EP1664389A1

EP1664389A1 - Electrolyte for the galvanic deposition of aluminum-magnesium alloys

Info

Publication number: EP1664389A1
Application number: EP04787118A
Authority: EP
Inventors: Richard Heller; Hans De Vries
Original assignee: Aluminal Oberflachentechnik GmbH
Current assignee: Aluminal Oberflachentechnik GmbH
Priority date: 2003-09-27
Filing date: 2004-09-09
Publication date: 2006-06-07
Also published as: RU2006116263A; KR20060090816A; CN1860257A; JP2007506862A; WO2005033374A1; US20070108061A1; EP1518945A1; RU2347857C2

Abstract

The invention relates to an electrolyte for the galvanic deposition of aluminum-magnesium alloys, which comprises at least one aluminum-organic complex compound of the formula MAIR4 or mixtures thereof and a magnesium alkyl compound, wherein M represents Na, K, Rb or Cs and R represents a C1 to C10 alkyl group, preferably a C1 to C4 alky group. The invention also relates to a method for producing an electrolyte, to a coating method, the use of the electrolyte and to an electrolysis kit.

Description

ELECTROLYTE FOR THE GALVANIC DEPOSITION OF ALUMINUM-MAGNESIUM ALLOYS

The invention relates to an electrolyte for the electrodeposition of aluminum-magnesium alloys containing at least one organoaluminum complex compound and a magnesium alkyl compound. 5 Further objects of the invention are a method for producing the electrolyte, a coating method, the use of the electrolyte and an electrolysis kit.

Magnesium-aluminum-organic complex compounds have recently been used for the electrolytic deposition of aluminum-magnesium alloys. This is described in WO 00/32847 A1. Interest in the electrolytic coating of metal workpieces with aluminum-magnesium alloys has increased significantly due to the excellent corrosion protection provided by the aluminum-magnesium layers and their ecological harmlessness. For this reason, electroplating with magnesium-15 aluminum-organic electrolytes, which takes place in closed systems at temperatures in the range of 60 - 150 ° C, has gained great technical importance.

In WO 00/32847 A1 complex compounds of the general type MAIR ₄ and mixtures thereof in combination with aluminum alkylene AIR _{3 have been} proposed as particularly suitable eleldrolytes. These are used in the form of their solutions in liquid, aromatic hydrocarbons. M can be an alkali metal such as sodium, potassium, rubidium and cesium, R are alkyl radicals with preferably one, two or four carbon atoms.

However, the use of these electrolyte systems has decisive disadvantages. The systems known hitherto are characterized in that the required magnesium-organic complex compounds are initially not available in the electrolyte and only have to be generated in a trochemically complex manner when the electrolyte is used in situ. So ready-to-use start only organic aluminum compounds but no magnesium compounds. Typical compositions of such starting mixtures contain, for example, molar ratios of 1: 0.1 to 0.1: 1 M ¹ AIR4 TO M ² AIR ₄ , where M ^{1 is} not equal to M ² with Na, K, Rb, Cs, in particular Na, K. , The molar ratios of all components are AIR ₃ to (M ¹ AIR ₄ + M ² AIR ₄ ): aromatic hydrocarbon = 1: 0.1: 1 to 1: 2: 10, in particular 1: 1: 3 to 1: 1 : 5th

[0005] In the case of these electrolytes, the above-mentioned magnesium-free starting electrolyte is first filled into the electrolysis cells suitable for coating. The required organic magnesium complex is then generated electrochemically by applying a current using separate aluminum and magnesium anodes or an aluminum-magnesium mixed electrode until the concentration of magnesium complex in the electrolyte required for coating is reached.

In addition, a deposition of aluminum-magnesium layers in the system already occurs up to this point in time, that is to say when the necessary concentration of magnesium complex is reached, which is undesirable since it has incorrect compositions of Al and Mg. It is therefore necessary to attach dummy sheets in the system to catch the deposited aluminum-magnesium layers. These deposits are made on dummy sheets until the required concentration of aluminum-magnesium complexes is reached. The dummy sheets are then removed and the desired layers with the desired aluminum-magnesium composition, such as, for example, Al: Mg = 75: 25 mol%, are deposited on the substrate. The dummy sheets must either be discarded or laboriously cleaned for further use.

