DE102009039887A1 - Method for surface-treatment of magnesium-containing component, comprises applying a chemical passivating solution that consists of thixotropic agent, on a part of the surface and leaving the passivating solution on the surface - Google Patents

Abstract

The method for surface-treatment of magnesium-containing component (1), comprises applying a chemical passivating solution that consists of thixotropic agent, on a part of the surface and leaving the passivating solution after the application during a processing time on the surface and subsequently rinsing. The thixotropic agent is hydrophilic silicic acid or aluminosilicate. An initial solution is added in such a quantity to the thixotropic agent for forming the passivating solution so that the passivating solution arises in a pasty condition. The method for surface-treatment of magnesium-containing component (1), comprises applying a chemical passivating solution that consists of thixotropic agent, on a part of the surface and leaving the passivating solution after the application during a processing time on the surface and subsequently rinsing. The thixotropic agent is hydrophilic silicic acid or aluminosilicate. An initial solution is added in such a quantity to the thixotropic agent for forming the passivating solution so that the passivating solution arises in a pasty condition. The passivating solution consists of 0.5-15 % of thixotropic agent related to a mass of the initial solution and is applied by a spatula, a brush or a dosing pin (2). An anticorrosion layer is stripped on the part of the surface. The dried surface is coated and the coating is carried out as lacquering. Before application of the passivating solution, the surface is combusted in alkaline manner and pickled in acidic manner. The passivating solution is used in the form of gel. An independent claim is included for a dosing pin for surface-treatment of magnesium-containing component.

Description

The invention relates to a chemical process for the treatment of surfaces of components of magnesium or magnesium alloys.

Components made of magnesium or magnesium alloys, in particular magnesium alloys, are increasingly used in the field of automobile production, for example as body components.

It is known that magnesium and magnesium alloys have a high tendency to corrosion due to their position in the electrochemical series. To make this group of materials more suitable for technical applications, efforts have been made for decades to develop functional layers for magnesium alloys. These efforts focused mainly on the development of processes that produce a high corrosion protection effect. These methods are assigned either to the group of anodic oxidation methods or to the chemical passivation method. If, in addition to a corresponding corrosion protection, the surface should also meet decorative requirements, then this is achieved in most cases with a coating. With the introduction of, above all, magnesium-wrought alloys in the field of automobile production, even higher demands are placed on the surfaces of the components produced therefrom, in particular in the field of corrosion protection. The components made of magnesium alloys are subject in use a certain wear z. B. in the form of rockfall and / or Ritz damage to body parts. Such local damage leads to an increased risk of corrosion at the affected site, especially if the damage leads to the base metal.

Various methods are known for improving the corrosion resistance of magnesium or magnesium alloy components, for example, anodic and plasma chemical oxidation processes, chromating and passivating.

In the US 4,184,926 describes anti-corrosion coatings on magnesium and magnesium alloys produced by anodic oxidation at high bath voltages (<350 V) in an electrolyte containing alkali silicates and alkali hydroxides.

In the US 4,770,946 For example, a coating system including anodic oxidation of magnesium and magnesium alloys to improve corrosion and thermal shock resistance is presented, which also has high surface conductivity. This layer system is produced using Cr (VI) -containing substances.

A process for surface treatment of magnesium and magnesium alloys using anodic oxidation is described in US Pat DE 38 08 610 described. The layers produced are white to whitish-gray or beige and are produced in an alkali-rich electrolyte bath.

In the DE 38 08 609 In a low-alkali electrolyte bath similar protective layers of the same color palette are produced.

In the WO 99/47729 describes a method that makes it possible to produce on magnesium parts for use in electronic assemblies, a chemical conversion layer with good anti-corrosion properties and good adhesion properties.

The DE 199 13 242 discloses a method of applying a chemical passivation layer to magnesium alloys. This conversion layer consists of MgO, Mn ₂ O ₃ , and MnO ₂ and at least one oxide from the group of vanadium, molybdenum and tungsten. These passivation layers are suitable as a primer for subsequent coatings or seals.

The US 5,470,664 describes a two-step process for producing hard, corrosion-resistant layers on magnesium alloys. The first step is to create a chemical conversion layer by immersion in an aqueous solution containing ammonium fluoride. The second step is the electrochemical treatment (anodic oxidation) in an aqueous electrolyte containing water-soluble hydroxides, fluorides and fluorosilicates.

From the RU 2 207 400 C1 For example, a method is known in which oxides are removed from the surface, the surface is degreased with an alkali solution, and then a protective coating is applied by means of an aqueous solution. The aqueous solution is provided with the thickener Aerosil and contains NaH ₂ Po ₄ , NH ₄ H ₂ Po ₄ , (NH ₄ ) 2SO ₃ , Mg (OH) ₂ .

