plating, coupling plating, and the like. Acontinuing problem associated with such prior art zinc alloy electrolytes has been the inability to achieve the desired grain-refinement of the alloy electrodepositto provide the requisite semi-bright appearance and associated physical properties including adhesion and ductility. Afurther problem has been the inability to increase the percentage of the alloying metal constituent such as nickel, cobalt and/or iron in the zinc alloy electrodeposit in order to achieve desired physical and chemical properties.The formation of dendrites on the substrate being plated at high current density areas has also been objectionable.

The present invention provides an improved electrolyte for electrodepositing zinc alloys incorporating an additive agent or mixture of additive agents which may provide improved grain-refinement, a reduction in dendrite formation, increase in adhesion and ductility while further adjusting the codeposition of the alloying metal ions achieving a zinc alloy electrodeposit of improved properties.

The benefits and advantages of the present invention in accordance with the composition aspects thereof may be achieved by an aqueous acidic zinc alloy electrolyte containing zinc ions in conventional amounts in further combination with controlled amounts of at least one additional alloying metal ion selected from a group consisting of nickel, cobalt, iron and mixtures thereof. The electrolyte further contains as an essential constituent, an additive agent present in an amount effective to achieve improved physical characteristics ofthe zinc alloy deposit comprising a bath soluble polyhydroxy compound having three or more hydroxyl groups of which at least one is substituted with a polyoxyalkylene group as well as mixtures thereof.The concentration ofthe polyoxyalisylene-su bstituted polyhydroxy additive agent is present in an amount effective to impart improved grain-refinement to the electrodeposit and the specific concentration will vary depending upon whether the electrolyte is of the chloride, sulphate, fluoroborate, sulphamate or mixed-chloride type.

In addition to the foregoing constituents, the zinc alloy electrolyte may additionally contain various other additive agents ofthetypes conventionally employed including buffering agents, supplemental brightening agents, bath soluble and compatible conductivity salts to increase the electrical conductivity of the electrolyte and the like.

In accordance with the process aspects of the present invention, a zinc alloy coating is electrodeposited on a conductive substrate employing the aforementioned aqueous acidic zinc alloy electrolyte which is controlled at a temperature typically ranging from room temperature (60"F, 1 6"C) upto 180 F (82 C) and is operated atan average cathode current density ranging from as low as 1 up to as high as 2000 amperes per square foot (ASF) (0.11 to 200 amperes per square decimetre (ASD)) or higher which will vary depending upon the specific type and composition of the electrolyte as well as the geometry and processing parameters employed in the plating operation.

Further benefits and advantages ofthe present invention will become apparent upon a reading of the following description ofthe preferred embodiments taken in conjunction with the specific examples provided.

The aqueous acidic zinc alloy electrolyte in accordance with the composition aspect of the present invention contains zinc ions present in an amount effective to electrodepositzincfrom the electrolyte and generally can range from as low as 10 g/l up to saturation, with concentrations offrom 15 to 225 g/l being more usual. Preferably, for most applications, the zinc ion concentration is controlled within a range of 20 to 200 g/l . The maximum concentration of zinc ions will vary depending upon the temperature of the electrolyte with higher temperatures enabling use of higher concentrations.

The zinc ion concentration will also vary depending upon the type of electrolyte employed which may be ofthe chloride, sulphate, mixed chloride-sulphate, sulphamate, aswell as thefluoroborate types. In acid chloride-type electrolytes, the zinc ion concentration is generally controlled at a level within the lower end of the permissible range whereas in acid sulphate-type electrolytes, the zinc ion concentration is generally controlled at a level within the upper range of the permissible concentrations.

The zinc ions are introduced into the electrolyte in the form of zinc anodes or soluble zinc salts such as a chloride, sulphate, sulphamate and/orfluoroborate salt in further combination with an acid such as sulphuric acid, hydrochloric acid, fluoroboric acid, suiphamic acid, or the like corresponding to the type of zinc salt employed. Generally the pH ofthe zinc alloy electrolyte is controlled within a range of from 0 up to 7 with a pH of from 2 to 6 being preferred.

In addition to the zinc ions, the electrolyte further contains controlled amounts of at least one ofthe alloying metal ions including nickel, cobalt, and/or iron which similarly are introduced in the form of soluble anodes or bath soluble salts ofthe alloying metal including the chloride, sulphate,fluoroborate, acetate, or suiphamate as well as mixtures thereof.