From the description given above, it is readily apparent that this method is very complex and requires a long lead time until the corresponding desired aluminum-magnesium concentrations are obtained. Furthermore, assembly, disassembly occurs as an additional step and cleaning of the dummy sheets used. The electrolyte solutions identified as particularly effective in WO 00/32847 A1 can therefore only be used via the above-described electrochemical production of organomagnesium complexes in a conditioning phase preceding the actual coating, with all the disadvantages mentioned above.

It is also known from the prior art of WO 00/32847 A1 to add a corresponding magnesium compound directly to the electrolyte in order to be able to omit the conditioning phase specified above. Here, a magnesium-aluminum alkyl Komptex Mg [Al (Et) ₄ ] _{2 is used} in the electrolyte. The disadvantage of this method is that although it can be carried out on a laboratory scale, it cannot be carried out on an industrial scale, because this complex is not technically available and is only very complex and expensive to produce.

A corresponding electrolyte for an industrial process for

Coating of substrates with Al-Mg alloys that can be carried out economically and effectively is not yet known. The further development of electrolytes for the galvanic deposition of aluminum-magnesium alloys is of great technical importance and of great economic and ecological interest.

[0010] The technical object of the invention is therefore to provide an electrolyte which can be produced as simply, efficiently and inexpensively as possible, which enables the aluminum-magnesium coating process to be introduced commercially and the conditioning phase mentioned above for formation of organic Mg complexes no longer necessary.

This technical problem is solved by an electrolyte for the electrodeposition of aluminum-magnesium alloys containing at least one aluminum-organic complex compound of the formula MAIR4 or mixtures thereof and a magnesium alkyl compound, where M is sodium, potassium, rubidium or cesium and R is a C1-C1 ₀ alkyl group, preferably a C 1 -C ₄ -alkyl group. In a particularly preferred embodiment, the electrolyte additionally contains an aluminum trialkyl compound.

[0012] It is particularly preferred to use an electrolyte which

AIR ₃ , M ¹ AIR ₄ , M ² AIR ₄ and Mg (R ¹ ) _x (R ² ) _y , where M ¹ and M ^{2 are} unequal and mean Na, K, Rb or Cs, R is a Ci to C10 alkyl group , preferably d to C ₄ denotes alkyl group, R ¹ and R ² independently denote ad to C2 ₀ , preferably a C ₂ to C1 ₀ alkyl group and x = 0 to 2 and y = 0 to 2 and x + y = 2 is.

[0013] It has surprisingly been found that the electrolyte according to the invention can be used for coating materials with aluminum-magnesium alloys without the in-situ generation of magnesium-organic complexes in a time-consuming and cost-intensive conditioning phase before actual coating process is necessary.

[0014] The magnesium alkyl compound is preferably in one

Amount of 0.01 to 10 mol%, preferably 0.1 to 1 mol% based on the aluminum complex contained in the electrolyte. Particularly preferred magnesium alkyl compounds which are used in the electrolyte are selected from the group MgButyl1, 5Octyl0.5, MgButyl1.0Ethyl1, 0, Mgsec-Bu1, 0nButyl1, O or mixtures thereof.

[0015] The aluminum-organic complex compound and the magnesium

Alkyl compounds can preferably be present in an organic solvent. The organic solvent is particularly preferably an aromatic solvent, and solvents such as benzene, toluene or xylene or mixtures thereof can be used here. The magnesium alkyl compounds mentioned have the advantage that they are industrially accessible and can be produced easily and inexpensively compared to the magnesium aluminum-ethyl complexes mentioned above Mg [Al (Et)) ₄ ] 2 Electrolytes are made according to the following steps. First, the aluminum-organic complex compound of the formula MAIR4 or a mixture thereof, if appropriate in combination with aluminum trialkyl, is initially introduced. A magnesium alkyl compound is then added as described above. M and R have the same meaning as described above. The metering of the magnesium-alkyl compounds in the manufacture of the electrolyte has the advantage that the necessary concentration of magnesium and aluminum can be set directly, so that the conditioning process described above can be completely dispensed with. It is also possible to add magnesium-alkyl compounds during the coating process in order to maintain the corresponding magnesium concentration which is desired and necessary for the coating.