In the RU 2 334 021 C1 is a chemical treatment for surfaces of magnesium alloys for use in aerospace, aerospace, automotive and electronics known. The surface is thereby degreased in an aqueous alkali solution, pickled in aqueous nitric acid and converted into an aqueous solution. The aqueous solution contains hydroxides of alkali metals, a or more nitrosic acid salts of alkali metals, nitro acid barium and / or NaVO ₃ or Na ₂ MoO ₄ or other oxidative compounds containing one of the metals of the fifth or sixth subgroup.

In the CN 101161862 A For example, a method for surface treatment of a magnesium alloy is known in which the metal surface is cleaned, treated in a treating solution and then dried with hot air.

The invention has for its object to provide an improved method for the surface treatment of magnesium-containing components in order to reduce the risk of corrosion.

The object is achieved by a method having the features of claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims.

In a method according to the invention for the surface treatment of magnesium-containing components, a chemical passivating solution containing a thixotropic agent is applied to at least part of the surface, the chemical passivating solution being left on the surface for a period of time after application, then rinsed off and optionally the surface dried. The passivation solution serves to passivate the surface. Passivation means in surface engineering the spontaneous formation or targeted generation of a non-metallic protective layer on a metallic material which prevents or greatly slows down the corrosion of the base material. Thixotropic agents are used for the gel-like thickening of liquids to which they are added, in the present case a starting solution which forms the passivation solution together with the thixotropic agent. The thixotropic agent forms a supporting network structure in the passivation solution in the state of rest, causing it to thicken. When shearing forces are applied, for example by stirring or shaking, the network is temporarily broken and the passivation solution becomes thin. After a short while at rest, the thixotropy rebuilds, that is, the passivation solution thickens again. The thixotropic passivation solution is easily dosed so that the required amount can be applied to the part of the surface to be treated with as little excess as possible. The thixotropic state causes the passivation solution does not drip even on vertical surfaces and as long as necessary, remains on the surface. After a given exposure time, the passivation solution is rinsed off and the surface is dried. The now passivated surface then has a corrosion protection, even without further treatment. Likewise, the passivated surface can also serve as a primer for subsequent coatings or adhesions. The method is particularly suitable for repairing damaged areas of the surface such as scratches or stone chips, especially on vehicle parts, the corrosion protection achieved corresponds to the protection existing before the damage.

With the described method, a broad spectrum of magnesium alloys can be provided with protection of layer injuries.

For example, all common die-cast, cast and wrought alloys as well as those alloys used in new forming technologies such as squeeze casting, thixomolding, thixoforming are coatable. Examples of these are, in particular, AZ91, AZ81, AM20, AM50, AM60, AE42, AS21, ZE41, ZK61, AZ31, AZ60, ZK30, ZK60 and WE54.

As thixotropic agents, for example, a hydrophilic silica, Aerosil ^® or aluminosilicates can be used.

For forming the passivating solution, the thixotropic agent is preferably added to the starting solution in such an amount that the passivating solution at rest is in a pasty state.

The passivation solution preferably contains a proportion of 0.5% to 15% thixotropic agent based on a mass of the starting solution.

The application of the passivation solution to the surface to be treated can be effected by means of a spatula or by means of a brush or preferably by means of a dosing pen (repair stick) or another auxiliary device.

The drying of the surface can be done for example by means of hot air.

After the surface has dried, it can be coated, for example in the form of a coating. The corrosion protection of the treated site does not depend on the coating but only on the previous passivation.

Preferably, the surface is degreased alkaline before the application of the chemical passivating solution and pickled acid. In this way, an optimal action of the passivation solution is ensured.

The chemical passivating solution may contain, for example, at least one of orthophosphoric acid, chromium (III) chloride, ammonium hydrogen difluoride, sodium fluoride, hexafluorotitanic acid, anionic surfactants and hexafluorozirconic acid.

Embodiments of the invention will be explained in more detail below with reference to a drawing.

It shows:

1 a magnesium alloy component and a dosing pen with a thixotropic chemical passivation solution.

1 shows a component 1 from a magnesium-containing material, for example a magnesium alloy and a metering pin 2 for applying a chemical passivating solution containing a thixotropic agent. The chemical passivation solution is applied at least to a part of the surface of the component 1 applied, wherein the chemical passivating solution after application for a contact time on the surface left and then rinsed off. Optionally, the surface can then be dried and a further treatment, for example a coating or coating carried out.

Embodiment 1

• – Orthophosphorsäure 30% bis 50%
• – Chrom(III)-chlorid 10% bis 25%
• – Ammoniumhydrogendifluorid oder Natriumfluorid 2,5% bis 10%
• – Thixotropiermittel hydrophile Kieselsäure ca. 0,5 Masse% bis 15 Masse% der Ausgangslösung, das heißt der übrigen Komponenten der Passivierungslösung.

A component 1 from the magnesium wrought AZ31 is degreased alkaline and then acidified in a mixture consisting of 300 g / l aluminum nitrate, 100 ml / l glycolic acid and 50 g / l citric acid. Subsequently, the chemical passivation solution is applied to the surface. The aqueous passivating solution may consist of a commercially available solution or have the following composition:

• Orthophosphoric acid 30% to 50%
• - Chromium (III) chloride 10% to 25%
• - Ammonium hydrogendifluoride or sodium fluoride 2.5% to 10%
• - Thixotropic hydrophilic silica about 0.5% by mass to 15% by mass of the starting solution, that is, the other components of the passivation solution.