When nickel and/orcobaltare employed as the alloying metal, each can be employed in the bath in amounts offrom 0.5 g/l up to 120 g/l to provide alloy deposits containing from 0.1 up to 30 percent by weight of nickel and/or cobalt. Preferablyrthe alloy deposit contains from 0.25 percent to a total of about 15 percent of nickel and/or cobalt, and the bath under such conditions contains nickel and/or cobalt ions in an amount usually ranging from 3 g/l to 65 g/l, respectively.

When iron comprises an alloying metal in the electrolyte, the operating iron ion concentration can range offrom 5 girl up to 140 g/lwithconcentrations offrom 40 g/l upto 100 g/l being preferred.

When iron ions are present in the electrolyte which is only weakly acidic or either neutral, such as at a pH offrom 4to about 6.5, it is generally preferred to incorporate conventional complexing or chelating agents to maintain an effective amountofthe iron metal ions in solution. Chelating orcomplexing agents which are particularly satisfactory forthis purpose include citric acid, gluconic acid, glucoheptanoic acid, tartaric acid, ascorbic acid, isoascorbic acid, malic acid, glutaric acid, muconic acid, glutamic acid, glycollic acid, aspartic acid, and the like as well as their alkaline metal, ammonium, zinc orferrous salts.

While the iron ions are introduced into the electrolyte in the ferrous state, ferric ions areformed during the plating operation and it has been found that excessive amounts of ferric ions are objectional resulting in the formation of striations on the zinc alloy plated surface. Accordingly, it has been found desirable to control the ferric ion concentration art a level usually less than about 2 g/l. This can be accomplished by employing a soluble zinc or iron anode in the electroplating bath or, alternatively, by immersing metallic zinc or iron in the holding tank through which the electroplating solution is circulated.When no soluble anodes are employed or no zinc oriron metal is provided in the holding tank, proper control of the ferric ion concentration can be achieved by employing suitable bath soluble and compatible organic and/or inorganic reducing agents such as, for example, bisulfite, isoascorbic acid, monosaccharides and disaccharides such as glucose or lactose.

It will be appreciated from the foregoing, that electrolytes can be formulated to provide for appropriate binary, ternary or quaternary alloys containing predominately zinc and at least one of the other three alloying metal constituents.

When ternary alloy deposits are desired containing zinc-nickel-iron or zinc-cobalt-iron, the concentration of the metal ions in the electrolyte are usually controlled so as to provide an alloy containing from 1 percent to 25 percent iron in combination with either 0.1 to 20 percent by weight nickel or 0.1 to 12 percent cobalt and the balance essentially zinc.

In addition to the metal ions present in the electrolyte, the electrolyte further contains as an essential ingredient an additive agent comprising a bath soluble polyhydroxy compound having three or more hydroxyl groups at least one of which is substituted with a polyoxyallcylene group. Typically, polhydroxy compounds such as sorbitol and methyl glucose having one or more oftheir hydroxyi groups substituted with oxyethylene or oxypropylene chains and mixtures thereof have been found particularly satisfactory for use in such zinc-alloy electrolytes.

The molecular weight of the additive agent or mixtures thereof is controlled to render the additive agent soluble in the electrolyte at the concentration desired. It will be appreciated that the additive agent may contain one polyoxyalkylene substitute group on the molecule or maycontaintwo,three ormore su bstitute groups depending upon the degree of substitution and the number of reactive hydroxyl groups on the molecule.

The concentration ofthe additive agent in the electrolyte will vary depending upon the concentration and types of other bath constituents present, the desired alloy deposit composition, and whethertheelectrodepositisto be employed for functional or decorative purposes. Generally speaking,the additive agent is employed in an amount effective to produce a refinement of the grain of the electrodeposit, to reduce the tendency to form dendrites during the electrodeposition process, to enhance the adhesion and ductility ofthe deposit to the substrate, and to adjustthecodeposition ofthe alloying metal ions in the zinc alloy deposit and to regulate the alloy content at a more uniform, desired level.For this purpose, concentrations as low as 0.005 upto 20 g/l have been found usable while concentrations of from 0.02 up to 10 g/l are more typical and preferred for most uses.