[0017] In a particularly preferred embodiment, the magnesium

Alkyl compound a mixed magnesium alkyl compound of formula Mg (R ¹⁾ _x, _y (R ²⁾ wherein R ¹ and R ^{2 are} independently a C ^, preferably a C ₂ -C 1 ₀ alkyl group and x = 0 to Is 2 and y = 0 to 2 and x + y = 2. In a particularly preferred embodiment, the magnesium-alkyl compounds are added in solution in a hydrocarbon and the aluminum-alkyl complexes are initially introduced in solution in an aromatic hydrocarbon. The hydrocarbon for the aluminum compound is selected from the group i-pentane, n-pentane, hexane, n-hexane, heptane, n-heptane, toluene and xylene.

With the electrolyte according to the invention it is possible in one

Production process Aluminum-magnesium layers of different concentration sequences of aluminum and magnesium by simply and freely choosing the amount of added magnesium-organic compounds. The corresponding concentration of aluminum-magnesium is determined by the amount added set of magnesium-organic compounds. The electrolyte according to the invention also has the advantage of good conductivity and scatterability.

The electrolyte according to the invention makes it possible to work with indifferent anodes which are used in the coating of geometrically complex shaped parts. Indifferent electrodes are those that do not dissolve during the coating process, i.e. do not consist of Al or Mg or their alloys. When coating with indifferent electrodes, Mg-organic compounds and Al-organic compounds must therefore be added to the electrolyte solution. The corresponding concentration of aluminum-magnesium is set via the amount of magnesium-organic compounds and aluminum-organic compounds added. Working with indifferent anodes was previously ruled out for the in-situ generation of organic magnesium complexes, as was the generation of layers of different aluminum-magnesium compositions in one operation. This is also not possible using the in-situ method described above with a conditioning step to produce the magnesium concentration in the electrolyte.

Another object of the invention is an electrolysis kit for the electrodeposition of aluminum-magnesium alloys on electrically conductive materials or electrically conductive layers, comprising: a) the aluminum-organic complex compounds described above, or aluminum-alkyl compounds of claims 1-3 and 1, 3, 5, 6 and b) a magnesium alkyl compound according to claims 1, 3, 5, 6.

In a preferred embodiment, the compounds a) and b) are dissolved in an organic solvent. Another object of the invention is a method for coating electrically conductive materials or layers with aluminum-magnesium alloys with the electrolyte according to claims 1-9, wherein during the coating phase, the magnesium-alkyl compound according to claims 1, 3, 5 and 6 is metered in in the desired amount in order to obtain or maintain a desired concentration of magnesium to aluminum

Another object of the invention is the use of the electrolyte according to the invention for the production of layers of aluminum alloys on electrically conductive materials or electrically conductive layers.

[0024] The following examples are intended to explain the invention in more detail:

example 1

Use of MgButylι, ₅ octyl ₀ , 5, 20% in heptane (product BOMAG ^® from Crompton)

The entire reaction was carried out under protective gas

argon

Step 1: The BOMAG ^® / heptane solution was adjusted to a content of 0.32 mmol / g after the heptane had been condensed with toluene.

2nd step: 55.4 g of an electrolyte of the following composition: 0.8 K [Al (Et) ₄ ] + 0.2 Na [Al (Et) ₄ ] + 1.17 Al (Et) ₃ + 3.85 g of BOMAG / toluene solution were added to 3.85 toluene (approx. 1.0 mol% based on the electrolyte formulation). About 58 g of an electrolyte were obtained.

coating test

General conditions:

[0030] All deposition experiments were carried out under standard conditions. The magnesium component was pipetted directly into the electrolyte.

Anode material: 2 alloy electrodes AIMg25, 55 x 10 x 5mm

Cathode hexagon screw 8.8, M8 x 25

Cathode pretreatment: degreasing, descaling in an ultrasonic bath with 8% HCI, H ₂ O washing, vacuum drying, argon storage.

