DE102007048043A1 - Galvanic deposition of metal layers on magnesium or magnesium alloy surfaces - Google Patents

Abstract

The present invention relates to a process for the galvanic coating of magnesium or magnesium alloy surfaces. For the deposition of different metal layers of magnesium or magnesium alloy surfaces, it is proposed with the method according to the invention to bring the surfaces to be coated into contact with process solutions and rinsing solutions until the deposition of a first metal layer on the surfaces, which have a pH> = pH 7 , It has been found that, while avoiding the contacting of the surfaces to be coated with process solutions having a pH <= 7, metal layers can be firmly adhered to a large number of magnesium or magnesium alloy surfaces with a good deposition result.

Description

The The present invention relates to a process for electrodeposition of metal layers on magnesium or magnesium alloy surfaces.

magnesium has been intensified in recent years and decades Range of the automotive industry, commercial aircraft construction and used in the electronics industry. Especially in the production high quality products are magnesium or magnesium alloys used to save weight. Here are magnesium or magnesium alloys over other light metals the advantage over to have excellent casting properties, so that both injection and diecasting from corresponding magnesium alloys or magnesium with a lot good strength properties can be produced. In particular, the production of components by means of magnesium injection molding seems in the future also of greater interest in particular to be in the automotive industry. In injection molding of magnesium or magnesium alloys, these are not until the warmed up completely, but only heated to about 100 ° below the melting point. This is then reaches a thixotropic state of magnesium, in which it can be injection-molded accordingly.

For decorative and functional applications, however, need the Substrates produced by appropriate casting usually surface-treated. This on the one hand the corrosion protection of the magnesium or magnesium alloy surface serve, on the other hand can be correspondingly shiny or matt decorative surfaces by means of deposition of metal layers be generated on the surface.

in the Range of galvanic and electroless plating processes currently on the market in addition to classic galvanic coating processes such as the deposition of copper, nickel, chromium, tin and the like Anodizing, plasma or conversion coatings such as For example, offered the chromating.

For the application in decorative surfaces are suitable for Time only galvanic coating process. The aforementioned Anodizing and conversion coatings are for convenience only as corrosion protection and basis for a subsequent Coating, for example by painting.

Galvanic processes for coating magnesium or magnesium alloys have been known for years. For example, in Modern Electroplating by FA Lowenheim, Wiley & Sons, London, 1974 Process for galvanic or electroless plating of magnesium and magnesium alloys presented.

One fundamental problem with the coating of magnesium or magnesium alloys is located on the substrate surface forming oxide film, which in the prior art by corresponding Pretreatments must be removed.

So are for example from the cited prior art for removal the oxide layer pretreatments (activations) by means of an ammonium chloride-containing Phosphoric acid solution known. In other procedures become the magnesium or magnesium alloy surfaces to be coated activated with hydrochloric acid.

In Of the industry are commonly used magnesium alloys those of type AZ31 to AZ91, AZ being for the alloyed ones Aluminum and zinc stands and the trailing number indicates how high is the proportion of this alloy on magnesium.

all Commonly known from the prior art method is that they in each case only for certain magnesium alloys sufficient Show coating results. In addition, many are To observe pore formation in the galvanization of magnesium, which leads to Schichtabplatzungen the applied metal layers being able to lead.

It is therefore the object of the present invention, a method for the galvanic coating of magnesium or magnesium alloys, which for a variety of different magnesium alloys leads to a sufficient coating result and avoids the pore formation known from the prior art.

Solved This task is achieved by a process for galvanic coating of magnesium or magnesium alloy surfaces which characterized in that the surfaces to be coated throughout the coating process until complete Covering with a metal layer of the metal to be deposited exclusively with process solutions and rinsing solutions be brought into contact, which has a pH ≥ pH 7, preferably ≥ pH 8.

Surprisingly, it has been found that avoiding acidic process steps leads to significantly improved deposition results. Thus, waiving acidic process steps can be a variety of different Magnesiumlegie electroplated without the formation of pores, blistering or detachment.

By the avoidance of acidic treatment solutions is prevented that magnesium from the surface of the to be coated Substrates is dissolved out. This reduces also the need for levelers, as he for example in the galvanic Coating in particular of high-alloyed magnesium alloys such as AZ91.

Especially well, the procedure works on the magnesium alloy AU-LITE. Here, the leveling can be almost completely omitted become.

• – Reinigen des zu beschichtenden Substrats aus Magnesium oder einer Magnesiumlegierung;
• – Beizen des zu beschichtenden Substrats mit einer Zinkatbeize;
• – Aufbringen einer ersten Metallschicht auf das Substrat.

In one embodiment of the method according to the invention, this is subdivided into three method steps. These process steps are:

• - Cleaning the substrate to be coated of magnesium or a magnesium alloy;
• - pickling of the substrate to be coated with a Zinkatbeize;
• - Applying a first metal layer on the substrate.

The Cleaning of the substrate to be coated can be done by means of a hot degreasing respectively. Here, the substrate to be cleaned at a temperature from about 70-80 ° C for 10 minutes with a suitable Treated degreaser solution. Here is in particular the Combination of different degreaser provided, with the selection the degreaser to be used depending on the existing substrates or substrate surfaces to be coated Pollution takes place. Basically it is in the degreaser to be used but alkaline degreasers.

Around a sufficient removal of the adhering dirt from To reach the substrate surfaces, according to the invention of Use of a Kavitec modulus or eductor nozzles provided be. Kavitec systems are high-pressure water nozzles, which support the cleaning by cavitation effects.

to Removal of coarse dirt particles from the degreaser or Degreaser solutions may involve the use of appropriate filtration systems be provided according to the invention.