In accordance with a preferred practice of the present invention, the additive agent is employed in sulphate-based zinc-iron electrolytes in a concentration range of about 0.005 to about 0.1 g/l providing both an increase in the codeposition of iron in the zinc-iron deposit and a grain refinement thereof. In sulfate-based zinc-nickel alloy electrolytes, a concentration range of from 0.005 to 0.1 g/l is also preferred providing improved ductility and adhesion of the deposit accompanied by a slight improvement in grain refinement. In sulfate-based zinc-cobalt alloy electrolytes, the preferred concentration range of the additive agent ranges from 0.05 to 5 g/l providing a grain refined, ductile and adherent electrodeposit. An all chloride system for alloy plating, on the otherhand, would require a preferred concentration of 0.1 to 10 g/l for all alloy versions to be produced.

The additive agent can be employed by itself in combination with the metal ions in the electrolyte to produce a semi-brightelectrodeposittypical of a functional plating. When a decorative electrodeposit is desired having enhanced brightness, supplemental brightening agents of the types known in the art can be incorporated in the electrolyte in the usual amounts.Typical of supplemental brighteners that can be employed to further enhance the crystal structure and brightness ofthe zinc alloy electrodeposit are those disclosed in United States Patents No. 4,170,526; 4,207,150; 4,176,017; 4,070,256 and 4,252,619.When employed, such supplemental brightening agents can be used at concentrations up to 10 g/l with concentrations as lows0.001 g/l being effective. Typically,the concentration of the supplemental brightening agents range from 0.01 upto5g/l.

In addition to the foregoing essential and optional constituents, the electrolyte can further include supplemental additives such as buffers and bath modifiers such as boric acid, acetic acid, citric acid, benzoic acid, salicylic acid, as well as their bath soluble and compatible salts, ammonium chloride and the like. Other bath soluble and compatible salts such as ammonium sulphate, ammonium chloride or bromide, sodium chloride, potassium chloride, ammonium fluoroborate, magnesium sulphate, sodium sulphate, and combinations thereof and the like can also be employed in amounts usually ranging from 20 up to 450 g/l to increase the electrical conductivity of the electrolyte. Typically, such conductivity salts comprise alkali metal salts such as chlorides, sulphate, sulphamates and fluoroborates.Also, bath modifiers such as bath soluble and compatible polyhydroxy compounds containing at least three hydroxyl groups and at least fourcarbon atoms ofthe class described in United States Patent No.4,515,663, the teachings ofwhich are incorporated herein by reference, can be used in amounts of 3 upto 30 g/l to inhibit insoluble polyborate compound formation during operation of the bath.

In accordance with the process aspect of the present invention, a zinc alloy electrolyte is employed to electrodeposit a desired zinc alloy on a conductive substrate employing electrolyte temperatures ranging from room temperature (60"F 16"C up to 180"F (82"C) and more typically, from 70"F (21 C) to 1400F (60"C). The electrodeposition ofthe zinc alloy can be carried out at current densities ranging from as low as 1(0.11 ASD) upto 2000ASF (220 ASD) or higher.For decorative chloride-type electrolytes, current densities of from 1 to 80 ASF (0.11 to 8.8 ASD) are generally preferred, whereas for functional sulphate-type or chloride-type electrolytes, current densities of from 20to 2000ASF (2.2to220ASD)can be employed. Duringthe electrodeposition process, the bath or electrolyte is preferably agitated mechanically or by solution circulation or part movement. While air agitation can be employed, the use of air agitation with electrolytes containing iron ions is less desirable due to the tendencyto increase the formation offerric ions in the bath.

In order to further illustrate the electrolyte composition and process ofthe present invention, the following examples are provided. Itwill be understood that the examples are provided for illustrative purposes and are not intended to be limiting the scope ofthe present invention as herein described and assetforth in thesubjoined claims.

Example 7 (A Comparison Example) For comparative purposes, an aqueous acidic sulphate-type zinc-iron alloy electrolyte was prepared for functional electrodeposits containing 110 g/l zinc sulfate monohydrate and 370 g/l ferrous sulfate heptahydrate. The pH of the electrolyte was about 2.

The electrolyte was employed for electrodepositing a zinc-iron deposit on a steel rod cathode rotating at a speed of 3,055 rpm to provide a surface velocity of about 200 feet per minutes (60m/mm). The electrolyte was controlled at a temperature of 50"C (1 22"F) and soluble zinc anodes were employed. The electrodeposition was carried out at an average cathode current density of about 500 ASF (55 ASD). The resultant zinc-iron alloy deposit was observed to be of a grey and grainy appearance which upon analysis contained 13.8 % by weight iron.