The thixotropic agent is added until a pasty state of the passivation solution is reached. This ensures that nothing can drip from a vertical surface and an order on the damaged and repaired area using a spatula, brush or dosing 2 (Repair stick) can be done. This thixotropic passivation solution is applied to the damaged areas of the surface of the magnesium component 1 applied. This job can with the spatula, the brush, the dosing 2 or another suitable auxiliary device. After a contact time of about 2 minutes to 10 minutes (depending on the size and depth of the injury), the passivation solution is rinsed with water and dried the treated area, for example, with warm air. The treated site is then ready for further processing, such as a refinish. The corrosion protection of the thus treated and repaired damaged spot is in no way inferior to the damage-free environment.

• – Hexafluorotitansäure 0,5% bis 5%
• – anionische Tenside 0,2% bis 0,8%
• – Thixotropiermittel hydrophile Kieselsäure 0,5 Masse% bis 15 Masse% der Ausgangslösung, das heißt der übrigen Komponenten der Passivierungslösung.

Alternatively, the passivation solution may be composed as follows:

• Hexafluorotitanic acid 0.5% to 5%
• Anionic surfactants 0.2% to 0.8%
• Thixotropic agent hydrophilic silica 0.5% by weight to 15% by weight of the starting solution, that is the remaining components of the passivation solution.

• – Hexafluorozirkoniumsäure 0,5% bis 10%
• – Tenside 0,2% bis 1,0%
• – Thixotropiermittel hydrophile Kieselsäure 0,5 Masse% bis 15 Masse% der Ausgangslösung

Another alternative composition of the passivation solution:

• Hexafluorozirconic acid 0.5% to 10%
• - Surfactants 0.2% to 1.0%
• Thixotropic agent hydrophilic silica 0.5% by mass to 15% by mass of the starting solution

The passivated surface of the component has a corrosion protection even without further treatment. Likewise, the passivated surface can also serve as a primer for subsequent coatings or adhesions.

The component 1 For example, it may be made of die-cast, cast or wrought alloys or an alloy formed by squeeze casting, thixomolding, thixoforming. In particular, the alloy may be one of the following: AZ91, AZ81, AM20, AM50, AM60, AE42, AS21, ZE41, ZK61, AZ31, AZ60, ZK30, ZK60 and WE54.

As thixotropic agents and aluminosilicates can be used.

LIST OF REFERENCE NUMBERS

1

component

2

metering

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4184926 [0005]
• US 4770946 [0006]
• DE 3808610 [0007]
• DE 3808609 [0008]
• WO 99/47729 [0009]
• DE 19913242 [0010]
• US 5470664 [0011]
• RU 2207400 C1 [0012]
• RU 2334021 C1 [0013]
• CN 101161862 A [0014]

Claims (14)

Process for the surface treatment of magnesium-containing components ( 1 ), wherein a chemical passivating solution containing a thixotropic agent is applied to at least part of the surface, wherein the chemical passivating solution is left on the surface after application for a contact time and then rinsed off. A method according to claim 1, characterized in that a hydrophilic silica or an aluminosilicate is used as the thixotropic agent. Method according to one of claims 1 or 2, characterized in that the formation of the passivating solution, the thixotropic agent is added to a starting solution in an amount such that the passivation solution results in a pasty state. A method according to claim 3, characterized in that the passivating solution contains a proportion of 0.5% to 15% thixotropic agent based on a mass of the starting solution. Method according to one of the preceding claims, characterized in that the passivation solution by means of a spatula or by means of a brush or by means of a dosing ( 2 ) is applied. Method according to one of the preceding claims, characterized in that the passivating solution is applied to such a part of the surface on which a layer of the surface, in particular an anti-corrosion layer, is damaged. Method according to one of the preceding claims, characterized in that the dried surface is coated. A method according to claim 7, characterized in that the coating is carried out as a finish. Method according to one of the preceding claims, characterized in that the surface is degreased alkaline and pickled acid before applying the chemical passivating solution. Method according to one of the preceding claims, characterized in that the chemical passivating solution contains at least one of the substances orthophosphoric acid, chromium (III) chloride, ammonium hydrogendifluoride, sodium fluoride, hexafluorotitanic acid, anionic surfactants and hexafluorozirconic acid. Use of a chemical passivating solution containing a thixotropic agent for passivation of damaged surfaces of magnesium-containing components ( 1 ). Use according to claim 11, characterized in that the passivation solution is used in the form of a gel. Use according to one of claims 11 or 12, characterized in that the passivation solution in a metering pen ( 2 ) and applied by means of the dosing on the damaged surface. Dosing pen ( 2 ) for carrying out the method according to one of claims 1 to 10.

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