Subsequent to the above-described cleaning of the substrate surface, after an optional rinsing step in the embodiment of the method according to the invention described here, a treatment of the substrate surface with an alkaline, cyanide-free adhesive dressing takes place. In one embodiment of the invention, such a Haftbeize is a Zinkatbeize, which in addition to sodium pyrophosphate (Na ₄ P ₂ O ₇ × 10H ₂ O), zinc sulfate, sodium carbonate and sodium chloride suitable wetting agents for reducing the surface tension of Zinkatbeize. The described zincate pickling to be used according to the invention has a pH value determined photometrically at 30 ° C. in the range between pH 10 and 11, preferably in the range between pH 10 and 10.5.

The substrate surface to be treated to be coated Magnesium or magnesium alloy substrate will stain with the zincate at a temperature between 60 and 80 ° C, preferably between 65 and 75 ° C contacted. The exposure time is in this case between 5 and 15 minutes, preferably between 9 and 11 minutes.

One Example of an invention to be used Zinkatbeize is given below:

zincate:

• 100-300 g / l sodium pyrophosphate × 10H ₂ O
• 25-75 g / l zinc sulfate × 7H ₂ O
• 3-6 g / l sodium carbonate
• 2-5 g / l sodium chloride
• 0.5-3 g / l wetting agent

In The zincate stain described above can be advantageously used as Wetting agent a known as Nonpitter 62 A wetting agent or a wetting agent known as EnPREP TTM WA. About that In addition, combinations of different wetting agents be used.

It it has been found that particularly good separation results are obtained when the surface tension of the inventively used Zinkatbeize ≤ 55 mN / m is. Here, the specified Surface tension as dynamic surface tension determined by means of a bubble pressure tensiometer. As blister life this determination is based on ≤ 500 ms placed. A suitable measuring instrument for the determination the dynamic surface tension is the scienceline T60 from Sita-Messtechnik GmbH.

By the treatment with a corresponding Zinkatbeize forms on the magnesium or magnesium alloy surface to be coated an adhesion-promoting zincate layer.

Subsequent to the above-described treatment of the surface with a zincate stain acting as an adhesive stain, a first metal layer is then deposited on the substrate surface to be coated in the process of the invention described here by way of example, with the optional interposition of a rinsing step. Here, different galvanic starting divorced metal layers such as copper, nickel or chromium layers may be provided. The deposition of a copper layer on the magnesium or magnesium alloy substrate pretreated in the manner described above will be described below by way of example.

The substrate surface of the magnesium or magnesium alloy substrate to be coated with a zincate layer in the manner described above is contacted with a cyanide bright copper electrolyte, for example, a CUPRALYTE 1545 electrolyte from Enthone Inc. at a temperature between 40 and 55 ° C. For the deposition of the copper layer, a current density between 0.5 and 2.0 A / dm ^{2 is} set. Here, according to the invention, when using plate or billet anodes, a lower current density is to be provided than when using copper pieces in corresponding anode baskets.

The voltage to be applied depends on the used one Anodes and the substrates or substrate surfaces to be coated in a range between 2.0 and 12.0 volts. The one described in the here Embodiment of the method according to the invention used cyanidic copper electrolyte has a photometric certain pH in the range between pH 11.0 and pH 12.0.

The concentration of copper in the copper electrolyte to be used according to the invention is between 20 g / l and 50 g / l. The concentration of free potassium cyanide in the cyanide copper electrolyte to be used here is between 20 g / l and 35 g / l. In addition, the electrolyte has a maximum potassium carbonate of 120 g / l. The density of an electrolyte as described above is about 1.15 g / cm ³ .

to Regeneration of the copper electrolyte used can according to the invention with Copper (I) cyanide can be added to from the electrolyte consumption to replace the copper. This is about 1.4 g / l copper (I) cyanide needed per 1 g / l to supplemental copper content. To adjust the content of free potassium cyanide can in the used here, a metered addition of potassium cyanide in the order of about 2 g per g supplemented Copper be provided.

From a copper electrolyte as described above, copper layers can be deposited at a deposition rate of the order of about 0.4 μm / min at a set current density of 1 A / dm ² in the substrate surfaces of the magnesium or magnesium alloy substrates pretreated as described above.

The deposited copper layers are adherent and show a uniform Shine.

On the thus deposited copper layers can according to the invention further Metal layers are applied, with the subsequent Deposition of metal layers in both acidic and basic Coating electrolyte can be carried out, insofar as the underlying Magnesium or magnesium alloy layer completely with a corresponding copper layer is covered.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Modern Electroplating by FA Lowenheim, Wiley & Sons, London, 1974 [0006]

Claims (4)

Process for the galvanic coating of magnesium or magnesium alloy surfaces with a metal layer, characterized in that the surfaces to be coated during the entire coating process to complete coverage with a metal layer of the deposited metal are brought into contact exclusively with process solutions and rinsing solutions, which have a pH ≥ pH 7, preferably ≥ pH 8. The method of claim 1, comprising the process steps: - Clean the to be coated Surfaces in an alkaline treatment solution; - Apply an adhesion-promoting layer on the surface to be coated by means of an alkaline adhesive stain; - Separate a first metal layer on the cleaned and with an adhesion-promoting Layer provided surface by means of galvanic processes an alkaline electrolyte. Process according to claim 2, characterized characterized in that for the deposition of an adhesion-promoting Layer used Haftbeize a dynamic surface tension ≤ 55 mN / m at a bubble life ≤ 500 ms. Process according to claim 2, characterized characterized in that for the deposition of an adhesion-promoting Layer used Haftbeize at least one wetting agent from the Group consisting of nonpitter 62 A and EnPREP TTN WA.