Example2 To the electrolyte as described in Example 1,0.01 g/l of an additive agent comprising ethoxylated sorbitol of an average molecular weight of 1400 was added. A rotating steel cathode was again plated underthe same conditions as described in Example 1. The resultant zinc-iron alloy deposit was of a silvery-blue and semi-bright appearance which upon analysis was found to contain 13.2 % by weight iron.

Example 3 To the electrolyte as described in Example 1,0.05 g/l of an additive agent was added comprising propoxylated sorbitol of an average molecular weight of 500. A rotating steel cathode was again electroplated underthe same conditions as described in Example 1. The resultant zinc-iron alloy deposit was of a blue-greyand semi-bright appearance which upon analysis was found to contain 18.6% byweightiron.

Example 4 To the electrolyte as described in Example 1,0.01 g/l of an additive agent was added comprising ethoxylated methyl glucose (ethoxylated with 10 moles of ethylene oxide). A rotating steel cathode was electroplated underthe same conditions as described in Example 1. The resultant zinc-i ron alloy deposit was of a satiny-grey and semi-bright appearance which upon analysis was found to contain 15.5%byweightiron.

Example 5 To the electrolyte as described in Example 1,0.01 g/l of an additive agent was added comprising a propoxylated methyl glucose (propoxylated with 10 moles of propylene oxide). A rotating steel cathode was electroplated under the same conditions as described in Example 1. The resultant zinc-iron alloy deposit was of a satiny-grey appearance and upon analysis contained 17.1 % by weight iron.

Example (Comparative Example) For comparative purposes, an aqueous acid zinc-nickel alloy electrolyte of the sulphate-type was prepared for functional plating. The electrolyte contained 310 g/l nickel sulphate hexahydrate, 205 g/l zinc-sulphate monohydrate and 36 g/l sulphuric acid. The electrolyte was adjusted to a temperature ranging from 600to 650C (1400to 1500F) and a rotating steel cathode was plated atan average cathode current density of 1,000 ASF (110 ASD) employing insoluble lead anodes. Solution agitation was provided by rotating the cathode. The cathode was rotated art a speed of 4,600 rpm providing a surface velocity of 325 feet per minute (100m/mm).

The resultant deposit was of a light grey colour, grainy appearance and evidenced poor adhesion in response to being bentthrough an angularity of greaterthan 900 as viewed under a 14X magnification. The thickness of the zinc-nickel alloy deposit was approximately 0.25 to 0.3 mil (7.6 microns). Upon analysis, the alloy contained 13.5% by weight nickel.

Example 7 To the electrolyte as described in Example 6,0.04 g/l of an additive agent was added comprising an ethoxylated sorbitol of an average molecularweight of 475. A rotating steel cathode was electroplated under the same conditions as described in Example 6. The resu Itant zinc-nickel alloy was of a fine-grained, semi-brightappearance and was adherent as evidenced by being substantially crack-free when bent through an angularity greater than 90" and viewed under 1 4X magnification. Upon analysis, the alloy contained 7% by weight nickel.

Upon atmospheric corrosion testing, this type of electrodeposit exhibits a 15%-20% improvement in corrosion protection as compared to the electrodeposit of Example 6, even though the nickel content is lower.

Example 8 To the electrolyte as described in Example 6,0.015 g/l of an additive agent was added comprising ethoxylated and propoxylated sorbitol of an average molecular weight of 7,200. A rotating steel cathode was electroplated underthe same conditions as described in Example 6. The zinc-nickel alloy deposit was of a fine-grained, semi-bright appearance and was adherent as evidenced by a substantially crack-free deposit when bent through an angularity greater than 90" and viewed under 14X magnification. Upon analysis, the zinc-nickel alloy contained 9.6% by weight nickel.

Example 9 To the electrolyte as described in Example 6,0.02 g/l of an additive agent was added comprising an ethoxylated methyl glucose (ethoxylated with 10 moles of ethylene oxide). A rotating steel cathode was electroplated under the same conditions as described in Example 6. The resultant zinc-nickel alloy deposit was of a fine-grained appearance and was adherent as evidenced by being substantially crack-free when bent through an angularity of greater than 90" and viewed under 14X magnification. Upon analysis, the alloy contained 6.7% by weight nickel.

Example 10 (A Comparison Example) For comparative purposes, an alternative aqueous acidiczinc-nickel electrolyteofthesulphate-typewas prepared forfunctional plating. The electrolyte contained 110 g/l nickel sulphate hexahydrate, 260 gn zinc sulphate monohydrate and 36 gn sulphuric acid.