Immersion depth cathode: complete

Cathode rotation: 60rpm

Distance to the anode: 10mm Effective cathode area: approx.10cm ²

Bath movement: 2cm magnet in a glass jacket, 250rpm

Bath temperature: 94 - 98 ° C

[0031] The deposition was started with a current density of 0.05A / dm ² b. After a few minutes, a light covering can be seen on the parts to be coated. The current density was gradually increased to 3.0 Vdm ² . The deposition was terminated after a current of 1.499mF corresponding to a layer thickness of 5μ. The layer is light and silvery.

RF analysis of the layer: 26.79 wt% Mg, 73.21 wt% AI Example 2

Use of MgEthy o Buty .o, 20% in heptane (BEM, AkzoNobel)

The reaction took place under protective gas argon.

Step 1: The BEM / heptane solution was after the condensation of

Heptane adjusted to a content of 0.41 mmol / g using toluene.

2nd step: 60.6 g of an electrolyte of the following composition: 0.8 K [Al (Et) ₄ ] + 0.2 Na [Al (Et) ₄ ] + 1.17 Al (Et) ₃ + 3.85 toluene were mixed with 2.0 ml BEM / toluene solution (about 0.9 mol% based on the electrolyte formulation). About 62 g of an electrolyte were obtained.

Coating Test:

The deposition conditions are as in Example 1. The deposition was started directly with a current density of 2.0 A / dm ² and was not changed during the entire electrolysis. There was an immediate bright separation of Al / Mg. The deposition was ended after a current of 3.38 mF corresponding to a layer thickness of 11 μ. An excellent, very uniform, silvery layer is obtained, without any visible defects.

RF analysis of the layer: 26.78% Mg, 73.22 wt. AI

Example 3

Use of MgEthylι, ₀ buty .o, 20% in iso-pentane (BEM from Albemarle)

The reaction was carried out under argon as a protective gas. Step 1: The BEM / isopentane solution is containing

1.85 mmol / g Mg component used without further pretreatment.

2nd step: 70.04 g of an electrolyte of the following composition 0.85 K [Al (Et) ₄ ] + 0.15 Na [Al (Et)] + 1.08 Al (Et) ₃ + 3, 15 toluene were mixed with 0.5 g BEM / isopentane solution (approx. 0.8 mol% based on the electrolyte formulation).

coating test

The deposition conditions are as described in Example 1.

The deposition took place at a current density of 1.0 to 3.0 A / dm ² . The deposition was terminated after a current of 6.8 mF corresponding to a layer thickness of 20 μ. A very uniform, silvery layer is obtained.

RF analysis of the layer: 41, 4% Mg, 58.9%. AI

Comparative Example I

Use of electrolytes from Albemarle for Al-Mg deposition, but without the direct addition of Mg-alkyl solution (conditioning electrolyte).

65.0 g of an electrolyte with the following composition were used: 0.8 K [Al (Et) ₄ ] + 0.2 Na [Al (Et) ₄ ] + 1.17AI (Et) ₃ + 3, 85 toluene were used for Al-Mg deposition with preparatory conditioning under the general conditions as described above, but without the prior addition of Mg-alkyl solution, so that, as was necessary in the prior art, the Mg complex compound in in a conditioning phase must first be generated electrochemically before the electrolyte is ready for the deposition of Al-Mg alloys. 1. Conditioning step: starting with a starting current density of

0.05 A / dm2 was electrolyzed with increasing current density up to the maximum possible value of 1.0 A / dm ² . After a current of 7.20 mF there is a matt, gray coating with poor spreading power.

2. Conditioning step: After replacing the cathode was at

1.0 to 1.2 A / dm ² further conditioned. After a current of 7.24 mF, with a little improved spreading power, a clearly brightened, sometimes slightly shiny layer is obtained.

3. Conditioning step: Again after renewal of the cathode was now obtained with a significant increase in the permissible maximum current density of 1.23 over 1.5 to 2.0 A / dm ² a uniform, shiny coating with significantly improved scatter. The amount of current used was 4.96 mF.

4. Conditioning step: When the final condition is reached, a glossy coating is obtained using a current density of 3.0 A / dm ² with unchanged scattering ability compared to step 3. The amount of current is 3.73 mF.

The electrolyte is conditioned and ready for use only after this process.