A rotating steel rod cathode was plated in the electrolyte at an average cathode current density of 1,000 ASF (110 ASD) with an electrolytetemperature controlled within a range of 500 to 55" C (120 -130 F).

Insoluble lead anodes were employed. Solution agitation was provided by rotating the steel rod cathode at a speed of 4,600 rpm to provide a surface velocity of 325 feet per minute (100m/mm). The rnsultantzinc-nickel alloy deposit was of a light gray appearance, grainy and cracked when bentthrough an angularity of more than 900 as viewed under 1 4X magnification. The electrodepositwas approximately 0.25 to 0.3 mils (6.4 to 7.6 microns) thick. Upon analysis, the nickel content was 6.7% by weight ofthethe alloy.

This example shows that a reduction ofthe nickel content in the electrolyte and in the resultant deposit in comparison to that employed in prior Example 7 to a magnitude as obtained in supplemental Examples 6 through 9, still did not produce a satisfactory zinc-nickel alloy electrodeposit in the absence of the additive agent.

Example 11 (A Comparison Example) For comparative purposes, an aqueous acidic sulphate-type zinc-cobalt alloy electrolyte adapted for functional electroplating was prepared containing 60 gil cobalt sulphate heptahydrate, 450 g/l zine sulphate monohydrate and 36 g/l sulphuric acid.

A rotating steel rod cathode was electroplated in the electrolyte at an average cathode current density of 1,000 ASF (110 ASD) with the electrolyte controlled at a temperature ranging from 400 to 45"C (104"-112" F) and employing insoluble lead anodes.

Agitation of the electrolyte was provided by rotating the cathode. The rotation of the cathode was at 4,600 rpm providing a surface velocity of 325 feet per mi nute (100m/mm). Upon inspection, the resultant zinc-cobalt alloy electrodepositwas of a light-grey, coarse-grained, dull appearance. Upon analysis, the cobalt content in the alloy deposit was 0.17% by weight.

Example 12 To the electrolyte as described in Example 11,4 g/l of an additive agent was added comprising ethoxylated, propoxylated sorbitol of an average molecular weight of 6475. A rotating steel cathode was electroplated underthe same conditions as described in Example 11 and the resultant zinc-cobalt alloy depositwas of a semi-bright, steel-grey appearance. Upon analysis, the alloy deposit contained 0.26% byweightcobalt.

Example 13 To the electrolyte as described in Example 11 ,an additive agent was added at a concentration of 0.5 g/l comprising a propoxylated methyl cellulose (propoxylated with 10 moles propylene oxide). A rotating steel cathode was electroplated underthe same conditions as described in Example 11 and the resultant zinc-cobalt alloy deposit was of a semi-bright and greycolourappearance. Upon analysis, the cobalt content was 0.29% by weight.

Example 14 To the electrolyte as described in Example 1110.2 g/l of an ethoxylated methyl glucose additive agent was added (ethyoxylated with 20 moles of ethylene oxide). A rotating steel cathode was electroplated underthe same conditions as described in Example 11 and the resultantzinc-cobaltalloy depositwas of a semi-bright grey appearance. Upon analysis, the alloy deposit contained 0.22% by weight cobalt.

Example 15(A Comparison Example) For comparative purposes, an aqueous acidic electrolyte ofthesulphate-type suitable for electrodepositing a zinc-iron-nickel-cobalt alloy was prepared containing 100 g/l zincsulphate monohydrate, 100 g/l ferrous sulphate heptahydrate, 50 gIl nickel sulphate hexahydrate and 50 g/l cobalt sulphate heptahydrate. The pH of the electrolyte was about 4.5.

A rotating steel cathode was electroplated employing the foregoing electrolyte atan average current density of 1,000 ASF (110 ASD) with the electrolyte controlled at a temperature between 50 to 55"C(122"-130" F) employing insoluble lead anodes. The cathode was rotated at a speed to provide a surface velocity of 300 feet per minute (91 m/mm). The electrodeposition continued until the deposit averaged about 6 micrometres (0.24 mils) in thickness. Upon inspection, the electrodepositwas of a satiny-grey appearance with dentrites. Upon analysis, the alloy composition contained 74.3% zinc, 14.3% iron, 6.4% cobalt and 5% by weight nickel.

Example 16 To the electrolyte as described in Example 15, 0.01 gil of an additive agent was added comprising ethoxylated sorbitol of an average molecular weight of 1,400. A rotating steel cathode was electroplated employing the same conditions as described in Example 15 and the resulting deposit evidenced an improvement in grain refinement and smoothness of the deposit. Upon analysis, the alloy electrodeposit contained 72.1% zinc, 15.6% iron, 7.6% cobalt and 4.7% by weight nickel.

Example 17 An aqueous acidic zinc-nickel alloy electrolyte of the chloride-type adapted for electrodepositing decorative zinc-nickel electrodepositswas prepared containing 90 g/l zinc-chloride, 115 gIl nickel chloride hexahydrate, 220 g/l ammonium chloride and 4 g/l of an additive agent comprising ethyoxylated glycerine (ethoxylated with 12 moles ethylene oxide). The electrolyte further contained as a secondary brightening agent 0.050 g/l benzylidene acetone. The electrolyte was of a pH of about 5.6.

A steel test panel was plated at an average cathode current density ranging from lotto 20 ASF (1.1 to 2.2 ASD) with the electrolyte controlled at a temperature of from 300 to 35" C (86"-95" F). The resultant zinc-nickel alloy deposit was fully bright, decorative and of uniform appearance. Upon analysis,the alloy deposit contained 11.6% by weight nickel.

Example 18 An aqueous acidic zinc-cobalt-nickel electrolyte was prepared suitable for electrodepositing a decorative alloy deposit ofthe chloride-type containing 90 g/l zinc chloride, 40 gIl cobalt chloride hexahydrate, 120 g/l nickel chloride hexahydrate, 200 g/l ammonium chloride, 3 g/l of an additive agent comprising ethoxylated glycerine (ethoxylated with 12 moles ethylene oxide) and 2 g/l of sodium benzoate.

The electrolyte was controlled at a pH of about 5 and a temperature of from 20 to 250 C (68"-76"F) was employed for electroplating a steel test panel at an average cathode current density ranging from 10 to 20 ASF (1.1 to 2.2 ASD). The resultant electrodeposit was of a uniform, silvery semi-bright appearance which was commercially acceptable. Upon analysis, the alloy deposit contained 12% by weight nickel, 6% by weight cobalt and the balance zinc.

Example 19 To the electrolyte as described in Example 18, a supplemental brightenermixturewas added comprising 0.06 gIl of 4-phenyl-3-buten-2-one, 0.02 g/l of butyl nicotinate dimethyl sulphate quaternary and 0.05 g/l of4-phenyl-4-sulphobutan-2-one, sodium salt.

Asteel test panel was electroplated employing zinc anodes in accordance with the procedure as set forth in Example 18. The resultant alloy deposit was very decorative and fully bright in appearance. Upon analysis, the alloy deposit contained 11.9% by weight nickel, 6.5% by weight cobalt with the balance comprising zinc.

Example 20 (A Comparison Example) For comparative purposes, an aqueous acidic zinc-cobalt electrolyte was prepared of the chloride-type suitable for electrodepositing a decorative zinc-cobalt deposit containing 46 g/l zinc chloride, 10.5 gIl cobalt chloride hexahydrate, 175 g/l sodium chloride, 20 g/l boric acid and 2 g/l sodium benzoate. The pH of the electrolyte was about 5.2.

Standard Hull cell panels were plated with the electrolyte at about75 F (24 C) at a current of 1 ampere for a period of 10 minutes in the absence of agitation. The resultant test panel was of a dull-black to grey-black grainy appearance. The average alloy content of the adherent electrodeposit in the current density range of 0-40 ASF (0-4.4ASD) was 5.03% by weight cobalt and the balance zinc.

Example2 1 To the electrolyte as described in Example 20,3 g/l of an additive agent was added comprising ethoxylated glycerine (ethoxylated with 12 moles of ethylene oxide). A Hull test panel was again plated under the same conditions as described in Example 20 and the resultant electrodepositwas of a uniform, silver-white, semi-bright appearance in the current density range offrom 2 to 60 ASF (0.22 to 6.6 ASD). The average alloy content was 1.03% by weight cobalt and the balance zinc. This amount of alloy content in the electrodeposit has been shown to increase corrosion resistance by 2 to 3 times over an ordinary zinc electrodeposit and is commercially acceptable.