Claims

claims

1. Electrolyte for the electrodeposition of aluminum-magnesium alloys containing at least one organoaluminum complex compound of the formula MAIR_t or mixtures thereof and a magnesium alkyl compound, where M is Na, K, Rb or Cs and R is a Ci to C1 ₀ alkyl group, preferably Ci to C ₄ means alkyl group.

2. Electrolyte according to claim 2, characterized in that it additionally contains aluminum trialkyl.

3. Electrolyte according to claim 1 or 2, characterized in that it contains AIR ₃ , M ¹ AIR4, M ² AIR and Mg (R ¹ ) _x (R) _y , where M ¹ and M ^{2 are} not the same and Na, K, Rb or Cs, R is a Ci to C10 alkyl group, preferably Ci to C ₄ alkyl group, R ¹ and R ² independently of one another are a Ci to C _20> preferably a C ₂ to C10 alkyl group and x = 0 to 2 and y = 0 to 2 and x + y = 2.

4. Electrolyte according to one or more of claims 1 to 3, characterized in that the magnesium alkyl compound is contained in an amount of 0.01 to 10 mol%, preferably 0.1 to 1 mol%, based on the aluminum complex.

5. Electrolyte according to one or more of claims 1 to 4, characterized in that the magnesium alkyl compound is selected from the group MgButyli.sOctylo.s, MgButylι, oEthylι _ι0 , Mgsec-Buι, on-Butylι, ₀ or mixtures thereof.

6. Electrolyte according to one or more of claims 1 to 5, characterized in that it contains an organic solvent.

7. Electrolyte according to claim 6, characterized in that the organic solvent is an aromatic solvent.

8. Electrolyte according to claim 7, characterized in that the aromatic solvent is benzene, toluene or xylene or a mixture thereof.

9. A method for producing the electrolyte according to claims 1 to 8, characterized by the following steps:

5 - presentation of an organoaluminum complex compound of the formula MAIR ₄ or a mixture thereof, if appropriate in combination with aluminum trialky,

- Addition of a magnesium alkyl compound, where M is Na, K, Rb or Cs and R is a Ci to C1 ₀ alkyl group, preferably Ci to C ₄ alkyl group.

10. The method according to claim 9, characterized in that the organoaluminum complex compound is a mixture of M ¹ AIR ₄ and M ² AIR ₄ , wherein M ¹ and M ^{2 are} not the same, mean Na, K, Rb or Cs and R is a Ci to C1 ₀ alkyl group, preferably a Ci to C ₄ alkyl group.

15. The method according to claim 9, characterized in that the magnesium alkyl compound is Mg (R ¹ ) _x (R ² ) _y , where R and R ² independently of one another are a Ci to C ^, preferably a C ₂ to C1 ₀ alkyl group and x = 0 to 2 and y = 0 to 2 and x + y = 2.

12. The method according to one or more of claims 9 to 11, characterized in that the magnesium alkyl compound is added dissolved in a hydrocarbon.

13. The method according to one or more of claims 9 to 11, characterized in that the aluminum alkyl complex is dissolved in aromatic hydrocarbon.

14. The method according to claim 12, characterized in that the hydrocarbon is a saturated or unsaturated hydrocarbon.

15. The method according to claim 14, characterized in that the hydrocarbon is selected from the group i-pentane, n-pentane, hexane, n-hexane, heptane, n-heptane, toluene, xylene.

16. Electrolyte for the production of layers of aluminum-magnesium alloys on electrically conductive materials or electrically conductive layers can be produced by the method according to claims 9 to 15.

17. A method for coating electrically conductive materials or layers with aluminum-magnesium alloys with the electrolyte according to claims 1 to 8, wherein the magnesium alkyl compound is metered in during the coating.

18. Use of the electrolyte according to claims 1 to 8 and 16 for the production of layers of aluminum-magnesium alloys on electrically conductive materials or layers.

19. Electrolysis kit for the galvanic deposition of aluminum-magnesium alloys on electrically conductive materials or layers containing

(a) the organoaluminum complex compounds or aluminum alkyl compounds of claims 1 to 3

(b) a magnesium alkyl compound according to claims 1,3,5.

20. Electrolysis kit according to claim 19, characterized in that the compounds (a) and (b) are present in an organic solvent.