Example 22 To the electrolyte as described in Example 20,4 g/l of an additive agent was added comprising ethoxylated glycerine (ethoxylated with 26 moles of ethylene oxide). A Hull test panel was again plated underthe same conditions as described in Example 20 and the resultant electrodepositwas of a uniform, silver-white, semi-bright appearance in the current density range between 2 to 60 ASF (0.22 to 6.6 ASD). The average alloy content was 1.59% by weight cobalt and the balance zinc.

Example 23 (A Comparative Example) For comparative purposes, an aqueous acidic electrolyte of the chloride-type was prepared suitable for electrodepositing a zinc-cobalt alloy containing 46 g/l zinc chloride,10.5 g/l cobalt chloride hexahydrate, 220 g/l potassium chloride, 20 g/l boric acid, and 3.5 g/l sodium benzoate. The pH ofthe electrolyte was controlled at about 5 and a temperature at 25"C (77" F).

Atest panel was plated in a standard Hull cell ata currentofl ampere for a period of 10 minutes employing a zinc anode in the absence of agitation.

The resultant electrodeposit was du l l-black to grey-black and of a grainy appearance. The average alloy composition was 1.2% by weight cobalt in the 0-20 ASF (0 to 2.2 ASD) current density range and about 5.7% by weight cobalt in the test panel area above 20ASF (2.2ASD) current density.

Example 24 To the electrolyte as described in Example 23,4 g/l of an additive agent was added comprising polyethyoxylated (15 moles) trimethylol propane.

A Hull cell test panel was again plated underthe same conditions as described in Example 23 and the electrodeposit was uniform and of a silver-white, semi-bright appearance across the entire surface of the test panel. The average alloy composition was 1.15% by weight cobalt in the 0-20 ASF (0-2.2 ASD) current density range and 6.82% by weight cobalt in the cathode current density range above 20 ASF (2.2ASD).

Example 25 To the electrolyte as described in Example 24, 0.06 gil was added of 4-phenyl-4-su lphobutan-2-one, sodium salt; 0.075 g/l benzylidene acetone and 0.003 g/l butyl nicotinate diethyl sulphate quaternary. A Hull test panel was again plated underthe same conditions as described in Example 23 and the electrodeposit was fully bright, uniform and of a decorative quality across the entire surface of the test panel. The cobalt alloy distribution was 1% by weight cobalt in the 0-20 ASF (0-2.2 ASD) current density range and 2.1% by weight cobalt in the cathode current density range above 20 ASF (2.2 ASD).

Claims

1. An aqueous acidic electrolyte suitablefor electrodepositing a zinc alloy on a conductive substrate comprising zinc ions and at least one additional metal ion selected from the group consisting of nickel, cobalt, iron and mixtures thereof, and an effective amount of an additive agent comprising a bath soluble polyhydroxy compound having three or more hydroxyl groups at least one of which is substituted with a polyoxyalkylene group.

2. An electrolyte as claimed in Claim 1 in which the zinc ions are present in an amount from 1 0 gel up to saturation.

3. An electrolyte as claimed in Claim 1 or 2 in which the zinc ions are present in an amount from 15 to 225 g/l.

4. An electrolyte as claimed in any one of Claims 1 to 3 in which the zinc ions are present in an amount from 20to 200 g/l.

5. An electrolyte as claimed in any one of Claims 1 to 4, in which the additional metal ion comprises nickel and/orcobalt present in an amount of 0.5to 120 girl.

6. An electrolyte as claimed in any one of Claims 1 to 5 in which ions are presentto provide a zinc alloy electrodeposit comprising from 0.1 %to 30% by weight of nickel and/or cobalt.

7. An electrolyte as claimed in any one of Claims 1 to 6 in which ions are presentto provide a zinc alloy electrodeposit comprising from 0.25%to 15% byweightofnickel and/or cobalt.

8. An electrolyte as claimed in Claim 7 in which the amount of nickel and/or cobalt ions is from 3 g/l to 65 g/l.

9. An electrolyte as claimed in any one ofthe Claims 1 to 4 in which the additional metal ion comprises iron ions present in an amount from Sto 140 g/l.

10. An electrolyte as claimed in any one of Claims 1 to 9 in which the additional metal ion comprises iron ions in an amount from 40to 100 g/l.

11. An electrolyte as claimed in any one of Claims 1 to 4 and 9to 10 in which the additional metal ion comprises iron ions and the electrolyte has a complexing or chelating agent present in an amountsufficientto maintain an effective amount of iron ions in solution,

12. An electrolyte as claimed in any one of Claims 1 to 4and 9to 11 in which the additional metal ion comprises iron ions and the electrolyte has a reducing agent present in an amount effective to reduce at least a portion of the ferric ions to the ferrous state.

13. An electrolyte as claimed in anyone of Claims 1 to 4 and 9to 12 in which the concentration of ferric ions is below 2 girl.

14. An electrolyte as claimed in Claim 1 in which the additional metal ion comprises iron ions and either nickel ions or cobalt ions in combination with zinc ions provide an alloy deposit containing 1 percent to 25 percent iron in combination with either 0.1 percent to 20 percent by weight nickel or 0.1 percentto 12percentcobalt.

15. An electrolyte as claimed in any one of Claims 1 to 14furthercontaining conductivity salts present in an amount sufficientto increase the eiectrica I conductivity of the electrolyte.

16. An electrolyte as claimed in any one of Claims 1 to 15 having pH of 0 to 7.

17. An electrolyte asciaimed in any one of Claims 1 to 16 having a pH of 2to 6.

18. An electrolyte as claimed in any one of Claims 1 to 17 in which the additive agent is present in an amount from 0.005 to 20 g/l.

19. An electrolyte as claimed in any one of Claims 1 to 18 in which the additive agent is present in an amount from 0.02 to 10 g/l.

20. An electrolyte as claimed in any one of Claims 1 to 19 which comprises substantially only one type of anion.

21. An electrolyte as claimed in Claim 20 in which the anion is a sulphate ion, the additional metal is iron or nickel and the additive agent is present in an amount from 0.005 to 0.1 g/l.

22. An electrolyte as claimed in Claim 20 in which the anion is a sulphate ion, the additional metal is cobalt and the additive agent is present in an amount of 0.05 to 5 g/l.

23. An electrolyte as claimed in Claim 20 in whichtheanion is a chloride ion, the additional metal is nickel, cobalt, iron or a mixture thereof and the additive agent is present in an amount from 0.1 to 10 g/l.

24. An electrolyte as claimed in any one of Claims 1 to 23 having a supplemental brightening agent present in an amount from 0.001 g/l to 10 g/l.

25. An electrolyte as claimed in any one of Claims 1 to 24 having a supplemental brightening agent present in an amount from 0.01 to 5 g/l.

26. An electrolyte as claimed in any one of Claims 1 to 25 having a bath soluble salt present in anamountfrom20to450g/l.

27. A process for electrodepositing a zinc alloy on a substrate comprising the steps of contacting a conductive substrate with an aqueous acidic electrolyte comprising zinc ions and at least one additional metal ion selected from the group consisting of nickel, cobalt, iron and mixtures thereof present in an amount sufficient to electrodeposit a zinc alloy, and an effective amount of an additive agent comprising a bath soluble polyhydroxy compound having three or more hydroxyl groups at least one of which is substituted with a polyoxyalkylene group and continuing the electrodeposition of the zinc alloy until the desired thickness is obtained.

28. A process as claimed in Claim 27 wherein the temperature ofthe electrolyte is from 600 to 180"F(16"to 82"C).

29. A process as claimed in Claim 27 or 28 wherein the temperature of the electrolyte is from 70" to 140 F (210to 6O0C).

30. A process as claimed in any one of Clai ms 27 to 30 in which the step of electrodepositing the zinc alloy is performed at an average cathode current density of 1 to 2000 ASF (0.11 to 22OASD).

31. A process as claimed in Claim 27 wherein the concentration of the zinc ions apd either one of the nickel and/or cobalt ions provide a zinc alloy electrodepositcontaining from 0.1 to 30% by weight nickel and/or cobalt.

32. A process as claimed in Claim 27 wherein the concentration of the zinc ions, iron ions, and either one of the cobalt ions and/or nickel ions are provided to electrodeposit a zinc alloy containing from 1 to 25% by weight iron, from 0.1 to 20% nickel and/or0.1 to 12% cobalt.

33. A process as claimed in any one of Clai ms 27 to 32 wherein the concentration of additive agent is within a range of from 0.005 to 20 g/l.

34. A process as claimed in any one of Claims 27 to 33 wherein concentration of additive agent within a rangeofabout0.O2toaboutl0g/l.

35. A process as claimed in anyone of Claims 27 to 30 in which the electrolyte is as claimed in any one ofthe claims 1 to 26.

36. A process substantially as herein described with reference to the accompanying examples but notthe comparative examples.

37. An electrolyte substantially as herein described with reference to the examples but not the comparative examples.